Study On Preparation And Characterization Of Novel Solid Basic Materials And Their Catalytic Performance

The solid base catalysts are novel environment-friendly catalytic materials,and have been applied to many kinds of organic synthesis,such as double bond isomerization of alkenes and alkynes,oxidation,reduction,transesterification,Aldol condensation,Michael addition,Knoevenagel condensation,side-chain alkylation of toluene et al.The results showed that the catalysts own the advantages of high activities,high selectivity and reusability.In order to explore the novel solid base catalysts and their application aspects, two kinds of novel solid base catalysts,including hydrotalcite like compounds and K₂CO₃ supported on Ce-Zr-mixed oxides have been present here in the thesis.Their applications in the synthesis of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy and biodiesel respectively were developed for the first time.1.Catalytic Synthesis of Hindered Amine Nitroxyl radicalsHindered amine light stabilizer(HALS)is a new kind of excellent light stabilizer developed in the late 1970s.They have shown excellent light stabilizing ability with the additional advantages of insolubility and synergism with ultraviolet absorbers and antioxidants.Thus,extensive attention has been paid to the aspect,which has become one of the most attractive research fields recently.The Hindered Amine Nitroxyl radicals produced from the traditional homogeneous catalyst of sodium tungstate involved serious problems,such as lower catalytic activates,lower yields,longer reaction time and harmful solvent such as tetrahydrofuran and N,N-dimethylformamide demanded.A green route for the synthesis of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy with hydrogen peroxide(30%)in the presence of Mg-A1 hydrotalcite or ZnMgAl hydrotalcite-like compound has been proposed to solve problems above.First,MgAl hydrotalcite and ZnMgAl hydrotalcite-like compounds with different of molar ratios of Mg to Al and the ZnO content are prepared using the co-precipitation method.The best catalytic activities and crystallinity of Mg-Al hydrotalcite has achieved with n(Mg)/n(Al)=3.The ZnMgAl hydrotalcite-like compounds are obtained with Zn²⁺partially substituted Mg²⁺in the course of co-precipitation.The ZnMgAl hydrotalcite-like compounds own even higher activities than Mg-Al hydrotalcite when ZnO mass was 6%.Then,the catalytic activities of MgAl hydrotalcite and ZnMgAl hydrotalcite-like compound were investigated through the synthesis of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy with hydrogen peroxide(30%).The results showed that the catalysts own the advantages of high activities,short reaction time,operational simplicity and reusability.Furthermore,the structure of product was validated by melting point,element analysis,FT-IR and GC-MS.The product is obtained through crystallization,which makes the separation and purification convenient.The reaction conditions such as reaction time,temperature,molar ratio of reactants and the catalyst dosage were optimized.The optimal reaction conditions and excellent results in catalyzed process of MgAl hydrotalcite was given as follow:mole ratio of H₂O₂ to 4-hydroxy-2,2,6,6-tetramethyl-piperidine was 3:1,the amount of catalyst(based on the amount of 4-hydroxyl-2,2,6,6-tetramethylpiperidine)is 2.5 wt%,reaction temperature is 70℃and reaction time is 2.5h.Under this condition,a high yield of 97%was achieved.Compared with MgA1 hydrotalcite,ZnMgAl hydrotalcite owned higher catalytic activities with shorter reaction time,lower reaction temperature and the amount of catalysts with the yield of 99.4%.Additionally,two other hindered amine N-oxyl light stabilizers were also obtained through the method by oxidizing 2,2,6,6-tetramethyl piperidine and 2,2,3, 4,5,5,hexamethylpyrrole.The catalysts also had high catalytic activities with the yields of over 95%.2.Catalytic synthesis Biodiesel via Transesterification MethodBiodiesel produced through transesterification method using vegetable oils and fats as raw material is one of the green substitution of petroleum.The traditional procedure for the synthesis of biodiesel using homogenous bases or acids(NaOH, H₂SO₄,et al.)as catalysts suffered from the many drawbacks including separation, waste water treatment and corrosion problems.The novel heterogeneous procedures for the synthesis of biodiesel using LiAl complex oxides and K₂CO₃ supported on Ce-Zr-mixed oxides have been introduced here.First,LiAl complex oxides,decomposed from precursor of LiAl hydrotalcite-like compounds using co-precipitation method were prepared to catalytic synthesis biodiesel.X-ray diffraction patterns of the precursor revealed thatwell-crystallized compounds with the typical structure of hydrotalcite-like compounds brucite-layer were synthesized.Calcination the precipitate at 500℃obtained a LiAl composite oxide catalyst which was active for the transesterification of rapeseed oil.The influence of reaction conditions involving reaction time,reaction temperature,the methanol/oil molar ratio and the catalyst dosage on the transesterification process was investigated.The optimized operation parameters were obtained.Under a condition of atmospheric pressure,65℃,methyl/oil mole ratio of 6:1 and catalyst dosage of 2 wt %(based on oil),the conversion of oil reached about 95.9%.The conversation of vegetable oils was also remained at constant(above 85%)after the sixth cycle.Then,Zr-Ce composite oxide as carrier,the K₂CO₃/Zr-Ce composite oxide sample was also prepared by an incipient wetness impregnation method.The supported solid base composite oxide was obtained from the K₂CO₃/Zr-Ce composite oxide sample upon calcination at 850℃.The activity of this catalyst for synthesis of biodiesel by transesterification between methanol and oil has been investigated.