Boosting SAPO-34 catalyst longevity and activity in MTO processes via indium oxide doping: an experimental and theoretical study

Abstract

Metal oxides play a critical role in controlling coke formation, balancing reaction pathways, and enhancing the performance and durability of SAPO-34 catalysts in the methanol-to-olefin (MTO) process. This study focuses on indium oxide (In₂O₃) doping as a novel approach to address coke formation and extend catalyst lifespan. A comprehensive experimental and theoretical methodology was adopted, including detailed catalyst characterization, catalytic performance testing, and molecular dynamics (MD) simulations. Structural analyses confirmed that the CHA framework of SAPO-34 is preserved after doping, with modifications such as reduced crystallite size and increased mesoporosity, which enhance active site accessibility. Physicochemical characterization revealed that nitrogen adsorption showed increased mesopore volume while NH₃-TPD analysis indicated a balanced acid site redistribution in In-doped SAPO-34 (SP-I), collectively enhancing intermediate species stability and catalytic activity. MD simulations provided a mechanistic understanding of the In₂O₃ impact, revealing its ability to suppress coke precursor (CHO-θ) formation, facilitate carbon removal via CO₂ activation and the reverse Boudouard reaction, and enhance reaction reversibility. Catalytic performance testing validated these findings, with SP-I achieving prolonged activity, higher selectivity for light olefins (up to 80.3%), and greater resistance to deactivation compared to pristine SAPO-34. These findings underscore the efficacy of In₂O₃ as a dopant for improving SAPO-34 catalysts and offer insights into the development of sustainable and efficient catalysts for industrial MTO applications.