Journal
JOURNAL OF CATALYSIS
Volume 412, Issue -, Pages 30-41Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2022.06.002
Keywords
DRIFTS; Palladium; NaY; Zeolite; Reaction intermediate; Dimethyl carbonate; Methanol
Categories
Funding
- National Natural Science Foundation of China [21908246, 21975285, 22175200, 21991090, 21991091]
- Sino-French International Research Network (IRN) Zeolites
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In this study, the reaction mechanism of methanol gas-phase indirect oxidative carbonylation for dimethyl carbonate (DMC) synthesis was investigated using a NaY zeolite catalyst doped with 1.0 wt% Pd. The reaction intermediates CO* and COOCH3* were identified and COOCH3* was determined as the rate-determining step. A Langmuir-Hinshelwood mechanism was proposed to explain the reaction process.
Gas-phase indirect oxidative carbonylation of methanol to dimethyl carbonate (DMC) has been industrialized, but the reaction mechanism is still ambiguous. In this work, the reaction mechanism of DMC synthesis using a NaY zeolite catalyst doped with 1.0 wt% Pd was revealed by combining in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results with density functional theory (DFT) calculations. Two key reaction intermediates CO* (*, a surface site) and COOCH3* were identified through the adsorption of a probe molecule of methyl chloroformate (CH3OCOCl), and characterized by steady-state, dynamic-pulse and time-resolved transient DRIFTS experiments. The CO* intermediate is predominant on the catalyst surface when the reaction reached steady-state. The DFT results also showed that the inclusion of OCH3* into CO* had the highest energy barrier of 150.1 kJ mol-1. This verified that the formation of COOCH3* is the rate-determining step for the DMC synthesis. A Langmuir-Hinshelwood mechanism including the fast formation of CO*, and rate-determining insertion of OCH3* into CO* toward generation of COOCH3* to yield DMC was proposed.(c) 2022 Elsevier Inc. All rights reserved.
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