不同钛含量TAPO-5分子筛的制备及催化环己酮氨肟化

以氢氧化铝、正磷酸和钛酸四异丙酯为原料,N-甲基二环己基胺为模板剂,采用水热晶化法合成一系列具有不同Ti含量的TAPO-5分子筛,通过XRD、N_2物理吸附-脱附、DR UV-Vis和XRF分别对分子筛结构、织构性质、Ti的存在状态以及Ti含量等进行表征。结果表明,TAPO-5分子筛为微孔-介孔材料,其中,Ti以骨架、非骨架和锐钛矿相3种形式存在;随着Ti含量增加,3种形式的Ti含量均增加,伴随着TAPO-5分子筛的结晶度、比表面积和孔容降低。环己酮氨肟化结果表明,随着Ti含量增加,环己酮转化率和环己酮肟选择性逐渐提高,当Ti质量分数为14.8%时,环己酮转化率和环己酮肟选择性分别为92.5%和95.4%,优于目前过渡金属掺杂磷酸铝分子筛催化环己酮氨肟化的最佳结果。

Preparation of TAPO-5 molecular sieves with different Ti contents and their catalytic performance for cyclohexanone ammoximation

Using aluminium hydroxide as Al source,phosphoric acid as P source,tetraisopropyl titanium as Ti source and N-methyldicyclohexylamine as the template,a series of TAPO-5 molecular sieves with different titanium contents were synthesized by the hydrothermal crystallization method.The structural and texture properties,titanium coordination status and titanium contents of TAPO-5 molecular sieves were characterized by X-ray diffraction,N2-physical adsorption-desorption,diffuse reflectance UV-Vis spectroscopy and X-ray fluorescence techniques.The results showed that TAPO-5 molecular sieves were microporous-mesoporous materials,and there existed 3 forms of titanium:framework titanium,extra framework titanium and anatase;the amounts of framework titanium,extra framework titanium and anatase increased with the increase of Ti loadings,while the crystallinity,BET surface area and pore volume of TAPO-5 molecular sieves decreased.The results of catalytic cyclohexanone ammoximation demonstrated that the selectivity to cyclohexanone oxime and cyclohexanone conversion increased with the increase of Ti contents.The selectivity to cyclohexanone oxime and cyclohexanone conversion on TAPO-5 molecular sieve with Ti mass fraction of 14.8% were 95.4% and 92.5%,respectively,which were better than those on transition metal doped aluminophosphate molecular sieve for catalytic cyclohexanone ammoximation.