HZSM‐5‐Catalyzed Vapor‐Phase Conversion of Dimethyl Adipate to Adiponitrile: The Influence of the SiO 2 /Al 2 O 3 Ratio on Reactivity

Abstract The vapor‐phase nitrilation of dimethyl adipate (DMA) with ammonia (NH 3 ) is an environmentally benign route leading to adiponitrile (ADN) with great application value. In this study, the performance of HZSM‐5 zeolites, widely used in industry as the solid acid catalysts, was investigated. It exhibits a strong correlation between the SiO 2 /Al 2 O 3 ratio (SAR) in HZSM‐5 zeolites and the reactivity (both activity and selectivity). The influence of Al density closely related to the value of SAR on the reactivity of HZSM‐5 was thus elucidated by mechanistic experiments. As a result, the introduction of Al element to the framework is beneficial to the activation of ester functionality, thus improving the activity, especially at a high liquid hourly space velocity (LHSV). However, a high Al density will lead to poor selectivity and deactivation due to too strong adsorption of esters and intermediates (e. g., amides). Herein, the balanced adsorption/desorption capability was reached on HZSM‐5 with SAR as 631 (i. e., HZSM‐5‐631), which provides the best selectivity to nitriles (S ADN+MCP , 92.5 %) at a high single‐pass conversion of DMA (C DMA , 98.0 %).