Study Of Silver-based Catalysts For Higher Alcohols And DEM Synthesis From Syngas

The synthesis of higher alcohols and dimethyl ether(DME)from syngas is one of the important routes for effectively and cleanly utilizing coal resource.The energy structure character of our country can be obviously depicted as "rich coal,less oil,shortage gas".At present,since it is mature to produce syngas from coal,it is significant to study the synthesis of higher alcohols and DME for utilizing coal resource and reducing environment pollutions.The present researches were further carried out on the basic of previous work by our team.Firstly,the effect of second active component on the structure and catalytic performance of Ag-M/ZnO-ZrO2 catalysts(M=Fe,Co,Cu)was investigated.The catalysts were prepared by co-precipitation method and characterized by N2-adsorption,XRD,H2-TPR,CO-TPD.The results showed that:1)The catalytic performance of Ag-M/ZnO-ZrO2 catalysts with different second component was mainly related with its active species,reduction capacity and CO adsorption-desorption properties.2)For the Ag-Fe/ZnO-ZrO2 catalyst,although the CO conversion was lower,it exhibited higher selectivity and space time yield for higher alcohols and DME;meanwhile,the alcohol products contain more C2+OH with better economic value.Secondly,the structure and catalytic performance of Ag-Fe/ZnO-ZrO2 catalysts prepared by different preparation methods were investigated.The catalysts were prepared by co-precipitation,modified deposition-precipitation,impregnation and hydrothermal methods,respectively,and characterized by above characterization methods.The results showed that:1).The physi-chemical properties of catalysts prepared by different preparation methods significantly changed,thus displayed different catalytic performance.2).The catalyst prepared by hydrothermal method showed lower dispersion of the σ-AgFeO2 species and reduction capacity;larger mean pore diameter and pore volume;more uniform of distribution of particles and more CO adsorption active sites could be obtained.Despite of its lower selectivity of higher alcohols and DME,the more C2+OH containment in the alcohols products could be result to a better catalytic performance.Finally,the effect of iron,silver content,hydrothermal condition,precipitant and calcination temperature on the structure and catalytic performance of catalysts prepared by hydrothermal method were also investigated.The catalysts were characterized by above characterization methods.The results showed that:1).The increase of Fe content in the catalyst is not favorable for the generation of methanol and DME,but could be helpful for CO hydrogenation conversion and the generation of C2+OH.On the other hand,the increase of Ag content in the catalyst is not favorable for CO hydrogenation conversion and the generation of higher alcohols and DME.Besides,the optimal Fe/Zr,Ag/Zr molar ratio were 0.4 and 0.1,respectively.2).The best preparation condition of the catalyst prepared by hydrothermal method:a reaction time of 6 h at the hydrothermal temperature of 150 ℃,K2CO3 as a precipitant,and a calcination temperature of 300 ℃.The catalyst prepared under this condition showed higher dispersion of σ-AgFeO2 specie,better reduction capacity,more CO non-dissociative adsorption active sites and weaker non-dissociative adsorption strength.Furthermore,the catalyst exhibited highest CO conversion and space time yield of higher alcohols and DME.