高硅β分子筛的原位合成及其在甲苯催化燃烧中的应用

In Situ Synthesis of High-Silica β Zeolite over Cordierite Support and Its Application in Catalytic Combustion of Toluene

采用水热合成法在堇青石蜂窝陶瓷载体上原位合成了整体化的高硅β分子筛(β/CH),采用XRD和SEM手段对其进行表征,筛选出有利于原位合成的堇青石预处理方式和晶化方式,并探索了最佳原位合成条件;考察了制备方法对Pd/β/CH整体催化剂催化燃烧性能的影响。实验结果表明,在用质量分数10%的HNO3溶液80℃下处理2 h后的堇青石蜂窝陶瓷载体的内外表面上,采用动态晶化方式一次水热合成,可均匀生长出β分子筛;在保证原位生长质量的情况下,最佳的凝胶投料比为n(四乙基氢氧化铵)∶n(SiO2)∶n(Al2O3)∶n(HF)∶n(H2O)=0.52∶1∶0.003 3∶(0.31～0.37)∶14.25,最佳晶化时间为5 d。与浸渍法相比,采用原位合成法制备的Pd/β/CH整体催化剂的催化燃烧性能明显提高,在β分子筛质量分数32.5%和Pd质量分数0.5%时,甲苯在270℃即可完全转化。

Monolithic high-silica β zeolite was synthesized on honeycomb-shaped cordierite by an in situ hydrothermal method.The β/cordierite was characterized by means of XRD and SEM.The optimal conditions for the β/cordierite synthesis,including cordierite pretreatment,crystallization mode,crystallization time,and the contents of tetraethyl ammonium hydroxide（TEAOH）,HF and H2O,were investigated.The effect of the in situ synthesis of β/cordierite on the catalytic combustion of toluene over Pd/β/cordierite was discussed.The results showed that under dynamic synthesis mode,a coating of β crystals was formed on the cordierite pretreated with 10%（w） nitric acid at 80 ℃ for 2 h.The optimal preparation conditions were confirmed as follows： silicon-aluminum sol prepared with n（TEAOH） ∶ n（SiO2） ∶ n（Al2O3） ∶ n（HF） ∶ n（H2O） 0.52 ∶ 1 ∶ 0.003 3 ∶（0.31-0.37） ∶ 14.25 and crystallization time 5 d.Compared to the catalyst prepared by impregnation method,the activity of the monolithic Pd catalyst prepared by the in situ synthesis method for the catalytic combustion of toluene was clearly heightened.When mass fraction of β zeolite and Pd loading were 32.5% and 0.5% respectively,toluene could be fully converted at 270 ℃.