SiO2 Catalysts for Hydrogenation of Stearic

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Characterization of Re-Pd/SiO catalysts for hydrogenation of stearic acid Yasuyuki Takeda, Masazumi Tamura, Yoshinao Nakagawa, Kazu Okumura, and Keiichi Tomishige ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.5b01054 • Publication Date (Web): 16 Oct 2015 Downloaded from http://pubs.acs.org on October 23, 2015

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ACS Catalysis

Characterization of Re-Pd/SiO2 catalysts for hydrogenation of stearic acid Yasuyuki Takeda,[a] Masazumi Tamura,[a] Yoshinao Nakagawa,[a] Kazu Okumura,[b] Keiichi Tomishige*[a]

[a]

Department of Applied Chemistry, School of Engineering, Tohoku University, 6-6-07, Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

[b]

Department of Applied Chemistry, Faculty of Engineering, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677, Japan

*

Corresponding author: Keiichi Tomishige

School of Engineering, Tohoku University, 6-6-07, Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan E-mail: [email protected]

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Abstract

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Silica supported Re-Pd bimetallic catalysts (Re-Pd/SiO2) with high molar ratio of Re/Pd, which were

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reported to be effective for selective hydrogenation of carboxylic acids to the corresponding fatty

4

alcohols in 1,4-dioxane solvent, were characterized by means of X-ray diffraction (XRD), X-ray

5

absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and CO adsorption.

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Various kinds of Re species (hexagonal closed packing (HCP) and face-centered cubic (FCC) Re0

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metals, Re3+, Re4+ and Re6+) were detected on the catalysts after reaction or reduction, and the ratio

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of these Re species was estimated by the combination of characterization results. The activity of

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these catalysts is sensitive to air because of high oxophilicity of Re, and the catalysts must be

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handled without contact to air. Pd addition and catalyst activation method (liquid-phase reduction and

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gas-phase reduction) influenced the ratio of the Re species. Liquid-phase reduced Re-Pd/SiO2 (Re/Pd

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= 8), which is the most effective catalyst, has Pd0, Re0 and Ren+ (Re3+ and Re4+) species on the

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catalyst, and the metal surface (Pd, Re0(HCP), Re0(FCC)) is modified with Ren+ species. This

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structure will be responsible for the high hydrogenation activity. Combined with kinetic studies with

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Re-Pd/SiO2 (Re/Pd = 8) and Re/SiO2 catalysts, Pd plays a role in promoting the reduction and

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dispersion of Re species, and strengthening the interaction of stearic acid with the catalytic surface,

17

and on the other hand, Ren+ plays a role in promoting the heterolytic dissociation of H2.

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Keywords

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Rhenium, Palladium, Hydrogenation of carboxylic acid, Bimetallic catalyst, Reaction mechanism

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Introduction

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Biomass is a promising material in substitution of fossil fuel to synthesize useful chemicals

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because biomass is the only renewable resource with an organic carbon [1]. Carboxylic acid is one of

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the biomass-derived chemicals from triglyceride, and hydrogenation of carboxylic acids can provide

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valuable alcohols as intermediates for organic synthesis, lubricants, surfactants, plasticizers, cosmetics

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and biofuels [1]. There are many reports on hydrogenation of carboxylic acids using heterogeneous

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catalysts, and the carboxylic acids include aliphatic monocarboxylic acids (fatty acids) [1a-d, 2], lactic

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acid [1a-d, 3], succinic acid [1a-d, 4], levulinic acid [1a-c, 5], amino acids [1a-c, 6] and so on.

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Conventionally, copper based catalysts have been used for hydrogenation of fatty acids [2c], but

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severe reaction conditions (20-50 MPa, 473-673 K) have been required. On the other hand, it has been

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also reported that Re black, which is obtained by ex-situ reduction of Re2O7, showed good

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performance in hydrogenation of fatty acids under milder reaction conditions (17-27 MPa, 410-538 K),

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and Re2O7 can be applicable in the same reaction as a catalyst by in-situ reduction under the same

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reaction conditions [2d]. The performance of these Re catalysts are superior to the copper based

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catalysts. Moreover, bimetallic catalysts containing Re have been reported to be more effective to

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hydrogenation of carboxylic acids than the corresponding monometallic catalysts [2a, b, 3-8]. In

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particular, the combination of Re species (Re metal or ReOx) with noble metals (Pd, Rh, Pt or Ru) has

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been significantly efficient [2a, b, 4, 5b, 7, 8]. For example, the combination of Re2O7 with M/C (M =

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Pd, Rh, Pt and Ru, Re/M = 0.36~1.1) (17 MPa, 443 K, in mixture solvent of dioxane + water) showed

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about 2-3 times higher activity than Re2O7 alone in the hydrogenation of octanoic acid [7]. Regarding

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the hydrogenation of levulinic acid to 1,4-pentanediol [5b], the modification of monometallic catalysts

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(Ru/C, Pt/C and Pd/C) with Re species was effective and, for example, Pt-Re/C catalyst provided high

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1,4-pentanediol yield (82%) in water solvent [5b]. It has been also reported that bimetallic Pt–Re/TiO2

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(Re/Pt = 0.95) catalyst showed 61–90% selectivity to C10–C18 fatty alcohols at 79–83% conversion

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in the hydrogenation of C10-C18 fatty acids under the mild conditions (2 MPa, 403 K, in dodecane

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solvent) [2b], and the activity was about 5 times higher than that over monometallic Pt/TiO2.

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Furthermore, Pd-Re/TiO2 catalyst (Re/Pd = 0.25~1.0, in water solvent) provided higher 1,4-butanediol

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yield (83%) in hydrogenation of succinic acid than Pd/TiO2 [4a-c]. According to the characterization

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results of Pd-Re/TiO2 catalyst with XPS, the presence of Pd0, Re0 and Re3+ species were verified, and

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it has been also proposed that the synergy between Pd and Re species enhanced the activity for

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hydrogenation [4a, c]. Pd-Re/C catalysts (Re/Pd = 0.3~1.1, in water solvent) showed about 3-4 times

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higher turnover frequency (TOF) (1650 h-1) based on CO adsorption amount for hydrogenation of

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succinic acid to tetrahydrofuran than monometallic catalyst (Pd/C: 582 h-1, Re/C: 405 h-1) [4d].

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Characterization of Pd-Re/C catalyst with TEM showed that the fringe spacing of metal species is

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between Pd and Re lattice plane spacing, which indicates the formation of Pd-Re alloy [4d].

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Re-Ru/MC catalysts (MC: mesoporous carbon, Re/Ru = 1, in 1,4-dioxane solvent) showed about 4~29

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times higher TOF based on CO adsorption amount (8.51 h-1) in hydrogenation of succinic acid to

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1,4-butanediol than monometallic catalysts (Re/MC: 2.05 h-1, Ru/MC: 0.29 h-1) [4e]. Characterization

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of Ru-Re/MC catalysts with H2-TPD suggested that the amount of weak hydrogen adsorption sites is

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related to the TOF [4e]. On these reported catalysts, the amount of Re was smaller than or comparable

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to that of noble metals on molar basis. Therefore, Re species is regarded as a cocatalyst in these

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reaction systems [2b, 4, 5b, 7], and also in other systems for hydrogenolysis of C-O bonds in polyols

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or ethers using Re modified noble metal catalysts [9].

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On the other hand, bimetallic catalysts containing higher molar ratio of Re/noble metal than 1 have

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been also reported; for example, Pd-Re/TiO2 (Re/Pd = 2.3) [10], Ru-Re/C (Re/Ru = 2.2 and 3.3) [11],

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Pt-Re-Sn/C (Re/Pt = 6.3) [12], which have been used for the hydrogenation of succinic acid and

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maleic acid. However, the role of Re species was unclear. We have recently reported that Re-Pd

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bimetallic catalysts supported on SiO2 (Pd = 1 wt%, Re = 14 wt%, Re/Pd = 8) was effective for the

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hydrogenation of higher fatty acids to alcohols with high selectivity and high yield (93-99%) at 413 K

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and 8 MPa H2 [2a]. According to this report, Pd/SiO2 alone showed no activity in the hydrogenation,

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Re/SiO2 alone showed some activity, and the combination of Re with Pd gave higher activity than the

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Re alone. This tendency suggests that the catalytically active site can be mainly formed from Re

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species and that the Pd species can be a cocatalyst. This interpretation can be also supported by the

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results that Re black and Re2O7 has been utilized in the hydrogenation of carboxylic acids [7].

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Totally, the role of Re species on the Re-noble metal bimetallic catalysts has two different aspects:

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an active species and cocatalyst. This behavior can be related to the presence of a variety of Re species

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such as Re0 and Re3+ on the catalyst surface [4a]. The simultaneous presence of various Re species

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makes it difficult to determine the state of the Re species and the structure of Re-noble bimetallic

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catalysts with high molar ratio of Re/noble metal has not been elucidated sufficiently.

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In the present study, Re-Pd/SiO2 catalysts were characterized by means of X-ray diffraction (XRD),

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X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), scanning

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transmission electron microscope (STEM), the measurement of CO adsorption amount. In particular,

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the catalyst activity was influenced by the activation treatment such as liquid-phase or gas-phase

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reduction. The proportion of various Re species after each activation treatment was estimated from the

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characterization results. In addition, combined with the kinetic study, the role of Pd metal species and

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Re species was clarified. Based on the structural analysis and kinetic study, we will propose the

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reaction mechanism of the hydrogenation of the carboxylic acid over the Re-Pd bimetallic catalyst.

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Experimental

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Catalyst preparation

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Pd/SiO2 (Pd = 1 wt%) and Re/SiO2 (Re = 14 wt%) catalysts were prepared by impregnating silica

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with an aqueous solution of PdCl2 (Wako Pure Chemical Industries, Ltd.) and NH4ReO4 (Mitsuwa

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Chemicals Co., Ltd.). The silica (G-6, BET surface area 535 m2/g) was supplied by Fuji Silysia

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Chemical Ltd. After the impregnation procedure and drying at 383 K for 12 h, they were calcined in

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air at 673 K for 3 h. Re-Pd/SiO2 catalysts were prepared by impregnating Pd/SiO2 after the drying

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procedure with an aqueous solution of NH4ReO4. The loading amount of Pd was 1 wt%, and that of

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Re was represented by the molar ratio of Re to Pd (Re/Pd = 2~12). The Re loading amount of

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Re-Pd/SiO2 (Re/Pd = 8) catalyst is the same as that of Re/SiO2 (Re = 14 wt%) catalyst. All catalysts

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were in powder form.

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Activity tests

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Activity tests were performed in a 190-mL stainless steel autoclave with an inserted glass vessel.

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The calcined catalyst was set in an autoclave with a spinner, stearic acid (STA, Wako Pure Chemical

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Industries, Ltd., >95.0%) and an appropriate amount of 1,4-dioxane. The solvent was selected based

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on the solubility of STA. After sealing the reactor, the air content was purged by flushing three times

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with 1 MPa hydrogen (99.99%; Showa Denko K.K.). The autoclave was then heated to 413 K, and

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the temperature was monitored using a thermocouple inserted in the autoclave. After the temperature

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reached 413 K, the H2 pressure was increased to the appropriate pressure. During the experiment, the

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stirring rate was fixed at 500 rpm (magnetic stirring). After an appropriate reaction time, the reactor

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was cooled down and the gases were collected in a gas bag. The autoclave contents were transferred

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to a vial, and the catalyst was separated by centrifugation. The standard conditions for the reaction

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were as follows: 1 g STA, 19 g 1,4-dioxane, 100 mg catalyst, 8.0 MPa initial hydrogen pressure, 413

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K reaction temperature, 2 h reaction time. In this activity test, the calcined catalyst was activated by

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the reduction with hydrogen at the initial stage in the presence of the substrate and the solvent.

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Therefore, the catalysts are called as “liquid-phase reduced catalysts” and are denoted, for example,

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as Re-Pd(L, 413), where L means liquid-phase and 413 means the reduction temperature. In addition,

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the samples after this activity test are denoted like Re-Pd(L, 413, Reaction). For comparison, we also

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evaluated the catalysts reduced in a different method. Here, the calcined catalysts were reduced

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under the gas-phase hydrogen flowing. The catalysts are called as “gas-phase reduced catalysts” and

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are denoted, for example, as Re-Pd(G, 473), where G means gas-phase and 473 means the reduction

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temperature under hydrogen flow. The experimental method of the activity tests of the gas-phase

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reduced catalysts is described below. The calcined catalysts were reduced in H2 flow (100% H2 30

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mL/min) at temperature (473 or 773 K) for 1 h by using a glass tube. The reduced catalysts were

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introduced to an autoclave under N2 atmosphere in order to avoid exposing the catalyst to air. After 6

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this catalyst transfer, the procedure for the activity test of the gas-phase reduced catalysts was the

2

same as the case of liquid-phase reduced catalysts. In addition, the samples after the activity test are

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denoted like Re-Pd(G, 473, Reaction) , where G means gas-phase and 473 is the reduction

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temperature.

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The products were analyzed using gas chromatographs (Shimadzu GC-2025 and GC-2015)

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equipped with FID. A HP-FFAP capillary column (diameter 0.25 mm, 30 m) was used for the

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separation of products in the liquid phase such as STA, 1-octadecanol (C18H37OH), n-octadecane

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(C18H38) and n-heptadecane (C17H36). A Porapak N (diameter 3.0 mm, 3.0 m) packed column was

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used for the separation of products in the gas phase such as CO2, CH4 and C2H6. The conversion,

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selectivity, conversion rate [mmol・g-Cat.-1・h-1] and TOF [h-1] were defined on the carbon basis and

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defined as Eqs. (1), (2), (3) and (4).

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Conversion [%] =

∑ (the product [mol])(number of carbon atoms in the product molecule)/18 × 100 (unreacted STA[mol]) + ∑ (the product [mol])(number of carbon atoms in the product molecule) / 18

Selectivity [%] =

(the product [mol])(number of carbon atoms in the product molecule) / 18 × 100 ∑ (the product [mol])(number of carbon atoms in the substrate molecule) / 18

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Conversion rate [mmol g - Cat.− 1 h −1 ] =

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TOF [h − 1 ] =

(2)

∑ (the product [mmol])(number of carbon atoms in the substrate molecule)/18 (reaction time [h])(the amount of catalyst[g])

∑ (the product [mmol])(number of carbon atoms in the substrate molecule)/18 (reaction time [h])(the loading amount of Re[mmol])

(1)

(3)

(4)

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Products were also identified using GC–MS (QP-2010, Shimadzu). The mass balance was also

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confirmed in each result and the difference in the mass balance was always in the range of the

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experimental error (±5%).

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Catalyst characterization

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X-ray diffraction (XRD) patterns were recorded by a diffractometer (MiniFlex600; Rigaku). Cu

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Kα (λ = 0.154 nm, 45 kV, 40 mA) radiation was used as an X-ray source. The samples after the

3

reaction or reduction were transferred to an atmosphere separator (Air-sensitive sample holder;

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Rigaku Corporation) using a glove bag under N2 atmosphere to avoid exposure to air. The XRD

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patterns were normalized by adjusting the area of raw SiO2 signals of the catalysts (2θ = 8 ° - 35 °) to

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the SiO2 amount of the catalysts (Table S1). The particle size (d) on the catalysts was calculated by

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the Scherrer's equation [13]. The dispersion (D) was calculated by the following method. In the

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spherical particle equivalent approximation, the D is related to the volume-area mean diameter d VA

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[nm] as D = 6(VM/aM)/ d VA , where aM and VM are respectively the effective average area occupied by

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a metal atom in the surface, and the volume per metal atom in the bulk [14]. The values of 6(VM/aM)

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were calculated from the data in the literature (VM = 1.47×10-2 (Re and Pd) nm3, aM = 6.49×10-2

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(Re) or 7.87×10-2 (Pd) nm2) [14]; 1.36 [nm] for Re and 1.12 [nm] for Pd. XRD patterns were fitted

13

by some Gaussian functions [15] expressed by Eq. (5):

14

y=

∑

Ai exp ( - (x-x0, i)2 / 2ωi2 ) + B

FWHM = 2ω 2ln2

(5)

i

15

here, A, x, x0, ω, B and FWHM are height of peak, the peak position, the center of peak position,

16

standard deviation, background and full width at half maximum, respectively. Subscript i represents

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metal species. The value of ω was fixed to the same value for peaks for the same metal phase. Ai

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ratio and x0, Re(HCP) was fixed (Table S2 in the Supporting information), as the values have been

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reported for Re(HCP) (ICDD 01-074-6603), Pd(FCC) (ICSD no. 41517) and Re(FCC) (ICDD

20

01-088-2340). The XRD patterns were fitted so as to minimize root mean square error (RMSE).

8

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The XAS was carried out at the BL01B1 station at SPring-8 with the approval of the Japan

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Synchrotron Radiation Research Institute (JASRI; Proposal No. 2013B1067, 2014A1119,

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2014B1248). The storage ring was operated at 8 GeV, and a Si (111) single crystal was used to

4

obtain a monochromatic X-ray beam. Ion chambers for I0 were filled with 100% N2 and 100% Ar for

5

Re L3-edge and Pd K-edge measurement, respectively. Ion chambers for I were filled with 50%

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N2+50% Ar and 100% Kr for Re L3-edge and Pd K-edge measurement, respectively. The samples

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after the reaction and the reduction were prepared under the same conditions. After cooling, the

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prepared catalyst powder was transferred to a ccommercially available UV/VIS cell (UV-Cuvette

9

micro 8.5 mm, BRAND GMBH + CO KG) in a glove bag filled with nitrogen to avoid exposure to

10

air. The thickness of the cell filled with the powder was 2 mm to give an edge jump of 0.6~2.5 and

11

0.1~2.0 for Re L3-edge and Pd K-edge measurement, respectively. The extended X-ray absorption

12

fine structure (EXAFS) data for Re L3-edge were collected in a transmission mode measurement, and

13

those for Pd K-edge were collected in a fluorescence mode measurement. For EXAFS analysis, the

14

oscillation was first extracted from the EXAFS data using a spline smoothing method [16]. Fourier

15

transformation of the k3-weighted EXAFS oscillation from the k space to the r space was performed

16

to obtain a radial distribution function. The inversely Fourier filtered data were analyzed using a

17

usual curve fitting method [17]. The empirical phase shift and amplitude functions for Re-O bonds

18

were extracted from the data of NH4ReO4. The empirical phase shift and amplitude functions for

19

Re-Re and Pd-Pd bonds were extracted from the data of Re powder and Pd foil, respectively.

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Analyses of EXAFS and X-ray adsorption near edge spectra (XANES) data were performed using a

21

computer program (REX2000, ver. 2.6.0; Rigaku Corp.).

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Regarding the XANES spectra, the white line area of the Re L3-edge XANES was analyzed. It has

2

been previously reported that the average valence of Re species can be estimated from the white line

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area in the L3-edge XANES spectra [18] on the basis of the linear relation between the white line

4

area and the valence of the Re species. In this analysis, the data of ReO2, ReO3 and Re2O7 were used

5

as reference data. The relation between the valence and the white line area is shown in Figure S1

6

(Supporting information), and the Re valence on the samples was determined by using Figure S1.

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X-ray photoelectron spectroscopy (XPS) experiments were conducted with an AXIS-ULTRA

8

DLD (Shimadzu Co., Ltd.) using a monochromatic Al Kα X-ray radiation (hν = 1486.6 eV) operated

9

at 20 mA and 15 kV at room temperature under 10−8 Pa. The binding energy was calibrated with C

10

1s (284.6 eV). The catalysts after the reaction or reduction were transported to the analysis chamber

11

in nitrogen atmosphere to avoid any exposure to air. Analysis of XPS data was performed by using

12

the computer program CasaXPS, ver. 2.3.15 (Casa software Ltd.). XPS patterns were fitted by Voigt

13

function [19]. Re 4f7/2 and Re 4f5/2 are separated by 2.43 eV and have relative peak area and full

14

width at half maximum (FWHM) with a fixed ratio of 4:3 and 1:1, respectively [20].

15

The amount of CO chemisorption was measured in a high-vacuum system using a volumetric

16

method. Before adsorption measurements, the catalysts were treated in H2 at 473 or 773 K for 1 h.

17

Subsequently the adsorption was performed at room temperature. Gas pressure at adsorption

18

equilibrium was about 1.5 kPa. The sample weight was about 0.15 g. The dead volume of the

19

apparatus was about 36 cm3.

20

Field emission scanning transmission electron microscope (FE-STEM) images and

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energy-dispersive X-ray (EDX) analysis were obtained on a Hitachi spherical aberration corrected

22

STEM/SEM HD-2700 instrument operated at 200 kV. The catalysts after the reaction were used as 10

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samples for the TEM observation. The samples were dispersed in ethanol by supersonic wave. A part

2

of Re species were dissolved in ethanol solvent (~24 wt% by ICP-AES). The samples were placed on

3

Mo grids under air atmosphere.

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Results and discussion

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Catalytic performance of Re-Pd catalysts with different composition and different reduction

8

method for the catalyst activation in hydrogenation of stearic acid

9

Effect of Re amount on Re-Pd(L, 413) on the performance in hydrogenation of STA over

10

Re-Pd(L, 413) catalysts reduced in liquid-phase was investigated at the constant Pd amount (1 wt%

11

Pd), and the results are listed in Table 1. The monometallic Pd catalyst, Pd(L, 413), showed no

12

activity (entry 1). On the other hand, the monometallic Re catalyst, Re(L, 413), showed moderate

13

activity with high selectivity (entry 7). These results indicate that some Re species are the active ones

14

for the reaction. TOF increased with increasing the loading amount of Re (entries 2-4) and became

15

constant at molar ratio of 6 and more (entries 4-6). In particular, Re-Pd(L, 413) with Re/Pd = 8 (entry

16

5) exhibited the highest TOF, and this behavior was also supported by our previous work [2a]. We

17

used Re-Pd/SiO2 with the Re/Pd = 8 in the following studies unless noted. Although the catalyst was

18

liquid-phase reduced under the reaction conditions, the coexisting carboxylic acid can influence the

19

reduction of the catalyst. To reveal the effect of the presence of the carboxylic acid during the

20

catalyst reduction, the liquid-phase reduction in only 1,4-dioxane solvent was conducted for the

21

reference: The catalyst in 1,4-dioxane was reduced under 8.0 MPa H2 for 1 h at 413 K. After cooling 11

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1

down to room temperature, the autoclave was opened in N2 atmosphere, and stearic acid was added

2

to the autoclave reactor, where all the procedure were carried out without the exposure to air. The

3

results of these two liquid-phase reduced catalysts were almost comparable (Table S3), indicating

4

that the presence of carboxylic acid does not influence the reduction and the reduction pretreatment

5

in the solvent is not necessary for the activity tests. This is why we did not conduct the reduction

6

pretreatment in the activity test of the liquid-phase reduced catalysts ((L, x) series).

7

Table 2 lists the results of the comparison between liquid-phase ((L, x) series) and gas-phase ((G,

8

x) series) reduced catalysts. The activity of Re-Pd(G, 473) was clearly lower than that of Re-Pd(L,

9

413) (entries 1 and 2). Similar tendency was also observed in the cases of monometallic Re catalysts

10

(entries 3-5). It is concluded that the reduction method is very influential for Re-Pd catalysts to

11

obtain the high activity. Although the partial pressure of H2 in the TPR experiment was much lower

12

than that of the gas-phase in the activity test, the gas-phase reduction behavior can be studied on the

13

basis of the TPR profile (Figure S2). The amount of H2 consumption is listed in Table S4. On

14

calcined Re-Pd catalyst, the gas-phase reduction temperature of 473 K can correspond to the Re

15

reduction degree of about 0.5 (average valence of Re 7.0 → 3.5), which suggests that the reduction

16

of Re species proceeds significantly. In addition, in the case of the Re catalyst, the gas-phase

17

reduction at 473 K can give very low reduction degree (reduction degree = 0), and that at 773 K can

18

give very high reduction degree (reduction degree = 0.86) (Table S4). Compared to the results of

19

activity tests (Table 2, entries 3-5), the very high reduction degree of Re species (Re(G, 773),

20

reduction degree = 0.86) as well as the very low reduction degree (Re(G, 473), reduction degree =

21

0) can be also connected to the low catalytic activity. These results suggest that there is the suitable

12

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1

reduction degree of Re species for high catalytic activity.

2

In order to verify the catalyst stability, the reusability of the catalyst was tested in two different

3

ways, methods (A) and (B). In the method (A), after the reaction over Re-Pd(L, 413), the autoclave

4

was opened under air atmosphere. The catalyst was separated by centrifugation and the separated

5

catalyst was dried at room temperature under air for 12 h. The obtained dried catalyst was used for

6

the next test. The same procedures were repeated. The results are listed in Table 3. The conversion

7

rate of the Re-Pd catalyst decreased significantly with increasing the number of uses in the method

8

(A). This behavior implies that the oxidation of the catalyst with air can decrease the amount of the

9

active species formed during the reaction because of high oxophilicity of Re species. Therefore, the

10

catalyst reusability test without exposing to the air was attempted in the method (B). Under N2

11

atmosphere, the autoclave was opened, and the catalyst was separated by decantation, and the

12

obtained wet catalyst was added to the autoclave reactor for the next test. Therefore, the precise

13

amount of the catalyst cannot be determined, and the catalyst amount in each number of uses was

14

calculated from that after 4th time reaction test. The results are also listed in Table 3. It is found that

15

the catalyst can be reused three times without significant loss of activity and selectivity (Table 3). In

16

addition, the hydrogenation of STA was carried out under the same reaction conditions for 2 h to

17

achieve 31% conversion, and then the catalyst was removed from the reaction mixture by filtration

18

(Figure S3 in the Supporting information). The filtrate was heated again at 8.0 MPa H2 for more 2 h.

19

STA hydrogenation reaction with the filtrate did not proceed furthermore. In addition, the leaching

20

amount of Re and Pd after the reaction at 4 h was negligible (< 0.1%) by using inductively-coupled

21

plasma atomic emission spectrometry (ICP-AES) in our previous work [2a]. These results indicate

13

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ACS Catalysis

that the STA hydrogenation is catalyzed by heterogeneous Re-Pd catalysts.

2 3

Characterization of Re-Pd and related catalysts: Analysis of the states of Re species and its

4

distribution

5

Figure 1 shows XRD patterns of Pd(L, 413, Reaction), Re-Pd(L, 413, Reaction) (Re/Pd = 2~12),

6

Re(L, 413, Reaction), Re-Pd(G, 473) (Re/Pd = 8), Re(G, 473), and Re(G, 773) catalysts. The sharp

7

signals at 21.7 and 24.1° (Figure 1 (a)-(c)) can be assigned to STA (ICDD 00-038-1923). The signal

8

due to amorphous SiO2 was observed around 20 o in all XRD patterns. Pd(L, 413, Reaction) shows

9

the signal due to Pd metal (Figure 1 (a)). Re-Pd(L, 413) (Re/Pd = 2~12) catalysts show the broad

10

signals at 2θ = 38~45 ° in addition to the peak due to Pd metal, and the intensity increased with

11

increasing the molar ratio of Re/Pd (Figure 1 (b)-(f)). On the other hand, Re(L, 413, Reaction)

12

provided similar broad signals at 2θ = 37.6, 40.1, 42.6 and 67.3 ° (Figure 1 (g)). In addition, no ReOx

13

species (ReO2, ReO3 and Re2O7) were observed in the range of 2θ = 20-30 °, which indicates that

14

ReOx species do not exist or was highly dispersed on SiO2. The broad signals at 2θ = 38~45 ° can be

15

assignable to Re metal species, and Re metal has two species; Re metal with hexagonal closed

16

packed structure (Re(HCP)) and with face-centered cubic structure (Re(FCC)) [21] (Re(HCP): ICDD

17

no. 01-074-6603, Re(FCC): ICDD 01-088-2340). In order to clarify the state of Re metal and Pd

18

metal, the broad signals were fitted using the signals of Pd metal, Re(HCP) and Re(FCC) (Figure S4).

19

It should be noted that it is impossible to fit the broad signals by only Re(HCP), for example the

20

fitting result of Re(L, 413, Reaction) (Figure S5). Based on the fitting results, we calculated the

21

particle size of Pd, Re(HCP) and Re(FCC), and the XRD area of Re(HCP) and Re(FCC) (Table 4).

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1

The particle sizes of Re(HCP) on Re-Pd(L, 413, Reaction) are smaller (1.6-2.4 nm) than that of Re(L,

2

413, Reaction) (4.2 nm) (entries 2-7), suggesting that addition of Pd species can promote dispersion

3

of Re metal, in particular, Re(HCP). The total area of Re(HCP) and Re(FCC) on Re-Pd(L, 413,

4

Reaction) increased gradually with the Re/Pd molar ratio (entries 2-6). The comparison of total Re

5

metal XRD area between Re(L, 413, Reaction) and Re-Pd(L, 413, Reaction) (Re/Pd = 8) with the

6

same loading amount of Re (Table 4, entries 5 and 7) shows that the addition of Pd promotes the

7

reduction of Ren+ species to Re0 species. In addition, we estimated the XRD area considering the Re

8

metal dispersion (D) calculated by the particle size; which is called as “effective XRD area”. The

9

relation between the effective XRD area and catalytic activity is discussed in another section below.

10

In order to analyze the Re species on the catalyst surface, XPS analysis was conducted. Figures 2

11

and 3, and Table 5 show the results of XPS analyses for Pd(L, 413, Reaction), Re(L, 413, Reaction),

12

Re-Pd(L, 413, Reaction) (Re/Pd = 8), Re(G, 473), Re(G, 773), Re-Pd(G, 473) (Re/Pd = 8) catalysts.

13

The signals due to Pd 3d5/2 and 3d3/2 core levels of Pd(L, 413, Reaction), Re-Pd(L, 413, Reaction),

14

and Re-Pd(G, 473) were also observed at 334.7-335.4 and 340.0-340.8 eV, respectively (Figure 2,

15

Table 5), and these signals can be assigned to Pd0 species [4a, 20]. Therefore, Pd species on the

16

catalyst surface was in the metallic state. As shown in Figure 3, the asymmetric signals were

17

observed in the Re 4f region. In Figure 3 (C), (D), (E), the signals have a shoulder at around 41.5 eV,

18

which implies the presence of Re3+ species. Similar species assignable to Re3+ was also observed

19

with other bimetallic catalyst systems such as Pt-Re, Ru-Re and Rh-Re [4a, 4c, 22]. The lines of the

20

Re 4f XPS data on the Re containing catalysts at 40.5-40.7, 41.4-41.7, 42.4-42.9, and 45.3-45.7 were

21

assigned to Re0, Re3+, Re4+, and Re6+, respectively [4a, 4c, 20-23]. These XPS data were

15

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1

deconvoluted into these Re species. In the case of Re-Pd(L, 413, Reaction), Re(L, 413, Reaction),

2

and Re(G, 773) catalysts, the signals can be deconvoluted into three components (Re0, Re3+, Re4+)

3

(Figure 3 F, G, and J). In the case of Re-Pd(G, 473) and Re(G, 473) catalysts, the signals can be

4

deconvoluted into four components (Re0, Re3+, Re4+, and Re+6) (Figure 3 H and I). Table 5 lists

5

results of the deconvolution of the XPS data. In the case of Re(L, 413, Reaction), the area ratio of

6

Re0 to total Re is clearly smaller than that of Re3+ and Re4+. On the other hand, the area ratio of Re0

7

to total Re is larger than that of Re3+ and Re4+ on Re-Pd(L, 413, Reaction), which is explained by the

8

promotion of the ReOx reduction by the presence of Pd in the liquid-phase reduction. In contrast,

9

from the comparison between Re-Pd(G, 473) and Re(G, 473) in terms of the area ratio of various Re

10

species, the promotion of the ReOx reduction by the presence of Pd was not observed clearly in the

11

gas-phase reduction. Although the TPR profiles indicates the low temperature shift of H2

12

consumption peak by the addition of Pd (Figure S2), the existence of Re0 species on Re-Pd/SiO2

13

catalysts detected by XPS cannot be explained by TPR because the peak position of TPR is higher

14

than the reduction temperature of 473 K. The difference of the H2 partial pressure and the time for

15

the gas-phase reduction may explain the disagreement of the TPR results and the XPS results. In

16

addition, the composition of surface Pd (Pd0S) to surface Si (SiS) (Pd0S/SiS) on Pd(L, 413, Reaction),

17

Re-Pd(L, 413, Reaction), and Re-Pd(G, 473) can be estimated from the XPS results, and the obtained

18

values are also listed in Table 5. Judging from the particle size of the Pd metal on these three

19

catalysts (Table 4), Pd0S/SiS values cannot be explained by the Pd particle size. This behavior can be

20

explained by the interaction between Pd metal surface and Re species as discussed below. Another

21

important point is that the surface ratio of Re species (ReS) to Pd species (ReS, total/Pd0S) is calculated 16

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1

to be 48 and 15 on Re-Pd(L, 413, Reaction) and Re-Pd(G, 473), which is much higher than that of the

2

bulk ratio of 8. This behavior suggests that Re species (Re0 and Ren+ species) are more highly

3

dispersed than Pd metal species considering the XRD results (Table 4).

4

XAS analyses were performed with Pd, Re, and Re-Pd (Re/Pd = 8) catalysts after the reaction or

5

reduction. Pd K-edge XANES spectra of all the catalysts were similar to that of Pd foil (Figure S6),

6

which indicates that Pd species was reduced to the metallic state, which is also verified by the Pd

7

K-edge EXAFS analysis (Figure S7 and Table S5). Formation of Pd metal is also supported by XRD

8

and XPS results. Figure 4 shows Re L3-edge XANES analysis of Re-Pd and Re catalysts. The

9

average valence of Re can be estimated from the white line area in the Re L3-edge XANES spectra

10

[18], and the obtained average Re valence is listed in Table 6. The average valences of Re(L, 413,

11

Reaction), Re(G, 473), and Re(G, 773) were determined to be +2.6, +1.6, and +0.6, respectively

12

(Table 6, entries 1, 2 and 4), which indicates that the reduction degree of Re species on Re(G, 473)

13

and Re(G, 773) is higher than that of Re(L, 413, Reaction). In addition, it is also verified that the

14

valence of Re on Re(G, 473) and Re(G, 773) was not changed during the reaction (Table 6, entries

15

2-5).

16

Figure 5 and Table 6 show the results of Re L3-edge EXAFS analysis for Re and Re-Pd (Re/Pd =

17

8) catalysts after the reaction, reduction or calcination. On these samples, Re=O , Re-O, and Re-Re

18

bonds were detected. In particular, the valence of Re can also be estimated approximately from the

19

CN of Re=O and Re-O (valence of Re = 2 × CNRe=O + 1 × CNRe-O) [9c, 24]. The calculated values of

20

the Re valence from EXAFS analyses agreed well with the Re valence from Re L3-edge XANES as

21

listed in Table 6. It is verified that the local structure around Re species on Re(G, 473) and Re-Pd(G,

17

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ACS Catalysis

1

473) was similar to Re(G, 473, Reaction) and Re-Pd(G, 473, Reaction), and the catalyst structure of

2

Re(G, 473) and Re-Pd(G, 473) was maintained during the reaction. The CNRe-Re is determined by two

3

factors: the molar ratio of Re metal to total Re species and the particle size of Re metal. The particle

4

size of Re metal can be given by the XRD results (Table 4). Using these values, we determined the

5

molar ratio of Re metal to total Re.

6

As shown by XPS results, various kinds of Re species such as Re0, Re3+, Re4+, and Re6+ were

7

present on the catalyst surface, but the signals due to Re3+, Re4+, and Re6+ were not detected at all by

8

XRD analyses. These results suggest that these cationic Re species (Re3+, Re4+, and Re6+) are highly

9

dispersed on the catalysts. In these cases, the molar ratio of Re3+, Re4+, and Re6+ in the whole sample

10

will be equal to the surface molar ratio of Re3+, Re4+, and Re6+ determined by the XPS analyses. On

11

the other hand, the particle size of Re0 species is adequately large (2~4 nm), which makes it

12

impossible to determine the bulk molar ratio of Re0 species by XPS analysis because not all Re0

13

species can be analyzed by XPS. The molar ratio of Re0 species in the whole sample can be

14

calculated from the following equation using the average Re valence determined by the Re L3-edge

15

XANES analyses and the molar ratio of Re3+:Re4+:Re6+ determined by XPS.

16

Average valence of Re (XANES) = M Re0 × 0 + M Re 3+ × 3 + M Re 4+ × 4 + M Re6 + × 6

17

(M Re 0 + M Re3+ + M Re 4 + + M Re 6+ = 1)

18

Here, M Re n + means the bulk molar ratio of Ren+ to the total Re species (n = 0, 3, 4 and 6). The

19

calculated values are listed in Table 7. The order of the molar ratio of Re0 to total Re is as follows:

20

Re(G, 773) > Re-Pd(G, 473) ≈ Re(G, 473) > Re-Pd(L, 413, Reaction) > Re(L, 413, Reaction), and

21

this tendency agreed with the XRD peak area due to Re metal as listed as Table 4, assuming that the

18

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1

diffraction intensity of Re0(HCP) and Re0(FCC) is the same. The amount ratio of Re0(HCP) to

2

Re0(FCC) is estimated from the XRD area ratio given in Table 4, and the molar ratio of surface Re

3

metal atoms of Re0(HCP) to Re0(FCC) [Re0(HCP)S and Re0(FCC)S] are also calculated by the

4

relation between the dispersion (DRe) and the metal particle size (dRe) [14] from the XRD results

5

(Table 4) as listed in Table 7. These obtained values enable the calculation of CNRe-Re (calculated)

6

assuming that CNRe-Re of the surface Re atoms on Re(HCP) and Re(FCC) is 9, and the CNRe-Re of the

7

bulk Re atoms in Re(HCP) and Re(FCC) is 12. The results are also listed in Table 7. The obtained

8

CNRe-Re (calculated) agreed to some extent with the CNRe-Re determined by the curve fitting analysis

9

of Re L3-edge EXAFS analysis, which indicates the validity of the assumption and calculation

10

method.

11

An important point is that the amount of Re metal atoms at the outer layer of Re metal particles

12

(Re0(HCP)S + Re0(FCC)S in Table 7) was not so different on these catalysts, however, the catalytic

13

activity of these catalysts is very different (Table 2). This disagreement suggests that the amount of

14

the active site should be different at each catalyst. Therefore, in order to determine the surface metal

15

sites, the amount of CO adsorption on the gas-phase reduced catalysts was investigated because CO

16

can be adsorbed on Re metal and Pd metal and not be adsorbed on Re3+, Re4+ and Re6+ [9d]. Table 8

17

lists the results of CO adsorption measurement for Re-Pd(G, 473), Re(G, 473), and Re(G, 473)

18

catalysts. The amount of CO adsorption on Re(G, 473) and Re(G, 773) was about one tenth of that on

19

Re-Pd(G, 473), and this tendency is similar to that of the catalytic activity as listed in Table 2. The

20

adsorption amount of CO was compared with the amount of surface Pd (Pd0S) and amount of surface

21

Re metal (Re0S = Re0(HCP)S + Re0(FCC)S) estimated from various catalyst characterization results. 19

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1

The amount of CO adsorption on Re-Pd(G, 473) is clearly larger than the number of surface Pd atoms

2

estimated by XRD analysis, indicating that CO is adsorbed on Re metal site. On all catalysts tested

3

by CO adsorption, the ratio of CO adsorption amount to total metal surface atoms (Pd0S + Re0S) was

4

clearly smaller than 1, suggesting that some surface species suppressed the CO adsorption on the

5

metal surface. One possible interpretation is that metal surface is covered with Ren+ species such as

6

Re3+, Re4+ or Re6+. It has been reported that the surfaces of Rh, Ir, and Pt metal were covered with

7

Ren+ species on Rh-ReOx, Ir-ReOx, and Pt-ReOx catalysts [9, 25]. Therefore, the molar ratio of Ren+

8

to Pd0S + Re0S is also calculated and listed in Table 8. These values indicate that the amount of Ren+

9

species is enough to suppress the CO adsorption.

10

The direct interaction between Re species and Pd was not observed by XRD and EXAFS results

11

on the Re-Pd catalysts, although the direct interaction between Ren+ species and metal surface (Rh

12

and Pt) has been observed by Re L3-edge EXAFS analysis [9a-c] and the formation of Pd-Re alloy

13

was observed by TEM [26]. The results of XRD and EXAFS on the Re-Pd catalysts can be due to

14

higher molar ratio of Re to Pd. Figure 6 exhibits FE-STEM images and EDX analysis of Re-Pd(L,

15

413, Reaction) (Re/Pd = 8). Considering the characterization results, the large particles can be

16

assigned to Pd metal particles and the small particles can be due to Re0(HCP) or Re0(FCC) particles.

17

Figure 6 (b), (c) and (d) shows the mapping images of Si, Re, Pd species, respectively. Re species

18

were highly dispersed over the catalyst and were also located near the Pd metal particles, suggesting

19

the presence of the interaction between Re species and Pd metal. This can be connected to the lower

20

value of Pd0S/SiS on Re-Pd(L, 413, Reaction) and Re-Pd(G, 473) than that on Pd(L, 413, Reaction) in

21

Table 5.

20

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1

From the above catalyst characterization results and the discussion, a model structure of Re-Pd(L,

2

413) (Re/Pd = 8) is proposed (Figure 7). The particle size of Pd is 7.1 nm (Table 4) and the surface of

3

Pd particles is partially covered with Ren+ (Re3+ + Re4+). The amount ratio of Re0:Re3+:Re4+ was

4

estimated to be 0.45:0.21:0.34, and the Re0 species form 2.3 nm Re0(HCP) particles and 2.7 nm

5

Re0(FCC) particles. The surface of both Re0(HCP) and Re0(FCC) particles can be also partially

6

covered with Ren+ (Re3+ + Re4+) species.

7 8

Relation between the catalytic hydrogenation activity and characterization results

9

In XRD analysis, we calculated the effective XRD area, which can be proportional to the number

10

of the outer layer of Re(HCP) and Re(FCC) metal particles (Figure 1, Table 4). Figure S8 shows the

11

plot of conversion rate as a function of the effective XRD area of the Re-Pd, Re and Pd catalysts.

12

Regarding the liquid-phase reduced Re-Pd catalysts, it seems that the conversion rate increased

13

monotonously with increasing the effective XRD area. In contrast, gas-phase reduced Re-Pd and Re

14

catalysts showed low conversion rate in spite of the large effective XRD area. As a result, the

15

conversion rate cannot be explained systematically by the effective XRD area. These behaviors

16

suggest that the surface structure of gas-phase reduced catalysts is very different from that of

17

liquid-phase reduced catalysts. The difference in the structure between liquid-phase and gas-phase

18

reduced catalysts is discussed on the basis of the characterization results. One suggestive difference

19

between Re-Pd(L, 413, Reaction) and Re-Pd(G, 473) is the molar ratio of Re0:Re3+:Re4+:Re6+ (=

20

0.45:0.21:0.34:0.0 for Re-Pd(L, 413, Reaction) and = 0.63:0.09:0.13:0.15 for Re-Pd(G, 473), Table 7).

21

Re-Pd(G, 473) gave larger amount of Re0 and Re6+ species than Re-Pd(L, 413, Reaction), which

21

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1

indicates that the gas phase reduction increases Re0 and Re6+ species. Taking into consideration much

2

higher activity of Re-Pd(L, 413) than Re-Pd(G, 473), the intermediate oxidation state of Ren+ such as

3

Re3+ and/or Re4+ can play a crucial role on the formation of the catalytically active site. At the same

4

time, as mentioned in the results of CO adsorption (Table 8), the larger CO adsorption amount over

5

Re-Pd(G, 473) than Re(G, 473) suggests that surface Re0 also contributes to the catalytic activity. As

6

above, the catalytically active species can be formed by the combination of Re0 with Re3+ and/or

7

Re4+.

8 9 10

Kinetic study and the reaction mechanism of STA hydrogenation over Re-Pd(L, 413) and Re(L, 413)

11

Reaction kinetics on hydrogenation of STA over Re-Pd(L, 413) (Re/Pd = 8) and Re(L, 413)

12

catalysts with the same Re loading amount were investigated. In the time dependence for STA

13

hydrogenation on the Re-Pd(L, 413), conversion of STA increased almost linearly with reaction time

14

below 50% conversion (Figure S3). Therefore, we discussed kinetic results below 50% conversion.

15

Figure 8 shows the effect of initial STA concentration over Re-Pd(L, 413) and Re(L, 413), and the

16

details are listed in Table S6. The reactions were performed at various initial STA concentration (3 to

17

15 wt%) by changing amount of 1,4-dioxane and STA. In addition, the reaction order was determined

18

by following method in order to evaluate the value more precisely: (1) the reaction order was decided

19

from the slope of double logarithmic plot for conversion rate vs initial STA concentration by using

20

least-square approach, where the conversion rate was calculated assuming the zero reaction order

21

(the slope obtained from the data at the specific reaction time and the origin) (Tables S7 and S8,

22

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1

entry 1, and Figures S9 and S10 (a)). (2) The reaction rate constant in this reaction order was

2

evaluated from each data point at the specific reaction time and concentration, and the initial

3

conversion rate was estimated again from the rate constant (Tables S7 and S8, entry 2). (3) The

4

calculations of (1) and (2) were repeated until the reaction order converged (Tables S7 and S8,

5

entries 2-4, Figures S9 and S10 (b)-(d), and Figure S11). As show in Table S7, the difference in the

6

conversion rate between zero and +0.8 reaction order is not so large because the conversion level was

7

sufficiently low. The reaction order with respect to the initial STA concentration over Re-Pd(L, 413)

8

and Re(L, 413) was estimated to be +0.1 and +0.8, respectively, in the range of initial STA

9

concentration between 3 and 15 wt%. The method for the determination of the reaction orders may

10

not be rigorous and the obtained values may have some uncertainty. However, the difference of the

11

obtained values (+0.1 and +0.8) between Re-Pd(L, 413) and Re(L, 413) was large enough to make

12

the determination method valid in the present case. As a result, it is strongly suggested that STA is

13

more strongly adsorbed on Re-Pd(L, 413) than Re(L, 413), and the presence of Pd can be connected

14

to the enhancement of the STA adsorption strength on the catalyst surface. Figure 9 shows the effect

15

of H2 pressure over Re-Pd(L, 413) and Re(L, 413) and the details are listed in Table S9. The

16

reactions were performed in the range from 2 MPa to 8 MPa H2. The reaction order with respect to

17

H2 pressure over Re-Pd(L, 413) and Re(L, 413) was estimated to be +1.3 and +1.2, respectively. The

18

positive reaction order indicates that the reaction rate was strongly influenced by the H2 pressure,

19

which means that dissociation of H2 or the reaction of the dissociated hydrogen species are involved

20

in the rate determining step. Considering that dissociation of H2 is very fast on Pd or Re metal

21

surface, the reaction of the dissociated hydrogen species will be the rate-determining step. According

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1

to our previous works [28], the reaction order of almost +1 with respect to H2 pressure means that

2

hydrogen is heterolytically dissociated to proton (H+) + hydride (H-) on metal surface modified with

3

the metal oxide, and the produced hydride is an active species for the hydrogenation and

4

hydrogenolysis reaction [28]. In the present case, it is suggested that both Re-Pd(L, 413) and Re(L,

5

413) catalysts have Re metal particles modified with Ren+, the interface between Re0 and Ren+ plays

6

an important role on the heterolytic dissociation of H2. The catalyst activity can be controlled by

7

highly dispersed Re0(HCP) and Re0(FCC) particles modified with Ren+ and also by the promoting

8

effect of Pd addition on the adsorption of STA. The number of the interface between Re metal and

9

Ren+ can be related to the reduction degree of Re species, and too high reduction degree can decrease

10

the amount of Ren+, and the number of the interface. In the case of Re-Pd(L, 413), the reduction

11

degree of the Re species can be adjusted by the liquid-phase reduction, and at the same time, the

12

presence of Pd maintains high dispersion of Re(HCP) and Re(FCC) particles and strengthen the STA

13

adsorption.

14

Based on the above results and discussion, we proposed the following reaction scheme of

15

hydrogenation of STA over the Re-Pd(L, 413) (Scheme 1). One of the reasons for high catalytic

16

activity of Re-Pd(L, 413) can be explained by the effect of Pd addition on the stronger adsorption of

17

the carboxylic acid. Therefore, one possible interpretation of the catalytically active sites is the

18

interface between Pd metal and Re metal, where both metals are modified with Ren+ species.

19

Considering the presence of Re=O and Re-O detected by EXAFS analysis, the structure of Ren+

20

species can be depicted in Scheme 1. At the first step (Step I), STA is adsorbed on Pd metal site, and

21

the adsorbed STA can diffuse to neighboring Re metal site (Step II). According to the previous

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1

reports [8, 29], carboxylic acid was adsorbed on the surface of Pd0 and Re0. The activity of Re(L,

2

413) catalyst is much higher than that of Pd(L, 413), and therefore Re metal-Ren+ interface can be the

3

main active site. H2 is activated heterolytically to give hydride and proton species at the interface

4

(Step III). The hydride species attacks the absorbed carboxylic acid, and the hydrogenolysis of C-OH

5

proceeds (Step IV) to give the adsorbed aldehyde. The remaining hydroxyl group over Re0 species is

6

hydrogenated by H2 to give H2O (Step V). It has been reported that Ir-ReOx/SiO2 catalyst exhibited

7

very high activity in the selective hydrogenation of unsaturated aldehyde to unsaturated alcohol [30].

8

This suggests that the hydrogenation of aldehyde to alcohol also proceeds with hydride at the

9

interface between Re metal-Ren+ species (Step VI). In this catalytic cycle, the rate determining step is

10

the Step IV [8], and the coverage of the active hydride species can be proportional to H2 pressure,

11

which can be explained by the first reaction order with respect to H2 pressure (Figure 9).

12 13

Conclusions

14

The catalytic activity of Re-Pd/SiO2 catalysts in the hydrogenation of stearic acid is influenced by

15

the reduction methods. The liquid-phase reduction is more suitable than the gas-phase reduction for

16

the catalyst activation. The activity of these catalysts is sensitive to air because of high oxophilicity

17

of Re, and the catalysts must be handled without contact to air. The Re-Pd/SiO2 (Re/Pd = 8) catalyst

18

can be reused if the catalyst is not exposed to air during the procedures for the catalyst reuse.

19

Catalyst characterization indicates that the liquid-phase reduced Re-Pd/SiO2 has Pd0, Re0(HCP),

20

Re0(FCC), Re3+ and Re4+, and the surface metal (Pd0, Re0(HCP), Re0(FCC)) will be covered with

21

Re3+, and Re4+ species. In contrast, the gas-phase reduced Re-Pd/SiO2 (Re/Pd = 8) has Pd0, 25

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Re0(HCP), Re0(FCC), Re3+, Re4+, and Re6+, and the molar ratio of Re0(HCP and FCC) and Re6+ to

2

total Re was larger than that on the liquid-phase reduced catalyst. The reduction method influences

3

the proportion of Re0, Re3+, Re4+, and Re6+ species. The presence of both Re0 and Ren+ species such

4

as Re3+ and Re4+ can be connected to the high catalytic activity. The kinetic results of hydrogenation

5

of stearic acid over Re-Pd/SiO2 (Re/Pd = 8) and Re/SiO2 with the same Re loading amount suggest

6

that the role of Pd is to strengthen the interaction of stearic acid with the active site and that of Ren+

7

is to promote the heterolytic dissociation of H2.

8 9 10 11

Acknowledgements

12 13

A part of this work is supported by the JSPS KAKENHI “Grant-in-Aid for Scientific Research

14

(A)” (26249121), “Grant-in-Aid for JSPS Fellows” (263554). We also appreciate the Technical

15

Division in School of Engineering in Tohoku University for XPS and STEM-EDX measurements.

16 17

Supporting information

18 19 20

Supporting Information Available: Details of kinetic and characterization results (Figures S1~S8 and Tables S1~ S8). This material is available free of charge via the Internet at http://pubs.acs.org.

21

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Tamura, M.; Nakagawa, Y. Chem. Rec. 2014, 14, 1041-1054. d) Tomishige, K.; Nakagawa, Y.;

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5 6 7 8

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ACS Catalysis

Figure caption

2 3

Figure 1. XRD patterns of Pd, Re-Pd and Re catalysts after the reaction or reduction.

4

(a) Pd(L, 413, Reaction), (b) Re-Pd(L, 413, Reaction) (Re/Pd = 2). (c) Re-Pd(L, 413, Reaction) (Re/Pd = 4),

5

(d) Re-Pd(L, 413, Reaction) (Re/Pd = 6), (e) Re-Pd(L, 413, Reaction) (Re/Pd = 8), (f) Re-Pd(L, 413,

6

Reaction) (Re/Pd = 12), (g) Re(L, 413, Reaction), (h) Re-Pd(G, 473) (Re/Pd = 8), (i) Re(G, 473), (j) Re(G,

7

773).

8

Reaction conditions are described in Table 1.

9

Peak assignment:
SiO2;
Re(HCP);  Pd.

10 11

Figure 2. The results of XPS for Pd 3d over (A) Pd(L, 413, Reaction), (B) Re-Pd(L, 413, Reaction) (Re/Pd =

12

8) and (C) Re-Pd(G, 473) (Re/Pd = 8)a catalysts.

13

Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 100 mg, reaction

14

temperature 413 K, H2 pressure 8.0 MPa, reaction time 4 h.

15

a

16

The analysis results are shown in Table 5.

Gas-phase reduction conditions: 100% H2 30 mL/min, temperature 473 K, time 1 h.

17 18

Figure 3. The results of XPS for Re 4f ((A) Re-Pd(L, 413, Reaction) (Re/Pd = 8), (B) Re(L, 413, Reaction)

19

(Re = 14 wt%), (C) Re-Pd(G, 473) (Re/Pd = 8)a, (D) Re(G, 473) (Re = 14 wt%)a and (E) Re(G, 773) (Re = 14

20

wt%)a), and the analysis results for Re 4f ((F) Re-Pd(L, 413, Reaction) (Re/Pd = 8), (G) Re(L, 413, Reaction)

21

(Re = 14 wt%), (H) Re-Pd(G, 473) (Re/Pd = 8)a, (I) Re(G, 473) (Re = 14 wt%)a and (J) Re(G, 773) (Re = 14

22

wt%)a).

23

Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 100 mg, reaction

24

temperature 413 K, H2 pressure 8.0 MPa, reaction time 4 h.

25

Black line: raw date, red line: 4f7/2 and 4f5/2 for Re0, blue line: 4f7/2 and 4f5/2 for Re3+, green line: 4f7/2 and 4f5/2

26

for Re4+, orange line: 4f7/2 and 4f5/2 for Re6+, yellow broken line: the result of fitting.

27

a

28

The analysis results are shown in Table 5.

Gas-phase reduction conditions: 100% H2 30 mL/min, time 1 h.

29 30

Figure 4. Re L3-edge XANES spectra of Re-Pd and Re catalysts after the reaction or reduction.

31

(a) Re(L, 413, Reaction) (Re = 14 wt%), (b) Re(G, 473) (Re = 14 wt%), (c) Re(G, 773) (Re = 14 wt%), (d)

32

Re(G, 473, Reaction) (Re = 14 wt%), (e) Re(G, 773, Reaction) (Re = 14 wt%), (f) Re-Pd (L, 413, Reaction)

33

(Re/Pd = 8), (g) Re-Pd(G, 473) (Re/Pd = 8), (h) Re-Pd(G, 473, Reaction) (Re/Pd = 8), (i) Re(Calcination), (j)

34

Re-Pd(Calcination), (k) Re powder, (l) ReO2, (m) ReO3, (n) Re2O7.

35 36

Figure 5. Results of Re L3-edge EXAFS analysis of Re-Pd (Re/Pd = 8) and Re catalysts after the reaction or

37

reduction.

38

(I) k3-Weighted EXAFS oscillations. (II) Fourier transform of k3-weighted Re L3-edge EXAFS, FT range: 32

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30–120 nm−1 (after the reduction treatment). (III) Fourier filtered EXAFS data (solid line) and calculated data

2

(dotted line), Fourier filtering range: 0.092–0.350 nm. (a) Re powder, (b) Re(L, 413, Reaction) (Re = 14 wt%),

3

(c) Re(G, 473) (Re = 14 wt%), (d) Re(G, 773) (Re = 14 wt%), (e) Re(G, 473, Reaction) (Re = 14 wt%), (f)

4

Re(G, 773, Reaction) (Re = 14 wt%), (g) Re-Pd (L, 413, Reaction) (Re/Pd = 8), (h) Re-Pd(G, 473) (Re/Pd = 8),

5

(i) Re-Pd(G, 473, Reaction) (Re/Pd = 8), (j) Re(Calcination), (k) Re-Pd(Calcination), (l) Re2O7.

6 7

Figure 6. TEM image and elemental mappings by STEM-EDX of Re-Pd(L, 413, Reaction) (Re/Pd = 8).

8

(a) TEM image, (b) Si elemental mapping, (c) Re elemental mapping, (d) Pd elemental mapping.

9 10

Figure 7. A model structure of Re-Pd(L, 413) (Re/Pd = 8).

11 12

Figure 8. Effect of initial STA concentration in the hydrogenation of STA over Re-Pd(L, 413) (Re/Pd = 8)

13

and Re(L, 413) catalysts.

14

Reaction conditions: 3~15 wt% STA solution 20 g, 1,4-dioxane solvent 5.7-20 g, STA 0.60-1.0 g, catalyst

15

0.060-0.10 g, reaction temperature 413 K, H2 pressure 8.0 MPa.

16

The detailed data are shown in Table S6.

17 18

Figure 9. Effect of H2 pressure in the hydrogenation of STA over Re-Pd(L, 413) (Re/Pd = 8) and Re(L, 413)

19

catalysts.

20

Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 100 mg, reaction

21

temperature 413 K.

22

The detailed data are shown in Table S9.

23 24

Scheme 1. Model scheme of hydrogenation of STA over Re-Pd(L, 413).

25 26

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(i)

Intensity / counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(h) (g) (f) (e) (d) (c) (b) (a)

8 9 10

0

11

20

40 2θ / degree

60

80

12 13

Figure 1. XRD patterns of Pd, Re-Pd and Re catalysts after the reaction or reduction.

14

(a) Pd(L, 413, Reaction), (b) Re-Pd(L, 413, Reaction) (Re/Pd = 2). (c) Re-Pd(L, 413, Reaction) (Re/Pd = 4),

15

(d) Re-Pd(L, 413, Reaction) (Re/Pd = 6), (e) Re-Pd(L, 413, Reaction) (Re/Pd = 8), (f) Re-Pd(L, 413,

16

Reaction) (Re/Pd = 12), (g) Re(L, 413, Reaction), (h) Re-Pd(G, 473) (Re/Pd = 8), (i) Re(G, 473), (j) Re(G,

17

773).

18

Reaction conditions are described in Table 1.

19

Peak assignment: :
SiO2;
Re(HCP);  Pd.

20

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ACS Catalysis

(A)

(C) 1800

2100

334.7

340.0

Intensity / cps

Intensity / cps

2000

1600 1400 1200 1000

340.8

2000 1900 1800 1700

341

339

337

335

333

345 343 341 339 337 335 333 331 Binding Energy / eV

Binding Energy / eV (B)

335.4

1600 343

Intensity / cps

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 54

3850

335.1 340.3

3800 3750 3700 3650 343

341 339 337 335 Binding Energy / eV

333

Figure 2. The results of XPS for Pd 3d over (A) Pd(L, 413, Reaction), (B) Re-Pd(L, 413, Reaction) (Re/Pd = 8) and (C) Re-Pd(G, 473) (Re/Pd = 8)a catalysts. Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 100 mg, reaction temperature 413 K, H2 pressure 8.0 MPa, reaction time 4 h. a

Gas-phase reduction conditions: 100% H2 30 mL/min, temperature 473 K, time 1 h.

The analysis results are shown in Table 5.

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52

50

48 46 44 42 40 Binding Energy / eV

38

50

48 46 44 42 40 Binding Energy / eV

38

50

48 46 44 42 40 Binding Energy / eV

38

52

50

48 46 44 42 40 Binding Energy / eV

38

52

50

48 46 44 42 40 Binding Energy / eV

38

52

50

48 46 44 42 40 Binding Energy / eV

38

52

50

48 46 44 42 40 Binding Energy / eV

38

7000 5000 3000 1000

(H) 4000 3000 2000 1000 0 52

50

48 46 44 42 40 38 Binding Energy / eV

(D) 8000 6000 4000 2000 0

Intensity / cps

Intensity / cps

Intensity / cps

52

(C) 4000 3000 2000 1000 0

Intensity / cps

52

(G) 9000

(I) 8000 6000 4000 2000 0

52

50

48 46 44 42 40 Binding Energy / eV

38

Intensity / cps

Intensity / cps

(B) 9000 7000 5000 3000 1000

Intensity / cps

(F) 5000 4000 3000 2000 1000

(J) 4000 3000 2000 1000 0

(E) 4000 3000 2000 1000 0 52

50

48 46 44 42 40 Binding Energy / eV

38

Intensity / cps

Intensity / cps

(A) 5000 4000 3000 2000 1000

Intensity / cps

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Figure 3. The results of XPS for Re 4f ((A) Re-Pd(L, 413, Reaction) (Re/Pd = 8), (B) Re(L, 413, Reaction) (Re = 14 wt%), (C) Re-Pd(G, 473) (Re/Pd = 8)a, (D) Re(G, 473) (Re = 14 wt%)a and (E) Re(G, 773) (Re = 14 wt%)a), and the analysis results for Re 4f ((F) Re-Pd(L, 413, Reaction) (Re/Pd = 8), (G) Re(L, 413, Reaction) (Re = 14 wt%), (H) Re-Pd(G, 473) (Re/Pd = 8)a, (I) Re(G, 473) (Re = 14 wt%)a and (J) Re(G, 773) (Re = 14 wt%)a). Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 100 mg, reaction temperature 413 K, H2 pressure 8.0 MPa, reaction time 4 h. Black line: raw date, red line: 4f7/2 and 4f5/2 for Re0, blue line: 4f7/2 and 4f5/2 for Re3+, green line: 4f7/2 and 4f5/2 for Re4+, orange line: 4f7/2 and 4f5/2 for Re6+, yellow broken line: the result of fitting. a

Gas-phase reduction conditions: 100% H2 30 mL/min, time 1 h.

The analysis results are shown in Table 5. 36

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ACS Catalysis

(n) (m) (l) (k)

Normalized absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 54

10520

(j) (i) (h) (g) (f) (e) (d) (c) (b) (a)

10530

10540

10550

10560

E / eV

Figure 4. Re L3-edge XANES spectra of Re-Pd and Re catalysts after the reaction or reduction. (a) Re(L, 413, Reaction) (Re = 14 wt%), (b) Re(G, 473) (Re = 14 wt%), (c) Re(G, 773) (Re = 14 wt%), (d) Re(G, 473, Reaction) (Re = 14 wt%), (e) Re(G, 773, Reaction) (Re = 14 wt%), (f) Re-Pd (L, 413, Reaction) (Re/Pd = 8), (g) Re-Pd(G, 473) (Re/Pd = 8), (h) Re-Pd(G, 473, Reaction) (Re/Pd = 8), (i) Re(Calcination), (j) Re-Pd(Calcination), (k) Re powder, (l) ReO2, (m) ReO3, (n) Re2O7.

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(I)

30

.

(II)

(l)

10

.

(l)

(k) (j)

(k) (j)

(i) (h) ×3

(i) (h)

(g)

k3 x(k)

×2

(e) (d) (c) ×3

(g)

|F(r)|

(f)

(f) (e) (d) (c) (b)

(b) ×2

(a)

(a) 2

4

6

8

10

12

0

k / 10 nm-1

(III)

1

2 3 4 Distance / 0.1 nm

.

5

6

.

10

.

(k) (j) (i) (h) k3 x(k)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(g)

×2

(f) (e) (d) (c)

×2

(b)

2

4

6

8 k / 10 nm-1

10

12

. catalysts after the reaction or Figure 5. Results of Re L3-edge EXAFS analysis of Re-Pd (Re/Pd = 8) and Re reduction. (I) k3-Weighted EXAFS oscillations. (II) Fourier transform of k3-weighted Re L3-edge EXAFS, FT range: 30–120 nm−1. (III) Fourier filtered EXAFS data (solid line) and calculated data (dotted line), Fourier filtering range: 0.092–0.350 nm. (a) Re powder, (b) Re(L, 413, Reaction) (Re = 14 wt%), (c) Re(G, 473) (Re = 14 wt%), (d) Re(G, 773) (Re = 14 wt%), (e) Re(G, 473, Reaction) (Re = 14 wt%), (f) Re(G, 773, Reaction) (Re = 14 wt%), (g) Re-Pd (L, 413, Reaction) (Re/Pd = 8), (h) Re-Pd(G, 473) (Re/Pd = 8), (i) Re-Pd(G, 473, Reaction) (Re/Pd = 8), (j) Re(Calcination), (k) Re-Pd(Calcination), (l) Re2O7.

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ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) 300 nm

(b) Si Ka1

(c) Re La1

(d) Pd Ka1

Figure 6. TEM image and elemental mappings by STEM-EDX of Re-Pd(L, 413, Reaction) (Re/Pd = 8). (a) TEM image, (b) Si elemental mapping, (c) Re elemental mapping, (d) Pd elemental mapping.

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Page 41 of 54

0

Re

Re0(FCC) Ren+ Re0

Re0(HCP) 2~3 nm Re0

7.1 nm

Re 0

Pd0 (FCC)

Re 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

SiO2

Figure 7. A model structure of Re-Pd(L, 413) (Re/Pd = 8).

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ln (Conversion rate / mmol・g-Cat-1・h-1)

ACS Catalysis

2.0 1.5

Re-Pd(L, 413) slope +0.1

1.0 0.5

Re(L, 413) slope +0.8

0.0

-0.5 0.5 1.0 1.5 2.0 2.5 3.0 ln (Initial STA concentration / wt%)

Figure 8. Effect of initial STA concentration in the hydrogenation of STA over Re-Pd(L, 413) (Re/Pd = 8) and Re(L, 413) catalysts. Reaction conditions: 3~15 wt% STA solution, 1,4-dioxane solvent 5.7-20 g, STA 0.60-1.0 g, catalyst 0.060-0.10 g, reaction temperature 413 K, H2 pressure 8.0 MPa. The detailed data are shown in Table S6.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

ln (Conversion rate / mmol・g-Cat-1・h-1)

Page 43 of 54

2.0 Re-Pd(L, 413) Re/Pd = 8 slope +1.3

1.0

0.0

-1.0

Re(L, 413) slope +1.2

-2.0 0.0 1.0 2.0 ln ( H2 pressure / MPa)

3.0

Figure 9. Effect of H2 pressure in the hydrogenation of STA over Re-Pd(L, 413) (Re/Pd = 8) and Re(L, 413) catalysts. Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 100 mg, reaction temperature 413 K. The detailed data are shown in Table S9.

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ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

O

OH

O

OH

Ren+ Pd0

R

Ren+

Pd0

Pd0 Pd0

Re0 Re0

Re0

Re0

O

OH R

H+ O

(VI)

Pd0

Pd0

O

CH Re0 Re0

Pd0 Pd0

OH

O

Re0

R

OH

Ren+

H-

O

OH

(I)

R

OH Ren+

Page 44 of 54

Re0

Pd0

O

H

Ren+

O

Pd0

Pd0 Pd0

OH Ren+

O Re0 Re0

Re0

Re0

H2O

(V)

(II)

H2 O

Ren+ Pd0

R

OH

Pd0

O Pd0 Pd0

O

CH H O

OH

O

Re0 Re0

Re0

R

OH

Ren+ Re0

Pd0

(IV)

O

Pd0

Pd0 Pd0

(III)

H2

O

OH

Pd0

Pd0

O H

Ren+

O

Pd0 Pd0

O

Re0 Re0

OH Ren+

HRe0

Re0

Scheme 1. Model scheme of hydrogenation of STA over Re-Pd(L, 413).

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OH Ren+

O

Re0 Re0

H+ R

O H

Ren+

Re0

Re0

Page 45 of 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Table 1 Effect of the amount of Re over Re-Pd catalysts reduced in liquid phase at 413 K in the STA hydrogenation. TOF Entry Catalyst Re/Pd Time Conv. Selectivity / % Conversion rate -1 -1 / h-1 /h /% C18H37OH C18H38 C17H36 Others / mmol・g-Cat ・h 1 2 3 4 5 6 7

Pd(L, 413)a

－

1

0.0

－

－

－

－

0.0

－

Re-Pd(L, 413)

a

2

9

7.9

97

1.4

0.8

0.6

0.2

1.3

Re-Pd(L, 413)

a

4

3

18

97

2.2

0.5

0.4

1.6

4.0

Re-Pd(L, 413)

a

6

2

33

97

2.6

0.4

0.4

3.7

6.8

Re-Pd(L, 413)

a

8

1

22

96

2.7

0.5

0.5

5.1

6.9

Re-Pd(L, 413) 12

1

26

97

2.6

0.5

0.4

6.2

5.5

4

15

92

3.9

0.9

2.8

1.3

1.8

a

Re(L, 413)

b

－

Reaction conditions: 5 wt% STA solution 20 g (STA 1 g, 1,4-dioxane 19 g), catalyst amount 150 mg, reaction temperature 413 K, H2 pressure 8.0 MPa, Others: CO2, CH4 and C2H6. a Pd loading amount is 1 wt%. b Re loading amount is 14 wt% and it corresponds to that of Re/Pd = 8.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Table 2 Effect of the reduction treatment for STA hydrogenation over Re-Pd (Re/Pd = 8) and Re catalysts. Entry Catalyst

Re/Pd Time Conv. Selectivity / %

Conversion rate

/h

/%

C18H37OH C18H38 C17H36 Others / mmol・g-Cat-1・h-1

1

Re-Pd(L, 413) 8

1

15

96

2.5

0.7

0.3

5.3

2

Re-Pd(G, 473) 8

4

13

97

1.6

0.6

0.5

1.2

3

Re(L, 413)

―

4

18

94

4.3

1.0

1.2

1.6

4

Re(G, 473)

―

4

89

2.1

3.4

5.4

0.1

5

Re(G, 773)

―

4

－

－

－

－

< 0.1

1.4