水滑石的合成及其对催化丙酮合成异佛尔酮的影响

Hydrotalcite synthesis and the effect on acetone catalytic condensation to isophorone

用共沉淀法合成镁铝水滑石,焙烧制得镁铝复合氧化物催化剂.采用连续微反装置,以丙酮缩合生成异佛尔酮为探针反应,探讨了镁铝水滑石的合成对镁铝复合氧化物催化性能的影响,采用XRD、TG-DTA等分析手段对催化剂前体镁铝水滑石进行表征.结果表明,镁铝水滑石的合成工艺对水滑石的微观晶体结构有较大影响,镁铝比是较为重要的影响因素,在镁铝比为1∶1时水滑石结晶度较好,晶形完整.活性评价结果表明,适宜的合成参数为:镁铝比为1∶1,金属离子总浓度为0.2 mol.L-1,沉淀剂用量为1.5倍.对优化合成工艺条件下制备的催化剂进行热重分析,结果显示:焙烧温度超过500℃时,水滑石的层状结构将被完全破坏,记忆效应将不再起作用,热稳定性大大提高.与活性评价结果关联,确定镁铝水滑石的适宜焙烧温度为550℃.丙酮在此条件下合成的催化剂上转化率为19.74%,异佛尔酮选择性为55.91%.

In this paper, we first prepare the Mg-Al LDHs by using co-precipitation method, and then derive Mg-Al composite oxides from the calcination of Mg-Al LDHs. Via continuous micro-reactor to generate acetone condensation reaction of isophorone as a probe, the effect that the Mg-Al hydrotalcite synthesis of mixed oxides on their catalytic properties is discussed. Moreover, the characteristics of Mg-Al LDHs and Mg-Al composite oxides are analyzed by useing XRD, TG-DTA. The experimental results demonstrate that the synthesis of hydrotalcite has a greater impact on the micro-crystal structure of hydrotalcite. When Mg/A1 = 1 ： 1, Mg-Al hydrotalcite has good crystallinity and crystal shape complete. Meanwhile, the optimal preparation parameters are obtained. Under optimal synthesis conditions, the catalyst TGA results show that the layered hydrotalcite structure is completely destroyed when calcination temperature is over 500℃, and the memory effect is not available, Meanwhile, thermal stability significantly improved. According to the active evaluation results, the suitability temperature for hydrotalcite calcination is determined to be 550℃. Under these conditions, the ratios for acetone conversion and isophorone selectivity are 19.74% and 55.91%, respectively.