Study of Thermodynamics and Experiment on Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol over Yttrium Oxide

The thermodynamics on the direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH was calculated and analyzed. Using Y(NO₃)₃·6H₂O as the precursor, a series of Y₂O₃ were prepared through the one-pot calcination method, which were employed to catalyze DMC synthesis. The decomposition temperature of Y(NO₃)₃·6H₂O was measured by thermogravimetric analysis, and Y₂O₃ was obtained after the precursor calcination at desired temperatures, denoted as Y₂O₃-T (°C). The catalysts were characterized by X-ray diffraction, Brunauer-Emmett-Teller method, transmission electron microscopy, NH₃/CO₂ temperature-programmed desorption, and X-ray photoelectron spectroscopy to detect the crystal phase, surface property, particle size, acidity-basicity amounts, and oxidation state, respectively. The characterization results indicated that Y₂O₃-750 can favor the formation of moderate acidic and basic sites and facilitate the activation of CO₂ and CH₃OH. The catalytic performance evaluation was experimentally investigated, and Y₂O₃-750 owned the highest DMC yield of 1.02 mmol/g·cat under 90 °C, 8 MPa, and 6 h, which also exhibited reliable recycle ability.