A combined theoretical and experimental approach is presented that uses a comprehensive mean‐field microkinetic model, reaction kinetics experiments, and scanning transmission electron microscopy imaging to unravel the reaction mechanism and provide insights into the nature of active sites for formic acid (HCOOH) decomposition on Au/SiC catalysts. All input parameters for the microkinetic model are derived from periodic, self‐consistent, generalized gradient approximation (GGA‐PW91) density functional theory calculations on the Au(111), Au(100), and Au(211) surfaces and are subsequently adjusted to describe the experimental HCOOH decomposition rate and selectivity data. It is shown that the HCOOH decomposition follows the formate (HCOO) mediated path, with 100% selectivity toward the dehydrogenation products (CO2 + H2) under all reaction conditions. An analysis of the kinetic parameters suggests that an Au surface in which the coordination number of surface Au atoms is ≤4 may provide a better model for the active site of HCOOH decomposition on these specific supported Au catalysts. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1303–1319, 2014

We report an approach by which the hemicellulose and cellulose fractions of biomass are converted through catalytic processes in a solvent prepared from lignin into high value platform chemicals and transportation fuels, namely furfural, 5-hydroxymethylfurfural, levulinic acid and γ-valerolactone.The production of second-generation biofuels from lignocellulosic biomass can be achieved through the intermediate production of oxygenated platform molecules, 1 such as furan intermediates (furfural (FuAl), furfuryl alcohol (FuOH) and 5-hydroxymethylfurfural (HMF)), levulinic acid (LA), and γ-valerolactone (GVL). 2 We report herein an approach by which the hemicellulose and cellulose fractions of biomass can be converted to these platform chemicals using an organic solvent obtained by depolymerization of lignin.Scheme 1 shows our proposed roadmap for the conversion of lignocellulosic biomass to fuels and chemicals. Solid biomass is first subjected to mild pre-treatment in an aqueous solution containing dilute acid to solubilize the hemicellulose as xylose, followed by heating of this aqueous stream to achieve dehydration of xylose to furfural. The use of a biphasic reactor is employed in this step to continuously extract the reactive FuAl from the aqueous phase. 3 The remaining biomass is then subjected to further treatment to solubilize cellulose as glucose, and a biphasic reactor is employed in the subsequent step to dehydrate glucose to HMF by enabling the continuous extraction of the reactive HMF product from the acidic aqueous phase. 4-7 HMF can then undergo acid hydrolysis to LA and equimolar amounts of formic acid (FA). Similarly, FuAl can be converted to LA by first undergoing reduction to FuOH over a metal catalyst, 8,9 followed by conversion to LA over an acid catalyst. The selective hydrolysis of FuOH and HMF to LA is favored at low concentrations of the reactant, and a biphasic reactor can be employed for these conversions, where the function of the organic solvent is to release the reactive reactant continuously into the acidic aqueous phase. In addition, the organic solvent enables extraction of LA from acidic aqueous solutions (e.g., as produced in the Biofine process 10 ), which can then be utilized as a chemical intermediate or can be selectively hydrogenated in the solvent to GVL, the latter serving as a chemical intermediate for polymers and solvents, as well as a blending agent for transportation fuels. The energy density of GVL for use as a transportation fuel can be increased by decarboxylation to form butene, followed by butene oligomerization to gasoline (branched C 8 species) or jet fuel (branched C 8 -C 16 species). 11 An underlying strategy to implement the roadmap outlined in Scheme 1 is to identify organic solvents that can be used to extract biomass-derived products and intermediates (such as FuAl, FuOH, LA, GVL) from acidic aqueous solutions. In our previous work, we have utilized 2-sec-butylphenol (SBP) as an effective solvent. 3,12 In the present report, we show that the catalytic depoly...

We show that MoO(x)-promoted Au/SiO2 catalysts are active for reverse water-gas shift (RWGS) at 573 K. Results from reactivity measurements, CO FTIR studies, Raman spectroscopy, and X-ray absorption spectroscopy (XAS) indicate that the deposition of Mo onto Au nanoparticles occurs preferentially on under-coordinated Au sites, forming Au/MoO(x) interfacial sites active for reverse water-gas shift (RWGS). Au and AuMo sites are quantified from FTIR spectra of adsorbed CO collected at subambient temperatures (e.g., 150-270 K). Bands at 2111 and 2122 cm(-1) are attributed to CO adsorbed on under-coordinated Au(0) and Au(δ+) species, respectively. Clausius-Clapeyron analysis of FTIR data yields a heat of CO adsorption (ΔH(ads)) of -31 kJ mol(-1) for Au(0) and -64 kJ mol(-1) for Au(δ+) at 33% surface coverage. Correlations of RWGS reactivity with changes in FTIR spectra for samples containing different amounts of Mo indicate that interfacial sites are an order of magnitude more active than Au sites for RWGS. Raman spectra of Mo/SiO2 show a feature at 975 cm(-1), attributed to a dioxo (O═)2Mo(-O-Si)2 species not observed in spectra of AuMo/SiO2 catalysts, indicating preferential deposition of Mo on Au. XAS results indicate that Mo is in a +6 oxidation state, and therefore Au and Mo exist as a metal-metal oxide combination. Catalyst calcination increases the quantity of under-coordinated Au sites, increasing RWGS activity. This strategy for catalyst synthesis and characterization enables quantification of Au active sites and interfacial sites, and this approach may be extended to describe reactivity changes observed in other reactions on supported gold catalysts.

Driven by mechanical forces, the acid-catalyzed depolymerization of solid biomass completely overcomes the problems posed by the recalcitrance of lignocellulose. The solid-state reaction leads to water-soluble oligosaccharides, which display higher reactivity than cellulose and hemicellulose. Here, we show that water-soluble oligosaccharides are useful feedstock for the high-yield production of 5-hydroxymethylfurfural (HMF) and furfural in biphasic reactors. This is because they readily undergo hydrolysis upon microwave heating, selectively forming monosaccharides as intermediates in the aqueous phase. Short reaction times are possible with the use of microwave heating and limit the extent of degradation reactions. This work provides an ionic-liquid-free approach to process lignocellulosic substrates into HMF and furfural with high yields. In fact, starting this novel approach with alpha-cellulose, yields of HMF of 79% and furfural of 80% at 443 K for 9 min were obtained. The processing of real lignocellulose (e.g., beechwood and sugar cane bagasse) also achieved high yields of HMF and furfural. Thereby, the current results indicate that the process limitation lies no longer in the recalcitrance of lignocellulose, but in the extraction of highly reactive HMF and furfural from the aqueous phase in the biphasic reactor