Poisoning of Copper Chabazite Catalyst by Biodiesel Metal Contaminants: Effect of Alkali and Alkaline Earth Metals

Biodiesel is an environmentally friendly fuel that maypartiallyreplace petroleum diesel in transportation. One possible disadvantageof biodiesel is that alkali and alkaline earth metals can significantlyaffect Cu speciation and the elemental composition of copper chabazite(Cu-CHA) catalysts used in vehicle emission control units. To investigatethis, we perform atomic-scale characterization of Cu-SSZ-13 zeolitescontaminated by Mg, K, and Na using inductively coupled plasma-opticalemission spectroscopy and Cu K-edge X-ray absorption spectroscopy(XAS) coupled with hydrogen temperature-programmed reduction. Theexperimental data decomposed by a multivariate curve resolution algorithmare interpreted using theoretical XAS spectra and reactive moleculardynamics. We find that Mg poisoning leads to a more severe dealuminationcompared to K or Na poisoning. Poisoning of catalysts also leads tothe aggregation of isolated Cu ions into CuO x clusters, while alkali and alkaline earth metal ions replaceCu ions in ion-exchange sites. The site preferences of Mg, K, andNa ions in Cu-CHA are thoroughly explored using density functionaltheory (DFT) calculations, suggesting an explanation of results fromelemental analysis. Our study provides important theoretical and experimentalinsights into the poisoning of Cu-CHA catalysts by biodiesel metalcontaminants.