The reusability of methylaminopropyl active sites grafted on mesoporous amorphous silica, either with cooperative silanol groups or trimethylsilated, was assessed in the aldol reaction of acetone with 4-nitrobenzaldehyde. Raman, ¹³C NMR, and UV–Vis spectroscopy demonstrated the presence of stable enamines on the spent catalysts. These enamines are produced as a side product from iminium intermediates in the catalytic cycle. Water co-feeding enhances the desorption of the iminium intermediates and, hence, suppresses the formation of these stable enamine species. The reusability of the cooperative catalyst increased to 70% with co-feeding 0.69 wt% water, while an almost complete reusability was achieved for the trimethylsilated catalyst. Continuous-flow experimentation showed that the cooperative effect of the silanol groups was lost during the first 7 h on-stream, yet activity losses continued, most likely due to silica hydrolysis. Activity losses persisted on the more hydrophobic trimethylsilated catalyst, but were significantly less pronounced.

在丙酮与4-硝基苯甲醛的醛醇缩合反应中评估了接枝到介孔无定形二氧化硅上的甲基氨基丙基活性位点的可重用性，该活性位点具有协同的硅烷醇基或三甲基甲硅烷基化。^13岁的拉曼13 C NMR和UV-Vis光谱证明废催化剂上存在稳定的烯胺。这些烯胺在催化循环中由亚胺中间体作为副产物产生。水共同进料增强了亚胺中间体的解吸，因此抑制了这些稳定的烯胺类的形成。通过共同进料0.69 wt％的水，协同催化剂的可重复使用性提高到70％，而三甲基硅烷基化催化剂则达到了几乎完全的可重复使用性。连续流实验表明，在运行的最初7小时内，硅烷醇基团的协同作用消失了，但活性损失仍在继续，这很可能是由于二氧化硅的水解所致。活性损失在疏水性更强的三甲基硅烷基化催化剂上持续存在，但明显不那么明显。