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The Aldolization Nature of Mn4+-Nonstoichiometric Oxygen Pair Sites of Perovskite-Type LaMnO3 in the Conversion of Ethanol

Chen, Ren-Kai, Yu, Ting-Fang, Wu, Meng-Xun, Tzeng, Tai-Wei, Chung, Po-Wen, Lin, Yu-Chuan
ACS sustainable chemistry & engineering 2018 v.6 no.9 pp. 11949-11958
acetaldehyde, acidity, catalysts, condensation reactions, ethanol, manganese, oxygen, particle size
This study reports that the C2–C2 aldolization in ethanol conversion to C4 products, particularly butadiene, can be catalyzed by silica-supported LaMnO₃ catalysts. The concentration and strength of Mn⁴⁺ was discovered to be related to the particle size of supported LaMnO₃: the smaller the particle size is, the higher the concentration and acidity of Mn⁴⁺ are. The presence of high concentration and acidity of Mn⁴⁺ of small LaMnO₃ particles concurrently increases the amount of weak basic nonstoichiometric oxygen, with which the surface concentration of Lewis acid–base adducts can be elevated. The Mn⁴⁺/nonstoichiometric oxygen pair is intrinsically active in C2–C2 aldolization, and the concentration of the paired site is positively correlated to the selectivity of C4 products. By coreacting ethanol with its evolved intermediates, that is, acetaldehyde and crotonaldehyde, we discovered the aldol condensation of acetaldehyde molecules to be rate-limiting. Accordingly, a plausible mechanism of aldolization of acetaldehyde molecules into C4 products mediated by the Mn⁴⁺/nonstoichiometric oxygen adduct of LaMnO₃ was established.