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      Reverse Water-Gas Shift on Interfacial Sites Formed by Deposition of Oxidized Molybdenum Moieties onto Gold Nanoparticles.

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          Abstract

          We show that MoO(x)-promoted Au/SiO2 catalysts are active for reverse water-gas shift (RWGS) at 573 K. Results from reactivity measurements, CO FTIR studies, Raman spectroscopy, and X-ray absorption spectroscopy (XAS) indicate that the deposition of Mo onto Au nanoparticles occurs preferentially on under-coordinated Au sites, forming Au/MoO(x) interfacial sites active for reverse water-gas shift (RWGS). Au and AuMo sites are quantified from FTIR spectra of adsorbed CO collected at subambient temperatures (e.g., 150-270 K). Bands at 2111 and 2122 cm(-1) are attributed to CO adsorbed on under-coordinated Au(0) and Au(δ+) species, respectively. Clausius-Clapeyron analysis of FTIR data yields a heat of CO adsorption (ΔH(ads)) of -31 kJ mol(-1) for Au(0) and -64 kJ mol(-1) for Au(δ+) at 33% surface coverage. Correlations of RWGS reactivity with changes in FTIR spectra for samples containing different amounts of Mo indicate that interfacial sites are an order of magnitude more active than Au sites for RWGS. Raman spectra of Mo/SiO2 show a feature at 975 cm(-1), attributed to a dioxo (O═)2Mo(-O-Si)2 species not observed in spectra of AuMo/SiO2 catalysts, indicating preferential deposition of Mo on Au. XAS results indicate that Mo is in a +6 oxidation state, and therefore Au and Mo exist as a metal-metal oxide combination. Catalyst calcination increases the quantity of under-coordinated Au sites, increasing RWGS activity. This strategy for catalyst synthesis and characterization enables quantification of Au active sites and interfacial sites, and this approach may be extended to describe reactivity changes observed in other reactions on supported gold catalysts.

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          Author and article information

          Journal
          J. Am. Chem. Soc.
          Journal of the American Chemical Society
          American Chemical Society (ACS)
          1520-5126
          0002-7863
          Aug 19 2015
          : 137
          : 32
          Affiliations
          [1 ] †Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706, United States.
          [2 ] ‡Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
          [3 ] §Chemical Science and Engineering, Argonne National Laboratory, Argonne, Illinois 60439, United States.
          Article
          10.1021/jacs.5b05945
          26225538
          119b7d4a-3a87-4125-879c-5632a312029a
          History

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