Effect Of Cu-ZnO-Al₂O₃ Pretreatment With Carbon Materials On The Performance Of CO₂ Hydrogenation To Methanol

As a greenhouse gas,CO2 mainly comes from the burning of fossil fuels,and the excessive emission of CO2 leads to a series of environmental problems.The conversion of CO2 into methanol by hydrogenation not only helps solve the environmental problems caused by CO2 emissions,but also alleviates the crisis of fossil fuel shortage.However,due to the chemical inertia and thermodynamic limitations of CO2,the conversion rate of COi hydrogenation to methanol has been low.In view of the deficiency of traditional Cu-ZnO-Al2O3(CZA)catalyst in the reaction of CO2 hydrogenation to methanol,adopting low copper content(40 wt.%)of CZA catalyst for reference,by carbon nitride(g-C3N4),benzene and benzene homologue of CZA catalyst pretreatment,get different valence state distribution of catalyst,applied to carbon dioxide hydrogenation to methanol catalytic activity,and to explore the factors that affect its catalytic performance.The main research contents and results are as follows:(1)The CZA catalyst pretreatment with carbon nitride:Due to the strong interaction and reductibility of g-C3N4 on copper,the addition of carbon nitride improves the dispersion of copper and the catalytic performance of low copper catalyst.When g-C3N4 content was 5 wt.%,CO2 conversion rate reached 7.6%and CH3OH selectivity reached 74.4%at 200℃ and 3.0 MPa.After 50 h reaction,the activity of the catalyst did not decrease significantly,indicating it had good catalytic stability.(2)The CZA catalyst pretreatment with benzene vapor:The CZA catalyst treated with benzene vapor has a large specific surface area and dispersion of copper,and contains copper particles with three valence states of Cu0,Cu+and Cu2+.The catalytic performance and stability of the catalyst are significantly improved.CO2 conversion and methanol selectivity were 8.0%and 72.5%,respectively.After 100 h reaction,the catalyst activity did not decrease significantly.(3)The CZA catalyst pretreatment with homologue of benzene:The CZA catalyst treated with toluene vapor has a large specific surface area and dispersion of copper,and contains Cu0 and Cu+.The reduction temperature of the catalyst moved towards low temperature,and the adsorption amount of CO2 and H2 increased.Compared with CZA catalyst,CO2 conversion rate and CH3OH selectivity reached 6.0%and 77.3%respectively,and methanol yield increased by 40.2%.(4)The effect of the amount of methyl on the catalytic performance of the catalyst was further investigated.As the number of methyl increased,the specific surface area and pore volume of the catalyst increased,the pore diameter of catalyst and the size of copper particles decreased,and the adsorption capacity of CO2 and H2 increased.The catalytic effect of trimethylbenzene was the best,with CO2 conversion rate and CH3OH selectivity reached 6.9%and 77.6%,respectively,and methanol yield reached 5.35%.