March 6, 2013

Ben Johnson and co-workers identify atomic role of sulfur poisoning in methanation

Atomic representation of a sulfur-poisoned catalyst.

The catalytic conversion of biomass into synthetic natural gas via supercritical-water gasification has the potential to be a high-efficiency, feedstock-agnostic means to produce conventional hydrocarbon fuels and fertilizers from waste biomass. However, the largest issue for this process is that the catalyst tends to deactivate over the course of many hours on stream. In prior work, this effect has been traced to the presence of trace amounts of sulfur in the biomass feedstocks. Now, in a collaboration between the Catalyst Design Lab at Brown and the Catalytic Process Engineering group at the Paul Scherrer Institut (Switzerland), the precise role of sulfur poisoning has been identified through a combination of electronic structure calculations, X-ray absorption spectroscopy, and isotopically labeled experiments. Specifically, sulfur has been shown to preferentially block below-step sites that are thought to be responsible for the complete scrambling (dissociation) of biomolecules necessary for complete gasification. This effect was observed in electronic-structure calculations that correctly predicted the change in product distribution that was experimentally observed in isotopically traced experiments in this work. This work adds more evidence to the detrimental effect of sulfur on gasification and highlights the need to search for sulfur-resistant catalysts in supercritical-water methanation.

Read the article at the Journal of Catalysis.