The selective hydrogenation of acetylene has been studied over AgPd and CuPd catalysts. Controlled surface reactions were used to synthesize these bimetallic nanoparticles on both TiO2 and SiO2 supports. Chemisorption measurements of the bimetallic catalysts indicate that Pd prefers to be on the nanoparticle surface with a Cu parent catalyst, while Pd prefers to be subsurface with a Ag parent catalyst. From energy-dispersive X-ray spectroscopy analysis, the composition of the nanoparticles is determined to be more uniform on the SiO2 support compared to that on the TiO2 support. X-ray absorption spectroscopy results indicate that, after reduction, the CuPd bimetallic catalysts have some Pd–Pd bonds, but the average number of Pd–Pd bonds decreases after reaction. Infrared spectra of the adsorbed CO show that an increased fraction of isolated Pd species are present on the bimetallic catalysts compared to those on the monometallic catalysts. Adsorption of acetylene and ethylene, however, indicates adsorbed surface species that require contiguous Pd ensembles. These results suggest that the surface structure of the catalyst is highly dynamic and influenced by the gas environment, as well as the support. The catalysts are active for the selective hydrogenation of acetylene in an ethylene-rich environment under mild conditions. Over all catalysts, the ethylene selectivity is greater than 92%; however, improved selectivity is observed over the bimetallic catalysts compared to that over the monometallic Pd catalysts. An ethylene selectivity of 100% is observed over the CuPd0.08/TiO2 catalyst. The highest acetylene conversion rate per gram of Pd is observed over the CuPd0.02/TiO2 catalyst, while the highest turnover frequency is found over the AgPd0.64/TiO2 catalyst. The bimetallic SiO2-supported catalysts have lower rates than Pd/SiO2 but still show improved selectivity. The combined characterization measurements and reaction kinetics studies indicate that the performance improvements of the bimetallic catalysts may be attributed to both electronic and geometric modifications of Pd by the parent Cu or Ag metal.

We studied the hydrogenation at temperatures from 313 – 393 K of a biomass-derived platform molecule, 5-hydroxymethyl furfural (HMF)-Acetone-HMF (HAH) over Pd, Ru, and Cu based catalysts. HAH was selectively...

Synthetic platform for production of biomass-derived monomers and performance-advantaged polymers with renewability, upgradability, and economic viability.

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We show that platinum displays a self-adjusting surface that is active for the hydrogenation of acetone over a wide range of reaction conditions. Reaction kinetics measurements under steady-state and transient conditions at temperatures near 350 K, electronic structure calculations employing density-functional theory, and microkinetic modeling were employed to study this behavior over supported platinum catalysts. The importance of surface coverage effects was highlighted by evaluating the transient response of isopropanol formation following either removal of the reactant ketone from the feed, or its substitution with a similarly structured species. The extent to which adsorbed intermediates that lead to the formation of isopropanol were removed from the catalytic surface was observed to be higher following ketone substitution in comparison to its removal, indicating that surface species leading to isopropanol become more strongly adsorbed on the surface as the coverage decreases during the desorption experiment. This phenomenon occurs as a result of adsorbate–adsorbate repulsive interactions on the catalyst surface which adjust with respect to the reaction conditions. Reaction kinetics parameters obtained experimentally were in agreement with those predicted by microkinetic modeling when the binding energies, activation energies, and entropies of adsorbed species and transition states were expressed as a function of surface coverage of the most abundant surface intermediate (MASI, C3H6OH*). It is important that these effects of surface coverage be incorporated dynamically in the microkinetic model (e.g., using the Bragg–Williams approximation) to describe the experimental data over a wide range of acetone partial pressures.

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Biomass conversion to alcohols using supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHO) with CuMgAl mixed metal oxide is a promising process for biofuel production.

We have developed lumped reaction schemes to optimize the yields of products from selective hydrogenations of HAH, a biomass-derived platform chemical produced by two-step aldol condensations of 5-hydroxymethyl furfural (H) with acetone (A). Reaction schemes consisting of 7, 9, and 11 steps were examined to describe the rates of formation of the observed products and reaction intermediates for hydrogenation of HAH over Ru and Pd catalysts, and a 3-step scheme was studied over Cu catalysts. Rate constants and activation energies were calculated using these reaction schemes, and we then apply the schemes to explore the effects of water addition on the hydrogenation pathways. The effects of water addition to isopropanol (IPA) solvents on the hydrogenation of HAH were markedly different over Pd, Ru, and Cu catalysts. Over the Pd catalyst, the addition of water to IPA increased hydrogenation rates and promoted the hydrogenation of furan rings. The addition of water to IPA yielded significant carbon losses over the Ru catalyst, and slowed hydrogenation steps over Cu, while significantly inhibiting hydrogenation of the ketone group. This behavior opened routes toward increased production rates of PHAHO (a partially hydrogenated, P, form of HAH containing a CO bond), a product in which the diene groups of the furan rings were not hydrogenated. The addition of water also allowed increased feed concentrations of HAH that were previously not possible in pure IPA solvents. The insights presented in this work provide a more mechanistic description of the hydrogenation of HAH, the behavior of specific intermediates, and the reactivity of key functional groups.