(770c) The Role of Zeolite Supports Nature and Cu Active Species Over Cu-Doped Zeolites for Catalytic Oxidative Carbonylation

Dialkyl carbonate, especially for dimethyl carbonate (DMC) and diethyl carbonate (DEC), are gaining popularity because of burgeoning applications in organic synthesis. Due to their diversified chemical properties, they were widely used for manufactures of agrochemicals, pharmaceuticals, paint, coating and fragrance. Recently, diakly carbonate have also been used as fuel oxygenated additives for reducing the emissions of diesel engine, in which particulate matters (e.g. PM10, PM2.5) would cause adverse health effects. As an environmentally benign process, the synthesis of dialkyl carbonate by oxidative carbonylation has attracted more attention to replace the conventional phosgene process. With the goal of chlorine avoidance, several researchers have investigated the potential of copper-doped zeolites as catalysts. However, the role of supports nature and the local environment of Cu active sites are not fully understood. With investigation over FAU with varied SiO₂/Al₂O₃ ratio and Beta using passivation, we solely determined the quantitative relationship between amount of Brønsted acid sites and catalytic performance for oxidative carbonylation. In addition, CO-adsorption FTIR results showed that the distribution of Brønsted acid sites influenced the location of Cu in zeolites, and thus apparent activation energy of reaction. We also explored the effect of zeolite supports with alkaline solution and sequential post-treatment. The treatment led to the generation of 4-6 nm mesopores and a wide range of macropores, which would facilitate the accessibility of active sties and molecular transport. Meanwhile, the increased OHs in supercages and extra-framework Al species also contributed to the improvement of catalytic activity. Different methods were used for preparation of the Cu-zeolite catalysts, with the goal of shedding light on the properties of Cu species in the reaction system. The main active species are Cu⁺ coordinated with zeolite framework, and CuO_x accelerate the formation of methoxy species.