TiO₂-Doped CeO₂ Nanorod Catalyst for Direct Conversion of CO₂ and CH₃OH to Dimethyl Carbonate: Catalytic Performance and Kinetic Study

摘要

A new class of TiO_(2)-doped CeO_(2) nanorods was synthesized via a modified hydrothermal method, and these nanorods were first used as catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO_(2) and CH_(3)OH in a fixed-bed reactor. The micromorphologies and physical–chemical properties of nanorods were characterized by transmission electron microscopy, X-ray diffraction, N_(2) adsorption, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia and carbon dioxide (NH_(3)-TPD and CO_(2)-TPD). The effects of the TiO_(2) doping ratio on the catalytic performances were fully investigated. By doping TiO_(2), the surface acid–base sites of CeO_(2) nanorods can be obviously promoted and the catalytic activity can be raised evidently. Ti_(0.04)Ce_(0.96)O_(2) nanorod catalysts exhibited remarkably high activity with a methanol conversion of 5.38% with DMC selectivity of 83.1%. Furthermore, kinetic and mechanistic investigations based on the initial rate method were conducted. Over the Ti_(0.04)Ce_(0.96)O_(2) nanorod catalyst, the apparent activation energy of the reaction was 46.3 kJ/mol. The reaction rate law was determined to be of positive first-order to the CO_(2) concentration and the catalyst loading amount. These results were practically identical with the prediction of the Langmuir–Hinshelwood mechanism in which the steps of CO_(2) adsorption and activation are considered as rate-determining steps.