Sulfur as a selective ‘soft’ oxidant for catalytic methane conversion probed by experiment and theory

Abstract

Developing efficient catalytic processes to convert methane into useful feedstocks relies critically upon devising new coupling processes that use abundant, thermodynamically 'mild' oxidants together with selective catalysts. We report here on elemental sulfur as a promising 'soft' oxidant for selective methane conversion to ethylene over MoS(2), RuS(2), TiS(2), PdS and Pd/ZrO(2) catalysts. Experiments and density functional theory reveal that methane conversion is directly correlated with surface metal-sulfur bond strengths. Surfaces with weakly bound sulfur are more basic and activate methane C-H bonds more readily. In contrast, experimental and theoretical selectivities scale inversely with surface metal-sulfur bond strengths, and surfaces with the strongest metal-sulfur bonds afford the highest ethylene selectivities. High CH(4)/S ratios, short contact times and the provision of a support maximizes the coupling of CH(x) intermediates and selectivity to ethylene, because these conditions yield surfaces with stronger metal-sulfur bonding (for example, Pd(16)S(7)), which suppresses the over-oxidation of methane.

Ethylene formation by methane dehydrogenation and C–C coupling reaction on a stoichiometric IrO2 (110) surface – a density functional theory investigation

“…When comparing all the dehydrogenation reactions, the C-H bond breaking activation energies follow the trend CH < CH 4 < CH 3 < CH 2 , which is the reverse order with previously reported values on some metal sulfide surfaces. 31 It is noteworthy that the order of C-H bond activation energies follows the same trend with the activated C-H bond length of the corresponding transition state. Since all dehydrogenation reactions occur on the IrO 2 (110) surface, entropy losses when changing from initial states to transition states are negligible.…”

Face the Edges: Catalytic Active Sites of Nanomaterials

“…They can be used in catalyzing hydrodesulfurization,8 and methane conversion 59. More researches need to be done in designing new structures utilizing the convenience of edge properties and searching new catalytic reactions.…”

Von Sonnenlicht zu Brennstoffen: aktuelle Fortschritte der C1‐Solarchemie

“…Die Tr ockenreformierung von Methan (dry reformation of methane,D RM) mit CO 2 als Oxidationsmittel (CH 4 + CO 2 !2CO+ 2H 2 )ist ein günstiger Wegz um Senken der Treibhausgasemissionen und zum Verringern des CH 4 -Verbrauchs.B ei der Entwicklung von Reformierungskatalysatoren konzentrierte sich die Forschung anfangs auf Edelmetallkatalysatoren, wie Rh, Ir,P t, Ru und Pd, von denen Ru und Rh die aktivsten sind. [78,79] 1.5. [77] Auch CH 3 X( X = F, Cl, Br oder I) und CS 2 kçnnen durch Oxidation von Methan hergestellt werden, wobei X 2 bzw.S chwefel als Oxidationsmittel verwendet werden.…”

“…[77] Auch CH 3 X( X = F, Cl, Br oder I) und CS 2 kçnnen durch Oxidation von Methan hergestellt werden, wobei X 2 bzw.S chwefel als Oxidationsmittel verwendet werden. [78,79] [80] Katalysatoren auf Cu/Zn/Al 2 O 3 -Basis, [81] Pt/a-MoC-Katalysatoren [82] und der Homogenkatalysator [RuHCl(CO)(HN(C 2 H 4 PiPr 2 ) 2 )], [83] die im Te mperaturbereich 65-300 8 8Ca rbeiten. Der von der Gruppe von Ma entwickelte Pt/a-MoC-Katalysator zeigt eine ausgezeichnete katalytische Aktivitätf ürd ie Wasserstofferzeugung durch Methanolreformierung mit einer Tu rnover-Frequenz (TOF) von 18 046 h À1 bei tiefen Te mperaturen (150-190 8 8C).…”