Catalysis and characterization of Pd/NaY for dimethyl carbonate synthesis from methyl nitrite and CO

Abstract

A vapor phase synthesis of dimethyl carbonate (DMC) from carbon monoxide and methyl nitrite (MN) has been carried out over Pd/NaY catalysts at 383 K, DMC was produced in a good yield. The selectivity to DMC was >85% on the basis of consumed CO or MN. The by-products were dimethyl oxalate, CO₂, N₂O, methyl formate and dimethoxymethane. The catalytic properties of Pd/NaY were investigated as a function of Pd content and calcination temperature. It was found that 1 wt.% Pd/NaY calcined at 473 K in air was the optimum catalyst for the present DMC synthesis. The oxidation state and dispersion of Pd in the Pd/NaY catalysts were characterized by EXAFS and XPS. It was revealed that Pd(NH₃)₄²⁺ in 1 wt.% Pd/NaY changed into Pd metal clusters during the catalytic reaction. Pd metal clusters/NaY showed a stable activity for the DMC synthesis even after 700 h. These results suggest that the cage structure of NaY and anchoring effects of protons suppress Pd metal sintering and stabilize very small Pd metal clusters (Pd₁₃) in the zeolite cages during the reaction.