Study On Direct Ethanol Synthesis From Syngas Over RhCu Bimetallic Catalyst

Based on Chinese energy structure with rich coal,poor oil and less gas,the realization of efficient and clean use of coal is of strategic significance for promoting the sustainable development of energy.With the continuous development of coal gasification to syngas technology towards large-scale and economicalization,this undoubtedly provides a strong guarantee for the innovative and green development of high value-added coal-based chemicals.Among them,ethanol,as an important chemical raw material and clean energy,has received extensive attention.Therefore,the promotion of research on the direct ethanol synthesis from syngas can meet China’s growing energy demand,which has important social and economic significance.The direct ethanol synthesis from syngas is thermodynamically advantageous,but due to the limitation of kinetics,the ethanol selectivity is low.Rh-based catalysts are the most potential catalysts in the direct ethanol synthesis from syngas.They have unique CO activation behavior and initial activity to form C-C bond,but high price limits industrial applications.Cu-based catalysts have the characteristics of low price,simple preparation,and easily adjustable structure.The Cu-based bimetallic catalysts modified by the second metal Rh in improving the ethanol selectivity and realizing the efficient synthesis of C-C bond have important application value.Therefore,this research will use the Rh Cu bimetallic catalysts to study the direct ethanol synthesis from syngas,including the effects of Rh content,Rh and Cu integration manner,Fe promoter and the Cu introduction way on the reaction performance.The main research contents and results are as follows:（1）A series of bimetallic catalysts with different Rh content were prepared by the combination of urea-assisted gel and impregnation method,and the influence of Rh content in the Rh Cu bimetallic catalyst on the reaction performance was investigated.Performance evaluation results showed that the Rh Cu bimetallic catalyst has the best reaction performance when the Rh mass content is 3.6%,the corresponding ethanol selectivity is 7.1%and the CO conversion rate is 17.1%.When Rh with a mass content of 1.4%was loaded on P25 carrier,the performance evaluation result showed that the CO conversion rate is 70.7%and the ethanol selectivity is 9.7%.Compared with a single 1.4Rh/P25 catalyst,it was found that the reaction performance is significantly reduced over Rh Cu bimetallic catalyst.Through TEM,XRD,H₂-TPR,XPS,DRIFT,CO-TPD and CO pulse adsorption characterization methods,it was concluded that the weakening of the reaction performance of the Rh Cu bimetallic catalyst is related to the inhibition of the CO adsorption under the close contact of the active species Rh and Cu in the form of clusters.（2）The close contact between the Rh and Cu active species over the Rh Cu bimetallic catalyst inhibits the adsorption of CO,resulting in weakening of the reaction performance.Therefore,increasing the spatial distance of the active species Rh and Cu to increase the CO adsorption capacity is essential to improve the reaction performance.The physical method of grinding and particle mixing was used to increase the spatial distance between the Rh and Cu active species to investigate the relationship between the CO adsorption behavior and the reaction performance under different integration manner of Rh and Cu.The results of DRIFT and CO-TPD showed that the CO adsorption capacity of the catalyst is enhanced when the spatial distance between Rh and Cu increases.At the same time,the performance evaluation results showed that as the spatial distance between the active species Rh and Cu increases,the CO conversion rate and ethanol selectivity are improved.Furthermore,the Cu-based catalyst with a mass content of 10%and the Rh-based catalyst with a mass content of 1.4%were layered packed in a double-layer and sandwich configuration in the reactor to study the direct ethanol synthesis from syngas.The results showed that the syngas is based on1.4Rh/P25│10Cu/P25│1.4Rh/P25 sandwich configuration to react,the ethanol selectivity reached a maximum of 25.7%at 230℃.And when the catalyst is reacted with the double-layer configuration of 1.4Rh/P25│10Cu/P25,the ethanol yield reached the maximum of 11.5%at250℃.（3）The reaction performance is effectively improved by adjusting the integration manner of the Rh and Cu active components in the Rh Cu bimetallic catalyst and the packed configuration in the reactor.Therefore,in order to further improve the reaction performance,the single Rh-based catalyst is modified by Fe firstly,then the Rh Fe Cu three-way catalytic system is used to study the direct ethanol synthesis from syngas by introduing Cu component.Firstly,Rh Fe bimetallic catalysts with different Fe contents were prepared by the co-impregnation method.The results showed that the addition of Fe significantly improved the ethanol selectivity.Among them,1.4Rh1Fe/P25 catalyst with 1%of the Fe mass content and1.4%of the Rh mass content has the best direct ethanol synthesis reaction performance.The corresponding CO conversion rate is 43.5%and the ethanol yield is 14.2%.Then,the Cu specie was introduced through three methods of co-impregnation,grinding and particle mixing to prepare Rh Fe Cu catalyst for the direct ethanol synthesis from syngas.The performance evaluation results showed that the close contact of Cu with other species on the catalyst surface will reduce the CO conversion rate and mainly promote the methanol production.The maximum ethanol selectivity is not much different under the three different Cu introduction methods,but the corresponding reaction temperature is different.Finally,when the1.4Rh1Fe/P25 and 10Cu/P25 catalysts were further reacted according to the double-layer packed configuration,the ethanol selectivity and methanol selectivity is higher under1.4Rh1Fe/P25│10Cu/P25 double-layer configuration than the 10Cu/P25│1.4Rh1Fe/P25reaction configuration,and the methane selectivity is lower.Under the layered packed reaction configuration of the catalysts,the ethanol yield is lower than 1.4Rh1Fe/P25 catalyst,and only the ethanol selectivity reaches a maximum of 40.2%at 220℃.