Cu-doped zeolites for catalytic oxidative carbonylation: The role of Brønsted acids

The aim of this work was to establish the role of Brønsted acidic sites in Cu-doped zeolites for the oxidative carbonylation of ethanol to diethyl carbonate (DEC). In order to eliminate the influences of other factors such as channel structure, faujasite (FAU) with different SiO2/Al2O3 ratios and Beta before and after passivation were investigated. Fourier Transform infrared spectroscopy (FTIR) of pyridine adsorption indicated that all of Brønsted acidic sites were exchanged with CuCl to form effective active sites for oxidative carbonylation. Characterization data showed that passivation on Beta zeolites has little effect on surface area and pore volume distribution except Brønsted acidic sites. The relationship between Brønsted acidic sites and catalyst activity was built on different types of zeolite supports. Diffuse reflectance infrared Fourier transform spectroscopy (DIRFTS) of CO adsorption revealed that the location of Cu active sites was related to the distribution of Brønsted acidic sites, which also influenced catalytic performance of oxidative carbonylation.

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► Nature of Brønsted acidic sites in Cu-doped zeolites was investigated.
► A quantitative relationship was drawn between Brønsted sites and reactivity.
► Effects of Brønsted acidic sites on anchoring Cu sites were examined.