Catalytic elemental sulfur-assisted methane activation at low temperature

Methane is the main component of natural gas, and the latter is a clean natural resource with an abundant reserve and wide distribution. Elemental sulfur is both naturally available on the earth and being artificially generated as a recalcitrant solid waste in chemical processes. The co-utilization of elemental sulfur and methane is thus of economic and environmental benefits. Here, a new catalytic route for elemental sulfur-assisted methane activation is demonstrated over metal-loaded zeolite catalysts at a low temperature of 400 degrees C. Over 10% methane conversion can be achieved even after the catalyst is recycled five times, and the selectivity is well controlled, generating over 90% C-2-C-4 hydrocarbons as the main products. Control experiments are employed to demonstrate the strategy developed for catalyst design, and a series of verification experiments accompanied by various catalyst characterizations are also performed to elucidate the involved reaction mechanism. The results are further substantiated by theoretical calculations for proposing the possible reaction network. It is suggested that the Langmuir-Hinshelwood surface reaction mechanism might be followed, in which elemental sulfur and methane are both adsorbed over the catalyst surface in a competitive way. When methane activation is triggered and significantly enhanced in the presence of sulfur, both surface reaction and gas-phase reaction can proceed, generating sulfides as complete oxidation products and light hydrocarbons as partial oxidation products, respectively. As a result, the product distribution can be well modulated by the adsorption properties of the charged catalyst. This process provides a transformative cost- and energy-effective way for the co-utilization of two low value-added feedstocks with unique advantages in the natural gas and petroleum industry.