Preparation Of Cu Cluster Supported Catalyst And Its Catalytic Properties In Utilization Of CO₂

CO₂ is a greenhouse gas which is harmful to the environment,and can be used by humans as a raw material for C₁ to convert into chemical chemicals that are useful to humans.At the same time,scientific and efficient use of CO₂ is of great significance for mitigating the energy crisis and the greenhouse effect,with important social effectresults and environmental values.The catalytic hydrogenation of CO₂ can produce fossil fuels with huge combustion potential and alternative energy methanol,which will be an effective way to dispose of the CO₂ pathway and turn it into a treasure.At present,the research on the catalytic hydrogenation of CO₂ to methanol is mainly based on the Cu-Zn-Al catalyst in the synthesis gas to methanol traditional process,And the hydrogenation temperature and pressure are also similar to the traditional methanol process.But so far,the activity of conventional methanol catalysts in the hydrogenation of CO₂ to methanol is not high,and the conversion rate of CO₂ in one pass is lower than25%.At the same time,there are also problems such as high product separation and recovery costs.Therefore,the development of a new catalyst with high activity,high stability,and high selectivity for the hydrogenation of CO₂ to methanol is an urgent problem in this field.On the basis of previous studies,this thesis used formaldehyde prereduction method to prepare supported copper cluster catalysts and applied it to syngas or CO₂hydrogenation to methanol.The following is the research content:1.A series of CuO-Al₂O₃ catalysts were prepared by co-precipitation method and modified by metal oxide?ZnO,ZrO₂?additives.Combining various characterization means?N₂O-H₂ titration,N₂-adsorption desorption,H₂-temperature program reduction?,we characterized the catalysts andexplored the effect of additives on the performance of them.Finally we selected ZnO-ZrO₂ as the optimal additive.2.In order to prepare a novel highly active Cu-based methanol catalyst,we added prereducing agents?hydrazine hydrate,oxalic acid,glucose,formaldehyde?to the co-precipitation precursor of the Cu-ZnO-ZrO₂-Al₂O₃ catalyst?CZZrA?to prereduce the catalyst.The effects of different types of prereductants and reduction process conditions on the physical and chemical properties of different catalysts?CA,CZA,CZrA,CZZrA?were investigated deeply.3.In the fixed-bed continuous catalytic high pressure reactor,the process of catalyst preparation was screened by the reaction of CO₂ hydrogenation to methanol.4.The catalytic performance of the selected catalyst CZZrA in the synthesis of methanol to methanol was investigated in detail.Some meaning results have been obtained as follows:1.The ZnO,ZrO₂,ZnO-ZrO₂ and other additives can increase the Cu^o surface dispersion and metal surface area in the Cu-based catalyst,the content of surface active CuO species.Thus,the catalytic performance in the reaction of CO₂hydrogenation to methanol is increased by:ZnO-ZrO₂>ZrO₂>ZnO.2.Pre-reduction of the precursor of the CZZrA catalyst using formaldehyde,glucose,oxalic acid or hydrazine hydrate can reduce the strong interaction between active Cu and the support on the CZZrA catalyst,increase the dispersion of active Cu in the catalyst,and its order of action is:formaldehyde>glucose>oxalic acid>hydrazine hydrate;3.The introduction of catalysts with prereductants and metal promoters can increase the catalytic performance of the catalysts.The order of the increase is:formaldehyde-ZnO-ZrO₂>formaldehyde-ZrO₂>formaldehyde-ZnO.4.The appropriate prereduction temperature allows formaldehyde to be oxidized by Cu²⁺to the pore former formic acid,and the catalytic activity is enhanced by the specific surface area of the formic acid that expands and the pore volume increases.5.Too high prereduction temperature will agglomerate Cu⁺,CuO and other active species in the catalyst,thus reducing the dispersion of the surface active Cu^o and inhibiting its catalytic performance.6.The proper pre-reduction time can make the dispersion and surface area of the active Cu^o on the catalyst be optimized to promote the CO₂ conversion.7.The optimal process conditions for formaldehyde prereduction of CZZrA catalyst precursor are as follows:molar ratio of formaldehyde to Cu is 0.4,molar ratio of CH₂O/Cu is 0.4,reduction temperature is 60?,and reduction time is 6h.8.CuO on the surface of the catalyst reacts with an appropriate amount of formaldehyde to generate formic acid,and the dispersibility and specific surface area of the Cu^o can be increased under the effect of formic acid pore formation,resulting in improved catalytic activity.9.Excess formaldehyde caused the CuO active component on the surface of the catalyst to interact with Zr,Zn and other additives.The activity of the catalyst decreased as the degree of interaction between the two increased.10.The space-time yield of CO₂ hydrogenation to methanol on formaldehyde prereduced CZZrA catalyst can reach 270 g·kg^-1·h^-1,and the conversion rate of CO₂can reach more than 30%.11.The catalytic effect was the best when the CO₂ content in synthesis gas was 3%on formaldehyde prereduced CZZrA catalyst,and the methanol space-time yield was725.19 g·kg^-1·h^-1.When the methanol was over 3%,the yield of methanol on the catalyst was higher.Decreases with increasing CO₂ content.