An investigation on the reaction mechanism for the partial oxidation of methane to synthesis gas over platinum

Abstract

. M. M. (1995). An investigation on the reaction mechanism for the partial oxidation of methane to synthesis gas over platinum. Catalysis Letters,, 291-304. DOI: 10.1007/BF00814232 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The partial oxidation of methane to synthesis gas has been investigated by admitting pulses of pure methane, pure oxygen and mixtures of methane and oxygen to platinum sponge at temperatures ranging from 973 to 1073 K. On reduced platinum the decomposition of methane results in the formation of surface carbon and hydrogen. No deposition of carbon occurs during the interaction of methane with a partly oxidised catalyst. Oxygen is present in three different forms under the conditions studied: platinum oxide, dissolved oxygen and chemisorbed oxygen species. Carbon monoxide and hydrogen are produced directly from methane via oxygen present as platinum oxide. Activation of methane involving dissolved oxygen provides a parallel route to carbon dioxide and water. Both platinum oxide and chemisorbed oxygen species are involved in the oxidation of carbon monoxide and hydrogen. In the presence of both methane and dioxygen at a stoiehiometric feed ratio the dominant pathways are the direct formation of CO and H2 followed by their consecutive oxidation. A Mars-van Krevelen redox cycle is postulated for the partial oxidation of methane: the oxidation of methane is accompanied by the reduction of platinum oxide, which is reoxidised by incorporation of dioxygen into the catalyst.

The Reaction Mechanism of the Partial Oxidation of Methane to Synthesis Gas: A Transient Kinetic Study over Rhodium and a Comparison with Platinum

“…The partial oxidation of methane to synthesis gas over platinum has been reported upon previously (32) and is summarized below. On reduced platinum the decomposition of methane results in the formation of carbon and hydrogen adatoms.…”

“…Lapsewicz and Jiang (19) reported that methane activation is the rate-limiting step in the partial oxidation of methane. The difference in methane conversion can then be explained by the observed difference in apparent activation energy for methane activation on platinum, 52 kJ mol −1 (32), and rhodium, 15 kJ mol…”

“…Knudsen diffusion, combined with adsorption and desorption processes are simulated by integrating the continuity equations for the reaction products in order to avoid interference of the latter with the reaction network analysis. The results are compared to previous work involving platinum as the catalyst (32).…”

Effect of different oxygen species originating from the dissociation of O2, N2O and NO on the selectivity of the Pt-catalysed NH3 oxidation

“…In general, the ideas about the participation of various oxygen species in different elementary steps of this Pt-catalysed reaction were later confirmed by Fathi et al [11]. In contrast to Mallens et al [10], the latter authors ascribed CO formation to chemisorbed oxygen species formed either via O 2 dissociation or to oxygen atoms diffusing from the bulk of Pt to the surface. Direct participation of adsorbed oxygen molecules in oxidation of methanol and methane over Pt(1 1 1) has been also reported in literature [12,13].…”

“…The catalytic relevance of these oxygen species has been highlighted earlier for various Pt-catalysed reactions. Mallens et al [10] have shown that in partial oxidation of methane to syngas (CO and H 2 ) over polycrystalline Pt oxygen species of PtO x nature contributed to CO formation and its further oxidation to CO 2 . The role of adsorbed oxygen atoms was restricted to oxidation of CO to CO 2 .…”