Water–gas shift catalysis over transition metals supported on molybdenum carbide

• WGS rates/total surface area at 120 °C for Metal/Mo2C 4–8 times higher than commercial Cu catalyst.
• Admetal sites perform CO activation, while Mo2C sites perform H2O dissociation.
• Metal/Mo2C catalysts exhibit Constable–Cremer relationship (compensation effect).
• Mo2C can be used as a support to make thermally robust supported metal catalysts.

We report here that WGS rates per total surface area at 120 °C, 7% CO, 22% H2O, 8.5% CO2, 37% H2 for Pt, Au, Pd and Ni supported over Mo2C were 4–8 times higher than those of the commercial Cu/ZnO/Al2O3 catalyst. In agreement with previous literature, the WGS rate per total moles of Pt over Pt/Mo2C at 120 °C has been shown to be higher than on any Pt/Metal oxide catalyst. We have made use of systematic changes in the apparent kinetic parameters with various admetals (decrease in apparent CO order and apparent activation energy and increase in apparent H2O order compared to unpromoted Mo2C) to conclude that the function of the rate-promoting admetals is to enhance the relative surface concentration of the adsorbed CO, thereby leading to a promotion in the WGS rate per total surface area of the catalyst. Temperature programmed desorption of CO was used to show that the CO adsorption properties of Mo2C were modified by the various admetals by creating new metallic sites. In situ X-ray absorption on Pt and Au and STEM–EELS experiments showed that the supported Au nanoparticles over Mo2C decrease in average particle size from ∼9 nm to 3 nm after a 600 °C carburization pretreatment. Pt was also shown to have assumed a stable structure at 600 °C in the form of a Pt–Mo alloy. We suggest that Mo2C can be used to synthesize thermally robust supported metal catalysts.

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