The Study On The Structure And Performance Of Carbon Materials And CuZnAl Composite Catalysts For CO Hydrogenation To Higher Alcohols

At present,the most fossil energy mined in China is still coal.It can be said that China’s chemical industry started from coal chemical industry.However,coal chemical industry has some weaknesses such as large carbon emissions and low energy efficiency.Under the constraints of the"2030 carbon peak,2060 carbon neutral ity"policy and the"double control"standard of energy consumption,the further development of coal chemical industry will face huge challenge.In C1 chemistry research,the conversion of coal to syngas,which is then converted to synthetic fuels or chemicals,is a promising way to provide clean fuels and chemicals for the chemical industry.Among them,higher alcohols have a significant increase in demand owing to their high octane number and high combustion efficiency.In order to meet the future demand for higher alcohols,the preparation of higher alcohols from synthesis gas has attracted much attention,which not only realizes the transformation of coal resources to clean energy,but also can obtain gas raw materials from renewable energy and unconventional natural gas.On the basis of the previous work of our research group,we combined the good chemical reactivity of hydrotalcite-like materials with the high conductivity of carbon materials to prepare composite catalyst in order to improve the C₂₊OH selectivity.Firstβ-cyclodextrin-modified carbon nanotubes（CDMWNTS）were used to investigate the effect of CDMWNTS and Cu Zn Al ratio on the catalyst structure and performance;Second,Cu Zn Al-MMOs/C was prepared by online carbonization usingβ-cyclodextrin as carbon source.The calcination temperature,the content and the addition methods ofβ-cyclodextrin in the preparation process were discussed.Finally,the structure and performance of the composite catalyst modified with formamide were investigated.The composite catalysts were characterized by XRD,H₂-TPR,N₂-physical adsorption,NH₃/CO₂-TPD-MS,EIS and SEM.The correlation between the structure and catalytic performance of the composite catalyst was revealed,and the following main conclusions were drawn:1.Addingβ-cyclodextrin-modified carbon nanotubes can affect the interlayer spacing of the catalyst precursor LDHs,the reducibility of Cu species,the crystallite size and the amount of weak acid on the surface.The catalyst with 8%CDMWNTS showed the largest interlayer spacing,the best Cu grain size stability,and less surface weak acid content,which resulted in the proportion of C₂₊OH in the total alcohol was 20.42%.2.Usingβ-cyclodextrin as the carbon source,the CuZnAl-MMOs/C catalyst prepared by online carbonization at 550℃had a higher degree of carbonization,the smallest resistance,the strongest electron transfer ability and more active components.The proportion of strong basic sites on the surface was relatively high.So-prepared catalyst showed the best catalytic activity.3.In the online carbonization process,the more β-cyclodextrin added,the smaller the spacing between the hydrotalcite-like layers.Moreover,the decomposition ofβ-CD during the calcination process can promote the reduction of some copper species,but the addition of too muchβ-cyclodextrin made Cu species in the catalyst more difficult to be reduced.When the addition amount ofβ-CD in the catalyst was 5%,the CO conversion and the proportion of C₂₊OH in the total alcohol were the best,reached 22.22%and 22.06%,respectively.4.The addition of β-CD showed a significant effect on the interlayer spacing and layer structure of the catalyst precursor.After calcination,the content and reducibility of Cu species were obviously different.Moreover,the CO₂ selectivity markedly decreased.The Cu grains in the CAT-C catalyst were smaller and more dispersed,and the content of weak acid sites on the surface was less.The CO conversion was 20.50%,and the proportion of C₂₊OH in the total alcohol reached 22.19%.5.The addition of formamide can weaken the interaction between the LDHs layer and the interlayer anions.Furthermore,the content of formamide affected the proportion of different alkali contents on the catalyst surface.However,the excess formamide increased the grain size of Cu species and reduced the dispersion of active Cu species.When adding 2 vol%DMF,the catalyst showed the best catalytic performance,the CO conversion was 21.52%,and the proportion of C₂₊OH in the total alcohol was 24.10%,among which butanol accounted for11.57%.