Fabrication And Catalytic Properties Of Novel Catalysts Originated From SBA-15

SBA-15,a type of ordered hexagonal array mesoporous silica with two-dimensional p6 mm hexagonal structure,one-dimensional channels and thicker walls,has received much attention because of its favorable catalytic activities for reactions involving the conversion of bulkier molecules such as those of heavy crude oils and heavier petroleum fractions.However,compared with the conventional microporous zeolites,SBA-15 has much weaker acidity and lower hydrothermal stability because of its neutral Si frameworks.Therefore,the improvement of the acidity and hydrothermal stability of SBA-15 has been an important issue for its actual industrial application in the future.Moreover,the morphology and mesochannel of SBA-15 also play an important role in the dispersion of the active components and the diffusion of the reactant molecules.However,the detailed investigation of the effect of the morphology and mesochannel of SBA-15 on the catalytic performance has been few reported according to reference.The interaction between the support and active component also has a great influence in the catalytic activities.Therefore,this research will be focus on the modification and morphology-controlled synthesis of SBA-15,and the interaction adjustment between the support and active component.The supports and catalysts were characterized by means of XRD,FT-IR,SEM,TEM,STEM,H2-TPR,129 Xe NMR,ICP-AES,Raman,UV-Vis DRS,GC-MS and Py-IR et al.The catalytic activities of the catalysts were evaluated by hydrogenation reaction(include hydro-upgrading of FCC gasoline,HDS of DBT,selective hydrogenation of 1,3-butadiene and cyclooctadiene).Based on the characterization results,the relationship between the preparation mehod,structure,physiochemical properties of catalysts and the catalytic performances for hydrogenation reaction were studied in details,and the catalytic reaction mechanisms for hydrogenation reaction were discussed and clarified.The main contents and results are as following:(1)NiMo/Al-SBA-15 hydrodesulfurization catalysts with sphere,hexagonal prism,short rod and long rod were synthesized,and the relationship between the catalytic activity and the morphology,acidity,porous structure and active component of the catalysts was systematical investigated.Mesoporous SBA-15 materials with different morphologies were successfully synthesized through different methods by using pluronic P123 triblock copolymer(EO20PO70EO20)and cosurfactant(CTAB)as structure-directing agent.Moreover,highly ordered mesoporous Al-SBA-15 with Si/Al molar ratio of 10 has been prepared with three different Al resources using post-synthesis methods.The characterization results of X-ray fluorescence spectroscopy,X-ray power diffraction,N2 adsorption-desorption and 27 Al nuclear magnetic resonance spectroscopy revealed that the chemical grafting of aluminum chloride on the surface of SBA-15 was the best post-synthesis route for the preparation of Al-SBA-15 with different morphologies.The corresponding Al-SBA-15-supported NiMo hydrodesulfurization(HDS)catalysts with different morphologies were prepared and evaluated using DBT as a probe reactant.The sphere NiMo/AS-SP catalyst has higher dispersion degree of MoS2 slabs and more acid sites than other catalysts.The catalytic results showed that the morphologies and mesochannels of SBA-15 played an important role in the catalytic performance of DBT HDS over NiMo catalysts,especially in the diffusivity of DBT molecules in the catalysts,while they have little effect on the selectivity of DBT HDS.The kinetics investigations confirmed that the activity of DBT HDS over these catalysts followed the order: long rod catalyst(Ni Mo/AS-LR)< hexagonal prism catalyst(NiMo/AS-HP)< short rod catalyst(NiMo/AS-SR)< sphere catalyst(NiMo/AS-SP).(2)In addition to the chemical grafting of aluminium species on the surface of SBA-15,the physical chemistry properties of SBA-15 can be also improved by micro-mesoporous composite method.Micro-mesoporous Beta-SBA-15 materials with platelet,sphere,short-rod and long-rod morphologies were in-situ synthesized by self-assembly of nanomicrocrystal method and used as the catalyst supports for hydro-upgrading of FCC gasoline.The characterization results revealed that the Beta-SBA-15 composites possessed both SBA-15 and Beta structures.And the materials with different morphologies exhibited different Br?nsted and Lewis acid sites and pore sizes due to their corresponding synthesis conditions.The platelet Beta-SBA-15 which possessed the short mesochannels with large pore diameter had high diffusion ability.The sphere Beta-SBA-15 with more mesopore cavities,high surface area and suitable acidity exhibited outstanding isomerization and aromatization abilities.The catalytic results confirmed that the platelet CoMo/ABS-PL exhibited the high hydrodesulfurization(HDS)conversion(97.6 %)while the sphere CoMo/ABS-SP catalyst showed the superior research octane number(RON)preservation ability,which were better than those of CoMo/ABS-SR(short-rod)and CoMo/ABS-LR(long-rod)catalysts.(3)Apart from the modification of SBA-15,this research also synthesized a novel catalyst with a high density of active sites,which can enhance the utilization and stability of noble-metal atoms.This novel catalyst consists of sub-nanosized Pt particles within hierarchically porous ZSBA material via mercaptosilane-assisted synthesis method.This strategy avoids the precipitation of metal hydroxide at the high pH in the process of zeolite crystallization.The alkoxysilane moiety of the ligands could form Si-O-Si or Si-O-Al bonds in the ZSM-5 zeolite synthesis system after hydrolysis in the alkaline media.Pt@ZSBA catalyst not only possesses the high stability and hierarchically porous properties of micro-mesoporous composite,but also has high density and stability of active sites by confinement of such sub-nanosized Pt particles within small-pore zeolite.The sub-nanosized Pt NPs are highly dispersed in ZSBA framework with average diameter of 0.5–1.5 nm,which enhances the the utilization ratio and stability of Pt atoms.Thus,Pt@ZSBA exhibits high catalytic activities and stabilities for 1,3-butadiene and cyclooctadiene hydrogenation at room temperature.(4)Based on the above research,a series of novel catalysts that consist of nanosized Au particles confined in hierarchically porous ZSM-5/SBA-15 materials with platelet,rod and hexagonal-prism morphologies have been in situ synthesized.The characterization results demonstrate that these catalysts possess a hierarchically porous structure of micro–mesoporous composite and exhibit excellent stability of active sites by confinement of Au nanoparticles within ZSM-5/SBA-15 materials.The catalytic results reveal that the platelet Au/ZSBA-PL with short mesochannels(210 nm)and large pore diameter(6.7 nm)has high catalytic performance in the reduction of 4-nitrophenol,while hexagonal-prism Au/ZSBA-HP and rod Au/ZSBA-RD with long mesochannels and relative smaller pore size show poor catalytic activities,demonstrating that the morphologies and mesochannels of the supports play an important role in the catalytic performance.