摘要
合成气(CO和H_(2)混合气)作为十分重要的C1化学平台分子,将其高选择性地转化为碳氢化合物特定目标产物是C1化学核心.在经典费托合成过程中,C–C键的生长服从聚合机理,目标产物选择性低.近年来研究者通过设计金属(氧化物)和分子筛构筑的双功能或多功能催化剂,利用接力催化策略对不同反应进行耦合,成功实现了合成气高选择性制液体燃料如汽油、航空煤油、柴油及大宗化学品如低碳烯烃、芳烃、C_(2+)含氧化合物.本文概述了近年来接力催化在合成气转化中的研究进展,讨论了影响催化性能的关键因素如催化剂组成,分子筛的酸性质、孔结构以及双组分间的亲密度等,并对接力催化策略应用在合成气转化中的未来发展进行了展望.
China’s energy resource structure is rich in coal but poor in crude oil.For a long time,China has to rely on importing crude oil to meet the domestic demand for liquid fuels(including gasoline,aviation fuel and diesel fuel)and basic chemicals(such as C2–C4 lower olefins,aromatics,and C_(2+)oxygenates).In 2019,China’s dependence on oil imports has exceeded70%,which has a negative impact on the social-economic development and national security.Thus,it is very urgent and important to produce liquid fuels and bulk chemicals based on coal resource.Syngas(a mixture of CO and H_(2))can be largely produced from the non-oil resources,such as coal,gas(natural gas,shale gas,and coal-bed methane),and biomass.From syngas,various hydrocarbon products can be produced as supplement of oil-derived products.The conversion of syngas to target products with high selectivity is the core of C_(1) chemistry.However,by the classical Fischer-Tropsch synthesis(FTS)route,the product selectivity is limited by the Anderson-Schulz-Flory(ASF)distribution,which results in the low selectivity of target products.In practice,the yields of liquid fuels and bulk chemicals are increased by a secondary process such as(hydro)cracking,isomerization and aromatization.The direct conversion of syngas to target products with high selectivity is attractive but challenging.Recently,the concept of relay catalysis has been successfully applied to the one-step transformation of syngas to liquid fuels and bulk chemicals with ultrahigh selectivity over bifunctional or multifunctional catalysts.The selectivity of target hydrocarbon products can break the limitation of the ASF distribution.In the conversion of syngas to liquid fuels,the used bifunctional catalysts are composed of FT catalysts and zeolites.FT catalysts,such as Fe(Fe_(x)C_(y)),Co and Ru,are responsible for the activation of CO and the growth of carbon chain.Zeolites are in charge of the hydrocracking and isomerization.High selectivity of middle-distillates,such as gasoline(C_(5)–C_(11)hydrocarbons),jet fuel(C8–C_(1)6hydrocarbons)and diesel fuel(C_(10)–C_(20)hydrocarbons),have been obtained via relay catalysis.It was found that the catalytic performances were strongly influenced by the topology,acidity and mesoporosity of zeolites as well as the metal sizes and promoters.The importance of hydrocracking on acid sites and hydrogenolysis on the metal nanoparticles for the selective C–C cleavage has also been analyzed.The selective synthesis of basic chemicals can also be achieved by relay catalysis,where the bifunctional catalysts consist of metal oxides(such as the solution solid ZnO-ZrO_(2),and the spinel structure of Zn Cr_(2)O_(4),Zn Al2O_(4))and zeolites(such as SAPO-34,ZSM-5,MOR).The activation of CO to intermediates(CH3OH/DME or ketene)proceeds on the metal oxides and the selective C–C bond formation proceeds on the zeolites.The reaction mechanism of such kind of bifunctional catalysts differs from that of the conventional FT catalysts,where the CO activation and C–C coupling are conducted over different sites.The selectivity of lower olefins and aromatics could reach up to 85%without the formation of undesired methane.Besides,multifunctional catalysts can offer an 80%selectivity towards C_(2+)oxygenates such as methyl acetate,acetic acid,and ethanol by coupling CO activation and carbonylation.The product selectivity of oxygenates was significantly impacted by the zeolite acidity and the proximity between the two functional components.The present review not only summarizes the major advantages and disadvantages of the relay catalysis in syngas conversion but also offers prospects for future development of relay catalysis in syngas conversion.
作者
周伟
成康
张庆红
王野
Wei Zhou;Kang Cheng;Qinghong Zhang;Ye Wang(State Key Laboratory of Physical Chemistry of Solid Surfaces,Collaborative Innovation Center of Chemistry for Energy,Materials,National Engineering Laboratoiy for Green Chemical Productions of Alcohols,Ethers and Esters,College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2021年第10期1157-1169,共13页
Chinese Science Bulletin
基金
国家重点研发计划(2017YFB0602201)
国家自然科学基金(91945301,22072120,21972116,21673188)资助。
