选择性铵离子交换MCM-49分子筛的酸性及催化性能研究

Acidity and catalytic performance of selectively ammonium ion exchanged MCM-49 molecular sieve

以动态水热合成方法制备了MCM-49分子筛,分别采用硝酸铵和四丙基溴化铵(TPABr)为铵化剂制备了HMCM-49(NH4NO3)和HMCM-49(TPABr)。采用NH3-TPD和乙腈吸附-红外光谱测试对HMCM-49的酸性进行了表征,对比研究了HMCM-49(TPABr)和HMCM-49(NH4NO3)催化苯与丙烯液相烷基化反应的催化性能。与HMCM-49(NH4NO3)相比,HMCM-49(TPABr)的酸强度保持不变,但总酸量和强酸酸量明显降低。调整TPABr离子交换条件,能够获得酸中心主要分布在外表面并具有不同强酸酸量的HMCM-49(TPABr)催化材料。催化反应结果表明,催化活性随着外表面强酸酸量的增加而提高,在140℃、n(苯)∶n(丙烯)=6的条件下HMCM-49(TPABr)的丙烯转化率比HMCM-49(NH4NO3)降低了2.5%,同时异丙苯选择性提高,达到85.47%。

MCM-49 zeolite was synthesized by dynamic hydrothermal method.Ammonium nitrate and tetrapropylammonium bromide were used as ammonium agent to prepare HMCM-49（NH4NO3）and HMCM-49（TPABr）respectively.NH3-TPD and acetonitrile adsorption-FTIR was used to study the acidic properties of HMCM-49.Catalytic performance of HMCM-49（TPABr）on benzene alkylation with propylene was investigated comparing with HMCM-49（NH4NO3）.Acidic properties characterizations indicated that the total acid amount of HMCM-49（TPABr）was much lower than HMCM-49（NH4NO3）and the acid strength remained unchanged.For HMCM-49（TPABr）,the acid sites were mainly distributed on the external surface as well as the internal acid sites were greatly suppressed.Catalytic reaction results showed that catalytic activity is increased with the amounts of external surface strong acids.When the reaction temperature is 140℃ and benzene to propylene molar ratio is 6,the catalytic activity of HMCM-49（TPABr）is 2.5%lower than HMCM-49（NH4NO3）,and the catalytic selectivity reaches to 85.47%,which is higher than HMCM-49（NH4NO3）.Combined with acidic characterization,reaction results indicated that the strong acid sites distributed on the external surface of HMCM-49 are the effective acid sites for the alkylation of benzene with propylene.