Effect of P modification on the structure and catalytic performance of Ti-MWW zeolite

Abstract

Ti-MWW zeolite has attracted much attention because of its excellent catalytic oxidation performance. As one of the essential components in zeolites, phosphorus (P) has been widely used for modification to enhance the hydrothermal stability and catalytic performance of aluminosilicate zeolite. Herein, a series of P-modified Ti-MWW zeolite samples were prepared with a simple way by directly adding various amounts of phosphoric acid into the acid-treated system. The effect of P modification on both structure and catalytic performance of Ti-MWW zeolite was systematically investigated. We demonstrated that some highly active framework TiO4* species with Ti–O–P structure are formed after modification with moderate P, leading to the remarkable improvement of catalytic activity in 1-hexene epoxidation. While introducing excess amounts of phosphoric acid would result in the formation of much inactive titanium phosphate species, which block the channels and finally decrease the catalytic performance significantly. Density functional theory calculations confirmed that the new formed Ti–H2PO4 site is more active than the Ti–OH site in Ti-MWW zeolite for model propene epoxidation, revealing the promotional effect of P modification. This work would deepen our understanding of P modification at the atomic level and benefit to improve the catalytic performance of titanosilicate zeolite.