Decarbonylation of dimethyl oxalate to dimethyl carbonate over Cs2CO3/HZSM-5

Abstract

In this study, the synthesis of dimethyl carbonate (DMC) via the decarbonylation of dimethyl oxalate (DMO) over supported Cs₂CO₃ catalysts is reported. The effects of different supports, calcination temperatures and Cs₂CO₃ loadings were investigated, and the reaction conditions were optimized using Cs₂CO₃/HZSM-5 as the catalyst with a Cs₂CO₃ loading of 20 wt% followed by calcination at 600 °C. Under these conditions, a DMO conversion of 99.4% and a DMC selectivity of 97.6% were obtained at 220 °C in 1.5 h. Several reaction cycles were performed to evaluate the stability of Cs₂CO₃/HZSM-5. The use of distillation to recover the catalyst could effectively avoid the loss of active components and increase the catalyst lifetime. To gain insights into the adsorption and activation of DMO on the surface of HZSM-5, NaZSM-5 and Cs₂CO₃/HZSM-5, in situ FT-IR studies were conducted. It was found that Na⁺ ions in NaZSM-5 could form stable bidentate chelating structures with DMO, impeding the contact between DMO and the active center and reducing the catalytic activity. Conversely, the acidic sites of HZSM-5 enhanced DMO adsorption on the catalyst, promoting interaction with catalytically active centers and accelerating the reaction. The acidity or basicity of the catalyst is also crucial, as the presence of weakly acidic and basic sites will promote the conversion of DMO and favor decarbonylation.