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

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 Brønsted acids in zeolite Y catalyzed the reaction more selectively toward the main product methyl methoxyacetate, and weak Brønsted acids catalyzed the reaction more selectively toward the byproduct methyl formate. Furthermore, the turnover frequency of Brønsted acids varied significantly among the Brønsted acids and decreased with acid strength. This finding suggested that only 10.1–18.3% of the total Al in zeolite Y with Si/Al ratios of 15, 30, and 40 contributed to the total framework Brønsted acids.