Bifunctional Ruthenium Nanoparticle-SILP Catalysts (RuNPs@SILP

Sep 30, 2016 - ... toward the synthesis of the deoxygenation product p-menthane, ... of limonene under mild reaction conditions (room temperature, 3 b...
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Bifunctional Ruthenium Nanoparticle-SILP Catalysts (RuNPs@SILP) for the Hydrodeoxygenation of Eucalyptol under Batch and Continuous Flow Conditions Kylie L. Luska,† Pedro Migowski,† Sami El Sayed,† and Walter Leitner*,†,‡ †

Institut für Technische und Makromolekulare Chemie, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany Max-Planck-Institut für Kohlenforschung, 45470 Mülheim an der Ruhr, Germany

‡

S Supporting Information *

ABSTRACT: Ruthenium nanoparticles immobilized on acidfunctionalized supported ionic liquid phases (RuNPs@SILPs) were applied in the hydrodeoxygenation of eucalyptol. RuNPs@ SILPs were highly effective and selective catalysts toward the synthesis of the deoxygenation product p-menthane, in which the catalytic properties of the bifunctional catalysts was dependent on the acidity of the SILP. Integration of the acid and metal catalytic species onto a single-support allowed for the implementation of RuNPs@SILP into a continuous flow process. The modular synthesis of these bifunctional catalysts also allowed for an investigation into the roles of the individual and combined acid and metal functionalities in the hydrodeoxygenation of eucalyptol. KEYWORDS: Biomass conversion, Multifunctional catalysis, Hydrodeoxygenation, Continuous flow, Ruthenium, Eucalyptol

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the millions of metric tons,27 and as such eucalyptol has been proposed as an attractive feedstock for the production of a range of C10-chemicals including: p-menthadienes,28 pmenthenes,29,30 p-menthanes31 and p-cymene.25 In particular, the deoxygenation products, p-menthene and p-menthane, have been identified as attractive building blocks for chemicals (e.g., pharmaceuticals, agrochemicals, perfumes, bioplastic monomers)32,33 and as biobased fuel additives.34−36 The deoxygenation of eucalyptol18 can be achieved through a hydrodeoxygenation pathway involving a series of acid and metal catalyzed steps as outlined in Scheme 1. An acidic species catalyzes the ring opening of the tertiary ether moiety yielding p-menthenol (alcohol) and a subsequent dehydration to form p-menthadiene (diene). A metal catalyst hydrogenates the diene intermediate to p-menthene (alkene) and further to the completely saturated product, p-menthane (alkane). The hydrodeoxygenation of eucalyptol has been previously achieved in the gas phase using Pd/SiO2 (200 °C, p-menthane yield >90%)31 or in the liquid phase (neat substrate) using a mixture of heterogeneous Pd/C and a homogeneous Lewis acid additive (e.g., Hf(OTf)4), (0.2 mol % metal, 0.5 mol % acid, 40 bar H2, 100 °C, p-menthane yield >99%).18 Although the latter bifunctional catalyst permitted the hydrodeoxygenation of

INTRODUCTION Biomass feedstocks represent a renewable resource for the production of chemicals and fuels to meet the requirements of our modern society with the potential for substitution of diminishing petroleum reserves and lessening of our impact on the environment.1−5 Depending on regional conditions, various sources of biomass (e.g., lignocellulose, chitin, plant oils) can be considered as alternatives to petrochemicals as they can be harvested from sustainable sources in large quantities and regenerated in short timeframes. The chemical processes for their valorization differ considerably from the refinement of petroleum due to the high degree of oxygenated moieties contained within renewable feedstocks.6,7 Hydrocarbons derived from fossil fuels require functionalization steps (e.g., hydration, hydroformylation, oxidation) to provide an array of base chemicals, whereas platform compounds obtained from renewables must undergo selective removal of oxygenated groups to produce a diverse range of value-added products for the chemical industry and tailor-made fuels components.8−14 Selective catalytic transformations and integrated processes are required to accomplish the efficient deoxygenation of biomass, in which the combination of an acid and metal catalyst, commonly known as a bifunctional catalyst, has been shown as a promising strategy to provide entry into the chemical and energy value chains.15−24 Eucalyptol, also known as 1,8-cineole, is the major component of eucalyptus oil (∼90%) and is obtained from eucalyptus leaves through steam-distillation25 or from crude biomass via a biocatalytic route.26 The potential global production of eucalyptus oil has been estimated to reach into © XXXX American Chemical Society

Special Issue: Building on 25 Years of Green Chemistry and Engineering for a Sustainable Future Received: August 2, 2016 Revised: September 7, 2016

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DOI: 10.1021/acssuschemeng.6b01779 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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under batch and continuous flow conditions. The modular synthesis of RuNPs@SILPs also allowed for an investigation into the roles of the acid and metal functionalities in this hydrodeoxygenation reaction network.

Scheme 1. Reaction Pathway toward the Hydrodeoxygenation of Eucalyptol Catalyzed Using RuNPs@SILP

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a

RESULTS AND DISCUSSION Acidic supported ionic liquid phases (SILPs) were prepared according to a previously reported procedure11,12 and involved the condensation of a sulfonic acid-functionalized IL, [1-(4sulfobutyl)-3-(3-triethoxysilylpropyl)imidazolium]NTf2 (IL 1), and a nonfunctionalized IL, [1-butyl-3-(3-triethoxysilylpropyl)imidazolium]NTf2 (IL 2), with dehydroxylated SiO2. The relative ratio of the acid-functionalized IL 1 and nonfunctionalized IL 2 was adjusted to obtain materials with different acid loadings, IL 1/[IL 1 + IL 2], defined as SILP acidity. The synthesis of Ru NPs immobilized onto SILPs (RuNPs@ SILPs) involved the wet impregnation of the SILP with a solution of [Ru(2-methylallyl)2(cod)] (for cod = 1,5-cyclooctadiene), followed by reduction of the dried SILP under an atmosphere of H2(g) (120 bar H2, 100 °C, 16 h). Characterization of RuNPs@SILPs showed the production of small and well-dispersed Ru NPs (1.6−1.9 nm) by STEM and a metal loading of 0.23 wt % as determined by ICP (see ESI for complete synthetic and characterization details). The reaction profile for the hydrodeoxygenation of eucalyptol catalyzed by [email protected] under batch conditions is shown in Figure 2 (1000 equiv neat sub., 120

Acid catalyzed reactions = red, metal catalyzed reactions = blue.

eucalyptol under milder conditions, this catalyst system showed limited recyclability under batch conditions.18 We were thus motivated to apply our bifunctional system composed of ruthenium nanoparticles immobilized on sulfonic acid-functionalized supported ionic liquid phases (RuNPs@SILPs) as catalysts for the hydrodeoxygenation of eucalyptol. Integration of both a metal and acid catalyst onto a single support can provide enhanced reaction rates and permit the construction of continuous flow processes for the deoxygenation of biobased substrates.12 The preparation of our NP@SILP bifunctional catalysts is based on a molecular approach to assemble the separate acid and metal components on inert support materials in an adaptable and controlled manner (Figure 1).11,12 Grafting

Figure 1. Bifunctional catalysts composed of an acid-functionalized supported ionic liquid phase and ruthenium nanoparticles (RuNPs@ SILP) employed for the hydrodeoxygenation of eucalyptol (for R = −CH2SO3H (IL 1), −CH3 (IL 2)).11,12 Figure 2. Reaction profile for the hydrodeoxygenation of eucalyptol catalyzed by [email protected] (for eucalyptol conversion = purple ●, alcohol = black + , diene = orange ▲, alkene = blue ◆, alkane = red ■). Reaction conditions: [email protected] (225 mg, 0.0072 mmol Ru), substrate (7.2 mmol, 1000 equiv neat), H2 (120 bar), 125 °C.

functionalized and/or nonfunctionalized imidazolium ionic liquids (ILs) onto silica provides solid materials in which the quantity of the acidic functionality can be controlled through the ratio of the functionalized to nonfunctionalized imidazolium units. Even though these surface layers are no longer “liquid phases”, immobilized ILs are commonly known as supported ionic liquids (SILPs).37−44 The functionalized surface provides an effective stabilization medium for metal nanoparticles due to the electrosteric stabilization of the IL and the steric protection of the inert support material.12,45−48 Further, the combination of the molecular diversity of the ILlike structure and the catalytic activity of metal nanoparticles provides a flexible methodology toward the preparation of innovative catalytic materials.11,12,49−52 Immobilization of Ru NPs onto an acidic SILP enabled the production of highly active and selective catalysts applied in the hydrodeoxygenation of eucalyptol for the production of p-menthene and p-methane

bar H2, 125 °C). [email protected] was an effective catalyst for the hydrodeoxygenation of eucalyptol resulting in ca. 40% conversion to a mixture of alkene and alkane products in ∼3:2 ratio after 1 h. The reaction profile follows the typical behavior of a sequential transformation sequence. The alcohol and diene intermediates were observed in very small quantities (99 14 64 >99 >99

0 0 0 0 0

>99 3 1 0 2

0 0 0 0 13

0 97 99 >99 85

a Reaction conditions: RuNPs@SILP (75 mg, 0.0024 mmol Ru), substrate (2.4 mmol, 1000 equiv neat), H2 (120 bar), 4 h, 150 °C. bDetermined by GC using hexadecane as an internal standard. cRu NPs stabilized in [1-butyl-3-(4-sulfobutyl)imidazolium]NTf2 (RuNPs@IL-SO3H): [Ru] (0.0024 mmol), acidic IL (0.051 mmol).

Table 2. Parameter Screening for the Hydrodeoxygenation of Eucalyptol under Continuous Flow Conditions Using RuNPs@ SILP-1.00 product selectivity (%)b entry

T (°C)

substrate flow (mL·min−1)

H2 flow (NmL·min−1)

conversion (%)

alcohol

diene

alkene

alkane

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

113 120 120 120 120 130 130 130 130 130 140 140 140 140 147

0.6 0.4 0.4 0.8 0.8 0.3 0.6 0.6 0.6 0.9 0.4 0.4 0.8 0.8 0.6

20 10 30 10 30 20 37 20 3 20 10 30 10 30 20

33 62 59 39 33 91 68 77 72 61 93 95 75 78 94

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 1 1 1 6 0 1 1 3 1 0 0 2 1 0

7 6 16 13 40 0 2 1 14 3 1 0 7 3 0

92 93 83 86 54 >99 97 98 83 96 99 >99 91 96 >99

a

Reaction conditions: [email protected] (535 mg, 0.0171 mmol Ru), substrate (0.05 M in heptane), H2 (80 bar). bDetermined by GC using hexadecane as an internal standard.

to only 4h upon increasing the reaction temperature to 150 °C (Table 1). Further experiments were conducted under batch conditions to identify the influence of the SILP acidity on the hydrodeoxygenation of eucalyptol at 150 °C (Table 1) (1000 equiv neat sub., 120 bar H2, 150 °C, 4 h). Using a material with 100% acid loading, but without the metal NP component (SILP-1.00) confirmed its effectiveness for acid catalyzed ether cleavage and dehydration of eucalyptol to p-menthadiene. Varying the acid loading with the metal-containing catalysts between 33% and 100% showed that the lower acid loaded catalysts [email protected] and [email protected] possessed low to moderate activities for the hydrodeoxygenation of eucalyptol (14% and 64% conversion, respectively), whereas the most acidic catalyst [email protected] reached full conversion after 4 h. The acid loading of the SILP had a much smaller effect on the catalytic selectivities as the product mixture was composed of >97% p-menthane for all of the bifunctional catalysts. The hydrodeoxygenation of eucalyptol was also performed using an unsupported bifunctional catalyst involving the stabilization of Ru NPs in a homogeneous sulfonic acidfunctionalized IL, [1-butyl-3-(4-sulfobutyl)imidazolium]NTf2 (RuNPs@IL-SO3H).10 Quantitative conversion of eucalyptol

was achieved also in this case; however, the alkane product selectivity toward p-menthane (85%) was reduced for the unsupported catalyst. The lower alkane selectivity resulted from the deactivation of the hydrogenation catalyst due to the instability of the colloidal Ru NPs under catalytic conditions as NP growth and aggregation was observed by TEM (Figure S6). Therefore, the immobilization of Ru NPs onto a SILP provided improved NP stability through the combination of electrosteric stabilization of the IL with the silica support material. Eucalyptol hydrodeoxygenation was implemented into continuous flow operation where a screening of the reaction parameters was conducted using the most active bifunctional catalyst. Continuous flow experiments involved passing a solution of eucalyptol (0.05 M in heptane) through a cartridge packed with [email protected] in an H-Cube Pro, in which a central composite design of experiments (DOE) approach was employed to evaluate the reaction conditions: temperature (113−147 °C), substrate flow (0.3−0.9 mL·min−1) and H2 flow (3−37 N mL·min−1, 80 bar total pressure). The DOE data allowed for the conversion profile to be modeled as a function of the selected reaction parameters using a quadratic model (Figure S1). The reaction temperature and substrate flow were identified as the most significant parameters on productivity, where the eucalyptol conversion increased at higher temperC

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Figure 3. Hydrodeoxygenation of eucalyptol (0.05 M in heptane, 0.6 mL·min−1) using (a) [email protected], (b) [email protected] and (c) [email protected] under continuous flow conditions at 130 °C H2 and 80 bar H2 (20 N mL min−1) (for eucalyptol conversion = purple ●, alcohol = black + , diene = orange ▲, alkene = blue ◆, alkane = red ■).

Table 3. Reaction Rates for the Hydrodeoxygenation of Eucalyptol Using SILP-Based Catalysts

entry

reaction

elementary reactions 1 eucalyptol dehydration 2 diene hydrogenation 3 alkene hydrogenation integrated/tandem reactions 4 bifunctional catalyst

−reucalyptol = 3.02 −rdiene = 30.6 −ralkene = 12.4

[email protected]

−reucalyptol = 0.24 +rtotal = 0.15 −reucalyptol = 0.63 +rtotal = 0.58 −reucalyptol = 3.24 +rtotal = 1.50 −reucalyptol = 3.25 +rtotal = 2.35

[email protected]

6

[email protected] physical mixture

reaction rates (M·h−1)

SILP-1.00 [email protected] [email protected]

5

7 a

catalyst

[email protected] + SILP-1.00

Reaction conditions: [email protected] (225 mg, 0.0072 mmol Ru), substrate (7.2 mmol, 1000 equiv neat), H2 (120 bar), 125 °C.

atures and lower substrate flows, as expected. The hydrogen flow rate had a smaller effect as an excess of H2 was effectively present throughout the studied range. Modeling of the DOE data with respect to the catalytic selectivity was unsuccessful due to poor adjustment of experimental data within the confidence interval; however, qualitative relationships between the continuous flow param-

eters and product selectivity can be extracted from the data shown in Table 2. The reaction temperature had a minor influence on the product selectivity as lowering the temperature from 147 to 113 °C caused a slight decrease in the alkane selectivity from >99% to 92% (Table 2, entries 1, 8 and 15), mainly due to less efficient overall conversion. The substrate flow also did not possess a significant influence on the alkane D

DOI: 10.1021/acssuschemeng.6b01779 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering selectivities as >96% p-menthanes were obtained for substrate flows between 0.3 and 0.9 mL·min−1 (Table 2, entries 6, 8 and 10). The H2 flow had the most prominent effect on the selectivity of the bifunctional catalysts as decreasing the flow from 37 to 3 N mL·min−1 caused a decrease in the alkane selectivity from 97% to 83%, whereas concurrently the alkene selectivity increased from 2% to 14% (Table 2, entries 7−9) at a roughly constant conversion of substrate of ca. 70%. Further studies were conducted using the reaction parameters at the centroid of the response surface obtained from the DOE data (T = 130 °C, substrate flow = 0.6 mL· min−1, H2 flow = 20 N mL·min−1, t = 300 min) to evaluate the influence of the SILP acidity and RuNP@SILP stability under continuous flow conditions. Hydrodeoxygenation of eucalyptol over the lowest acid loaded bifunctional catalyst [email protected] showed low substrate conversion (94% (Figure 3c). Although the product selectivity toward p-menthane remained nearly constant at values close to 100% throughout the continuous flow experiment, the eucalyptol conversion decreased to 60% at the later stages of the reaction. Analysis of [email protected] after catalysis showed no significant growth or aggregation of the Ru NPs by STEM, ICP analysis did not evidence any leaching of Ru or IL, and changes to the textural properties were not observed by BET (Table S2). As the bifunctional catalysts appeared to be stable materials under continuous flow conditions, we sought an explanation for the alteration to the catalytic properties of RuNPs@SILPs while on-stream under continuous conditions. To obtain more detailed insight into the sequential hydrodeoxygenation process of eucalyptol, materials composed of the individual acid and metal functionalities were investigated to determine kinetic parameters for the elementary steps involved. The reaction rates for the elementary steps were evaluated under a set of standard conditions (1000 equiv neat sub., 120 bar H2, 125 °C) by GC-FID analysis of reaction samples or H2uptake experiments of the individual substrates, where pseudozero-order kinetics was observed during the initial stages of the reactions (Table 3 and Figure S2). Using the metal-free material (SILP-1.00), the dehydration of eucalyptol (−reucalyptol) to a mixture of dienes possessed a reaction rate of 3.02 M·h−1 (Table 3, entry 1). The subsequent diene (−rdiene) and alkene hydrogenations (−ralkene) carried out with an acid-free catalyst ([email protected]) had reaction rates of 30.6 and 12.4 M· h−1, respectively (Table 3, entries 2 and 3). The hydrogenation reaction rates validated the data of the time profile (Figure 2) as the formation of diene was negligible throughout the reaction, whereas considerable quantities of alkene built up in the early stages of the reaction. The lower −ralkene may result from a decreased access of p-menthene to the active metal sites due to the IL-like phase of the SILP; a phenomenon that has also been previously reported for the hydrogenation of diene substrates using solid catalysts with ionic liquid layers (SCILLs)53 or NP@IL catalysts.54 Next, kinetic experiments were performed for the integrated reaction using the RuNP@SILP bifunctional catalysts and for

the tandem reaction employing a physical mixture of the individual components, [email protected] and SILP-1.00. The strong influence of the SILP acidity on the catalytic activity of the bifunctional catalysts was confirmed as [email protected] and [email protected] possessed low eucalyptol conversion rates (−reucalyptol = 0.24 and 0.63 M·h−1, respectively), whereas −reucalyptol for the most acidic bifunctional [email protected] improved to 3.24 M·h−1 (Table 3, entries 4−6). The tandem reaction catalyzed using a physical mixture of [email protected] and SILP-1.00 exhibited a −reucalyptol of 3.25 M·h−1 (Table 3, entry 7). Thus, the catalytic activities of the bifunctional [email protected] catalyst and the physical mixture of [email protected] and SILP-1.00 showed similar eucalyptol conversion rates as that for the SILP-1.00 catalyzed dehydration of eucalyptol (Table 3, entry 1). Thus, the acid catalyzed dehydration of eucalyptol was determined to be the rate-limiting elementary reaction, which was ca. 10 and 4 times slower than the metal catalyzed diene and alkene hydrogenation, respectively. This kinetic data may at least partly explain the catalytic performance of [email protected] under continuous flow conditions (Figure 3c), in which the reduced catalytic activity while on-stream likely results from a rate decrease for the acid catalyzed dehydration of eucalyptol (the rate-limiting step). As [email protected] were shown to be stable materials under continuous flow conditions, the decreased activity of the bifunctional catalyst is possibly caused by the accumulation of water formed during the reaction within the catalyst bed, leading to a decrease of the surface acidity of the material.55,56 The kinetic data was also used to evaluate the overall deoxygenation rates toward the production of p-menthane (+rtotal) for the bifunctional, [email protected], and the physically mixed, [email protected] + SILP-1.00, catalysts (Table 3, entries 6 and 7). The total reaction rates, + rtotal, were found to be lower than the rate of eucalyptol conversion, −reucalyptol, providing evidence that the deoxygenation rate was not solely governed by the acid catalyzed dehydration of eucalyptol (the slowest elementary step). Thus, the subsequent hydrogenation reactions also influence the overall deoxygenation rates of the tandem reactions for both the bifunctional and physically mixed catalysts, as reflected in lower −ralkene in comparison to −rdiene. This effect likely arises from hindered mass transport of p-menthene to the active metal sites, which can result from its low solubility in the SILP layer, as outlined above.53,54 Differences in the polarity, H-bonding ability, or hydrophilicity of the sulfonic acid-functionalized SILP-1.00 in comparison to the nonfunctionalized SILP-0.00 may also influence the hydrogenation rates of the bifunctional catalysts.

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SUMMARY AND CONCLUSIONS In summary, the hydrodeoxygenation of eucalyptol was studied using bifunctional catalysts comprising ruthenium nanoparticles stabilized on acid-functionalized support ionic liquid phases (RuNPs@SILP) toward the production of the C10-chemicals pmenthene and p-menthane. RuNPs@SILPs were active and selective catalysts for the hydrodeoxygenation of eucalyptol to p-menthane, in which integration of the acid and metal functionalities onto silica allowed for the implementation of this process into continuous flow operation. The bottom-up synthesis of these SILP-based materials also allowed for a kinetic evaluation of the elementary and tandem reactions involved in the hydrodeoxygenation of eucalpytol using the individual and combined acid and metal constituents. The acid E

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providing the Ru precursor, [Ru(2-methylallyl)2(cod)]. K.L.L. thanks Deutscher Akademischer Austaush Dienst (DAAD) for financial support. P.M. thanks the Alexander von Humboldt Foundation for funding.

catalyzed deoxygenation of eucalyptol was identified as the ratelimiting elementary step, and thus the ability to modulate the acidity of the SILP allowed for the production of highly active bifunctional catalysts. Future work within our group focuses on the utilization of NP@SILP catalysts in the deoxygenation of other classes of bioderived substrates and toward the construction of continuous flow processes using supercritical carbon dioxide as a mobile phase to allow for removal of in situ produced water from the catalyst bed during hydrodeoxygenation transformations, as this appears to be a major cause for catalyst deactivation.

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EXPERIMENTAL SECTION

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ASSOCIATED CONTENT

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(1) Corma, A.; Iborra, S.; Velty, A. Chemical routes for the transformation of biomass into chemicals. Chem. Rev. 2007, 107, 2411−2502. (2) Climent, M. J.; Corma, A.; Iborra, S. Conversion of Biomass Platform Molecules into Fuel Additives and Liquid Hydrocarbon Fuels. Green Chem. 2014, 16, 516−547. (3) Chheda, J. N.; Huber, G. W.; Dumesic, J. A. Liquid-phase catalytic processing of biomass-derived oxygenated hydrocarbons to fuels and chemicals. Angew. Chem., Int. Ed. 2007, 46, 7164−7183. (4) Alonso, D. M.; Bond, J. Q.; Dumesic, J. A. Catalytic conversion of biomass to biofuels. Green Chem. 2010, 12, 1493−1513. (5) Besson, M.; Gallezot, P.; Pinel, C. Conversion of Biomass into Chemicals Over Metal Catalysts. Chem. Rev. 2014, 114, 1827−1870. (6) Schlaf, M. Selective deoxygenation of sugar polyols to alpha,omega-diols and other oxygen content reduced materials - a new challenge to homogeneous ionic hydrogenation and hydrogenolysis catalysis. Dalton Trans. 2006, 4645−4653. (7) Nakagawa, Y.; Liu, S. B.; Tamura, M.; Tomishige, K. Catalytic Total Hydrodeoxygenation of Biomass-Derived Polyfunctionalized Substrates to Alkanes. ChemSusChem 2015, 8, 1114−1132. (8) 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. (9) Geilen, F. M. A.; Engendahl, B.; Holscher, M.; Klankermayer, J.; Leitner, W. Selective Homogeneous Hydrogenation of Biogenic Carboxylic Acids with [Ru(TriPhos)H](+): A Mechanistic Study. J. Am. Chem. Soc. 2011, 133, 14349−14358. (10) Julis, J.; Leitner, W. Synthesis of 1-Octanol and 1,1-Dioctyl Ether from Biomass-Derived Platform Chemicals. Angew. Chem., Int. Ed. 2012, 51, 8615−8619. (11) Luska, K. L.; Julis, J.; Stavitski, E.; Zakharov, D. N.; Adams, A.; Leitner, W. Bifunctional nanoparticle-SILP catalysts (NPs@SILP) for the selective deoxygenation of biomass substrates. Chem. Sci. 2014, 5, 4895−4905. (12) Luska, K. L.; Migowski, P.; El Sayed, S.; Leitner, W. Synergistic Interaction within Bifunctional Ruthenium Nanoparticle/SILP Catalysts for the Selective Hydrodeoxygenation of Phenols. Angew. Chem., Int. Ed. 2015, 54, 15750−15755. (13) Ruppert, A. M.; Weinberg, K.; Palkovits, R. Hydrogenolysis Goes Bio: From Carbohydrates and Sugar Alcohols to Platform Chemicals. Angew. Chem., Int. Ed. 2012, 51, 2564−2601. (14) vom Stein, T.; Klankermayer, J.; Leitner, W. Tailor-Made Fuels and Chemicals from Biomass. In Catalysis for the Conversion of Biomass and its Derivatives; Behrens, M.; Datye, A. K., Eds.; epubli: Berlin, Germany, 2013; pp 411−434. (15) Zhao, C.; Kou, Y.; Lemonidou, A. A.; Li, X. B.; Lercher, J. A. Highly Selective Catalytic Conversion of Phenolic Bio-Oil to Alkanes. Angew. Chem., Int. Ed. 2009, 48, 3987−3990. (16) Zhao, C.; Kou, Y.; Lemonidou, A. A.; Li, X. B.; Lercher, J. A. Hydrodeoxygenation of bio-derived phenols to hydrocarbons using RANEY (R) Ni and Nafion/SiO2 catalysts. Chem. Commun. 2010, 46, 412−414. (17) Peng, B. X.; Yao, Y.; Zhao, C.; Lercher, J. A. Towards Quantitative Conversion of Microalgae Oil to Diesel-Range Alkanes with Bifunctional Catalysts. Angew. Chem., Int. Ed. 2012, 51, 2072− 2075. (18) Li, Z.; Assary, R. S.; Atesin, A. C.; Curtiss, L. A.; Marks, T. J. Rapid Ether and Alcohol C-O Bond Hydrogenolysis Catalyzed by Tandem High-Valent Metal Triflate plus Supported Pd Catalysts. J. Am. Chem. Soc. 2014, 136, 104−107.

Catalyst Preparation. RuNPs@SILP were synthesized as previously reported.11,12 Full experimental and characterization data are provided in the Supporting Information. Batch Conditions. In a typical experiment, RuNPs@SILP (75 mg, 0.0024 mmol Ru) and eucalyptol (2.4 mmol, 1000 equiv) were combined in a glass insert and placed in a high-pressure autoclave. After the autoclave was purged with H2(g), the reaction mixture was stirred at 150 °C for 4 h in an aluminum heating block under 120 bar H2(g) (pressurized to 100 bar H2(g) at rt). Once the reaction was finished, the reactor was cooled in an ice bath, carefully vented and the reaction mixture was analyzed via GC using hexadecane as an internal standard. Continuous Flow Conditions. A 70 mm CatCart was filled with [email protected] (547 mg, 0.0175 mmol Ru) and placed into the HCube Pro. Prior to catalysis, the catalyst was heated at 100 °C under a flow of heptane (0.3 mL min−1) and H2(g) (80 bar, 60 N mL min−1) for 60 min. The substrate solution (0.05 M eucalyptol in heptane) was introduced into the system with a flow of H2(g) (80 bar) and the reaction parameters (temperature = 113−147 °C, substrate flow = 0.3−0.9 mL min−1, H2 flow = 3−37 N mL min−1) were varied. The system was allowed to equilibrate under the desired reaction conditions for 20 min before ∼6 mL of reaction solution was collected. The reaction mixture was analyzed via GC using hexadecane as an internal standard. S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b01779. Complete synthetic, characterization and catalysis data for RuNPs@SILP (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*W. Leitner. E-mail: [email protected]; Fax: (+49) 241-80-22177; Tel: (+49) 241-80-26481. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was performed as a part of the Cluster of Excellence “Tailor-Made Fuels from Biomass”, which is funded by the Excellence Initiative of the German federal and state government to promote science and research at German universities. The authors thank Karl-Josef Vaeßen (ITMC, RWTH Aachen University) for N2(g) adsorption measurements, Bernd Spliethoff and Hans-Josef Bongard for TEM and STEM analyses (Max-Planck-Institut für Kohlenforschung) and Dr. Nils Theyssen (Max-Planck-Institut für Kohlenforschung) for his generous support. We also thank Umicore for graciously F

DOI: 10.1021/acssuschemeng.6b01779 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

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DOI: 10.1021/acssuschemeng.6b01779 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX