Study On Cu-based Catalysts For Methanol Synthesis From Greenhouse Gas CO₂ Hydrogenation

As well known, enerage crisis and green-house effect are the hot topics at present. As a C1 raw material and major green-house gas, CO2 has attracted more and more attentions. The reasonable utilization of CO2 emmitted from various sources has been one of the hottest researchs. Among them, the CO2 catalytic hydrogenation to methanol(Me OH) is one of potential paths, due to the fact that Me OH is an important chemical material and alternative fuel. Therefore, “methanol economy” has been put forward by some resesrchers.The reported research results show that CO2 hydrogenation to MeOH has a strong technical fessibility, but it is hard to realize industrialization due to economic cost, H2 resources, reaction energy consumption, the activity and stability of catalysts, and the low Me OH selectivity and the difficult of products separation. Therefore, it is of significance to prepare Me OH synthesis catalysts with a high activity, selectivity and stability. In the present work, a series of Cu-based catalysts have been prepared based on commercial Me OH synthesis catalysts of Cu-Zn O. The CO2 catalytic hydrogenations to Me OH over these Cu-based catalysts are investigated in a fixed bed catalytic system, and the catalysts characterization are also carried out.In the present work, 12 kinds of Cu O/γ-Al2O3 catalysts with a Cu content of 10wt% are prepared by impregnation method, and the modification of Cu O/γ-Al2O3 catalysts by using Zn O, Zr O2, Mg O and Ti O2 as modifiers has also been studied. The functions of these modifiers in CO2 hydrogenation to Me OH and the hydrogenation parameters of the obtained Cu O/γ-Al2O3 catalysts are investigated. Meanwhile, the catalytic performances of Cu-based catalysts from different methods have also been compared in CO2 hyddrogenation.. Forthermore, the preparation conditions of typical Cu-Zn O-Zr O2 catalysts for synthesis Me OH from CO2 have also been studied. Combining with catalysts characterization such as N2-adsorption/desorption, N2O-H2 titration, H2 temperature-programmed desorption, CO2 temperatureprogrammed desorption, H2 temperature-programmed reduction and X-ray diffraction so on, som meaning results have been obtained as follows:(1) Cu O/γ-Al2O3 catalysts have a high Cu dispersion, metal surface area and a smaller Cu0 practicle size after the simultaneous modification by using Zn O, Zr O2 and Mg O. Metal Cu0 practicles are the active centers of CO2 hydrogenation to Me OH.(2) Activation temperature has a direct impact on the catalytic performance of Cu-Zn O-Zr O2-Mg O/Al2O3 catalyst in CO2 hydrogenation. A high hydrogenation temperature can inhibit the generation of Me OH, and high space velocity and reaction pressure are beneficial to improving the space-time yield of Me OH.(3) The modification of Zn O, Zr O2, Mg O and Ti O2 oxides can decrease the strong interaction between active component Cu and supports by the order of Zr O2> Zn O> Mg O> Ti O2.(4) The order of modifiers on improving the Cu dispersion of Cu/Al2O3 catalyst is Mg O> Zr O2> Ti O2> Zn O, and the ability order of generating hydrogen spillover and activating CO2 is Ti O2> Mg O> Zr O2> Zn O.(5) Cu dispersions, metal suface areas, Cu practicles and hydrogen spillover exhibit important functions in CO2 hydrogenation to Me OH on Cu/γ-Al2O3 catalysts.(6) In CO2 hydrogenation to MeOH, the catalytic performances of Cu-Zn O-Zr O2 catalysts from sol method by using glucose as complex are superior to those from precipitation and sol-precipitation method.(7) Cu-Zn O-Zr O2 catalysts from sol method exhibit a small metal-support strong interaction between Cu and supports, and give rise to a higher Cu dispersion, a bigger metal Cu surface area and smaller Cu0 practicles, therefore have a high catalytic activity in CO2 hydrogenation to Me OH.(8) The catalytic properties of Cu-ZnO-ZrO2 catalysts from sol method are relative to their surface areas and pore size distribution. The catalyst with a big surface areawill give a high catalytic activity in CO2 hydrogenation to MeOH, and however a different reaction path CO2 catalytic hydrogenation to Me OH will be carried out in the pores with an appropriate size.(9) Duing the preparation of Cu-Zn O-Zr O2 catalyst by using sol method, the contents of glucose have an importanteffect on the interaction between active Cu and oxides supports.(10) A high calcination temperatrecan can increase the strong interaction reaction between active Cu and oxide support in Cu-Zn O-Zr O2 catalyst from sol method, which will inhibit CO2 hydrogenation to Me OH.(11) The Cu-ZnO-ZrO2 catalyst with a high Zn/(Zn+Zr) molar ratio exhibit a low catalytic activity, and however the presence of Al will benifical to the decrease on strong interaction between active Cu and metal oxides support.(12) In CO2 catalytic hydrogenation over Cu-Zn O-Zr O2 from sol method, a high space velocity or an appropriate catalyst activation temperature will be advantageous to Me OH production. However, a high space velocity can imprve reverse water-gas shift(RWGS) and Cu-Zn O-Zr O2 reduced at a high temperature will exhibit a low activity in RWGS.