Preparation And Performance Studies Of Cobalt Based Catalysts For Alcohol Amination And Amine Oxidation

Amine oxide is a kind of special amphoteric surfactant,which has been widely used in the fields of daily chemical industry,resource exploitation,biology and pharmaceutical engineering.In this paper,catalysts of alcohol amination and amine oxidation were studied respectively.Firstly,the silica supported cobalt catalyst Co/SiO₂-T was prepared by sol-gel method at different calcination temperatures.Then,the catalyst Co-Ag_x/SiO₂modified by Ag was prepared,and the catalyst was characterized by SEM,EDX,XRD,XPS,H₂-TPR,BET,FT-IR,TEM,etc.The model reaction was amination of dodecanol and dimethylamine.The effects of calcination temperature,silver loading and reaction conditions on the amination reaction were studied.Using 3-aminopropyl trimethoxy silane as linker,the colbalt Schiff base catalyst Co（Ⅱ）-Schiff@SiO₂-NH₂supported by silica was prepared by grafting method.The effects of different reaction conditions on the oxidation of dodecyl dimethylamine and the stability of the catalyst were studied.The results are as follows:（1）The specific surface area of Co/SiO₂-T increases first and then decreases with the calcination temperature increasing from 450 to 750℃,and the average pore size increases gradually.The average particle size of Co gradually increased,and the reduction degree and dispersion degree decreased.The catalyst Co/SiO₂-550 with small particle size and largest specific surface area has the best performance in the amination reaction.The average Co particle size of catalyst Co/SiO₂-550 was 13.22 nm,the S_BETwas 288 m²·g^-1,the average pore size was 7.83 nm,and the reduction and dispersion of Co were 83.75%and 7.42%.The results of the amination experiment showed that the optimum reaction conditions were200℃and 55%hydrogen intake ratio.The conversion of Co/SiO₂-550 and selectivity for dodecyl dimethylamine are 94.45%and 85.94%,and the catalyst has good stability.（2）The modification of Co/SiO₂-550 showed that with the addition of Ag,the specific surface area and average pore diameter of the catalyst increased,the average particle size of Co decreased,the dispersion and reduction degree increased.The results of the amination experiment between dodecyl alcohol and dimethylamine show that 3 wt%is the best modification loading,the average Co particle size of Co-Ag₃/SiO₂is 9.12 nm,the specific surface area is 327 m²·g^-1,the average pore size is 12.64 nm,and the Co reduction and dispersion degree are 91.62%and 12.29%.Under the optimal conditions,the conversion of Co-Ag₃/SiO₂and selectivity for dodecyl dimethylamine are 97.42%and 93.71%,and the catalytic performance can be maintained after 10 cycles.（3）During the synthesis of catalyst Co（Ⅱ）-Schiff@SiO₂-NH₂,the specific surface area,average pore size and pore volume of the catalyst decreased with the support of the active component.The S_BETof the catalyst was 215 m²·g^-1,and the average pore size was 7.76 nm.The optimum reaction conditions were 35℃,3 times the volume of substrate and 6 hours.The conversion of tertiary amine and the selectivity to dodecyl dimethyl amine oxide of Co（Ⅱ）-Schiff@SiO₂-NH₂were 96.45%and 87.28%.The catalyst still showed good activity after 6 cycles,and 25%of the cobalt fixation load was lost during the cycle.