In a number of heterogeneous catalysis processes, the promotion effect toward active sites is of vital importance and remains a challenge to obtain largely-improved catalytic performance. Herein, rehydrated Ca₄Mn_xAl-layered double hydroxides (denoted as re-Ca₄Mn_xAl-LDH) were prepared based on a structure memory effect of LDH precursors, which exhibited extremely high heterogeneous catalytic performance for the aldol condensation reaction, with the assistance of the promotion effect of Mn. A combination study including XRD, EXAFS, XPS, CDCl₃-FTIR and DFT calculations confirms that re-Ca₄Mn_xAl-LDH samples with Ca–O–Mn^IV structure show a highly-exposed Ca²⁺ s-orbital and strengthened coordination between Ca²⁺ with 7-fold OH⁻, providing a weakened Brønsted basic site compared with the reference sample re-Ca₄Al-LDH. The optimized re-Ca₄Mn_0.5Al-LDH catalyst exhibits prominent catalytic performance toward the condensation of isobutyraldehyde (IBD) and formaldehyde (FA) to produce hydroxypivaldehyde (HPA), with a HPA yield of 70.3%. This is significantly higher than re-Ca₄Al-LDHs (63.3%) and even comparable to the level of liquid alkali catalysts (73.2%). Studies on the structure–property correlation reveal that the weakened basic site originating from Ca–O–Mn^IV serves as a promoted active center, which accelerates the product desorption and thus largely improves HPA selectivity. This promoted re-Ca₄Mn_0.5Al-LDH catalyst can be potentially applied as a promising candidate in heterogeneous aldol condensation reactions.

中文翻译：

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CaMnAl-水滑石固体碱性催化剂，可与液态碱催化剂相比，可进行羟醛缩合反应

在许多非均相催化过程中，对活性位的促进作用至关重要，并且对于获得大大提高的催化性能仍然是一个挑战。在此，根据LDH前体的结构记忆效应，制备了复水化的Ca ₄ Mn _x Al层状双氢氧化物（表示为re-Ca ₄ Mn _x Al-LDH），该化合物对醛醇缩合反应表现出极高的非均相催化性能，借助锰的促进作用。包括XRD，EXAFS，XPS，CDCl ₃ -FTIR和DFT计算在内的组合研究证实，使用Ca–O–Mn ^IV的re-Ca ₄ Mn _x Al-LDH样品结构示出了高度暴露的Ca ²⁺的Ca之间s轨道和加强协调²⁺ 7倍OH ^- ，与参考样品重新钙相比提供削弱布朗斯台德碱性位点₄的Al-LDH。优化的re-Ca ₄ Mn _0.5 Al-LDH催化剂对异丁醛（IBD）和甲醛（FA）缩合生成羟基戊醛（HPA）表现出突出的催化性能，HPA收率为70.3％。这大大高于re-Ca ₄ Al-LDHs（63.3％），甚至可以与液态碱催化剂的水平（73.2％）相提并论。对结构-性质相关性的研究表明，弱碱性位点源自Ca-O-Mn ^IV用作促进的活性中心，可加速产物的解吸，从而大大提高HPA的选择性。这种促进的re-Ca ₄ Mn _0.5 Al-LDH催化剂可潜在地用作非均相羟醛缩合反应中的有希望的候选物。