Methane synthesis and sulfur removal over a Ru catalyst probed in situ with high sensitivity X-ray absorption spectroscopy

Catalytic conversion of natural feedstocks, such as wood, into synthetic natural gas (SNG) has much potential for sustainable energy supply. Sulfur, which is present in virtually all biomass – albeit in low quantities, needs to be removed from the gas to protect catalysts. Current technology using wet scrubbing to remove sulfur species between the gasification and the catalytic conversion decreases overall efficiency and therefore impedes commercialization. We show that sulfur removal from the gas stream with integrated methane synthesis at high temperatures is possible over many cycles, using supported Ru catalysts. The sensitivity of in situ X-ray absorption spectroscopy was improved by using a “modulated excitation” approach, showing that the catalyst is poisoned by sulfur, and it can be fully regenerated. The proposed mechanism for sulfur removal highlights the role of the support for sulfur poisoning and efficient regeneration. The integrated process of methanation and sulfur removal can make the biomass-to-SNG process significantly more efficient by replacing wet scrubbing.