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

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. Ti_0.04Ce_0.96O₂ 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 Ti_0.04Ce_0.96O₂ 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.