Knoevenagel condensation reaction over acid-base bifunctional MgO/HMCM-22 catalysts

Abstract

MgO/HMCM-22 catalysts were prepared by impregnation and characterized by X-ray diffraction, N 2 physical adsorption-desorption, scanning electron microscopy, Fourier-transform infrared spectroscopy, temperature-programmed desorption of NH 3 , and temperature-programmed desorption of CO 2 . The results show that there were no significant structural changes in the MCM-22 zeolite after modification. Increasing the MgO loading increased the strength and content of the base, whereas the strength of the strong acid decreased significantly and the amount of weak acidic sites increased slightly. Knoevenagel condensation reactions were carried out as the probe reactions over the catalysts. Both acidic sites and basic sites significantly promoted the reaction. The conversion of benzaldehyde reached 92.6% under the optimal conditions. The catalytic performance of MgO/HMCM-22 and MgO/NaMCM-22 was better than that of HMCM-22 and MgO. The MgO/HMCM-22 catalysts gave good catalytic performance for Knoevenagel condensation reactions and exhibited obvious acid-base synergetic effects. 采用浸渍法制备了一系列MgO改性催化剂MgO/HMCM-22, 利用X射线衍射、N 2 物理吸附-脱附、扫描电镜、傅里叶变换红外光谱、NH 3 及CO 2 程序升温脱附等技术对所制催化剂进行了表征. 结果表明, MgO改性后MCM-22分子筛仍保持原有的结构; 随着MgO负载量的增加, 催化剂的碱强度和碱含量显著增加, 而强酸含量明显减少, 弱酸酸位有所增加. 以Knoevenagel缩合为探针反应, 考察了所制催化剂的性能. 在优化的反应条件下, MgO/HMCM-22上苯甲醛转化率高达92.6%. 催化剂 MgO/HMCM-22和MgO/NaMCM-22的催化性能明显优于HMCM-22和MgO. 酸中心和碱中心均对该缩合反应起着重要的促进作用. MgO/HMCM-22对Knoevenagel缩合反应显示出较高的催化活性, 体现出明显的酸碱协同催化作用. The possible mechanism of acid-base bifunctional catalyst MgO/HMCM-22 for the Knoevenagel condensation reaction was presented. The results show that the catalyst MgO/HMCM-22 exhibited obvious acid-base synergetic effects with good catalytic performance for Knoevenagel condensation reactions.