合成体系中NO_3^-与HMT的物质的量比对AlOOH结构及催化性能的影响

Effects of molar ratio of NO_3^- to HMT on structure and catalytic performances of Al OOH

采用HMT水热分解法,通过调控NO_3^-与HMT的物质的量比(n(NO_3^-)/n(HMT))在不同合成体系下制备Al OOH催化剂,并就其在苯甲醛和乙醇一步合成安息香乙醚中的催化性能进行评价。通过XRD,FT-IR,TG-DTG,BET,TEM及NH3-TPD-MS对催化剂进行表征。研究结果表明:调控合成体系中n(NO_3^-)/n(HMT)可以制备出结构和形貌不同的勃姆石。合成环境在构建Al OOH组成结构的基础上进而影响着其催化性能。取苯甲醛3 m L、乙醇40 m L、不同n(NO_3^-)/n(HMT)制备的Al OOH催化剂0.2 g,当反应温度为70℃,时间为40 min时,安息香乙醚的选择性均可达100%。高n(NO_3^-)/n(HMT)下制备的Al OOH能使苯甲醛的转化率达68.9%,低n(NO_3^-)/n(HMT)下制备的Al OOH仅使苯甲醛的转化率为32.3%,而调控n(NO_3^-)/n(HMT)使最终合成体系为中性条件下制备的Al OOH几乎没有催化活性(苯甲醛的转化率仅为3.08%)。不同的催化性能与制备所得Al OOH结构和形貌密切相关,而Al OOH催化剂酸量的不同构建是催化差异的本质原因。

AlOOH were fabricated by hexamine （HMT） hydrolysis method through modulating the molar ratio of NO3 to HMT （n（NO3-）/n（HMT） and their catalytic performances toward synthesis of benzoin ethyl ether from benzaidehyde and ethanol were evaluated. Samples obtained at various molar ratio of NO3 to HMT were characterized by XRD, FT-IR, TG-DTG; BET, TEM and NH3-TPD-MS. The results show that AlOOH obtained at different molar ratios of NO3 to HMT has different structures and morphologies. The further evaluation of catalytic activity demonstrates that ambient atmosphere can alter the structure of AlOOH, which has a significant effect on the catalytic behavior. All synthesized catalysts present 100% selectivity of benzoin ethyl ether under following reaction condition： temperature 70 ℃, benzaldehyde 3 mL, ethanol 40 mL, catalyst 0.2 g, reaction time 40 min, at higher molar ratio of NO3 to HMT, AlOOHdisplays fine catalytic activity （68.9% conversion of benzaldehyde）, while at lower molar ratio of NO3- to HMT a poor activity （32.3% conversion of benzaldehyde） is obtained and at neutral ambient atmosphere there is almost no catalytic activity （3.08% conversion of benzaldehyde）. The totally different catalytic activity has close relation to the structures and morphologies of AlOOH synthesized under different pH values, and the amount of acid is responsible for the different catalytic performances.