Metal/oxide interface is of fundamental significance to heterogeneous catalysis because the seemingly “inert” oxide support can modulate the morphology, atomic and electronic structures of the metal catalyst through the interface. The interfacial effects are well studied over a bulk oxide support but remain elusive for nanometer-sized systems like clusters, arising from the challenges associated with chemical synthesis and structural elucidation of such hybrid clusters. We hereby demonstrate the essential catalytic roles of a nanometer metal/oxide interface constructed by a hybrid Pd/Bi2O3 cluster ensemble, which is fabricated by a facile stepwise photochemical method. The Pd/Bi2O3 cluster, of which the hybrid structure is elucidated by combined electron microscopy and microanalysis, features a small Pd-Pd coordination number and more importantly a Pd-Bi spatial correlation ascribed to the heterografting between Pd and Bi terminated Bi2O3 clusters. The intra-cluster electron transfer towards Pd across the as-formed nanometer metal/oxide interface significantly weakens the ethylene adsorption without compromising the hydrogen activation. As a result, a 91% selectivity of ethylene and 90% conversion of acetylene can be achieved in a front-end hydrogenation process with a temperature as low as 44 °C.

The stabilities and catalytic performances of single-atom alloy (SAA) structures under the reaction conditions of acetylene hydrogenation are thoroughly examined utilizing density functional theory (DFT) calculations. Four Cu-based alloys with stable SAA structures reported before, namely PdCu, PtCu, RhCu and NiCu alloys, are investigated here. We find that the SAA structures of PdCu and PtCu are stable during the reaction, whilst the RhCu-SAA and NiCu-SAA structures are thermodynamically unstable upon acetylene adsorption and surface restructuring through the aggregation of the Rh and Ni atoms on the surfaces may also happen. It is also found that all the investigated structures of RhCu and NiCu alloys may give rise to the further hydrogenation of ethylene. However, desorption of ethylene is favored over the PdCu-SAA and PtCu-SAA surfaces, indicating that acetylene could be selectively hydrogenated to ethylene over these two surfaces, which is consistent with the experimental observations reported in the literature. Our work provides new understandings regarding SAA surface structures under reaction conditions and their catalytic reaction performances upon aggregation of the doped metal atoms.

Selective hydrogenation of butadiene to butenes is an important industrial process, and a single Pt atom alloyed with a Cu(111) surface shows superior activity and selectivity for this reaction. By utilizing density functional theory calculations combined with microkinetic modeling, herein, we systematically studied the hydrogenation of butadiene over the Pt/Cu(111) single-atom alloy (SAA) catalyst and identified the active sites and probed the product selectivity at different sites under reaction conditions. Although the structure of the SAA is found stable in vacuum, it is likely that aggregation of surface Pt atoms could be induced upon butadiene adsorption, and the aggregated structure shows lower activity than the single Pt site. In addition, we found that the Cu site shows almost identical hydrogenation activity with the Pt site, while considering the concentration of the surface Pt sites, which gives a good explanation on the experimental observations reported previously that the activity of the Pt/Cu(111) SAA catalyst was unaffected by the occupation of CO at Pt sites. Furthermore, all butene isomers produced would preferably desorb rather than being further hydrogenated to butane at the surface sites considered. Although the selectivity between butene isomers over the single Pt sites is different from that over the Cu sites, the overall SAA catalyst gives the same selectivity trend with the single Pt sites. Our work shows, at the molecular level, how different sites over the Pt/Cu(111) SAA catalyst contribute to the hydrogenation activity and product selectivity.

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The electrochemical ammonia oxidation reaction (AOR) has attracted considerable attention in the past decades. However, the AOR mechanism on the electrode surface is still ambiguous, and the identification of reactive OH species during dehydrogenation reactions is under debate. Herein we combined density functional theory-based ab initio molecular dynamics simulations with free-energy sampling method slow-growth to study the stepwise dehydrogenation from NH3 to N during the electrochemical AOR on Pt(100). We found that the dehydrogenation assisted by adsorbed OH is almost insensitive to potentials applied, while the dehydrogenation by OH in bulk water is potential-dependent and the barrier of such reactions would increase with lowering the potentials. Our results revealed that the adsorbed OH is the reactive species during NH3 dehydrogenation under reaction conditions rather than OH– in bulk water. These findings bring new insights into the fundamental understandings of the AOR process under realistic electrochemical conditions.