Study On Highly Active And Stable Catalysts For Methanol/Higher Alcohols Synthesis From Syngas

Along with the increased concerns on the depleting crude oils,the development of clean coal-based alternative process for fuel productions became the important strategy during National "12th five-year plan".The low carbon alcohol-ether fuels synthesis from coal-based syngas can reduce our dependence on oil imports and break away from the "oil crisis" in the future.The low carbon alcohol ether fuels contain methanol,DME and ethanol as well other higher alcohol components,which not only can be used as the clean alternative fuel and additives,but also as the important chemical raw materials.Syngas can be readily obtained from coal gasificsation.The current catalysts for higher alcohols synthesis from syngas have the problems of low activity and poor selectivity for C2+ alcohols as well as catalyst deactivation.Therefore development of highly active and stable catalysts is highly desired.In this work,two classes of catalysts were studied:1)Cu-Co catalysts for higher alcohols synthesis;and 2)PdZn catalysts for methanol/DME synthesis.We attempted to establish the structure-activity relationship of these two classes of catalysts.??Research results for CuCo-based catalystsA wet impregnation and a hydrothermal method were used to prepare 20wt%CuCo/Mo-SBA-15 and CuCo2O4 catalysts respectively.The influence of promoter Mo on the catalytic performance of 20wt%CuCo/Mo-SBA-15 catalyst over CO hydrogenation was studied.The purpose of synthesizing CuCo2O4 catalyst is to obtain a CuCo bifunctional system containing strong synergistic effect with high stability through reducing CuCo2O4 spinel.The main conclusions are summarized as follows:It was experimentally demonstrated that the addition of Mo has significant effect on the reactivity and selectivity of alcohols.After introducing 5wt%Mo,over the 20wt%CuiCo2/SBA-15 catalyst under 503K,5.4MPa,GHSV=3750mL g'1 h-1,the CO conversion increases from 5.5%to 11.2%,the selectivity of total alcohols increases from 5.7%to 45.7%.While the Co/Cu molar ratio has no significant influence on the selectivity of total alcohols,methanol is still the major product in alcohols.For the CuCo2O4 catalyst,it was experimentally confirmed that under the optimum reaction conditions(543K,5.4MPa,GHSV=3750mL g-1 h-1),catalyst exhibits CO conversion of 31.6%with the selectivity to total alcohols and the proportion of C2+ alcohols in total alcohols of 17.8%?80%respectively.The results of XRD and H2-TPR revealed that Cu and Co phase segregation occurs to some extent during the catalyst reduction process.The higher C2+ alcohols selectivty may be associated with the coexist of Cu spices and Co spices on the surface of reduced catalyst.??Research results for Pd/ZnAl2O4 catalystsPd/ZnAl2O4 catalysts were synthesized by isopropanol-mediated controlled hydrolysis method and wet impregnation method.The influence of reaction condition?reduction temperature of catalyst and the loading of Pd on the CO hydrogenation was studied.The difference between ZnAl2O4 and ?-Al2O3 as support for PdZn-based catalysts was conducted.Higher reaction temperature was found to favor the activity of catalyst,but also re-duce the total selectivity of methanol and DME(Sel(MeOH+DME)).Under the conditions that all the catalysts have similar CO conversion,the Sel(MeOH+DME)gradually decreases with increasing Pd loading,while the selectivity of alkane gradually increases,meanwhile the CO2 selectivity remains between 10%to 40%.The XRD characterizations of reduced catalysts indicate that PdZn ? phase formation on surface of ZnAl2O4 support is facile at a low Pd loading,while for the catalysts containing higher Pd loadings,the Pd-rich PdZn a phase can be transformed to PdZn P phase under higher reduction temperature.ZnAl2O4 is superior to ?-Al2O3 as a support with respect to the formation of PdZn alloy.Further analysis showed that PdZn a phase can facilitate the dissociation of CO to form more alkane byproducts,while PdZn ? phase suppresses the formation of alkane.NH3-TPD studies suggest that compared to Pd/ZnO/Al2O3 catalyst,Pd/ZnAl2O4 has weaker acid sites over reduced catalyst,which reduces the rate of MTD reaction(methanol to DME)over acid sites,leading to the different selectivity to methanol and DME.