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.
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