CeO₂ Modified CuAl Hydrotalcite For The Preparation Of Methanol By CO₂ Hydrogenation And Production Process Design

With the development of human society,the industrialisation of excessive CO₂emissions has caused the greenhouse effect and led to a series of environmental problems,such as acid rain,melting glaciers and land sanding.CO₂ capture and conversion has become a hot topic of current research.Currently,the synthesis of methanol by hydrogenation of H₂ produced from renewable energy sources with CO₂,a major greenhouse gas,is an effective way for mankind to effectively address the greenhouse effect.However,the thermodynamic limitations of the present reaction of CO₂hydrogenation to prepare methanol and the low selectivity and conversion of the product by catalysts are problems.Since catalysts play a key role in improving the conversion of CO₂ and the selectivity of methanol,it is meaningful to be developed with efficient and stable catalysts.This paper takes Cu O-Al₂O₃ catalyst as the basis of research,and explores the best catalytic performance through different preparation methods.Experiments show that CuAl hydrotalcite as precursor catalyst has better catalytic performance,and on the basis of this research,we use rare earth metal cerium element doped hydrotalcite for modification research,through SEM,TEM,XPS,H₂-TPR,CO₂-TPD and other test characterization means,high pressure hydrogenation fixed bed reactor for performance evaluation,etc.,we conduct systematic research and analysis on the prepared catalysts,and speculate on the reaction mechanism through literature research,the specific research content is as follows:（1）Preparation of CuAl hydrotalcite catalysts:The Cu O-Al₂O₃ catalysts were prepared at a material weight ratio of n（Cu）:n（Al）=2.Various characterization analyses showed that the hydrothermal Cu O-Al₂O₃ catalysts were highly dispersed flower-like spheres with a combination of hexagonal lamellar structures and had a high specific surface area of 80.36 m²/g,compared to those prepared by co-precipitation,impregnation and grinding and calcination methods The catalysts have a lower reduction temperature than those prepared by co-precipitation,impregnation and grinding and calcination,and have a strong basic site on the catalyst surface.Combining the apparent activation energy and the reaction mechanism,it was inferred that the hydrothermal catalyst had a lower apparent activation energy for methanol production and that the CO₂ on the catalyst surface might be hydrogenated to methanol via the formate pathway.The CO₂ conversion was 24.4%and the time-to-time yield of methanol was 94.4 g _{Me OH}·h^-1·kg_cat^-1.（2）Preparation of Ce doped CuAl hydrotalcite catalysts:Preparation of Ce/CuAl-MMO catalysts by a one-step hydrothermal method.Basic sites play an important role in improving the selectivity and conversion of CO₂ conversion.Doping the catalyst with different amounts of Ce can change the number of basic sites in the catalyst.It has been shown that the doped and modified hydrotalcite retains its original flower-like spherical structure,and the modified Cu O crystals undergo lattice distortion,resulting in a large number of oxygen vacancies,which enhances the reduction activity of the catalyst and the number of strong basic sites on the catalyst surface.The best performance was obtained at a Ce content of 0.5 mmol,with a CO₂ conversion of 25.8%and a time-space yield of 129 g _{Me OH}·h^-1·kg_cat^-1 of methanol at reaction conditions of 3 MPa,310°C and12000 m L/（g·h）for pressure,temperature and air velocity,respectively.The results indicate that the increase in oxygen vacancy content on the catalyst surface due to Ce doping and the synergistic effect of Ce O₂ as a carrier resulted in a lower apparent activation energy for the preparation of methanol by CO₂ hydrogenation.The CO₂ on the catalyst surface may be hydrogenated to methanol via the formate pathway.（3）The preliminary design of the industrial production of CuAl hydrotalcite in combination with the catalysts studied in this paper.The content includes the drawing of the production process flow diagram,material accounting,reactor selection and preliminary design of reactor process drawings to provide a reference basis for the industrial preparation of CuAl hydrotalcite.This Paper aims to improve the activity and the time-space yield of methanol from CO₂ hydrogenation with CuAl hydrotalcite catalysts by increasing the Cu O dispersion,the content of oxygen vacancies on the surface and the number of strongly basic sites in the catalyst surface.The possible reaction mechanism of methanol production from CO₂hydrogenation on the catalyst surface was postulated.Finally,the preliminary design of CuAl hydrotalcite catalyst precursor hydrotalcite was used to provide a reference for the industrial preparation of CuAl hydrotalcite.