Synthesis Of Solid Solution And Spinel Metal Oxides And Their Application In Synthesis Gas Conversion

Lower olefins(ethylele,propylene,and butene)are important basic chemicals,which are currently mainly produced by cracking naphtha.Due to the energy endowment of "lean oil,less gas,and rich coal" in China,the development of synthesis of lower olefins from non-petroleum carbon-based resources has become one of the important research directions.The direct conversion of synthesis gas which can be produced from the above carbon-based resources to lower olefins has attracted much attention.In recent years,the bifunctional catalysts composed of metal oxides and zeolites have been developed for the synthesis of lower olefins from syngas.The selectivity of lower olefins exceeds 80%,which breaks the ASF product distribution limitation of 58%on the traditional Fischer-Tropsch synthesis route.On the bifunctional catalyst,the synthesis gas was first activated on the surface of the metal oxide and converted into a methanol/dimethylether intermediate.The intermediates were further subjected to a C-C coupling reaction on a zeolite to form lower olefins.In this thesis,high-performance bifunctional catalysts were prepared by changing the composition and structure of metal oxides,and the effects of different synthesis parameters and reaction conditions on the catalytic performances are explored.The thesis first synthesized Zr-Zn solid solution oxide by sol-gel method,and then coupled with SAPO-34 zeolite to prepare a bifunctional catalyst.The effects of alkali metal elements addtion,the element contents,the calcination method,the raw material feeding during catalyst preparation of the solid solution oxide were investigated.The catalytic reaction conditions on catalytic performances of syngas to lower olefins(C24-)were also studied.On the optimized K+-ZnO-ZrO2/SAPO-34 catalyst,the CO conversion was 43%and the selectivity of C2-C4 lower olefins was 78%.It is speculated that the role of Zn is responsible for the activation of H2,Zr improves the hydrogenation activity of CO,and K is as an electron promoter which not only activates CO but also promote the desorption of adsorbed olefin species,thus improves the target product with high selectivity.The catalyst showed good selectivity and almost unchanged with time on stream.During the 500 h test time,the lower olefins selectivity was maintained at about 80%.However the CO conversion rate has decreased with time on stream.This thesis also synthesized spinel oxide by co-precipitation method.The catalysts combined with spinel oxide(ZnCr2O4)and SAPO-34 showed relative good stability.Then the spinel oxide was mixed with solid solution oxide and zeolite to prepare a bifunctional catalyst with more excellent performances.The ZnCr2O4+ K+-ZnOZrO2/SAPO-34 catalyst has a CO conversion of 46%and a C2-C4 olefins selectivity of 80%.We found that the addition of ZnCr2O4 was beneficial to improving the CO conversion and we speculated that the addition of spinel contributed to the activation of H2,thereby improving the activity.The catalyst also has good stability.During the reaction time of 500 h,there was no significant change in the CO conversion rate and lower olefin selectivity on the catalyst.