Study On A-pinene Hydrogenation By Ru Nanoparticle Immobilized In Functionalized Amphiphilic Mesoporous Sieve

Cis-pinane is widely used in producing medicines,perfume,pharmaceutical intermediates,functional materials,chemicals,including agricultural chemicals,etc.This study explores the concept of an environmental friendly catalyst and simple separation.Pure silicon mesoporous molecular sieves SBA-15 and SiO₂ were synthesized by the hydrothermal synthesis method.SBA-15-MPTS and MM@MN were prepared by SiO₂ functionalized with 3-（methacry-loyloxy）propyltrimethoxy silane（MPTS）and（3-aminopropyl）trimethoxysilane（APTS）.Ru nanoparticles were embedded in the SBA-15-MPTS and MM@MN by the impregnation method,and the effect of hydrogenation ofα-pinene was investigated.The structure and morphology of the mesoporous silica were characterized and confirmed by transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,thermogravimetric（TG）,X-ray diffraction（XRD）,Fourier transfer infrared spectroscopy（FT-IR）,and N₂adsorption-desorption.Ru/SBA-15-MPTS and Ru/MM@MN were applied in the selective hydrogenation ofα-pinene,the results show that the catalytic activity of the amphiphilic catalyst Ru/MM@MN with the core-shell structure is superior to that of Ru/SBA-15-MPTS with the two-dimensional pore structure.Under the optimum reaction conditions（25 ^oC,1.5 MPa H₂,1 h,m（H₂O）:m（α-pinene）:m（Ru/MM@MN）=125:38:1）,the conversion can reach 99.9%and 98.9%selecvity when Ru/MM@MN was applied in the selective hydrogenation ofα-pinene.Further,the catalyst still retains a high activity and selectivity after repeated use for five times.The amphiphilic molecular sieve MC₁₈@MN was prepared by modifying SiO₂with octadecyltrimethoxysilane and 3-aminopropyltrimethoxysilane.During the synthesis of the amphiphilic molecular sieve,the effects of the amount of the template agent,the dispersion time of the template agent,the alkalinity,the synthesis temperature,and the stirring speed on the morphology and pore structure of the amphiphilic molecular sieve were observed by TEM.The effects on the pore structure of the molecular sieve were investigated when adjusting the alkalinity of the system with sodium hydroxide and ammonia,respectively.The influence of different methods for extracting the organic templating agents on the surface area and pore size of molecular sieves was analyzed.The Ru/MC₁₈@MN was prepared by loading Ru nanoparticles on MC₁₈@MN,and it was employed in the catalytic hydrogenation ofα-pinene.Under the optimum reaction conditions(40 ^oC,2 MPa H₂,1 h,m（H₂O）:m（α-pinene）:m(Ru/MC₁₈@MN)=143:44:1),the conversion ofα-pinene could reach99.9%and the selectivity for cis-pinane was 98.8%,but there is a significant deterioration in activity owing to the poor stability of catalyst.The amphiphilic mesoporous sieve modified with trimethoxy（3,3,3-trifluorop-ropyl）silane（TFPS）and（3-aminopropyl）trimethoxysilane was prepared by one-step synthesis.The structure and morphology of the mesoporous silica were characterized and confirmed by solid-state nuclear magnetic resonance（MAS-NMR）,XRD,N₂adsorption-desorption analyses.Highly dispersed Ru nanoparticles supported on the amphiphilic mesoporous silica（marked as Ru/MF@MN）were synthesized by the wet impregnation method with ultrasonication.The catalyst was characterized by X-ray photoelectron spectroscopy（XPS）and inductively coupled plasma-atomic emission spectrometry（ICP-AES）.In water,Ru/MF@MN was involved inα-pinene hydro-genation to cis-pinane.The optimum reaction conditions were 35 ^oC,2 MPa H₂,1 h,m（H₂O）:m（α-pinene）:m（Ru/MF@MN）=200:60:1.When Ru/MF@MN was recycled six times,the conversion slightly decreased and the selectivity remained nearly unchanged.Highly dispersed Ru nanoparticles,supported on amphiphilic molecular sieves modified by doping with heteroatoms to adjust the acidity,were prepared with the assistance of ultrasonication and applied in the catalytic hydrogenation ofα-pinene.The molecular sieve doped with B was characterized by XRD,FT-IR,temperature-programmed-desorption of ammonia curves（NH₃-TPD）,and MAS-NMR studies.It was found that Si atoms in the frame of the molecular sieve were replaced by B atoms and existed as the four-coordinated state and three-coordinated state,thus forming a certain amount of acid centers.The electron valence state of the Ru/B/MC₁₂@MN catalyst and the loading amount of Ru onto the Ru/B/MC₁₂@MN catalyst was analyzed by XPS and ICP-AES.Under the optimum reaction conditions(25 ^oC,1 MPa H₂,1 h,m（H₂O）:m（α-pinene）:m(Ru/B/MC₁₂@MN)=143:44:1),the conversion ofα-pinene could reach 99.9%and the selectivity for cis-pinane was 99.1%.The catalyst was recycled by centrifugation after the reaction,and retained the high activity and selectivity even after five cycles.In this work,the amphiphilic catalyst with the"micelle-like"structure was prepared by grafting amphiphilic functional groups into the structure of the molecular sieve.The catalyst was applied in the catalytic hydrogenation ofα-pinene and mild conditions,highly efficient,highly selective catalyticα-pinene hydrogenation were achievedd.Thus,a new approach is presented for the catalysis of the hydrogenation ofα-pinene in the aqueous phase,and the separation,recycling and reuse of the catalyst.