Selective removal of acid sites in mordenite with the assistance of tetraethylammonium bromide for high performing dimethyl ether carbonylation reaction

The distribution of acid sites in Mordenite (MOR) is crucial for its carbonylation performance. In this paper, MOR was subjected to acid treatment to selectively remove acid sites in 12 member-ring (MR) with the assistance of tetraethylammonium bromide (TEABr) used during synthesis process. The impact of acid treatment on structure, morphology, framework atoms and acidity were systematically studied. The characterization results indicated that the structure of the samples was only slightly impacted while the mesopore volume slightly increased. Due to the excessive removal of acid sites, the sample treated by nitric acid (0.1 mol/L) exhibited lower carbonylation activity whether with or without the protection of templates. However, the acid sites in the 12 MR were selectively removed in the citric acid treatment process by two different ways: the etching effect of H+ and the complexation of citric ions. The protection effect of templates for the acid sites in 8 MR was remarkable. Therefore, selective removal of acid sites in 12 MR was successful realized with assistance of template, leading to considerable improvements in activity for DME carbonylation reaction.