Pd catalysts are industrially used in the selective hydrogenation of acetylene to ethylene. Terrace Pd atoms of the closely packed {111} facets on supported Pd particles are generally considered to be the catalytically active sites. We herein report that deposition of an appropriate amount of Ga2O3 adlayers on Pd particles supported on alumina by the atomic layer deposition (ALD) technique substantially enhanced the catalytic activity, selectivity, and stability in the selective hydrogenation of acetylene to ethylene. Structural characterization results demonstrate that Ga2O3 is preferentially deposited at the edges and open facets of Pd particles with the ALD technique. This transforms the poisoning edge sites of the {111} facets into the catalytically active terrace-like sites, leading to an increase in the number of active sites and subsequently the enhancement of the catalytic activity; this also suppresses the formation of poisoning carbonaceous deposits on the open facets and blocks the migration of carbonaceous deposits from the open facets to the neighboring active {111} facets, leading to a significant improvement in catalytic stability. These results demonstrate a concept of selective oxide decoration to comprehensively improve the performance of supported metal catalysts and provide a practical strategy.Keywords: activity; atomic layer deposition; density functional theory; selectivity; stability; subsurface carbon

With density functional theory, all elementary steps of methanol (CH3OH) dehydrogenation and oxidation on atomic-oxygen-covered or OH-covered Au (111) surfaces are systematically studied. Our results suggest that on low oxygen coverage Au (111) surface the production of CH2O and CO start from α-H elimination and β-H elimination, respectively. The selective oxidation pathway is controlled by thermodynamics of the first step rather than kinetics. The overall energy barrier to produce CO is 0.39 eV corresponding to gas-phase methanol, which indicates that the reaction can proceed at low temperature. On high oxygen coverage Au (111) surface, the elimination of α-H and one β-H can take place simultaneously to form CH2O for the cooperative interaction of two nearby atomic oxygen. The missing observation of CH2O may come from the fact that the newly formed CH2O is ready to react with surface atomic oxygen and hydroxyl to form CH2OO(H) rather than desorption from the surface. The rate-limiting step of the oxidation of CH2OO(H) is the dehydrogenation of CHO2 with an energy barrier of 0.95 eV. Also, the newly formed CH2O can be dehydrogenated by surface atomic oxygen to form CO and then to CO2 with low energy barrier. Our results give good explanation for experimental observations and make up the discrepancy between experimental observation and previous theoretical work.

•Au surfaces are active in catalyzing low-temperature NO decomposition.•Low-temperature decomposition of NO on Au surfaces is structure sensitive.•(NO)2 dimer dominates the low-temperature decomposition of NO on Au surfaces.•The decomposition activity of (NO)2 on Au surfaces is opposite to its adsorption energy.•The origin of high activity of Au surfaces in catalyzing low-temperature NO decomposition is revealed.We have comparatively studied adsorption and decomposition of NO on Au(9 9 7) and Au(1 1 0)-(1 × 2) surfaces by means of TDS, XPS, and DFT theoretical calculation. The lowest-coordinated Au atoms on both surfaces are 7-coordinated, but the surface chemistry of NO differs very much on these two surfaces. An α-NO species dominates on the Au(9 9 7) surface, while besides the similar α-NO species, another less stable and more abundant β-NO species also appear on the Au(1 1 0)-(1 × 2) surface. Part of α-NO species decomposes into O adatom and N2O upon heating, but the less stable β-NO species exhibits a much higher decomposition reactivity than α-NO species and facilely decomposes into O adatom and N2O on the Au(1 1 0)-(1 × 2) surface during the NO exposure at 105 K. The accompanying DFT theoretical calculation results demonstrate that chemisorbed (NO)2 dimer species dominate the surface chemistry of NO on the Au surfaces. α-NO species is the most stable (NO)2 dimer species that chemisorbs on the 7-coordinated ridge Au atoms of both Au(9 9 7) and Au(1 1 0)-(1 × 2) surfaces via the N atoms and exhibits a high activation barrier for the decomposition reaction. β-NO species corresponds to less stable (NO)2 dimer species that chemisorbs on the trench Au atoms of the Au(1 1 0)-(1 × 2) surface via both N and O atoms and exhibits a low activation barrier for the decomposition reaction. These comprehensive experimental and theoretical calculation results reveal at the molecular level the origin of structure sensitivity and low-temperature catalytic activity of supported Au nanocatalysts in NO decomposition reaction.Chemisorbed (NO)2 species are the active surface species for low-temperature NO decomposition into N2O on Au surfaces and their decomposition reactivities vary in a trend contrast to their adsorption energies.Download high-res image (196KB)Download full-size image