Oxide support metal nanoparticles have been core to conventional automotive emission control technologies for many years, and rely strongly on precious metal catalysts. Bimetallic nanoparticles have been intensively studied for heterogeneous catalysis in general because they offer the opportunity for systematic control of catalytic activity and selectivity. In recent years AuNi bimetallic catalysts for CO oxidation and now for the reaction of CO and NO under typical temperature and pressure conditions found in vehicle exhaust systems has been found to be a both selective and efficient alternative, but remains relatively poorly understood. Here the use of colloidal nanoparticles comprising various compositions of gold and nickel supported on alumina and thoroughly characterized ex situ by TEM, EDS, XRD and XPS have been used to understand the structural changes that occur to the catalyst during exposure to reaction conditions at various temperatures (25 to 550 oC). Catalytically the bimetallic nanoparticles significantly outperform their monometallic counterparts both in activity for CO2 production and selectivity avoiding N2O production. Synchrotron X-ray absorption spectroscopy has been used to follow the process in situ and reveals a key role for the presence of gold is in stabilising the metallic oxidation state of nickel (which otherwise becomes oxidised under reaction conditions). Insights from complimentary Au LIII and Ni K edge EXAFS spectroscopy in understanding the changing location of the two metals during the reaction will also be reported. Complimentary results from XPS using a high pressure cell to monitor the end states for the XAS in situ experiment in which shifts in the binding energy of both Ni 2p and Ni Auger features are seen in the alloy nanoparticles (especially then oxidised) confirm the Au and Ni are in good electronic communication and support the hypothesis that the gold has the ability to regulate the Ni oxidation state during reaction.

In situ x-ray absorption spectroscopy of bimetallic gold–nickel nanoparticle catalyst for the CO + NO reaction

254th National Meeting (2017)

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