Study Of CuO-ZnO-based Catalyst For CO₂ Hydrogenation To Methanol

With the increase of CO2 concentration in the atmosphere, global warming caused by the greenhouse effect is becoming more and more serious. To reduce CO2 emissions, many governments and scientific researchers focus on the study of the reduction and/or the recycle of CO2. Converting CO2 into useful fuels and chemicals is an effective way of CO2 recycling, which has important significance in the field of environment and energy. On the other hand, methanol is a very important chemical raw material and a potential alternative to fossil fuel. Therefore, CO2 hydrogenation to methanol has the vital significance in green energy and chemical industry and other fields. In the technology of CO2 hydrogenation to methanol, the development of an efficient catalyst is the key to realize the industrialization of this process.In this paper, the effect of TiO2 content, supports (TiO2, ZrO2 and TiO2-ZiO2) on the performance of CuO-ZnO-based catalysts for CO2 hydrogenation to methanol has been studied. Then, the effect of assistant complexing agents on the CuO-ZnO-TiO2-ZrO2 catalyst prepared by the simple thermal decomposition method was also studied. The physicochemical properties of the prepared catalysts were characterized by N2 adsorption, XRD, reactive N2O adsorption, XPS, AAS, TPR, H2-TPD and CO2-TPD techniques and the catalytic activity for methanol synthesis from CO2 hydrogenation was evaluated. The main results obtained are as follows.1. The influence of TiO2 content on the CuO-ZnO-TiO2 catalystsA series of CuO-ZnO-TiO2 catalysts with various TiO2 loadings were prepared by using carbonate co-precipitation method. The results indicate that the addition of TiO2 enhances the dispersion of CuO and ZnO, and increases the interaction between CuO and ZnO, leading to the easier reduction of CuO. With the increase in T1O2 loading, both the metallic copper surface area (Scu) and the number of basic sites take on a volcano-shaped variation trend. A linear relationship exists between the methanol yield and the Scu. A maximum yield is obtained at the TiO2 loading of 10%.2. The effect of TiO2, ZrO2 and TiO2-ZrO2 on the CuO-ZnO catalystsCuO-ZnO catalysts promoted with TiO2, ZrO2 or TiO2-ZrO2 mixed oxide were prepared by an oxalate co-precipitation method in order to avoid the complex washing process. The results indicate that the additions of TiO2, ZrO2s and TiO2-ZrO2 make the CuO and ZnO crystallites smaller, increase the Scu and the amount of basic sites and H2 adsorption. The relationship between the methanol yield and the Scu is not a straight line. However, the yield of methanol increases linearly with increasing the number of weak basic sites of the catalysts. The additives increase both the CO2 conversion and methanol selectivity, and TiO2-ZrO2 is more effective than TiO2 or ZrO2.3. The effect of complexing agents on the CuO-ZnO-TiO2-ZrO2 catalyst prepared by the thermal decomposition methodThermal decomposition method is a simple, rapid, solvent-free, and energy-saving process. Therefore, we adopted the method to study the effect of different complexing agents on the performance of CuO-ZnO-TiO2-ZrO2 catalyst. The results indicate that the complexing agents control catalyst texture and adsorption properties, thus affecting catalytic functionality of the CuO-ZnO-TiO2-ZrO2 catalyst. Oxalic acid as the assistant complexing agent exhibits the highest performance, which also has the lowest optimum reaction temperature.