(583af) Synergistic Effect of Catalyst Support and Operating Parameters On Low-Temperature Methane Activation

Efforts to convert methane directly, through oxidative or non-oxidative conditions, into higher value products have received great interest.  Since the methane molecule has strong equivalent C–H bonds, no polarity and no functional groups to facilitate the chemical conversion into liquid hydrocarbons, most of its reactions require significant energy inputs as well as properly designed catalytic systems that would lower kinetic barriers in its activation. It has already been shown that various metals can dissociatively chemisorb CH₄ at moderate temperatures resulting in H₂ evolution and adsorbed CH_x species (x=0, 1, 2 or 3). The CH_xspecies formed during dissociative CH₄ adsorption on a reduced transition metal surface are a function of metal, metal structure, support, metal–support interactions, and operational parameters (residence time, temperature, and pressure). Studying the factors that influence the reactivity of adsorbed CH_x species is of critical importance in advancing the knowledge about methane activation and rational catalyst design. Two-step temperature programmed desorption experiments on Pt/ceria and Pt/silica catalysts are used to determine the total amount of chemisorbed CH₄, study the state of the adsorbed layer after the CH₄ chemisorption step and determine the optimal operating conditions that would result in more reactive carbon species. The effect of support and operating conditions (temperature, CH₄ partial pressure) on the structure of resulting carbonaceous film, the reactivity of the adsorbed species and the strength of their bonding to the catalyst surface are investigated. The identification of surface intermediates is an important step in determining the mechanism of a reaction and in developing an in-depth understanding of a catalytic process.