Unique Coordination Structure of Mo Species on MSilicalite-1 Robustly Boosting the Reaction Activity of Oxidative Dehydrogenative Coupling of Alcohols with Aromatic Diamines

Abstract

The synthesized mesoporous pure silica zeolite (MSilicalite-1) had abundant surface silanols that could interact appropriately with the Mo species, which was conducive to promoting the formation of numerous highly active octahedral Mo species in the form of Mo₇O₂₄^6– and Mo₈O₂₆^4– (Mo_oct.) on MSilicalite-1, robustly boosting the reaction activity with an initial reaction rate of 2.23 mmol·L^–1·min^–1 in the oxidative dehydrogenative coupling of alcohols with aromatic diamines, as compared to the Mo catalysts supported on MZSM-5 (0.66 mmol·L^–1·min^–1), γ-Al₂O₃ (0.28 mmol·L^–1·min^–1), and SiO₂ (0.14 mmol·L^–1·min^–1). This is because the formed Mo_oct. species had abundant oxygen-negative anions in the Mo–O–Mo bond, which benefited the chemisorption of benzyl alcohol through the oxygen anions binding to the benzylic carbon or benzylic hydrogen in benzyl alcohol, promoting the oxidation transformation to form a key intermediate of benzaldehyde under the assistance of another reactant of 1,2-diaminobenzene, inducing the formation of the final product benzimidazoles.