Operando sulfur speciation during sulfur poisoning-regeneration of Ru/SiO 2 and Ru/Al 2 O 3 using non-resonant sulfur Kα 1,2 emission.

A periodic oxidative regeneration of a sulfur-poisoned methanation catalyst is an alternative to the expensive state-of-the-art process of syngas cleaning using wet scrubbers. Here we have employed operando X-ray emission spectroscopy (XES) to study sulfur speciation on Ru/SiO 2 and Ru/Al 2 O 3 during methanation in the presence of H 2 S and subsequent regeneration in dilute O 2 at 360 °C. XES allowed us to obtain semi-quantitative sulfur speciation and to monitor changes in the absolute sulfur concentration. It was established that Al 2 O 3 , in contrast to SiO 2 , forms sulfite/sulfate species by reacting with SO 2 , which is released from the poisoned Ru surface upon oxidative treatment. The concentration of sulfite/sulfate species is reduced upon switching the feed to H 2 /CO while no simultaneous increase in sulfide concentration is observed. For both catalysts, the regenerative treatment removes adsorbed sulfur as SO 2 only partially, which we propose is the main reason for the incomplete activity recovery of the poisoned catalyst after regeneration.