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Polymeric Ruthenium Porphyrin-Functionalized Carbon Nanotubes and Graphene for Levulinic Ester Transformations into γ‑Valerolactone and Pyrrolidone Derivatives Ting Zhang,†,‡,§,∥ Yao Ge,†,‡,§,∥ Xuefeng Wang,† Jinzhu Chen,*,‡,§ Xueli Huang,† and Yinnian Liao† †

Key Laboratory of Xinjiang Coal Clean Conversion and Chemical Process, College of Chemistry and Chemical Engineering, Xinjiang University, 14 Sheng Li Road, Urumqi 830046, P. R. China ‡ College of Chemistry and Materials Science, Jinan University, No. 601 Huangpu Avenue West, Tianhe District, Guangzhou 510632, P. R. China § Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No. 2 Nengyuan Road, Wushan, Tianhe District, Guangzhou 510640, P. R. China S Supporting Information *

ABSTRACT: Polymeric ruthenium porphyrin-functionalized carbon nanotubes (Ru-PP/CNTs) were prepared by the metallation of polymeric porphyrinfunctionalized carbon nanotubes (PP/CNTs) with Ru3(CO)12, whereas PP/CNTs were obtained by the condensation of terephthaldehyde and pyrrole in the presence of CNTs. The Ru-PP/CNTs have a thin layer of highly cross-linked polymeric ruthenium porphyrin coating over the CNT surface via strong π−π stacking interactions, thus showing a bilayered structure with an amorphous polymeric outer surface and an internal CNT core. Polymeric ruthenium porphyrin-functionalized reduced graphene oxide (Ru-PP/RGO) was prepared with a synthetic procedure similar to Ru-PP/CNTs, with RGO as the internal core. Both Ru-PP/CNTs and Ru-PP/RGO showed excellent catalytic performance toward hydrogenation of biomass-related ethyl levulinate (EL) to γ-valerolactone (GVL) with Ru-centered porphyrin units as the catalytic active species. Under optimized reaction conditions, a GVL yield higher than 99% with a complete conversion of EL was observed over both Ru-PP/CNTs and Ru-PP/RGO. In addition to GVL preparation, the versatile Ru-PP/ CNTs can efficiently promote reductive amination of EL with various amines for the synthesis of pyrrolidone derivatives, with the corresponding yields ranging from 96.3 to 88.7%. Moreover, the composite materials of both Ru-PP/CNTs and Ru-PP/RGO behave as heterogeneous catalysts in the reaction system and can be easily reused. excellent activity and selectivity.7−9 Various Ru-based catalysts have been reported for the hydrogenation of LA and levulinic ester to GVL, including homogeneous catalysts of RuCl3− PPh3,10 Ru(acac)3−PBu3 (acac, acetylacetonate),11 Ru(acac)3− P(n-oct)3,12 Ru(acac)3−TPPTS [TPPTS, tris(3-sulfophenyl)phosphine trisodium salt],13 and Shvo catalyst,14 heterogeneous catalysts of Ru/C,15−20 Ru/MOFs (metal−organic frameworks),21 Ru/TiO2,22,23 Ru/SiO2,24 Ru/Beta-12.5 (DeAl-Hbeta),25 Ru/hydroxyapatite26 Ru3(CO)12-derived Ru nanoparticles (NPs),27 Ru/SBA-SO3H (sulfonic acid-functionalized mesoporous silica),28 and Ru/SPES (sulfonated polyethersulfone),29 and bimetallic catalysts of Ru−Re/C,30,31 Ru−Sn/ C,32,33 Ru−Ni/Meso-C,34 Ru−Pd/TiO2,35 and Ru−La/ Al2O3.36 Ru-based homogeneous catalysts generally showed outstanding catalytic performance for GVL synthesis; however,

1. INTRODUCTION The over reliance of our society on the diminishing and nonrenewable fossil resources such as petroleum, coal, and natural gas is pushing researchers to find a renewable alternative for a sustainable supply of chemicals and fuels. In this aspect, renewable and abundant biomass is considered as a promising and potential resource to reduce our dependence on fossil resources.1−3 In addition, the carbon-neutral nature of the biomass can maintain the carbon balance of our environment and diminish the negative effects triggered by the use of fossil resources such as CO2 emission and environmental degradation. Among the biomass-derived platform molecules, γvalerolactone (GVL) is a versatile building block for valuable chemicals and a green and efficient solvent for biomass conversion.4 In addition, GVL is widely used in the food industry and has high potential applications in the production of fuel precursors for gasoline and diesel.5,6 GVL is generally prepared by the hydrogenation of cellulosederived levulinic acid (LA) with homogeneous or heterogeneous catalysts, and ruthenium (Ru) catalysts generally exhibit © 2017 American Chemical Society

Received: April 10, 2017 Accepted: June 16, 2017 Published: July 7, 2017 3228

DOI: 10.1021/acsomega.7b00427 ACS Omega 2017, 2, 3228−3240

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toxic and air- and moisture-sensitive phosphorus ligands were applied in the hydrogenation reactions.37 Therefore, inspired by nature, multidentate nitrogen ligands such as porphyrins should be an excellent candidate to promote the catalytic reactions under phosphane-free conditions. In fact, ruthenium porphyrin complexes were reported as versatile catalysts in various reactions such as selective hydrogenation of trans-cinnamaldehyde,38 epoxidation of olefins,39 hydroxylation of hydrocarbons,40 disproportionation of nitricoxide,41 aziridination of styrenes,42,43 amination of olefins and benzylic C−H bond,44,45 and photocatalytic reactions.46 Hence, we think that ruthenium porphyrin complexes should be promising catalysts for the hydrogenation of LA and levulinic ester into GVL. However, in most cases, ruthenium porphyrin complexes function as homogeneous catalysts resulting in a separation problem for catalyst recycling. In this research, polymeric ruthenium porphyrin-functionalized carbon nanotubes (Ru-PP/CNTs, Scheme 1c) and polymeric ruthenium porphyrin-functionalized reduced graphene oxide (Ru-PP/RGO) were prepared as recyclable heterogeneous catalysts for ethyl levulinate (EL) hydrogenation to GVL (Scheme 2a). The Ru-PP/CNTs were obtained by the metallation of polymeric porphyrin-functionalized CNTs (PP/CNTs) with Ru3(CO)12 (Scheme 1c), whereas PP/CNTs were prepared by the condensation of terephthaldehyde and pyrrole in the presence of CNTs (Scheme 1b). The Ru-PP/CNTs have a thin layer of highly cross-linked polymeric metalloporphyrin coating over the CNT surface via strong π−π stacking interactions, thus showing a bilayered structure with an amorphous polymeric outer surface and an internal CNT core. Under optimized reaction conditions, a GVL yield higher than 99% with a complete conversion of EL was observed over both Ru-PP/CNTs and Ru-PP/RGO. In addition to GVL preparation, the versatile RuPP/CNTs can efficiently promote reductive amination of EL with various amines for the synthesis of pyrrolidone derivatives (Scheme 2a). Pyrrolidine derivatives are widely used in many regions such as solvents, surfactants, and complexing agents.47−49 Generally, pyrrolidines are obtained by the amination of LA or levulinic ester with amines under a noncatalytic process by using formic acid50 or under catalytic hydrogenation/transfer hydrogenation conditions by using carbon- or metal oxide-supported transition metal catalysts, including Pt,51,52 Ru,53 Au,54,55 and Ir.56 In our case, the developed Ru-PP/CNTs smoothly catalyzed the transformation of EL and primary amines into 5-methyl-2pyrrolidone and 5-methyl-N-alkyl-2-pyrrolidones under a hydrogen atmosphere. Notably, the 5-methyl-2-pyrrolidone and 5-methyl-N-alkyl-2-pyrrolidones (alkyl = n-propyl, n-butyl, and n-octyl) were obtained in one pot with excellent yields from 96.3 to 88.7% under the investigated conditions.

Scheme 1. Proposed Structures of (a) PP and (b) PP/CNTs and (c) Active Species Over PP/CNT-Derived Composite Materials

presumably attributed to the strong π−π stacking interactions between the porphyrin units of highly cross-linked PP and the external wall of the CNTs (Scheme 1b). Ru-PP/CNTs were achieved by the metallation of PP/CNTs with Ru3(CO)12 (Scheme 1c), whereas polymeric rhodium porphyrin complex-functionalized CNTs (Rh-PP/CNTs) and polymeric iridium porphyrin complex-functionalized CNTs (Ir-PP/ CNTs) were prepared by the metallation of PP/CNTs with RhCl3 and IrCl3, respectively (Scheme 1c). PP-functionalized RGO (PP/RGO) and Ru-PP/RGO were synthesized following the same synthetic procedure used for PP/CNTs and Ru-PP/ CNTs, respectively, except that the corresponding support CNTs were replaced by RGO. The resulting composite materials PP/CNTs, PP/RGO, Ru-PP/CNTs, Rh-PP/CNTs, Ir-PP/CNTs, and Ru-PP/RGO were systematically characterized by scanning electron microscopy (SEM), high-resolution

2. RESULTS AND DISCUSSION Polymeric porphyrin (PP, Scheme 1a) was synthesized via direct condensation of terephthaldehyde with pyrrole.57 The resulting PP bears highly cross-linked and covalently linked porphyrin units throughout the whole polymer matrices, whereas PP/CNTs (Scheme 1b) were obtained by the condensation of terephthaldehyde and pyrrole in the presence of CNTs. The porphyrin ring is a π-conjugated system in a planar arrangement with a total of 26 electrons and an 18π aromatic character, whereas CNTs have a sp2-hybridized graphite structure and a π-conjugated backbone. Therefore, the formation of a stable and uniform PP/CNT composite is 3229


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Scheme 2. (a) Conversions of LA and Levulinic Ester into GVL and Pyrrolidone Derivatives and (b) Proposed Mechanism for Ru-PP/CNT-Promoted EL to GVL Transformation

transmission electron microscopy (HRTEM), X-ray diffraction (XRD), nitrogen adsorption−desorption, X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). In addition, Ru-PP/CNTs, Rh-PP/CNTs, Ir-PP/CNTs, and Ru-PP/RGO were used as heterogeneous catalysts in the transformations of biomassderived LA and levulinic ester into GVL and pyrrolidone derivatives (Scheme 2a). SEM of PP/CNTs and typical HRTEM images of CNTs, PP/CNTs, and Ru-PP/CNTs are compared in Figure 1. Pristine CNTs exhibited a smooth surface with a graphitized structure (Figure 1a,b). By contrast, a composite material of PP/CNTs had a thin layer of PP coating of around 3−5 nm over the CNT surface, thus showing a bilayered structure with an amorphous and rough outer surface and an internal CNT core (Figure 1e,f). SEM of PP/CNTs demonstrated a uniform deposition of CNTs with a thin layer of PP (Figure 1c,d). Both SEM (Figure 1c,d) and transmission electron microscopy (TEM) (Figure 1e,f) analyses of PP/CNTs indicated the fibrous and uniform composite PP/CNTs with a diameter of around 30 nm and length of several micrometers. After metallation of the composite PP/CNTs with Ru3(CO)12 to give Ru-PP/CNTs, TEM analysis indicated the supported ruthenium porphyrin species homogeneously and highly distributed throughout the surface of the Ru-PP/CNTs (Figure 1g−i). The formation of these uniform and highly distributed electrondense regions can be attributed to the presence of ruthenium porphyrin complexes. The mean diameters of these electrondense regions were around 0.72 nm (Figure 1g), which was presumably caused by the beam damage during the TEM

Figure 1. TEM images of CNTs (a,b), PP/CNTs (e,f), Ru-PP/CNTs (g−i), Ru NPs/PP/CNTs (j,k), and Ru NPs/N-CNTs (l,m) and SEM of PP/CNTs (c,d).

analysis and the light-sensitive nature of ruthenium porphyrin complexes, leading to decarbonylation of ruthenium porphyrin species, ruthenium atom migration, ruthenium cluster formation, and even resulting in the formation of ruthenium NPs. A similar phenomenon was previously observed by the TEM analysis on iridium N-heterocyclic carbene complexes covalently attached on CNTs,58 Ir(C2H4)2 species bonded to MgO, and the zeolite surface.59 At this stage, our XPS analysis on RuPP/CNTs also confirmed the presence of Ru-centered porphyrin units in Ru-PP/CNTs (Figure 6b, will be discussed below). Reduction of Ru-PP/CNTs with H2 at 200 °C led to the partial formation of ruthenium NPs supported on PP/ CNTs (Ru NPs/PP/CNTs). The TEM images of Ru NPs/PP/ 3230


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CNTs showed that the Ru NPs were uniform and highly dispersed throughout the surface of PP/CNTs with a mean NP size of around 1.7 nm (Figure 1j,k), suggesting polymeric immobilization effect of PP/CNTs on the Ru NPs. The formation of Ru(0) NPs over PP/CNTs was indicated by the subsequent XPS analysis (Figure 6c, will be discussed below). Moreover, Ru NPs encapsulated in N-doped CNTs (Ru NPs/ N-CNTs) were obtained by the heat treatment of Ru-PP/ CNTs with a pyrolysis temperature of 800 °C under a N2 atmosphere. HRTEM analysis showed that the Ru NPs were encapsulated in a carbon shell with a NP size of around 10 nm (Figure 1l,m). Figure 2 shows typical HRTEM images of RGO, PP/RGO, and Ru-PP/RGO. RGO nanosheets have a wrinkled, rippled, Figure 3. XRD patterns of CNTs, RGO, Ru-PP/CNTs, and Ru-PP/ RGO.

plane.64,65 However, the diffraction peaks corresponding to Ru crystallite were unobserved over both two Ru catalysts, indicating the major active species of Ru-centered porphyrin units for the two samples. In addition, the intensity of the two characteristic diffraction peaks at 25° and 43° observed in RuPP/CNTs significantly decreased compared with those of the pristine CNTs.66 Similar changes in the intensity of the XRD patterns were also observed between Ru-PP/RGO and RGO, as shown in Figure 3. The nitrogen adsorption−desorption isotherm, the pore size distribution curve, and the textural properties for Ru-PP/CNTs, Ru-PP/RGO, Rh-PP/CNTs, Ir-PP/CNTs, CNTs, and RGO are shown in Figure 4 and Table 1. The Brunauer−Emmett−

Figure 2. TEM images of RGO (a,b), PP/RGO (c−e), and Ru-PP/ RGO (f−h).

Figure 4. Nitrogen adsorption−desorption isotherms and pore-size distribution curves for the series of CNTs, RGO, Ru-PP/CNTs, recovered Ru-PP/CNTs, Ru-PP/RGO, Rh-PP/CNTs, and Ir-PP/ CNTs.

60,61

After the functionand crumpled structure (Figure 2a,b). alization of RGO with PP, the composite material of PP/RGO showed a thin layer of PP with a rough outer surface (Figure 2c−e). Metallation of the composite PP/RGO with Ru3(CO)12 gave Ru-PP/RGO; TEM analysis showed the electron-dense regions uniformly and highly distributed on the surface of RuPP/RGO (Figure 2f−h), indicating successful formation of ruthenium porphyrin species on Ru-PP/RGO. The obtained Ru-PP/CNTs and Ru-PP/RGO were further characterized by powder XRD. Both Ru-PP/CNTs and Ru-PP/ RGO showed two characteristic peaks at 2θ values around 25° and 43°, as shown in Figure 3.62,63 The peak at 2θ of 25° with high intensity was assigned as the hexagonal graphite characteristic diffraction peak (002) plane, whereas the peak at 2θ of 43° with low intensity was related to the (100)

Teller (BET) surface area of the precursor CNTs is 148.6 m2 g−1, which significantly decreased to 99.3 m2 g−1 for Ru-PP/ CNTs, 91.1 m2 g−1 for Rh-PP/CNTs, and 92.5 m2 g−1 for IrPP/CNTs. Similarly, Ru-PP/RGO showed a decreased BET surface area compared with the precursor RGO. The reduced surface area of Ru-PP/CNTs, Rh-PP/CNTs, Ir-PP/CNTs, and Ru-PP/RGO is attributed to the formation of composite materials of PP-CNTs and PP-RGO. The solid-state 13C NMR spectra of RGO and Ru-PP/RGO are compared in Figure 5. RGO showed one main peak at 120 ppm designating the resonance as a result of sp2 graphitic 3231


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to the oxidation state of Ru(VI) corresponding to the transdioxo Ru(VI) porphyrin species [RuVI(O)2PP].77,78 The formation of dioxygen species [RuVI(O)2PP] was presumably attributed to the exposure of RuII-PP/CNTs to air atmosphere leading to the oxidation reaction. This assumption can be proved by the fact that the oxidation of (5,10,15,20tetramesitylporphyrinato)ruthenium(II)carbonyl [RuII(TMP)(CO)] led to the formation of trans-dioxoruthenium (VI) porphyrin species [RuVI(TMP)(O)2].79 The Ru 3d3/2 XPS signal of Ru-PP/CNTs at 286.0 eV strongly overlaps with the intense C 1s peak from the support, which prevents the accurate analysis of the Ru-oxidation state from this binding energy value.76,80−82 The Ru 3d XPS of Ru-PP/RGO is very close to that of Ru-PP/CNTs (Figure 6b,f). In the case of Ru NPs/PP/CNTs, the Ru 3d XPS spectrum can be deconvoluted into two sets of doublet peaks with different intensities (Figure 6c). The doublet with peaks at 281.4 (assigned to Ru 3d5/2) and 286.0 eV (assigned to Ru 3d3/2) can be indexed to the RuII state. The other set with binding energies at 279.8 (assigned to Ru 3d5/2) and 284.1 eV (assigned to Ru 3d3/2) was ascribed to the Ru0 state.83,84 This result proved that the Ru-centered porphyrin species in Ru-PP/CNTs was partially reduced to give Ru0 NPs supported on PP/CNTs after H2 treatment at 200 °C. In addition, the separation distance between the Ru 3d5/2 and Ru 3d3/2 peaks was 4.0−4.1 eV. Therefore, the Ru 3d3/2 line could be expected to fall in the range of 284.1−284.2 eV, close to the C 1s line (284.6 eV). Therefore, the broad peak centered at 284.6 eV is attributed to a coincidence of Ru0 3d and C 1s.85 For the Rh-PP/CNT sample, the Rh 3d XPS signal can be deconvoluted into two distinguishable doublets with different intensities. The doublet observed with higher binding energies at 314.0 eV (assigned to Rh 3d3/2) and 309.4 eV (assigned to Rh 3d5/2) can be attributed to the Rh3+ species, indicating the formation of Rh(III)Cl-centered porphyrin species in Rh-PP/ CNTs.86,87 The other set of doublet at 311.8 eV (assigned to Rh 3d3/2) and 306.9 eV (assigned to Rh 3d5/2) can be indexed to the Rh0 state, suggesting the presence of Rh0 NPs supported on PP/CNTs in the Rh-PP/CNT sample,88,89 whereas the Rh3+ oxidation state was observed as the major phase (69%) on the surface of the Rh-PP/CNT sample according to the integration areas of the two doublets. The Ir 4f XPS region of the Ir-PP/CNTs showed a doublet at 62.1 eV (assigned to Ir 4f7/2) and 65.1 eV (assigned to Ir 4f5/2) with a 4f7/2/4f5/2 ratio of 4:3. The single signal of the Ir 4f7/2 peak at a binding energy of 62.1 eV was fully consistent with iridium in the Ir(III) oxidation state, confirming the presence of Ir(III)Cl-centered porphyrin units in the Ir-PP/CNTs.90,91 After a systematical characterization of Ru-PP/CNTs, RuPP/RGO, Rh-PP/CNTs, and Ir-PP/CNTs, the catalytic performance of the resulting Ru, Rh, and Ir catalysts was subsequently investigated with EL hydrogenation to GVL in methanol as a model reaction, using NaHCO3 as the cocatalyst (Scheme 2a). The influence of metallic sites was initially conducted. As expected, the target product GVL was unobserved under catalyst-free conditions (Table 2, entry 1). Under such conditions, NaHCO3 functioned as Brønsted base and promoted transesterification of EL with methanol to quantitatively give methyl levulinate (ML, Table 2, entry 1). Actually, the NaHCO3-promoted transesterification can be smoothly performed at room temperature by producing an ML yield around 59.6% (Table 2, entry 21). When PP/CNTs were examined as a transition metal-free catalyst for the blank experiment, EL was again quantitatively converted into ML

Table 1. Textural Properties of Various Samples sample

surface area [m2 g−1]a

average pore diameter [nm]b

pore volume [cm3 g−1]b

metal content [wt %]

CNT RGO Ru-PP/CNTs Ru-PP/CNTsc Ru-PP/RGO Rh-PP/CNTs Ir-PP/CNTs

148.6 34.8 99.3 102.3 12.7 91.1 92.5

20.7 4.0 10.0 4.5 5.8 7.5 7.7

2.7 0.4 1.0 0.9 0.2 0.5 0.6

2.0d 0.9d 1.5d 1.2e 2.9d

a

Obtained by the BET method. bPore size distribution curves were calculated using the adsorption branch of the isotherms and the density functional theory (DFT) method; whereas the pore sizes were obtained from the peak positions of the distribution curves. c Recovered Ru-PP/CNTs after five-time recycling with the reaction conditions described in Figure 7. dBased on ICP-AES analysis. eBased on XPS analysis.

Figure 5. Solid-state 13C NMR spectra of RGO and Ru-PP/GRO.

carbon,67 whereas Ru-PP/RGO revealed six main peaks from 192 to 104 ppm (Figure 5). The peak at 192 corresponded to the carbonyl group binding to the Ru(II) center.68 The resonances from 134 to 130 ppm were indexed to the phenylene linkages, whereas the signals at 112 and 104 ppm were assigned to porphyrin macrocycles.57,69−71 Finally, the peak at 120 ppm was designated to the sp2 graphitic carbon from the RGO support. The 13C NMR analysis of Ru-PP/RGO indicated the formation of composite materials of polymeric ruthenium porphyrin and RGO. The XPS analysis was further performed to study the chemical composition of the sample surface. Figure 6a shows the scan survey XPS spectrum of Ru-PP/CNTs, Ru-PP/RGO, Ru NPs/PP/CNTs, Rh-PP/CNTs, and Ir-PP/CNTs, confirming the existence of ruthenium for Ru-PP/CNTs, Ru-PP/RGO, and Ru NPs/PP/CNTs, rhodium for Rh-PP/CNTs, iridium for Ir-PP/CNTs, and nitrogen for all of the five samples (Scheme 1c). In addition, chlorine peaks were observed at 198.7 eV for Rh-PP/CNTs and at 198.4 eV for Ir-PP/CNTs (Figure 6a), which confirms the counterion function of the Cl− ion for the positively charged Rh3+ ion in the Rh-PP/CNT and Ir3+ ion in the Ir-PP/CNT samples (Scheme 1c).72 The Ru 3d5/2 XPS of Ru-PP/CNTs showed two signals at 281.4 and 282.3 eV. The signal at 281.4 eV was characteristic of those typical Ru2+ complexes coordinated with N-ligands, confirming the existence of Ru(II)-centered porphyrin units in Ru-PP/ CNTs,73−76 whereas the other signal at 282.3 eV was assigned 3232


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Figure 6. (a) XPS scan survey of Ru-PP/CNTs, Ru-PP/RGO, Ru NPs/PP/CNTs, Rh-PP/CNTs, and Ir-PP/CNTs; Ru 3d XPS of (b) Ru-PP/ CNTs, (c) Ru NPs/PP/CNTs, and (f) Ru-PP/RGO; (d) Rh 3d XPS of Rh-PP/CNTs; and (e) Ir 4f XPS of Ir-PP/CNTs.

compared in terms of the GVL formation rate. Herein, the formation rate of GVL was measured under a moderate GVL yield level of around 50%, given as the amount of formed GVL per amount of transition metal atoms per hour for the investigated catalyst. The resulting GVL formation rates from EL hydrogenation were 25.9 molGVL molRu−1 h−1 for Ru-PP/ CNTs, 10.3 molGVL molRh−1 h−1 for Rh-PP/CNTs, and 6.9 molGVL molIr−1 h−1 for Ir-PP/CNTs, further indicating an outstanding catalytic performance of Ru-PP/CNTs over RhPP/CNTs and Ir-PP/CNTs. To prove whether the organometallic Ru-porphyrin species is the true active site of Ru-PP/CNTs for the hydrogenation

with a negligible GVL yield (Table 2, entry 2). However, the contribution from PP/CNTs to the transesterification was very limited at room temperature (Table 2, entry 22). As transition metal catalysts, Rh-PP/CNTs and Ir-PP/CNTs were moderately active to EL hydrogenation, affording GVL yields of 59.8 and 52.1% (Table 2, entries 3 and 4), respectively. In the case of Ru-PP/CNTs, a quantitative GVL yield of 99.1% with a full conversion of EL was obtained, suggesting an excellent catalytic performance of Ru-PP/CNTs over Rh-PP/CNTs and Ir-PP/ CNTs in terms of GVL yield under the investigated conditions (Table 2, entry 5). The catalytic performance of Ru-PP/CNTs, Rh-PP/CNTs, and Ir-PP/CNTs was further quantitatively 3233


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reaction, Ru-PP/CNTs were calcined at 800 °C for 2 h under a nitrogen atmosphere, and Ru NPs/N-CNTs were obtained (Figure 1l,m). However, a significantly low GVL yield of 24.3% was obtained from the Ru NPs/N-CNTs (Table 2, entry 7). Under such conditions, the reduced catalytic performance of Ru NPs/N-CNTs on the GVL formation can presumably be related to the significantly increased Ru NP size and the encapsulated structure of Ru NPs, which inhibits the access of EL and the migration of GVL away from the active site of the Ru catalyst. In addition, Ru-PP/CNTs were further treated with H2 (3.0 MPa) at 200 °C to give Ru NPs supported on the PP/ CNT composite (Ru NPs/PP/CNTs) (Figure 1j,k). A reduced GVL yield of 72.6% was observed from the Ru NPs/PP/CNTs compared with a GVL yield of 99.1% from Ru-PP/CNTs (Table 2, entries 5 and 6). The above results indicate that the Ru-porphyrin species of Ru-PP/CNTs is the true active site for the hydrogenation reaction. The influence of Ru-PP/CNT loading levels on the EL-to-GVL transformation revealed a rise in the GVL yield with an increasing catalyst dosage under the investigated reaction conditions (Table 2, entries 5, 8−11). The influence of various cocatalysts on the hydrogenation of EL to GVL was further studied. In the absence of the cocatalyst, the catalytic performance of Ru-PP/CNTs by itself was inferior, producing a GVL yield of 9.4% (Table 2, entry 12). Notably, a combination of Ru-PP/CNTs and NaHCO3 significantly promotes the EL-to-GVL transformation, and GVL yields of 99.1% were dramatically achieved (Table 2, entry 5). Cocatalysts Na2CO3 and NaOH were moderately active to promote the transformation (Table 2, entries 13 and 14), whereas both potassium tert-butoxide (KOtBu) and 4dimethylaminopyridine (DMAP) showed limited effects on GVL formation (Table 2, entries 15 and 16). In general, NaHCO3 was superior to other cocatalysts in terms of GVL yields under the examined conditions. Reducing the loading level of the cocatalyst NaHCO3 resulted in a significantly decreased yield of GVL (Table 2, entries 5, 17−20). The effect of reaction temperature on the GVL yield indicated that the GVL yield increased from 53.2% at room temperature to 99.1% at 100 °C under the investigated conditions (Table 3, entries 1−5). Although the transesterification of EL with methanol was suppressed at room temperature, ML was still observed as intermediate for the ELto-GVL transformation. The effect of reaction time on the reactions showed an increase in the GVL yield with the reaction time (Table 3, entries 1 and 6−9). In addition, an increase in the hydrogen pressure efficiently promoted the EL-to-GVL transformation (Table 3, entries 1 and 10−11). Methanol was an excellent solvent for EL hydrogenation to GVL over Ru-PP/ CNTs, producing a quantitative yield of GVL (Table 3, entry 1), whereas ethanol was a good reaction medium for the hydrogenation, and a moderate GVL yield of 86.9% was obtained (Table 3, entry 12). tert-Butanol and tetrahydrofuran (THF) were not suitable solvents for the reaction, giving low yields of the desired product (Table 3, entries 13−14). To probe the reaction scope, both ML and LA were subjected to the Ru-PP/CNT-promoted hydrogenation reaction, and GVL was obtained in moderate and low yields, respectively, under the investigated conditions (Scheme 2a and Table 4, entries 1−4). The catalytic activities of Ru-PP/CNTs and Ru-PP/RGO were further compared. The Ru-PP/RGOpromoted EL-to-GVL transformation gave a quantitative GVL yield of 99.3% with excellent GVL selectivity when the reaction was carried out at 100 °C. Notably, 87.2% yield of GVL was

Figure 7. Catalyst recycling. Reaction conditions: EL (144 mg, 1.0 mmol), Ru-PP/CNTs (50 mg), NaHCO3 (50 mg, 0.6 mmol), MeOH (5 mL), PH2 (3.0 MPa), T (100 °C), and t (10 h).

Table 2. Effects of Catalysts and Cocatalysts on EL Hydrogenation to GVLa entry

catalyst (mg)

1 2

PP/CNTs (50)

3

Rh-PP/CNTs (50)

4

Ir-PP/CNTs (50)

5

Ru-PP/CNTs (50)

6

8

Ru NPs/PP/CNTs (50) Ru NPs/N-CNTs (50) Ru-PP/CNTs (40)

9

Ru-PP/CNTs (30)

10

Ru-PP/CNTs (20)

11

Ru-PP/CNTs (10)

12 13 14 15 16 17

Ru-PP/CNTs Ru-PP/CNTs Ru-PP/CNTs Ru-PP/CNTs Ru-PP/CNTs Ru-PP/CNTs

18

Ru-PP/CNTs (50)

19

Ru-PP/CNTs (50)

20

Ru-PP/CNTs (50)

7

(50) (50) (50) (50) (50) (50)

21b 22b

PP/CNTs (50)

co-catalyst (mmol) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) NaHCO3 (0.60) Na2CO3 (0.60) NaOH (0.60) KOtBu (0.60) DMAP (0.60) NaHCO3 (0.48) NaHCO3 (0.36) NaHCO3 (0.23) NaHCO3 (0.12) NaHCO3 (0.60)

EL conv (%)

GVL yield (%)

99.0 99.5

1.2

99.9

59.8

99.2

52.1

99.9

99.1

79.4

72.6

95.8

24.3

98.4

81.2

99.2

79.9

95.7

73.1

95.4

51.3

39.4 97.3 99.1 96.9 88.2 98.1

9.4 52.0 45.8 34.4 28.5 84.3

96.8

80.0

96.1

77.9

91.5

68.7

59.6 0.5

0.2

a

Reaction conditions: EL (144 mg, 1.0 mmol), catalyst (0−50 mg), cocatalyst (0−0.6 mmol), methanol (5 mL), PH2 (3.0 MPa), T (100 °C), and t (10 h). bThe reactions were performed at room temperature rather than 100 °C. For the reactions of EL hydrogenation to GVL, refer to Scheme 2a.

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yields of 5-methyl-N-benzyl-2-pyrrolidone and 5-methyl-Ncyclohexyl-2-pyrrolidone were observed, respectively, with RuPP/CNTs. Ru-PP/CNTs were recycled several times in the hydrogenation of EL to GVL to further investigate the stability of the catalyst. EL conversions slightly decreased from 98.4 to 94.2% after a five-cycle experiment, and GVL yields accordingly reduced from 90.4 to 72.7% with the recycling times. The partial loss of the catalyst activity in the EL hydrogenation was presumably owing to a reduced Ru content during catalyst recycling (Table 1). Scheme 2b illustrates the proposed mechanism for Ru-PP/ CNT-promoted EL transformation to GVL. Initially, the NaHCO3 promoted the transesterification of EL with the solvent methanol to give ML (Table 2, entry 21). A heterolytic cleavage of H2 by the ruthenium porphyrin species [Ru(Por), Scheme 2b] on the Ru-PP/CNT catalyst in the presence of a base led to the formation of ruthenium porphyrin hydride species [Ru(Por)(H)].92 At this stage, the in situ formed Ru(Por)(H) readily transferred the hydride ions to attack the carbonyl group of ML to yield methyl 4-hydroxypentanoate. Meanwhile, Ru(Por)(H) was converted into Ru(Por) with the loss of the hydride ion.93 A fast intramolecular transesterification of methyl 4-hydroxypentanoate into GVL went together with the equimolar production of methanol.

Table 3. Effects of Reaction Temperature, Reaction Time, Hydrogen Pressure, and Solvent on EL-to-GVL Transformationa entry

T [°C]

t [h]

P H2 [MPa]

solvent

EL conv [%]

GVL yield [%]

1 2 3 4 5 6 7 8 9 10 11 12 13 14

100 90 80 60 r.t. 100 100 100 100 100 100 100 100 100

10 10 10 10 10 8 6 4 2 10 10 10 10 10

3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 2.0 1.0 3.0 3.0 3.0

MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH EtOH tert-butanol THF

99.9 99.7 96.9 85.1 73.5 99.9 99.9 95.7 92.0 94.9 92.3 88.2 69.4 27.2

99.1 89.2 79.4 65.5 53.2 92.0 88.7 83.7 80.3 76.1 73.6 86.9 42.2 10.4

a

Reaction conditions: EL (144 mg, 1.0 mmol), Ru-PP/CNTs (50 mg), NaHCO3 (50 mg, 0.60 mmol), solvent (5 mL), PH2 (1.0−3.0 MPa), T (r.t.−100 °C), and t (2−10 h). For the reactions of EL hydrogenation to GVL, refer to Scheme 2a.

Table 4. Comparison of Ru-PP/CNT- and Ru-PP/RGOPromoted Transformations of EL, ML, and LA to GVLa entry

catalyst

Rb

T [°C]

1 2 3 4 5 6 7 8 9 10

Ru-PP/CNTs Ru-PP/CNTs Ru-PP/CNTs Ru-PP/CNTs Ru-PP/RGO Ru-PP/RGO Ru-PP/RGO Ru-PP/RGO Ru-PP/RGO Ru-PP/RGO

Me Me H H Et Et Me Me H H

100 r.t. 100 r.t. 100 r.t. 100 r.t. 100 r.t.

solvent

conv [%]

GVL yield [%]

MeOH MeOH THF THF MeOH MeOH MeOH MeOH THF THF

82.4 67.0 41.8 9.3 99.3 98.7 92.8 62.8 47.1 12.2

71.3 59.6 40.9 7.5 99.3 87.2 87.4 68.3 44.7 10.9

3. CONCLUSIONS In summary, to heterogenize porphyrin complexes for the hydrogenation of biomass-based LA and levulinic ester into GVL, Ru-PP/CNTs were prepared by the metallation of PP/ CNTs with Ru3(CO)12, whereas PP/CNTs were obtained by the condensation of terephthaldehyde and pyrrole in the presence of CNTs. Ru-PP/RGO was prepared with a synthetic procedure similar to Ru-PP/CNTs with RGO as the support. Both Ru-PP/CNTs and Ru-PP/RGO showed excellent catalytic performance toward EL hydrogenation to GVL, with Ru-centered porphyrin units as the catalytic active species. Under optimized reaction conditions, a GVL yield higher than 99% with a complete conversion of EL was observed over both Ru-PP/CNTs and Ru-PP/RGO. In addition to GVL preparation, the versatile Ru-PP/CNTs can efficiently promote reductive amination of EL with various amines for the efficient synthesis of pyrrolidone derivatives. Moreover, the two composite materials of Ru-PP/CNTs and Ru-PP/RGO behave as heterogeneous catalysts in the reaction system and can be easily reused.

a

Reaction conditions: substrate (1.0 mmol), catalyst [Ru-PP/CNTs (50 mg), Ru-PP/RGO (50 mg)], NaHCO3 (50 mg, 0.60 mmol), solvent (5 mL), PH2 (3.0 MPa), T (r.t.−100 °C), and t (10 h). bFor the reactions of EL, ML, and LA hydrogenation to GVL and the substituent group R in the table, refer to Scheme 2a.

obtained over Ru-PP/RGO even at room temperature (Table 4, entry 6), which is remarkably higher than that over Ru-PP/ CNTs producing a GVL yield of 53.2% (Table 3, entry 5), indicating outstanding catalytic performance of Ru-PP/RGO over Ru-PP/CNTs. As expected, Ru-PP/RGO can also promote ML-to-GVL and LA-to-GVL transformations under the investigated conditions (Table 4, entries 7−10). In addition to the catalytic transformation of EL, ML, and LA to GVL, the developed Ru-PP/CNTs were further investigated as the catalyst for one-pot reductive amination of EL with various primary amines to give 5-methyl-2-pyrrolidone and 5methyl-N-alkyl-2-pyrrolidones (Scheme 2a). As shown in Table 5, 5-methyl-2-pyrrolidone was obtained with NH4HCO3 as the nitrogen source under the investigated conditions. For npropylamine, n-butylamine, and n-octylamine, Ru-PP/CNTs efficiently promoted the reductive amination reaction, yielding outstanding yields of the corresponding pyrrolidone products. In the cases of benzylamine and cyclohexylamine, relatively low

4. METHOD 4.1. Materials. Reduced graphene oxide (RGO) was prepared according to the method in the literature.94 The details of materials are provided in the Supporting Information. 4.2. Catalyst Preparation. 4.2.1. Synthesis of PP/CNTs and PP/RGO. In a typical experimental procedure for PP/CNT synthesis (Scheme 1b), a mixture of terephthaldehyde (600 mg, 4.5 mmol) and CNTs (400 mg) in propanoic acid (600 mL) was ultrasonicated for 30 min. The freshly distilled pyrrole (304 mg, 4.5 mmol) was diluted in propionic acid (40 mL) and then added dropwise to the above-mentioned mixture under vigorous stirring and reflux conditions. The mixture was refluxed for an additional 3 h and then cooled to room temperature and filtered. The filter residue was washed with deionized water, methanol, and dichloromethane and then 3235


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Table 5. Ru-PP/CNT-Promoted Reductive Amination of EL with Various Amines for the Synthesis of Pyrrolidone Derivativesa

Reaction conditions: EL (144 mg, 1.0 mmol), NH4HCO3 or amine (1.2 mmol), Ru-PP/CNTs (50 mg), THF (5 mL), PH2 (3.0 MPa), T (120 °C), and t (24 h). bMethanol (5 mL) was used as the solvent rather than THF. For the reductive amination reactions, refer to Scheme 2a. a

dried overnight in an oven at 80 °C overnight. Then, the mixture was extracted with deionized water, dichloromethane, methanol, and THF separately for 1 day by Soxhlet extraction and then vacuum dried at 80 °C for 12 h. PP/RGO was synthesized using a similar synthetic procedure of PP/CNTs with RGO (400 mg) as the support. 4.2.2. Synthesis of Ru-PP/CNTs and Ru-PP/RGO. For RuPP/CNT synthesis (Scheme 1c), a mixture of PP/CNTs (150 mg) and Ru3(CO)12 (50 mg, 78 μmol) was refluxed in decalin (50 mL) for 6 h under a nitrogen atmosphere, after which it was cooled and filtered. The filter cake was washed thoroughly with dichloromethane and then vacuum dried at room temperature overnight to give the ruthenium catalyst Ru-PP/ CNTs. Ru-PP/RGO was synthesized using a similar synthetic procedure of Ru-PP/CNTs with PP/RGO (150 mg) as the support. 4.2.3. Synthesis of Rh-PP/CNTs and Ir-PP/CNTs. For RhPP/CNT synthesis (Scheme 1c), a mixture of PP/CNTs (150 mg) and RhCl3 (50 mg, 24 μmol) in benzonitrile (50 mL) was refluxed for 6 h under a nitrogen atmosphere, after which it was cooled and filtered. The filter cake was washed thoroughly with dichloromethane and then vacuum dried at room temperature overnight to give the rhodium catalyst Rh-PP/CNTs. Ir-PP/CNTs were synthesized using a similar synthetic procedure of Rh-PP/CNTs with IrCl3 (50 mg, 14 μmol) as the Ir catalyst precursor. 4.3. Catalyst Characterization. ICP-AES analysis was performed using a PerkinElmer Optima 8000 instrument. Powder XRD patterns of the catalysts were obtained from an X’Pert Pro MPD diffractometer (PANalytical) from 5° to 80° operated at 40 kV and 40 mA with Ni-filtered Cu Kα (λ =

0.15406 nm) radiation. SEM images were recorded using a Hitachi S-4800 instrument operated at 10 kV. The samples were placed on a conductive carbon tape adhered to an aluminum sample holder. The morphological analysis of the metal NPs was carried out using HRTEM (JEM-2100HR). Samples for the HRTEM analysis were prepared by placing a drop of the suspension of the catalyst sample in ethanol onto a carbon-coated copper grid, followed by evaporating the solvent. XPS spectra was obtained with a Kratos Axis Ultra (DLD) photoelectron spectrometer operated at 15 kV and 10 mA at a pressure of about 5 × 10−9 Torr using Al Kα as the exciting source (1486.6 eV). C 1s photoelectron peak [binding energy (BE) = 284.6 eV] was used for the binding energy calibration. 4.4. Catalytic Performance. The experiments for the synthesis of GVL from EL were executed using a 25 mL cylindrical stainless steel high pressure reactor. In a typical reaction, Ru-PP/CNTs (50 mg), EL (144 mg, 1.0 mmol), NaHCO3 (50 mg, 0.60 mmol), and MeOH (5 mL) were added successively to a batch autoclave reactor. After the reactor was purged several times with H2, the outlet valve was closed and maintained at 3.0 MPa (ambient temperature) in the system controlled by a large H2 gas reservoir that was connected to the reaction cell. The stainless steel was heated at 100 °C for 10 h with 600 rpm stirring speed. After the reaction, the reactor was cooled to room temperature, and the reaction mixture was centrifuged at 6000 rpm for 5 min. The products in the liquid phase were then analyzed using gas chromatography (GC) (FL 9790II) equipped with a capillary column (KB-5, 0.32 mm × 30 m) and a flame ionization detector (FID) with N2 as the carrier gas, using N-methyl-2-pyrrolidone as the internal standard. The experiments for the reductive amination of EL to various pyrrolidone compounds were executed in a 25 mL cylindrical 3236


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stainless steel high pressure reactor. In a typical reaction, RuPP/CNTs (50 mg), EL (144 mg, 1.0 mmol), n-butylamine (88 mg, 1.2 mmol), and THF (5 mL) were added successively to a batch autoclave reactor. After the reactor was purged several times with H2, the outlet valve was closed and maintained at 3.0 MPa (ambient temperature) in the system controlled by a large H2 gas reservoir that was connected to the reaction cell. The stainless steel was heated at 120 °C for 24 h with stirring speed of 600 rpm. After the reaction, until the reactor was cooled to room temperature, the reaction mixture was centrifuged at 6000 rpm for 5 min. The products in the liquid phase were then analyzed using GC (FL 9790II) equipped with a capillary column (KB-5, 0.32 mm × 30 m) and an FID with N2 as the carrier gas, using pentadecane as the internal standard. 4.4.1. GVL. 1H NMR (400 MHz, 25 °C, CDCl3): δ 4.66− 4.50 (m, 1H), 2.59−2.40 (m, 2H), 2.31 (dt, J = 13.0, 6.6 Hz, 1H), 1.87−1.69 (m, 1H), 1.42−1.28 (m, 3H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 177.29, 77.27, 29.63, 29.03, 20.98. 4.4.2. 5-Methyl-2-pyrrolidone. 1H NMR (400 MHz, 25 °C, CDCl3): δ 6.97 (s, 1H), 3.74 (d, J = 6.2 Hz, 1H), 2.43−2.13 (m, 3H), 1.71−1.51 (m, 1H), 1.18 (d, J = 6.1 Hz, 3H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 178.14, 49.70, 30.27, 28.52, 21.53. 4.4.3. 5-Methyl-N-propyl-2-pyrrolidone. 1H NMR (400 MHz, 25 °C, CDCl3): δ 3.77−3.61 (m, 1H), 3.53 (ddd, J = 13.8, 8.9, 7.3 Hz, 1H), 2.90 (ddd, J = 13.8, 8.8, 5.1 Hz, 1H), 2.49−2.25 (m, 2H), 2.24−2.08 (m, 1H), 1.64−1.51 (m, 2H), 1.51−1.38 (m, 1H), 1.19 (d, J = 6.3 Hz, 3H), 0.89 (t, J = 7.4 Hz, 3H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 174.87, 53.41, 41.77, 30.48, 26.97, 20.83, 19.93, 11.51. 4.4.4. 5-Methyl-N-butyl-2-pyrrolidone. 1H NMR (400 MHz, 25 °C, CDCl3): δ 3.68−3.43 (m, 2H), 2.82 (td, J = 13.6, 6.9 Hz, 1H), 2.38−2.01 (m, 3H), 1.46 (ddd, J = 45.5, 34.6, 20.1 Hz, 4H), 1.29−0.96 (m, 6H), 0.83 (t, J = 7.1 Hz, 4H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 174.53, 53.17, 39.66, 30.29, 29.47, 26.75, 20.12, 19.72, 13.73. 4.4.5. 5-Methyl-N-octyl-2-pyrrolidone. 1H NMR (400 MHz, 25 °C, CDCl3): δ 3.64−3.51 (m, 1H), 3.45 (ddd, J = 13.8, 9.1, 7.0 Hz, 1H), 2.79 (ddd, J = 13.8, 8.9, 5.1 Hz, 1H), 2.35−2.12 (m, 2H), 2.06 (dddd, J = 13.2, 9.3, 7.4, 6.0 Hz, 1H), 1.53−0.98 (m, 17H), 0.75 (t, J = 6.8 Hz, 3H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 174.49, 53.12, 39.87, 31.63, 30.20, 29.10, 27.29, 26.75, 22.47, 19.64, 13.91. 4.4.6. 5-Methyl-N-benzyl-2-pyrrolidone. 1H NMR (400 MHz, 25 °C, CDCl3); δ 7.26 (ddd, J = 18.5, 14.5, 7.0 Hz, 5H), 4.94 (d, J = 15.0 Hz, 1H), 3.97 (d, J = 15.0 Hz, 1H), 3.73−3.46 (m, 1H), 2.66 (dt, J = 54.5, 6.5 Hz, 1H), 2.53−2.33 (m, 2H), 2.19−2.14 (m, 1H), 1.63−1.51 (m, 1H), 1.14 (d, J = 6.3 Hz, 3H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 175.34, 136.96, 128.80, 128.17, 127.61, 53.07, 44.12, 30.44, 26.84, 19.76. 4.4.7. 5-Methyl-N-cyclohexyl-2-pyrrolidone. 1H NMR (400 MHz, 25 °C, CDCl3): δ 3.92−3.53 (m, 2H), 2.46 (dt, J = 17.4, 8.9 Hz, 1H), 2.21 (dddd, J = 30.4, 26.7, 13.9, 6.6 Hz, 2H), 2.00−0.97 (m, 13H). 13C NMR (101 MHz, 25 °C, CDCl3): δ 174.97, 53.19, 52.80, 31.89, 30.38, 30.16, 27.56, 26.04, 25.99, 25.63, 22.43.

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Materials, product analysis, and 1H and 13C {1H} NMR spectra of GVL and pyrrolidone derivatives synthesized (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: (+86)-20-8522-0223. Fax: (+86)-20-8522-0223 (J.C.). ORCID

Jinzhu Chen: 0000-0002-6475-1431 Author Contributions ∥

T.Z. and Y.G. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support from the National Natural Science Foundation of China (21172219, 21472189), the Science and Technology Planning Project of Guangzhou City, China (201707010238), and the Guangdong Provincial Key Laboratory of the Atmospheric Environment and Pollution Control.

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REFERENCES

(1) Sheldon, R. A. Green and sustainable manufacture of chemicals from biomass: state of the art. Green Chem. 2014, 16, 950−963. (2) Morais, A. R. C.; da Costa Lopes, A. M.; Bogel-Łukasik, R. Carbon Dioxide in Biomass Processing: Contributions to the Green Biorefinery Concept. Chem. Rev. 2015, 115, 3−27. (3) Palkovits, R. Pentenoic Acid Pathways for Cellulosic Biofuels. Angew. Chem., Int. Ed. 2010, 49, 4336−4338. (4) Tang, X.; Zeng, X.; Li, Z.; Hu, L.; Sun, Y.; Liu, S.; Lei, T.; Lin, L. Production of γ-valerolactone from lignocellulosic biomass for sustainable fuels and chemicals supply. Renewable Sustainable Energy Rev. 2014, 40, 608−620. (5) Wright, W. R. H.; Palkovits, R. Development of Heterogeneous Catalysts for the Conversion of Levulinic Acid to γ-Valerolactone. ChemSusChem 2012, 5, 1657−1667. (6) Bond, J. Q.; Alonso, D. M.; Wang, D.; West, R. M.; Dumesic, J. A. Integrated Catalytic Conversion of γ-Valerolactone to Liquid Alkenes for Transportation Fuels. Science 2010, 327, 1110−1114. (7) Zhang, Z. Synthesis of γ-Valerolactone from Carbohydrates and its Applications. ChemSusChem 2016, 9, 156−171. (8) Liguori, F.; Moreno-Marrodan, C.; Barbaro, P. Environmentally Friendly Synthesis of γ-Valerolactone by Direct Catalytic Conversion of Renewable Sources. ACS Catal. 2015, 5, 1882−1894. (9) Yan, K.; Yang, Y.; Chai, J.; Lu, Y. Catalytic reactions of gammavalerolactone: A platform to fuels and value-added chemicals. Appl. Catal., B 2015, 179, 292−304. (10) Deng, L.; Li, J.; Lai, D.-M.; Fu, Y.; Guo, Q.-X. Catalytic Conversion of Biomass-Derived Carbohydrates into γ-Valerolactone without Using an External H2 Supply. Angew. Chem., Int. Ed. 2009, 48, 6529−6532. (11) Mehdi, H.; Fábos, V.; Tuba, R.; Bodor, A.; Mika, L. T.; Horváth, I. T. Integration of Homogeneous and Heterogeneous Catalytic Processes for a Multi-step Conversion of Biomass: From Sucrose to Levulinic Acid, γ-Valerolactone, 1,4-Pentanediol, 2-Methyl-tetrahydrofuran and Alkanes. Top. Catal. 2008, 48, 49−54. (12) Geilen, F. M. A.; Engendahl, B.; Harwardt, A.; Marquardt, W.; Klankermayer, J.; Leitner, W. Selective and Flexible Transformation of Biomass-Derived Platform Chemicals by a Multifunctional Catalytic System. Angew. Chem., Int. Ed. 2010, 49, 5510−5514. (13) Delhomme, C.; Schaper, L.-A.; Zhang-Preße, M.; RaudaschlSieber, G.; Weuster-Botz, D.; Kühn, F. E. Catalytic hydrogenation of

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.7b00427. 3237


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Article

levulinic acid in aqueous phase. J. Organomet. Chem. 2013, 724, 297− 299. (14) Fábos, V.; Mika, L. T.; Horváth, I. T. Selective Conversion of Levulinic and Formic Acids to γ-Valerolactone with the Shvo Catalyst. Organometallics 2014, 33, 181−187. (15) Abdelrahman, O. A.; Heyden, A.; Bond, J. Q. Analysis of Kinetics and Reaction Pathways in the Aqueous-Phase Hydrogenation of Levulinic Acid to Form γ-Valerolactone over Ru/C. ACS Catal. 2014, 4, 1171−1181. (16) Yan, Z.-p.; Lin, L.; Liu, S. Synthesis of γ-Valerolactone by Hydrogenation of Biomass-derived Levulinic Acid over Ru/C Catalyst. Energy Fuels 2009, 23, 3853−3858. (17) Galletti, A. M. R.; Antonetti, C.; De Luise, V.; Martinelli, M. A sustainable process for the production of γ-valerolactone by hydrogenation of biomass-derived levulinic acid. Green Chem. 2012, 14, 688−694. (18) Al-Shaal, M. G.; Wright, W. R. H.; Palkovits, R. Exploring the ruthenium catalysed synthesis of γ-valerolactone in alcohols and utilisation of mild solvent-free reaction conditions. Green Chem. 2012, 14, 1260−1263. (19) Selva, M.; Gottardo, M.; Perosa, A. Upgrade of Biomass-Derived Levulinic Acid via Ru/C-Catalyzed Hydrogenation to γ-Valerolactone in Aqueous−Organic−Ionic Liquids Multiphase Systems. ACS Sustainable Chem. Eng. 2013, 1, 180−189. (20) Yan, K.; Lafleur, T.; Wu, G.; Liao, J.; Ceng, C.; Xie, X. Highly selective production of value-added γ-valerolactone from biomassderived levulinic acid using the robust Pd nanoparticles. Appl. Catal., A 2013, 468, 52−58. (21) Guo, Y.; Li, Y.; Chen, J.; Chen, L. Hydrogenation of Levulinic Acid into γ-Valerolactone Over Ruthenium Catalysts Supported on Metal−Organic Frameworks in Aqueous Medium. Catal. Lett. 2016, 146, 2041−2052. (22) Luo, W.; Deka, U.; Beale, A. M.; vanEck, E. R. H.; Bruijnincx, P. C. A.; Weckhuysen, B. M. Ruthenium-catalyzed hydrogenation of levulinic acid: Influence of the support and solvent on catalyst selectivity and stability. J. Catal. 2013, 301, 175−186. (23) Ruppert, A. M.; Grams, J.; Jędrzejczyk, M.; Matras-Michalska, J.; Keller, N.; Ostojska, K.; Sautet, P. Titania-Supported Catalysts for Levulinic Acid Hydrogenation: Influence of Support and its Impact on γ-Valerolactone Yield. ChemSusChem 2015, 8, 1538−1547. (24) Bourne, R. A.; Stevens, J. G.; Ke, J.; Poliakoff, M. Maximising opportunities in supercritical chemistry: the continuous conversion of levulinic acid to γ-valerolactone in CO2. Chem. Commun. 2007, 4632− 4634. (25) Piskun, A.; Winkelman, J.; Tang, Z.; Heeres, H. Support Screening Studies on the Hydrogenation of Levulinic Acid to γValerolactone in Water Using Ru Catalysts. Catalysts 2016, 6, 131. (26) Sudhakar, M.; Kantam, M. L.; Jaya, V. S.; Kishore, R.; Ramanujachary, K. V.; Venugopal, A. Hydroxyapatite as a novel support for Ru in the hydrogenation of levulinic acid to γvalerolactone. Catal. Commun. 2014, 50, 101−104. (27) Ortiz-Cervantes, C.; García, J. J. Hydrogenation of levulinic acid to γ-valerolactone using ruthenium nanoparticles. Inorg. Chim. Acta 2013, 397, 124−128. (28) Pan, T.; Deng, J.; Xu, Q.; Xu, Y.; Guo, Q.-X.; Fu, Y. Catalytic conversion of biomass-derived levulinic acid to valerate esters as oxygenated fuels using supported ruthenium catalysts. Green Chem. 2013, 15, 2967−2974. (29) Yao, Y.; Wang, Z.; Zhao, S.; Wang, D.; Wu, Z.; Zhang, M. A stable and effective Ru/polyethersulfone catalyst for levulinic acid hydrogenation to γ-valerolactone in aqueous solution. Catal. Today 2014, 234, 245−250. (30) Sen, S. M.; Henao, C. A.; Braden, D. J.; Dumesic, J. A.; Maravelias, C. T. Catalytic conversion of lignocellulosic biomass to fuels: Process development and technoeconomic evaluation. Chem. Eng. Sci. 2012, 67, 57−67. (31) Braden, D. J.; Henao, C. A.; Heltzel, J.; Maravelias, C. C.; Dumesic, J. A. Production of liquid hydrocarbon fuels by catalytic

conversion of biomass-derived levulinic acid. Green Chem. 2011, 13, 1755−1765. (32) Alonso, D. M.; Wettstein, S. G.; Bond, J. Q.; Root, T. W.; Dumesic, J. A. Production of Biofuels from Cellulose and Corn Stover Using Alkylphenol Solvents. ChemSusChem 2011, 4, 1078−1081. (33) Wettstein, S. G.; Bond, J. Q.; Alonso, D. M.; Pham, H. N.; Datye, A. K.; Dumesic, J. A. RuSn bimetallic catalysts for selective hydrogenation of levulinic acid to γ-valerolactone. Appl. Catal., B 2012, 117−118, 321−329. (34) Yang, Y.; Gao, G.; Zhang, X.; Li, F. Facile Fabrication of Composition-Tuned Ru−Ni Bimetallics in Ordered Mesoporous Carbon for Levulinic Acid Hydrogenation. ACS Catal. 2014, 4, 1419−1425. (35) Luo, W.; Sankar, M.; Beale, A. M.; He, Q.; Kiely, C. J.; Bruijnincx, P. C. A.; Weckhuysen, B. M. High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone. Nat. Commun. 2015, 6, 6540−6549. (36) Zhang, L.; Zheng, X.; Li, R. Effect of Lanthanum on Catalytic Performance of Ru/Al2O3 Catalyst for Hydrogenation of Esters to Corresponding Alcohols. Chem. Res. Chin. Univ. 2015, 31, 615−620. (37) Biswas, S.; Sarkar, D.; Kundu, S.; Roy, P.; Mondal, T. K. Rhodium(III)-triphenylphosphine complex with NNS donor thioether containing Schiff base ligand: Synthesis, spectra, electrochemistry and catalytic activity. J. Mol. Struct. 2015, 1099, 297−303. (38) Stangel, C.; Charalambidis, G.; Varda, V.; Coutsolelos, A. G.; Kostas, I. D. Aqueous−Organic Biphasic Hydrogenation of transCinnamaldehyde Catalyzed by Rhodium and Ruthenium PhosphaneFree Porphyrin Complexes. Eur. J. Inorg. Chem. 2011, 4709−4716. (39) Gallo, E.; Caselli, A.; Ragaini, F.; Fantauzzi, S.; Masciocchi, N.; Sironi, A.; Cenini, S. Structural Determination of Ruthenium− Porphyrin Complexes Relevant to Catalytic Epoxidation of Olefins. Inorg. Chem. 2005, 44, 2039−2049. (40) Wang, C.; Shalyaev, K. V.; Bonchio, M.; Carofiglio, T.; Groves, J. T. Fast Catalytic Hydroxylation of Hydrocarbons with Ruthenium Porphyrins. Inorg. Chem. 2006, 45, 4769−4782. (41) Azizyan, A. S.; Kurtikyan, T. S.; Martirosyan, G. G.; Ford, P. C. Tracking Reactive Intermediates by FTIR Monitoring of Reactions in Low-Temperature Sublimed Solids: Nitric Oxide Disproportionation Mediated by Ruthenium(II) Carbonyl Porphyrin Ru(TPP)(CO). Inorg. Chem. 2013, 52, 5201−5205. (42) Gallo, E.; Buonomenna, M. G.; Viganò, L.; Ragaini, F.; Caselli, A.; Fantauzzi, S.; Cenini, S.; Drioli, E. Heterogenization of ruthenium porphyrin complexes in polymeric membranes: Catalytic aziridination of styrenes. J. Mol. Catal. A: Chem. 2008, 282, 85−91. (43) Fantauzzi, S.; Gallo, E.; Caselli, A.; Ragaini, F.; Macchi, P.; Casati, N.; Cenini, S. Origin of the Deactivation in Styrene Aziridination by Aryl Azides, Catalyzed by Ruthenium Porphyrin Complexes. Structural Characterization of a Δ2-1,2,3-Triazoline RuII(TPP)CO Complex. Organometallics 2005, 24, 4710−4713. (44) Intrieri, D.; Mariani, M.; Caselli, A.; Ragaini, F.; Gallo, E. [Ru(TPP)CO]-Catalysed Intramolecular Benzylic C−H Bond Amination, Affording Phenanthridine and Dihydrophenanthridine Derivatives. Chem.Eur. J. 2012, 18, 10487−10490. (45) Intrieri, D.; Caselli, A.; Ragaini, F.; Macchi, P.; Casati, N.; Gallo, E. Insights into the Mechanism of the Ruthenium−PorphyrinCatalysed Allylic Amination of Olefins by Aryl Azides. Eur. J. Inorg. Chem. 2012, 569−580. (46) Funyu, S.; Kinai, M.; Masui, D.; Takagi, S.; Shimada, T.; Tachibana, H.; Inoue, H. Key reaction intermediates of the photochemical oxygenation of alkene sensitized by RuII−porphyrin with water by visible light. Photochem. Photobiol. Sci. 2010, 9, 931−936. (47) Xia, Q.-H.; Ge, H.-Q.; Ye, C.-P.; Liu, Z.-M.; Su, K.-X. Advances in Homogeneous and Heterogeneous Catalytic Asymmetric Epoxidation. Chem. Rev. 2005, 105, 1603−1662. (48) Anouti, M.; Jones, J.; Boisset, A.; Jacquemin, J.; CaillonCaravanier, M.; Lemordant, D. Aggregation behavior in water of new imidazolium and pyrrolidinium alkycarboxylatesprotic ionic liquids. J. Colloid Interface Sci. 2009, 340, 104−111. 3238


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Article

(67) Gao, W.; Alemany, L. B.; Ci, L.; Ajayan, P. M. New insights into the structure and reduction of graphite oxide. Nat. Chem. 2009, 1, 403−408. (68) Reven, L.; Oldfield, E. Carbon-13 Nuclear Magnetic Resonance Spectroscopic Study of Fe3(CO)12 and Ru3(CO)12 Supported on Metal Oxide Surfaces. Inorg. Chem. 1992, 31, 243−252. (69) Chen, A.; Ju, P.; Zhang, Y.; Chen, J.; Gao, H.; Chen, L.; Yu, Y. Highly recyclable and magnetic catalyst of a metalloporphyrin-based polymeric composite for cycloaddition CO2 to epoxide. RSC Adv. 2016, 6, 96455−96466. (70) Chen, L.; Yang, Y.; Jiang, D. CMPs as Scaffolds for Constructing Porous Catalytic Frameworks: A Built-in Heterogeneous Catalyst with High Activity and Selectivity Based on Nanoporous Metalloporphprin Polymers. J. Am. Chem. Soc. 2010, 132, 9138−9143. (71) Modak, A.; Nandi, M.; Mondal, J.; Bhaumik, A. Porphyrin based porous organic polymers: novel synthetic strategy and exceptionally high CO2 adsorption capacity. Chem. Commun. 2012, 48, 248−250. (72) Le Vot, S.; Roué, L.; Bélanger, D. Electrodeposition of iridium onto glassy carbon and platinum electrodes. Electrochim. Acta 2012, 59, 49−56. (73) Battistoni, C.; Furlani, C.; Mattogno, G.; Tom, G. ESCA spectra of some N-bonded osmium complexes. Inorg. Chim. Acta 1977, 21, L25. (74) Haga, M.-a.; Hong, H.-G.; Shiozawa, Y.; Kawata, Y.; Monjushiro, H.; Fukuo, T.; Arakawa, R. Synthesis and proton-coupled electrontransfer reaction of self-assembled monolayers of a ruthenium(II) complex containing tridentate 2,6-bis(benzimidazol-2-yl)pyridine on a gold surface: Comparison of acid/base chemistry with bulk solution chemistry. Inorg. Chem. 2000, 39, 4566−4573. (75) Zubavichus, Y. V.; Slovokhotov, Y. L.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Gratzel, M.; Shklover, V. Structural Characterization of Solar Cell Prototypes Based on Nanocrystalline TiO2 Anatase Sensitized with Ru Complexes. X-ray Diffraction, XPS, and XAFS Spectroscopy Study. Chem. Mater. 2002, 14, 3556−3563. (76) Grelaud, G.; Gauthier, N.; Luo, Y.; Paul, F.; Fabre, B.; Barrière, F.; Ababou-Girard, S.; Roisnel, T.; Humphrey, M. G. Redox-Active Molecular Wires Derived from Dinuclear Ferrocenyl/Ruthenium(II) Alkynyl Complexes: Covalent Attachment to Hydrogen-Terminated Silicon Surfaces. J. Phys. Chem. C 2014, 118, 3680−3695. (77) Kim, J. Y.; Choi, J.; Kim, H. Y.; Hwang, E.; Kim, H.-J.; Ahn, S. H.; Kim, S.-K. Activity and stability of the oxygen evolution reaction on electrodeposited Ru and its thermal oxides. Appl. Surf. Sci. 2015, 359, 227−235. (78) Chan, H. Y. H.; Takoudis, C. G.; Weaver, M. J. High-pressure oxidation of ruthenium as probed by surface-enhanced Raman and Xray photoelectron spectroscopies. J. Catal. 1997, 172, 336−345. (79) Groves, J. T.; Quinn, R. Models of oxidized heme proteins. Preparation and characterization of a trans-dioxoruthenium(VI) porphyrin complex. Inorg. Chem. 1984, 23, 3844−3846. (80) Guczi, L.; Schay, Z.; Stoch, J.; Czeppe, J.; Haber, J. XPS study on the decomposition of Ru3(CO)12 and Fe3(CO)12 carbon clusters. React. Kinet. Catal. Lett. 1981, 18, 199−202. (81) Chakrabarty, D. K.; Joshi, A.; Unnikrishnan, S.; Prabhawalkar, P. D. Preparation of a Ru/Al2O3 catalyst from Ru3(CO)12 infrared and XPS study. React. Kinet. Catal. Lett. 1984, 26, 143−147. (82) Lamouri, A.; Gofer, Y.; Luo, Y.; Chottiner, G. S.; Scherson, D. A. Low-Energy Electron Diffraction, X-ray Photoelectron Spectroscopy, and CO-Temperature-Programmed Desorption Characterization of Bimetallic Ruthenium−Platinum Surfaces Prepared by Chemical Vapor Deposition. J. Phys. Chem. B 2001, 105, 6172−6177. (83) Yu, C.; Zhao, P.; Chen, G.; Hu, B. Al2O3 supported Ru catalysts prepared by thermolysis of Ru3(CO)12 for catalytic wet air oxidation. Appl. Surf. Sci. 2011, 257, 7727−7731. (84) Chen, J.; Xu, Q. Hydrodeoxygenation of biodiesel-related fatty acid methyl esters to diesel-range alkanes over zeolite-supported ruthenium catalysts. Catal. Sci. Technol. 2016, 6, 7239−7251. (85) Suñol, J. J.; Bonneau, M. E.; Roué, L.; Guay, D.; Schulz, R. XPS surface study of nanocrystalline Ti−Ru−Fe materials. Appl. Surf. Sci. 2000, 158, 252−262.

(49) Bhadani, A.; Singh, S.; Kamboj, R.; Chauhan, V. Synthesis and self aggregation properties of ester-functionalized heterocyclic pyrrolidinium surfactants. Colloid Polym. Sci. 2013, 291, 2289−2297. (50) Wei, Y.; Wang, C.; Jiang, X.; Xue, D.; Liu, Z.-T.; Xiao, J. Catalyst-free transformation of levulinic acid into pyrrolidinones with formic acid. Green Chem. 2014, 16, 1093−1096. (51) Vidal, J. D.; Climent, M. J.; Concepcion, P.; Corma, A.; Iborra, S.; Sabater, M. J. Chemicals from Biomass: Chemoselective Reductive Amination of Ethyl Levulinate with Amines. ACS Catal. 2015, 5, 5812−5821. (52) Touchy, A. S.; Siddiki, S. M. A. H.; Kon, K.; Shimizu, K.-i. Heterogeneous Pt Catalysts for Reductive Amination of Levulinic Acid to Pyrrolidones. ACS Catal. 2014, 4, 3045−3050. (53) Huang, Y.-B.; Dai, J.-J.; Deng, X.-J.; Qu, Y.-C.; Guo, Q.-X.; Fu, Y. Ruthenium-Catalyzed Conversion of Levulinic Acid to Pyrrolidines by Reductive Amination. ChemSusChem 2011, 4, 1578−1581. (54) Budroni, G.; Corma, A. Gold and gold−platinum as active and selective catalyst for biomass conversion: Synthesis of γ-butyrolactone and one-pot synthesis of pyrrolidone. J. Catal. 2008, 257, 403−408. (55) Du, X.-L.; He, L.; Zhao, S.; Liu, Y.-M.; Cao, Y.; He, H.-Y.; Fan, K.-N. Hydrogen-Independent Reductive Transformation of Carbohydrate Biomass into γ-Valerolactone and Pyrrolidone Derivatives with Supported Gold Catalysts. Angew. Chem., Int. Ed. 2011, 50, 7815− 7819. (56) Wei, Y.; Wang, C.; Jiang, X.; Xue, D.; Li, J.; Xiao, J. Highly efficient transformation of levulinic acid into pyrrolidinones by iridium catalysed transfer hydrogenation. Chem. Commun. 2013, 49, 5408− 5410. (57) Chen, A.; Zhang, Y.; Chen, J.; Chen, L.; Yu, Y. Metalloporphyrin-based organic polymers for carbon dioxide fixation to cyclic carbonate. J. Mater. Chem. A 2015, 3, 9807−9816. (58) Blanco, M.; Á lvarez, P.; Blanco, C.; Jiménez, M. V.; FernándezTornos, J.; Pérez-Torrente, J. J.; Oro, L. A.; Menéndez, R. Enhanced Hydrogen-Transfer Catalytic Activity of Iridium N-Heterocyclic Carbenes by Covalent Attachment on Carbon Nanotubes. ACS Catal. 2013, 3, 1307−1317. (59) Uzun, A.; Ortalan, V.; Browning, N. D.; Gates, B. C. A siteisolated mononuclear iridium complex catalyst supported on MgO: Characterization by spectroscopy and aberration-corrected scanning transmission electron microscopy. J. Catal. 2010, 269, 318−328. (60) Lu, J.; Serna, P.; Aydin, C.; Browning, N. D.; Gates, B. C. Supported Molecular Iridium Catalysts: Resolving Effects of Metal Nuclearity and Supports as Ligands. J. Am. Chem. Soc. 2011, 133, 16186−16195. (61) Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558−1565. (62) Sheng, G.; Alsaedi, A.; Shammakh, W.; Monaquel, S.; Sheng, J.; Wang, X.; Li, H.; Huang, Y. Enhanced sequestration of selenite in water by nanoscale zero valent iron immobilization on carbon nanotubes by a combined batch, XPS and XAFS investigation. Carbon 2016, 99, 123−130. (63) Lin, Y.; Cui, X.; Yen, C. H.; Wai, C. M. PtRu/Carbon Nanotube Nanocomposite Synthesized in Supercritical Fluid: A Novel Electrocatalyst for Direct Methanol Fuel Cells. Langmuir 2005, 21, 11474− 11479. (64) Li, W.; Liang, C.; Zhou, W.; Qiu, J.; Zhou, Z.; Sun, G.; Xin, Q. Preparation and Characterization of Multiwalled Carbon NanotubeSupported Platinum for Cathode Catalysts of Direct Methanol Fuel Cells. J. Phys. Chem. B 2003, 107, 6292−6299. (65) Li, C.; Shao, Z.; Pang, M.; Williams, C. T.; Zhang, X.; Liang, C. Carbon Nanotubes Supported Mono- and Bimetallic Pt and Ru Catalysts for Selective Hydrogenation of Phenylacetylene. Ind. Eng. Chem. Res. 2012, 51, 4934−4941. (66) Liu, H.; Chen, J.; Chen, L.; Xu, Y.; Guo, X.; Fang, D. Carbon Nanotube-Based Solid Sulfonic Acids as Catalysts for Production of Fatty Acid Methyl Ester via Transesterification and Esterification. ACS Sustainable Chem. Eng. 2016, 4, 3140−3150. 3239


ACS Omega

Article

(86) Contour, J. P.; Mouvier, G.; Hoogewys, M.; Leclere, C. X-ray photoelectron spectroscopy and electron microscopy of Pt−Rh gauzes used for catalytic oxidation of ammonia. J. Catal. 1977, 48, 217−228. (87) Suárez, S.; Yates, M.; Petre, A. L.; Martín, J. A.; Avila, P.; Blanco, J. Development of a new Rh/TiO2−sepiolite monolithic catalyst for N2O decomposition. Appl. Catal., B 2006, 64, 302−311. (88) Kondarides, D. I.; Verykios, X. E. Effect of chlorine on the chemisorptive properties of Rh/CeO2 catalysts studied by XPS and temperature programmed desorption techniques. J. Catal. 1998, 174, 52−64. (89) Larichev, Y. V.; Netskina, O. V.; Komova, O. V.; Simagina, V. I. Comparative XPS study of Rh/Al2O3 and Rh/TiO2 as catalysts for NaBH4 hydrolysis. Int. J. Hydrogen Energy 2010, 35, 6501−6507. (90) Casella, I. G.; Contursi, M.; Toniolo, R. Anodic electrodeposition of iridium oxide particles on glassy carbon surfaces and their electrochemical/SEM/XPS characterization. J. Electroanal. Chem. 2015, 736, 147−152. (91) da Silva, L. A.; Alves, V. A.; de Castro, S. C.; Boodts, J. F. C. XPS study of the state of iridium, platinum, titanium and oxygen in thermally formed IrO2+TiO2+PtOX films. Colloids Surf., A 2000, 170, 119−126. (92) Collman, J. P.; Wagenknecht, P. S.; Lewis, N. S. Hydride Transfer and Dihydrogen Elimination from Osmium and Ruthenium Metalloporphyrin Hydrides: Model Processes for Hydrogenase Enzymes and the Hydrogen Electrode Reaction. J. Am. Chem. Soc. 1992, 114, 5665−5673. (93) Valekar, A. H.; Cho, K.-H.; Chitale, S. K.; Hong, D.-Y.; Cha, G.Y.; Lee, U.-H.; Hwang, D. W.; Serre, C.; Chang, J.-S.; Hwang, Y. K. Catalytic transfer hydrogenation of ethyl levulinate to γ-valerolactone over zirconium-based metal−organic frameworks. Green Chem. 2016, 18, 4542−4552. (94) Zhang, K.; Zhang, L. L.; Zhao, X. S.; Wu, J. Graphene/ Polyaniline Nanofiber Composites as Supercapacitor Electrodes. Chem. Mater. 2010, 22, 1392−1401.

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