Stability of self-assembled monolayer coated Pt/Al2O3 catalysts for liquid phase hydrogenation

Multiple Roles of Alkanethiolate-Ligands in Direct Formation of H2 O2 over Pd Nanoparticles

Coadsorbed organic species including thiolates can promote direct synthesis of hydrogen peroxide from H₂ and O₂ over Pd particles. Here, density functional theory based kinetic modeling, augmented with activity measurements and vibrational spectroscopy are used to provide atomistic understanding of direct H₂ O₂ formation over alkylthiolate(RS) Pd. We find that the RS species are oxidized during reaction conditions yielding RSO₂ as the effective ligand. The RSO₂ ligand shows superior ability for proton transfer to the intermediate surface species OOH, which accelerates the formation of H₂ O₂ . The ligands promote the selectivity also by blocking sites for unselective water formation and by modifying the electronic structure of Pd. The work rationalizes observations of enhanced selectivity of direct H₂ O₂ formation over ligand-funtionalized Pd nanoparticles and shows that engineering of organic surface modifiers can be used to promote desired hydrogen transfer routes.

An experimental approach for controlling confinement effects at catalyst interfaces

Catalysts are conventionally designed with a focus on enthalpic effects, manipulating the Arrhenius activation energy. This approach ignores the possibility of designing materials to control the entropic factors that determine the pre-exponential factor. Here we investigate a new method of designing supported Pt catalysts with varying degrees of molecular confinement at the active site. Combining these with fast and precise online measurements, we analyse the kinetics of a model reaction, the platinum-catalysed hydrolysis of ammonia borane. We control the environment around the Pt particles by erecting organophosphonic acid barriers of different heights and at different distances. This is done by first coating the particles with organothiols, then coating the surface with organophosphonic acids, and finally removing the thiols. The result is a set of catalysts with well-defined "empty areas" surrounding the active sites. Generating Arrhenius plots with >300 points each, we then compare the effects of each confinement scenario. We show experimentally that confining the reaction influences mainly the entropy part of the enthalpy/entropy trade-off, leaving the enthalpy unchanged. Furthermore, we find this entropy contribution is only relevant at very small distances (<3 Å for ammonia borane), where the "empty space" is of a similar size to the reactant molecule. This suggests that confinement effects observed over larger distances must be enthalpic in nature.

Selective hydrogenation of 2-pentenal using highly dispersed Pt catalysts supported on ZnSnAl mixed metal oxides derived from layered double hydroxides

Highly dispersed Pt catalysts supported on ZnSnAl mixed metal oxides showed high selectivity for 2-pentenol in selective hydrogenation of 2-pentenal.

The role and fate of capping ligands in colloidally prepared metal nanoparticle catalysts

In this Perspective article, we highlight emerging opportunities for the rational design of catalysts upon the choice, exchange, partial removal or pyrolysis of ligands.

Synergistic effect of Mo2N and Pt for promoted selective hydrogenation of cinnamaldehyde over Pt–Mo2N/SBA-15

Pt–Mo₂N/SBA-15 exhibits high activity for selective hydrogenation of cinnamaldehyde due to the synergistic effect between Mo₂N and Pt.

Controlling Catalytic Selectivity via Adsorbate Orientation on the Surface: From Furfural Deoxygenation to Reactions of Epoxides

Specificity to desired reaction products is the key challenge in designing solid catalysts for reactions involving addition or removal of oxygen to/from organic reactants. This challenge is especially acute for reactions involving multifunctional compounds such as biomass-derived aromatic molecules (e.g., furfural) and functional epoxides (e.g., 1-epoxy-3-butene). Recent surface-level studies have shown that there is a relationship between adsorbate surface orientation and reaction selectivity in the hydrogenation pathways of aromatic oxygenates and the ring-opening or ring-closing pathways of epoxides. Control of the orientation of reaction intermediates on catalytic surfaces by modifying the surface or near-surface environment has been shown to be a promising method of affecting catalytic selectivity for reactions of multifunctional molecules. In this Perspective, we review recent model studies aimed at understanding the surface chemistry for these reactions and studies that utilize this insight to rationally design supported catalysts.