催化剂酸碱性与催化酯醛缩合性能的关系

Relationship between catalyst acid-base property and condensation performance for ester aldehydes

以γ-Al_(2)O_(3)和SiO_(2)为载体,采用浸渍法引入不同含量Na^(+)、K^(+)和Cs+碱金属离子,制备了一系列酯醛气相缩合催化剂。利用XRD、BET、NH3-TPD和CO_(2)-TPD对催化剂的结构和表面酸、碱性进行了表征,并以丙酸甲酯与甲醛为原料,考察了其催化酯醛气相缩合反应性能。结果表明,在0.2 MPa、370℃和质量空速为1.2 h^(-1)的条件下,以10%(以载体SiO_(2)质量为基准,下同)Cs/SiO_(2)为催化剂时,丙酸甲酯转化率最高(41.03%),甲基丙烯酸甲酯选择性为99.20%。在有丰富碱活性中心的前提下,催化剂表面弱碱性位点含量与其催化酯醛气相缩合反应性能呈正相关关系,催化剂表面酸性位点和中强碱性位点的存在会导致催化剂催化活性和选择性的降低。

A series of catalysts with different contents of Na^(+),K^(+)and Cs+for vapor phase condensation of ester aldehydes were prepared by impregnation method usingγ-Al_(2)O_(3)and SiO_(2)as carriers.The catalysts obtained were then characterized by XRD,BET,NH_(3)-TPD and CO_(2)-TPD for analysis on structure,acidity and basicity,followed by evaluation on their catalytic performance on condensation of methyl propionate and formaldehyde in vapor phase.The results showed that,under the reaction conditions of pressure 0.2 MPa,temperature 370℃,mass space velocity 1.2 h^(-1),10%(on the basis of the mass of SiO_(2),the same below)Cs/SiO_(2)catalyst exhibited better activity with the highest methyl propionate conversion rate of 41.03%and methyl methacrylate selectivity of 99.20%.When there were abundant alkali center,a positive correlation was found between the proportion of weakly basic sites on the surface of the catalyst and its catalytic performance for condensation of ester aldehydes in vapor phase.However,the presence of acidic and moderately strong alkaline sites of the catalyst could lead to a decrease in activity and selectivity.