Impact of Biodiesel-Based Phosphorus and Sulfur on Copper Speciation of Cu-SSZ-13 Catalysts: XAFS Scanning during H₂-TPR

Abstract

Biodiesel is a promising renewable fuel, which may help to limit our dependence on fossil fuels. However, the presence of contaminants in biodiesel can affect the Cu speciation of the Cu-SSZ-13 selective catalytic reduction (SCR) catalyst, resulting in its deactivation and decreased durability. In situ Cu K-edge X-ray absorption fine structure (XAFS) scanning during a temperature-programmed reduction in hydrogen (H2-TPR) has been applied here for the analysis of Cu speciation in Cu-SSZ-13 catalysts aged using pure and contaminated biodiesel fuels. XAFS data were analyzed using the multivariate curve resolution alternating least-squares (MCR-ALS) method. While only reduction from CuII to CuI was observed at temperatures below 500 °C for the catalyst aged using pure biodiesel, a one-step reduction of CuII to Cu0 at temperatures between 400 and 500 °C was found for the catalyst aged using P-doped biodiesel. The transformation of isolated CuII species to CuII clusters was suggested for the catalyst as a result of aging using P-doped biodiesel. The catalyst aged using S-doped biodiesel showed mainly the reduction of isolated CuII to CuI, which was inhibited as compared to that observed for the catalyst aged using pure biodiesel. The reduction of the catalyst aged using P+S-doped biodiesel led to the reduction of CuII to both CuI and Cu0. The phosphorus was responsible for the formation of CuII clusters during aging of the catalyst using P+S-doped biodiesel. This study reveals that the presence of phosphorus in biofuels should be strictly regulated to avoid major changes in the Cu speciation of Cu-SSZ-13 catalysts.