Reducing the Surface Acidity of Pd/NaY Catalyst by Alkali Phosphates Modification to Improve the Selectivity of Dimethyl Carbonate

CO esterification to dimethyl carbonate (DMC) routes holds significant economic and environmental value. Nevertheless, industrial routes suffer from drawbacks, such as raw material methyl nitrite (MN) was decomposed into by-products dimethoxymethane (DMM) and methyl formate (MF), which caused subsequent separation problem for the product/reactant mixture, which results in additional production cost. Previous studies have demonstrated that the acid site of NaY play an essential role in promoting the decomposition of MN. Herein, a series of Na₂HPO₄ -modified Pd/NaY catalysts were prepared to solve these problems. The results indicated that the introduction of Na₂HPO₄ increased the DMC selectivity (from 55% to 83%) and decreased the by-products selectivity [DMM (from 22% to 10%), MF (from 23% to 7%)] of Pd/PNaY-12 significantly. Based on the results of Py-IR, the amounts of Lewis acidic sites decreased, and NH₃-TPD analysis shown that the amounts of weak acid sites (from 0.33 mmol/g to 0.14 mmol/g) and medium strong acid sites (from 0.46 mmol/g to 0.10 mmol/g) also reduced obviously. The outstanding performance should be attributed to the fact that the important intermediate *COOCH₃ was more readily obtained after Na₂HPO₄ was incorporated. This work provides a convenient strategy for developing catalysts with high selectivity and low by-products.

Graphical Abstract