多级孔HZSM-5分子筛的制备及其催化丙烷脱氢反应性能

以十八水合硫酸铝、硅溶胶、四丙基氢氧化铵(TPAOH)、硝酸铵(NH_4NO_3)为原料,合成硅铝物质的量比为100的HZSM-5分子筛。采用乙酸钠溶液处理HZSM-5分子筛后加入TPAOH溶液进行二次晶化,通过对处理前、后的HZSM-5分子筛负载Pt,制得Pt/HZSM-5催化剂用于丙烷脱氢反应。利用XRD、SEM、XRF、BET、NH_3-TPD和H_2化学吸附对处理前、后的HZSM-5分子筛进行了表征,考察了不同浓度的TPAOH溶液对HZSM-5分子筛的晶体结构、表面形貌、孔结构、表面酸性及丙烷脱氢性能的影响。结果表明,采用乙酸钠溶液处理后的HZSM-5分子筛在TPAOH溶液中发生了二次晶化,不仅形成了微孔-介孔多级孔结构,还能调变分子筛的表面酸性;当TPAOH溶液浓度为0.3 mol/L、晶化温度为170℃、晶化时间为24 h时,得到的Pt/HZSM-5催化丙烷的初始转化率和丙烯选择性均达到最高值,分别为34.2%和99.0%。

Preparation of hierarchical HZSM-5 zeolites and their catalytic performance in propane dehydrogenation

Aluminium sulphate (Al2(SO4)3·18H2O), silica sol, tetrapropylammonium hydroxide (TPAOH) and ammonium nitrate (NH4NO3) were used as the raw materials to synthesize HZSM-5 zeolite with a SiO2/Al2O3 mol ratio of 100. HZSM-5 zeolites were treated by adding TPAOH solution for secondary crystallization after pre-treating with sodium acetate solution. Pt/HZSM-5 catalysts were prepared for propane dehydrogenation by loading Pt on to HZSM-5 zeolites before and after treatment. The sam-ples were characterized by XRD, SEM, XRF, BET, NH3-TPD and H2 chemisorption. The effects of different TPAOH crystallization concentrations on the crystal structure, surface morphology, pore structure, surface acidity and propane dehydrogenation of HZSM-5 zeolites were investigated. The results showed that HZSM-5 zeolite treated with CH3COONa solution was recrystallized in TPAOH solution, which not only formed microporous-mesoporous hierarchical structure, but also modulated the surface acidity of the zeolite. If HZSM-5 zeolite is first pre-treated with CH3COONa and then crystallized for the second time in the presence of 0.3mol/L TPAOH and at 170°C for 24h, the Pt/HZSM-5 catalyst exhibited the highest initial propane conversion and propene selectivity, which were 34.2% and 99.0%, respectively.