Construction of highly dispersed active copper species on Y molecular sieve and performance of methanol oxidation carbonylation

The control of copper species on the surface of CuY catalyst is the key to improve the performance of methanol oxidation carbonylation to dimethyl carbonate. In this work, a series of CuY catalysts with different copper loads were prepared by solution ion exchange method, and the N₂-physisorption, XRD, TEM, H₂-TPR, XPS, NH₃-TPD and CH₃OH-TPD were used to characterize the microstructure of the catalyst. The effects of Cu-ammonia solution concentration and activation temperature for structure and properties of CuY surface copper were investigated. The results indicated that although the porosity of the catalyst was reduced by increasing the concentration of solution, the amount of copper was significantly increased from 2.11% to 9.95%, and the high dispersion of copper species was maintained, with the particle size less than 4 nm. The high concentration of solution exchange reduced the weak acid sites on the surface and inhibited side reactions to improve the selectivity of DMC. The copper species of low loading catalysts were mainly ionic copper. Increasing the content of copper increased the content of ionic copper, but also significantly increases the amount of CuO_x, which could rapidly improve the catalytic performance, methanol conversion and DMC yield reached 9.07% and 396.27 mg/(g·h), respectively. The activation at suitable temperature promoted the diffusion of copper species from the external surface to the internal pores, increasing the exchange of Cu species with NaY and weakening the adsorption strength of methanol, which was conducive to the improvement of catalytic performance. Compared with low loading catalysts, high loading catalysts could be activated to obtain more Cu⁺ and CuO_x at low temperature, thus showing higher catalytic performance. The results of this work provided a theoretical basis for the design and preparation of high-performance CuY catalysts.