PNNL

Abstract

Developing sulfur-resistant selective catalytic reduction (SCR) catalysts to replace the current commercial V2O5/TiO2 catalyst for stationary applications remains a grand challenge in environmental catalysis. In this work, we report a remarkable sulfur tolerant TiO2 supported Fe2O3 (Fe2O3/S-TiO2) catalyst using sulfur doped TiO2 as the catalyst support. Via SCR reaction tests, an array of spectroscopic and microscopic characterizations including angle resolved X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectroscopy, in situ gas molecule adsorption breakthrough, in situ DRIFTs, and theoretical calculations of DFT, we demonstrate here that the active form of sulfur dopant is SO42-, which resides in subsurface TiO6 locations. This dopant exerts strong electronic perturbation to the TiO2 support, causing a net charge transfer from the Fe2O3 active site to the TiO2 support via increased Fe-O coordination and thus, enhanced Lewis acidity of surface Fe3+ species. This electronic effect simultaneously weakens charge transfer from Fe2O3 to SO2 and enhances that from NO and NH3 to Fe2O3, resulting in a remarkable “killing two birds with one stone” scenario, i.e., improvement of NO/NH3 adsorption that benefits SCR activity, and inhibits sulfur poisoning that benefits catalyst long term stability.