Influence of CO2 presence on propane conversion routes over Cr- and Ga-doped PtCe/Al2O3 catalysts

Abstract

A set of catalysts containing Cr- or Ga-doped Pt-CeO₂ supported on alumina (PCA, Cr-PCA and Ga-PCA) were synthesized by incipient wetness impregnation and tested in propane conversion processes. The catalysts were studied in the propane conversion process with or without CO₂ in the feed. In all cases, an enhancement in stability was found when CO₂ was present in the reaction medium despite the lower catalytic activity. As well, all catalysts presented a higher propylene selectivity in the absence of CO₂, indicating that the direct dehydrogenation of propane is the main reaction route. Moreover, CO₂-assisted propane cracking to ethylene is favoured over propane reforming or direct cracking, given the minimal selectivity to other products like methane. With regards to the catalyst composition, Cr-PCA catalyst was the most active catalyst both in the absence and presence of CO₂, due to the presence of weak acidity and coexistence of Cr^3 + and Cr⁶⁺ redox species, as evidenced by XPS analysis. Ga-PCA catalyst was more selective to propylene, indicating that higher acidity of weak-to-medium nature along with formation of low coordinated Ga³⁺ species is beneficial for the CO₂-ODH process. Raman, DTG and XPS analyses after reaction with CO₂ showed that the deactivation of the catalysts was mainly due to carbon deposits of amorphous and graphitic nature on the surface of the catalysts.