Modifying the acidity of H-MOR and its catalytic carbonylation of dimethyl ether

Abstract

Among the reactions catalyzed by zeolites there are some that exhibit high selectivity due to the spatial confinement effect of the zeolite framework. Tailoring the acidity, particularly the distribution and location of the Brönsted acid sites in the zeolite is effective for making it a better catalyst for these reactions. We prepared a series of H-mordenite (H-MOR) samples by varying the composition of the sol-gel, using different structure directing agents and post-treatment. NH3-TPD and IR characterization of adsorbed pyridine were employed to determine the amount of Brönsted acid sites in the 8-membered ring and 12-membered ring channels. It was shown that controlled synthesis was a promising approach to improve the concentration of Brönsted acid sites in MOR, even with a low Al content. Using an appropriate composition of Si and Al in the sol-gel favored a higher proportion of Brönsted acid sites in the 8-membered ring channels. HMI as a structure-direct agent gave an obvious enrichment of Brönsted acid sites in the 8-membered ring. Carbonylation of dimethyl ether was used as a probe reaction to examine the modification of the acid properties, especially the Brönsted acid sites in the 8-membered ring channels. There was a linear relationship between methyl acetate formation and the number of Brönsted acid sites in the 8-membered ring channels, demonstrating the successful modification of acid properties. Our results provide information for the rational design and modification of zeolites with spatial constraints.