NiAu bimetallic model catalysts from thin films to nanoparticles  were prepared by vapor deposition in ultrahigh vacuum conditions on Mo(110) and SiO2/Mo(110), respectively. The surface composition and structures were studied by polarization modulated infrared spectroscopy (PMIR) and CO TPD experiments. CO adsorbs on atop and bridge sites on Ni thin films. With increase Au coverage, atop site CO adsorption on Ni increases while the bridge site CO adsorption decreases. After 0.6 ML Au on 15 ML Ni, the absence of bridge site CO adsorption indicates the surface Ni atoms are totally isolated by Au atoms. Similar results were observed on NiAu nanoparticles supported on SiO2/Mo(110). Cyclohexane dehydrogenation reactions were performed on both NiAu thin films and NiAu nanoparticles. The kinetics results show with increase Au coverage, the surface reactivity increases to a maximum when the surface Ni atoms were totally isolated by Au on NiAu thin films or NiAu nanoparticles. Post reaction Auger spectra shows a significant decrease in carbon deposition on NiAu compared to pure Ni. H2 TPD shows weakened hydrogen adsorption by adding Au on Ni, and a new H2 desorption peak at 170 K related to H2 desorption from isolated Ni atoms. C2H4 and C6H12 TPD shows H2 desorbs from dissociation of CH species at lower temperatures after modified Ni by Au. Combined kinetics and surface science studies show that carbon deposition during cyclohexane dehydrogenation reaction is suppressed by forming isolated Ni atoms by Au, and indicate an optimized Au coverage for cyclohexane dehydrogenation reactions over NiAu bimetallic catalysts.

Role of Au in NiAu bimetallic catalysts in cyclohexane dehydrogenation reactions

243rd National Meeting (2012)

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