We showed that alumina (Al(2)O(3)) overcoating of supported metal nanoparticles (NPs) effectively reduced deactivation by coking and sintering in high-temperature applications of heterogeneous catalysts We overcoated palladium NPs with 45 layers of alumina through an atomic layer deposition (ALD) process that alternated exposures of the catalysts to trimethylaluminum and water at 200°C When these catalysts were used for 1 hour in oxidative dehydrogenation of ethane to ethylene at 650°C, they were found by thermogravimetric analysis to contain less than 6% of the coke formed on the uncoated catalysts Scanning transmission electron microscopy showed no visible morphology changes after reaction at 675°C for 28 hours The yield of ethylene was improved on all ALD Al(2)O(3) overcoated Pd catalysts

Coking- and Sintering-Resistant Palladium Catalysts Achieved Through Atomic Layer Deposition

Selective catalytic hydrogenation has wide applications in both petrochemical and fine chemical industries, however, it remains challenging when two or multiple functional groups coexist in the substrate. To tackle this challenge, the "active site isolation" strategy has been proved effective, and various approaches to the site isolation have been developed. In this review, we have summarized these approaches, including adsorption/grafting of N/S-containing organic molecules on the metal surface, partial covering of active metal surface by metal oxides either via doping or through strong metal-support interaction, confinement of active metal nanoparticles in micro- or mesopores of the supports, formation of bimetallic alloys or intermetallics or core@shell structures with a relatively inert metal (IB and IIB) or nonmetal element (B, C, S, etc.), and construction of single-atom catalysts on reducible oxides or inert metals. Both advantages and disadvantages of each approach toward the site isolation have been discussed for three types of chemoselective hydrogenation reactions, including alkynes/dienes to monoenes, α,β-unsaturated aldehydes/ketones to the unsaturated alcohols, and substituted nitroarenes to the corresponding anilines. The key factors affecting the catalytic activity/selectivity, in particular, the geometric and electronic structure of the active sites, are discussed with the aim to extract fundamental principles for the development of efficient and selective catalysts in hydrogenation as well as other transformations.

Selective Hydrogenation over Supported Metal Catalysts: From Nanoparticles to Single Atoms

This critical review describes the reactivity of heterogeneous catalysts from the point of view of four simple, but essential for Chemistry, molecules (namely dihydrogen, carbon monoxide, nitrogen monoxide and ethylene) that are considered as probes or as reactants in combination with “in situ” controlled temperature and pressure Infrared spectroscopy. The fundamental properties of H2, CO, NO and C2H4 are shortly described in order to justify their different behaviour in respect of isolated sites in different environments, extended surfaces, clusters, crystalline or amorphous materials. The description is given by considering some “key studies” and trying to evidence similarities and differences among surfaces and probes (572 references).

/pdf/probing-the-surfaces-of-heterogeneous-catalysts-by-in-situ-2mmpzxpkqu.pdf

Probing the surfaces of heterogeneous catalysts by in situ IR spectroscopy

Pd/ZnO catalysts for direct CO2 hydrogenation to methanol

Atomic layer deposition-Sequential self-limiting surface reactions for advanced catalyst "bottom-up" synthesis

Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1–7.3wt%). Collectively, this series of catalysts provides a range of metal particle sizes (1.2–8.5nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)∕(111) and (111)∕(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1wt% loaded catalysts, with the relative inactivity of the cataly...

/pdf/the-application-of-infrared-spectroscopy-to-probe-the-1xj7qq9kqh.pdf

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts.

Erratum: „The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts“ (J.Chem. Phys. 123, 174706 (2005))

J. Antonio Lopez-Sanchez

Papers

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts.

Erratum: „The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts“ (J.Chem. Phys. 123, 174706 (2005))