Study of the Nature of High-Silica H–Y Acid Sites in Dimethoxymethane Carbonylation by NH3 Poisoning

Abstract

The nature of high-silica H–Y acid sites in dimethoxymethane carbonylation is investigated by NH3 poisoning with a combination of reaction results, diffuse reflection infrared Fourier transform spectra, and NH3 temperature-programmed desorption. After NH3 poisoning of H–Y, ammonia desorption of zeolites NH4–Y was conducted at different temperatures to obtain catalysts HNH4–Y that gradually exposed different acid sites. The zeolites thus produced catalyzed dimethoxymethane carbonylation with a linear dependence of the conversion on the ammonia desorption temperature before the plateau stage. It was observed that strong Bronsted acids in zeolite Y catalyzed the reaction more selectively toward the main product methyl methoxyacetate, and weak Bronsted acids catalyzed the reaction more selectively toward the byproduct methyl formate. Furthermore, the turnover frequency of Bronsted acids varied significantly among the Bronsted acids and decreased with acid strength. This finding suggested that only 10.1–18.3% ...