Author: ["Qingjun Zhu","Staci L. Wegener","Chao Xie","Obioma Uche","Matthew Neurock","Tobin J. Marks"]
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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 MoS2, RuS2, TiS2, PdS and Pd/ZrO2 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 CH4/S ratios, short contact times and the provision of a support maximizes the coupling of CHx intermediates and selectivity to ethylene, because these conditions yield surfaces with stronger metal–sulfur bonding (for example, Pd16S7), which suppresses the over-oxidation of methane. The oxidation of methane to create useful feedstocks is hampered by over-oxidation when using O2. Now a process using gaseous sulfur as a ‘soft’ oxidant for selective conversion to ethylene over metal sulfide catalysts has been developed. Simulations show that both methane activation and ethylene selectivity is linearly correlated with catalyst metal-sulfur bond strength. Cite this article
Zhu, Q., Wegener, S., Xie, C. et al. Sulfur as a selective ‘soft’ oxidant for catalytic methane conversion probed by experiment and theory. Nature Chem 5, 104–109 (2013). https://doi.org/10.1038/nchem.1527 