Rape Pollen-biotempled Synthesis Of Porous Materials Toward 1,3-butadiene Selective Hydrogenation

Porous materials can be used as support in catalysis,which can improve the catalytic performance by dispersing the active sites and enhancing the mass transfer of reactants or products.Hence,it is an important research object in catalyst design.The selective hydrogenation of 1,3-butadiene values in industrial application and scientific research,and Pd catalysts are widely used in this reaction.Currently,the support design by adjusting the pore structure,geometry and electronic structure of Pd is one of the effective ways to achieve better butene selectivity at higher conversion rates.Particularly,materials with special morphologies,pore structures and chemical properties can achieve by natural biomass as template.Therefore,in this dissertation,rape pollen was selected as the biotemplate to prepare a variety of porous metal oxides and macroporous carbons due to the uniform particle size,rich pore structure,thermal stability and mechanical strength.Then the obtained hierarchical porous TiO₂ and macroporous C were used in the selective hydrogenation of 1,3-butadiene after loading of Pd.Furthermore,a series of characterization methods were used to study the special properties resulting from the introduction of pollen and the relationship between the structure and performance of the catalyst.Firstly,various metal oxides commonly used for catalysts or supports,including TiO₂,CeO₂,ZnO,ZrO2 and Al₂O₃,were prepared by using rape pollen as template.The rule of replication and regulation of the pollen-like porous materials was systematically studied,by changing the amount of precursor,reaction temperature,solvent calcination temperature and other conditions.The results showed that,various pollen-like metal oxides were obtained in approximate procedure,however,the influence of surface pore shape and preparation conditions on the shape of pollen,pore structure,crystal form and yield of different metal oxides was different Besides,the character of as-prepared TiO₂ and C was studied in detail.It was found that the pollen-TiO₂ owned pollen-like hierarchical porous structure,and contained more Ti3+due to the self-doping of C and N.The poilen-C displayed pollen shape,macroporous structure and more pyridine N.In addition,the successful synthesis of pollen ZIF-8,LaMnO3,ZSM-5 and TS^-1 showed the universality of this preparation method and expanded the application of pollen template in the preparation of MOF materials,perovskites and molecular sieves.Secondly,in order to improve the 1-butene selectivity in the selective hydrogenation of 1,3-butadiene under milder conditions,the catalyst of Pd/pollen-TiO₂ was prepared by using the obtained pollen-like hierarchical porous pollen-TiO₂ as support.The effects of calcination temperature,Pd loading,calcination temperature and reaction temperature during the synthesis on the catalytic effect were investigated.The optimal catalyst preparation and reaction conditions were manifested as follows:pollen roasting temperature was 600?,Pd theory loading was 0.4 wt%,the catalyst did not need to be calcined and the reaction temperature was 50?.Under this optimized condition,the conversion of 1,3-butadiene reached 87%,and butenes selectivity and 1-butene selectivity were as high as 97%and 67%respectively,which was better than the commercial TiO₂ with three different crystal phases after loading Pd.The excellent catalytic performance was derived from the synergic effects of hierarchical porous structure,C,N element doping and the presence of biomass.Specifically,hierarchical porous structure was favorable for mass transfer,while C and N doping and biomass could enhance the reduction degree of TiO₂,which make the catalysts achieve an increase in the selectivity of butene,especially 1-butene,without the need of H2 high temperature treatment.Finally,in order to reduce the cost of the catalyst,the catalyst of Pd/pollen-C was applied to the selective hydrogenation of 1,3-butadiene,in which the obtained pollen-like macroporous pollen-C was used as the support.The preparation conditions such as loading method,plant extract concentration,Pd loading and pollen calcination temperature during the preparation of pollen-C,and the reaction conditions such as reaction temperature and feed gas space velocity were investigated.The optimal catalyst preparation and reaction conditions were manifested as follows:the plant extract concentration was 5 g·L^-1,the Pd loading was 1 wt%,the pollen calcination temperature was 500 the catalyst did not need to be calcined,the reaction temperature was 80 ?,and the gas space velocity was 36000 mL·gcat.^-1·h^-1.Under the above conditions,the conversion of 1,3-butadiene reached 100%and the total butene selectivity was as high as 95%.It was demonstrated that the content and type of doping elements or groups contained in the macroporous pollen-C were different,which tuned the particle size,morphology and valence state of the supported Pd,and thus affected the catalytic performance.Furthermore,the comparison of between Pd/pollen-C and commercial AC after loading Pd showed that,the excellent catalytic performance was derived from the introduction of N and the macroporous structure.Namely,N dopant weakened the interaction between Pd and pollen-C,then increased the content of Pd2+and separated active sites,while the macroporous structure made easily to realize the desorption of the butene product.In summary,the bio-inspired synthesis of various porous materials with rape pollen as template and their application toward the selective hydrogenation of 1,3-butadiene were have been systematically studied,which will not only offer an effective way for the design of catalyst supports,but also provide reference to use other biomass as a template to prepare porous materials and to study the special properties of the as-synthesized materials.