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.

Pt and PtSn catalysts supported on SiO2 and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO2 increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO2:Al2O3 = 280 in comparison to those over PtSn(3:1)/SiO2. H-ZSM-5-supported catalysts were also active for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is subsequently converted to benzene and naphthalene on Brønsted acid sites within the zeolite support. The most active and stable PtSn catalyst forms carbon products at a rate, 2.5 mmol of C/((mol of Pt) s), which is comparable to that of state-of-the-art Mo/H-ZSM-5 catalysts with same metal loading operated under similar conditions (1.8 mmol of C/((mol of Mo) s)). Scanning transmission electron microscopy measurements suggest the presence of smaller Pt nanoparticles on H-ZSM-5-supported catalysts, in comparison to SiO2-supported catalysts, as a possible source of their high activity. A microkinetic model of methane conversion on Pt and PtSn surfaces, built using results from density functional theory calculations, predicts higher coupling rates on bimetallic and stepped surfaces, supporting the experimental observations that relate the high catalytic activity to small PtSn particles.

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AuPd/TiO2 bimetallic catalysts, synthesized using controlled surface reactions, exhibit enhanced rates for amination of hexanol using ammonia compared to monometallic Au and Pd catalysts.

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.

Catalysts consisting of transition metals (Ni, Co, Cu, and Ru) supported on molybdenum oxide synthesized by atomic layer deposition (ALD) on silica were studied for synthesis gas conversion at 523 K and a pressure of 580 psi. Transition-metal-promoted Mo-based catalysts (M/MoO3/SiO2) showed different selectivity patterns from the transition metal supported on silica (M/SiO2). All molybdenum-based catalysts displayed a similar selectivity pattern, consisting of 15–20% of CH4, 30–40% of C2+ hydrocarbons, and 35–40% of oxygenates. The addition of transition metals to molybdenum oxide promoted the catalytic activity by an order of magnitude. Temperature program reduction indicated hydrogen spillover from the transition metals to molybdenum species. H2–D2 exchange rate measurements showed that the addition of the transition metal enhanced the rate of H2 dissociation on the catalyst. CO chemisorption measurements indicated that transition-metal-promoted molybdenum catalysts consist of a similar amount of strong adsorption sites, which may originate from the reduced transition metal, and weak adsorption sites, which may originate from reduced molybdenum oxides. A dual-site mechanism is suggested in which low-valent molybdenum species dissociate CO and generate CH x groups that are hydrogenated to hydrocarbons or react with adsorbed CO on higher-valent Mo sites to form higher alcohols. Ni, Co, and Ru are able to generate CH x groups and enhance the production of C2+ oxygenates, whereas all of the transition metals studied are able to provide sites for H2 dissociation and H spillover to molybdenum oxide, leading to further enhancement in catalytic activity compared to MoO x /SiO2.