The role of metal–support interaction on catalytic methane activation

• Strong metal–support interaction is present in Pt/ceria but not Pt/silica.
• It affects the amount and structure of adsorbed carbonaceous species.
• Upon short exposure to CH4, mainly H-deficient species remain on catalyst surfaces.
• Above 400 °C, Pt/ceria promotes less strongly bound, more reactive, CHx species.
• Below 300 °C, Pt/silica promotes less strongly bound, more reactive CHx species.

In this work, we study CH4 chemisorption over Pt-containing catalysts at low temperature (200–450 °C) in a fixed bed reactor. We report the systematic investigation of the effect of temperature, support (ceria vs. silica), and Pt content, on the amount of chemisorbed CH4 and the structure and reactivity of adsorbed CHx species, as formed during 1 min exposure of the catalyst to the CH4 flow. The total CH4 chemisorbed and the state of carbonaceous film were determined by Temperature Programmed Desorption (TPD) and Temperature Programmed Surface Reaction (TPSR), as performed immediately upon catalyst exposure to the CH4 flow. The hydrogenation of carbon ad-species produced only methane. It was found that the strong metal–support interaction, present in ceria samples, plays an important role in CH4 conversion, and lends further evidence to the hypothesis that the metal–support interface causes a large spillover of adsorbed C and H species from Pt onto ceria – thus clearing the Pt active sites for further CH4 dehydrogenation. Not only did the ceria based samples activate up to 5 times more CH4 than the silica based samples, but the nature of the adsorbed CHx species and how they bond to the Pt surface varied on different supports. Thus, both the catalyst structure and operating conditions were found to play key roles in controlling the amounts of chemisorbed CH4 and the structure and the reactivity of the adsorbed carbonaceous film, so they should be carefully considered when rationally designing catalysts for methane activation and conversion.

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