A Strategy for Efficiently Enhancing the Hydrothermal Stability of ZSM-5 Zeolites: TMPO Selective Adsorption

Zeolites have been widely employed in industrial catalysis, but the application of zeolites was often limited by their hydrothermal stability. As a successfully applied method for enhancing hydrothermal stability of zeolites, phosphorus (P) modification has been faced with issues such as polymerization and low utilization of P precursor. In this work, we developed a strategy for the P modification of zeolites via trimethylphosphine oxide (TMPO) selective adsorption. Thanks to its alkaline property, TMPO could be adsorbed selectively on the acid sites of zeolites and maintains strong interaction with framework aluminum during further redistribution and oxidation treatments. Extensive characterizations, such as 27Al and 31P MAS NMR, pyridine-FTIR, and P K-edge XANES, were employed to study the transformation of P–Al interaction in zeolites during hydrothermal treatment. It was revealed that the P species adsorbed on strong acid sites were beneficial to the production of a stronger P–Al interaction. Hydrothermal experimental results proved that the P-modified zeolites with a stronger P–Al interaction exhibited higher retention of Bro̷nsted acid sites, resulting from the greatly reduced polymerization of P to protect more framework aluminum. Our approach demonstrates the potential of TMPO modification in controlling P–Al interaction to enhance the hydrothermal stability of zeolites for the methanol to hydrocarbon reaction.