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

Abstract

A new class of TiO2-doped CeO2 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 CO2 and CH3OH in a fixed-bed reactor. The micromorphologies and physical–chemical properties of nanorods were characterized by transmission electron microscopy, X-ray diffraction, N2 adsorption, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). The effects of the TiO2 doping ratio on the catalytic performances were fully investigated. By doping TiO2, the surface acid–base sites of CeO2 nanorods can be obviously promoted and the catalytic activity can be raised evidently. Ti0.04Ce0.96O2 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 Ti0.04Ce0.96O2 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 CO2 concentration and the catalyst loading amount. These results were practically identical with the prediction of the Langmuir–Hinshelwood mechanism in which the steps of CO2 adsorption and activation are considered as rate-determining steps.