Hydrothermally stable ITH-type zeolite directed by a simple nonquaternary ammonium pyrrolidine derivative: Synthesis, characterization and catalytic performance

Abstract

Researchers are currently shifting their focus towards the synthesis of zeolites using new commercially available organic structure-directing agents (OSDA). Herein, we report for the first time the preparation of ITH-type zeolite with 2-(aminomethyl)-1-ethylpyrrolidine (AMEP), a simple and commercially available nonquaternary ammonium derivative of pyrrolidine. This work also explores the effects of various synthesis parameters on the product, which is key in the synthesis of a highly crystalline ITH-type zeolite in a wide range of Si/Ge molar ratios. Multiple techniques (XRD, SEM, FTIR, solid-state NMR and N2 physisorption) have been adopted to characterize the ITH-type zeolites with different Ge contents. Si and Ge elements are present in the different crystallographic positions. Particularly, Ge atoms preferentially occupy the double-four-ring (D4R) units. The ITH-type zeolites are characterized by high surface area and micropore volume. They are hydrothermally stable towards 700 °C 90% steam heating without significant loss of crystallinity and microporosity. Also, ITH-type zeolites demonstrate high cyclohexanone conversion, selectivity for the main product ε-caprolactone and cycle use stability in the Baeyer–Villiger oxidation of cyclohexanone. Collectively, these features imply a wide application prospect of ITH-type zeolites in the conversion of ketones into valuable esters and lactones. This contribution presents a facile and low-cost synthesis of hydrothermally stable ITH-type zeolite and opens avenue to develop nonquaternary ammonium pyrrolidine derivatives as a novel OSDA family.