Synthesis of Hierarchical Zeolite ETS-10 and Its Catalytic Performance in the Biomass Hydrogenation Reactions

Author:Xiang Mei

Supervisor:zhou jian cheng


Degree Year:2019





Issues concerning the conversion of biomass into fuels have attracted significant attention in view of related environmental concerns.However,the conversion of biomass to hydrocarbon biofuels faces two general chemical challenges:increasing the energy density of renewable feedstocks by reducing their high oxygen contents,and the formation of C-C bonds such that parent monomers(generally limited to 6 carbon atoms)can be coupled to form hydrocarbons of appropriate molecular weight and volatility for use as transportation fuels.Several promising routes for the conversion of biomass to fuels have been developed.While,it is noted that the produced biofuels still possess significant problems for their direct utilization because of the high oxygen content,high water content,molecular complexity,coking propensity,and corrosiveness.Therefore,extensive oxygen removal is required for upgrading of biofuels with properties similar to those of petroleum fuels.Catalytic hydrotreating of biofuels is one of the most common methods to reduce the oxygen content of biofuels and,therefore,has attracted the most attention in recent decades.This requires catalysts with high deoxygenation activity,good resistance to coke formation,and high tolerance to water and poisons to metal(e.g.,sulfur-and nitrogen-containing molecules).A preferred catalyst system should also have low hydrogen consumption and a high carbon yield when taking the production cost into consideration.Hence,the work will also mainly focus on biomass hydrogenation.1.Hierarchical ETS-10 zeolite was directly synthesized with rather cheap silicon source and organic macromolecular polymer and without using small moleculer template.A series of characterization including XRD,SEM,TEM,UV-Vis,FT-IR,TPR and TPD were employed and related to the correspondingly catalytic performance to investigate the reaction mechanism.It is shown that almost 100%guaiacol conversion and 96.9%cyclohexane yield are achieved under mild conditions,which can be demonstrated by that the moderate Lewis acid on the prototonated hierarchical ETS-10-based catalyst benefits the oriented conversion of lignin derivatives.Furthermore,part of the active Co species can highly disperse on the support surface after reduction,and the others are located on the support framework by strongly interacting with catalyst support,which greatly facilitates the selective hydrogenolysis of C-O bond and promotes the yields of desired products.Moreover,for comparation,the Co/HMZSM-5 and Co/HMBeta were prepared,and the experiment results suggest that the catalyst support is significant for products distribution.In particular,the unique framework and physicochemical properties of ETS-10 zeolite endows the corresponding catalyst with distinct advantage.2.Based on previous studies,it has been found that ETS-10 zeolite with unique framework,chemical composition and porous structure has played excellent performance in adsorption,separation,ion exchange and shape catalysis.However,the application of non-noble metal supported ETS-10 zeolite catalyst is lack of attention.Thus,for further investigation,Ni-based ETS-10 zeolite catalyst(Ni-METS-10)was prepared and modified for cellulose conversion,during which full conversion of cellulose and remarkably high yield(91.0%)of levulinic acid were achieved.The catalytic efficiency,especially the influence of hierarchical pores and Lewis acid on reactivity was explored.Then,the reaction condition and catalytic system were optimized to better catalyze the conversion of cellulose to levulinic acid.3.The important role of zeolite morphology that is sensitive to synthesis condition in catalytic activity and selectivity except for the porous structure was proposed and explored.Nevertheless,at present,the researches about ETS-10 morphology are all limited to microporous level,and the formed crystals are often accompanied by impure phases such as quartz,ETS-4 and AM-3.Hence,it is desirable to conduct in-depth stdudy and obtain ETS-10 zeolite with high crystallinity,controllable morphology and hierarchical pores.Given that in the last chapter,the incorporation of Ni species has been found to be capable of adjusting both the porous structure and chemical properties in differet degrees,the further research effort was carried out and focused on using a range of transition metals as additives and their interaction with inorganic species especially the titanium species in the synthesis gel.Various metal precursors were also adopted to study their impact on porous structure and morphology of ETS-10 zeolite.Finally,the formed ETS-10 zeolite with transition metal doped is directly used as hydrogenation catalyst for biomass conversion.4.Polyethylene polyamine(PEPA)and sodium lignosoulphonate(LnNa)as mesoporogen,morphology-and structure-directing agents were used to develop novel pore-and morphology-controllable ETS-10 zeolite.The XRD,N2 adsorption/desorption,SEM,TEM and 29Si NMR MAS results proved that a series of hierarchical ETS-10 zeolites was successfully synthesized and more importantly,their morphology and pore size can be freely confined in the desired range.What’s more,the close relationship between additives and raw materials especially titanium source was discussed,which played an active part in morphology change and hierarchical pore formation.This can be ascribed to the special reducibility from inorganic Ti source,system liquidity and pH,and the enhanced inoganic species dissolution.Finally,the synthesized hierarchical ETS-10materials were used as heterogeneous catalysts for different biomass-derivatives hydrogenation,during which the conversion of guaiacol in the aqueous solution was close to 90.0%and the yield of cyclohexane reached up to 84.3%.This remarkably catalytic performance can be attributed to the unique TiO6 octahedra carrying two negative charges that strengthens the interaction with active metal species,and thus improve their dispersion.Moreover,the inherent strong Lewis basicity favor the oriented conversion of reactants.The controllably hierarchical structure and morphology benefit exposure of more highly dispersed active sites and prolong the catalyst life circle.In particular,the method adopted here for generating hierarchical pores and cavities into METS-10-L by using LnNa is analogous to the molecular-recognition pattern,which is identified as the leading role in allowing for the noticeable improvement of catalytic activity and selectivity.5.A new type of soft functional material,ionic liquids(ILs)that are composed of larger organic cations and smaller inorganic anions at room temperature or adjacent temperatures was employed for zeolite synthesis.In the field of material synthesis,in addition to the conventional use of ILs as organic solvents,its template action and the dual function of both solvent and template agent,especially its own strong self-assembly ability and structural adjustability are obviously different from traditional quaternary ammonium salt template agents,which has attracted extensive research interest.In the previous study,we used sodium lignosulfonate with excellent dispersion and enthalpy,strong interaction with the inorganic species especially the titanium species in the synthesis syetem to affect the crystallization process of ETS-10 zeolite,particularlly the crystal growth rate,and then,to prepare ETS-10 zeolite with significantly different pore size distribution and morphology.The synthesized ETS-10 zeolite-based catalyst gives a unique selective recognition,which greatly enhances its catalytic activity and selectivity in the hydrogenation reaction.Therefore,based on this research,further improvement and modification of hierarchical ETS-10 zeolite under the action of sodium lignosulfonate were carried out by combining the distinguished template and structure-directing action of ionic liquid and sodium lignosulfonate,which can better adjust the pore structure,morphology and surface properties of the synthesized zeolite.Then,the catalytic performance of the correspondingly improvrd ETS-10 zeolite catalyst in the biomass hydrogenation reaction was investigated.The guaiaconl conversion in the aqueous solution has increased to 92.5%,and the corresponding cyclohexane yield got close to 90.0%.