Study On The Role Of CuAl₂O₄ Spinel For Synthesis Higher Alcohols From Syngas

With relatively few oil and gas resources and relatively abundant coal resources in our country,the pressure to reduce emissions is even more severe.As a clean and low-carbon chemical technology route,the conversion of coal to syngas and the subsequent catalytic conversion to higher alcohols has received widespread attention.Higher alcohols have a high octane number and can be used not only as a fuel additive,but also as a direct substitute for traditional liquid fuels.The previous work of our group found that the CuZnAl slurry catalyst prepared by the complete liquid-phase method contained CuAl₂O₄spinel phase when the precursor was heat treated under high pressure（1-4 MPa）.Studies showed the existence of CuAl₂O₄spinel will greatly improve the performance of CuZnAl slurry catalyst to catalyze synthesis gas to produce higher alcohols.However,it was impossible to control the structure and content of CuAl₂O₄ spinel in CuZnAl slurry catalysts through the complete liquid-phase method.Therefore,the structural changes and effect of CuAl₂O₄ spinel in CuZnAl slurry catalyst have not been achieved.Based on this,in this thesis CuAl₂O₄ spinel was first prepared by conventional methods to find the law of its structure change in carbon monoxide hydrogenation reaction in slurry reactor.Then,the CuAl₂O₄ spinel was mixed with the CuZnAl slurry catalyst by different methods,aiming to reveal the role of CuAl₂O₄ spinel in the CuZnAl slurry catalyst for synthesis higher alcohols from syngas.The catalyst structures were characterized by XRD,N₂ physical adsorption,SEM,TEM,NH₃-TPD-MS,H₂-TPR,XPS and FT-IR,and combined with the evaluation results,the following conclusions were drawn:1.CuAl₂O₄ spinel prepared by different methods shows obvious differences in texture parameters,surface enrichment degree and decomposition and reduction performance,which affects the catalytic performance.The spinel prepared by the solid-phase method has larger pore size and pore volume,and the highest surface enrichment of CuAl₂O₄,resulting in incomplete decomposition of the spinel.But the Cu O released by the decomposition is reduced completely,and the Cu⁺/Cu⁰ ratio is quite high,which is beneficial to increase the C₂₊OH/ROH ratio（31.1%）.However,the other three spinels with relatively low surface enrichment are completely decomposed,but part of the Cu O is not reduced,and the proportion of Cu⁰ in the reduced product increases.Cu⁰ andγ-Al₂O₃ has a synergistic effect to promote the production of dimethyl ether,and its selectivity can reach up to 72.9%.2.When CuAl₂O₄ spinel prepared by solid-phase method,the ratio of Cu⁺/Cu⁰ is relatively high,and the copper source mainly affects its pore volume and pore size,which causes different catalytic performance.When copper hydroxide is adopted as the copper source,the CuAl₂O₄ spinel shows the largest pore volume and pore size,resulting in the best CO hydrogenation ability to generate higher alcohols.3.The CuAl₂O₄ spinel heat treated individually and then recombined with CuZnAl slurry catalyst can make suitable interaction between the spinel and the CuZnAl slurry catalyst.The spinel is easily decomposed and reduced,which is beneficial to the improvement of CO conversion and higher alcohols selectivity.4.The combination of CuZnAl slurry catalyst and CuAl₂O₄ spinel will affect the decomposition and reduction ability of spinel.CuAl₂O₄ spinel prepared by sol-gel method is easily decomposed and reduced in the composite catalyst,providing higher content of Cu⁺.The results show that the composite slurry catalysts not only take the advantage of CuZnAl slurry catalysts with larger pore volume and pore size of,but also exploit the advantage of CuAl₂O₄ spinel which is easy to generate Cu⁺during the reaction process,so as to improve the selectivity of higher alcohols.5.The CuAl₂O₄ spinel prepared by the sol-gel method is easy to decompose and reduce,and the Cu⁺enrichment degree on the surface after the reaction is as high as 63.3%.The C₂₊OH/ROH ratio in the catalyst product obtained by combining with CuZnAl slurry catalyst after separately heat treated can be from 5.4%increase to 16.5%.