Dioxygen Activation by a Hexagonal SrMnO₃ Perovskite Catalyst for Aerobic Liquid‐Phase Oxidation

Abstract

Heterogeneous catalysts, which allow a reductive activation of dioxygen (O2) under mild reaction conditions, are promising candidates for highly efficient aerobic oxidation. An effective hexagonal SrMnO3 (SMO) perovskite catalyst for liquid‐phase selective oxidation with O2 was successfully synthesized by the polymerized complex method. The activity of SMO for the aerobic oxidation of alcohols was higher than those of typical manganese oxide‐based catalysts and was heterogeneous, so that the recovered catalyst could be reused without heat treatment under oxidative conditions while keeping its high catalytic performance. The reversible reaction on the surface Mn species on SMO with O2 leads to the formation of Mn–superoxo species, which catalyze the selective oxidative transformation of various types of organic substrates into the desired oxygenated or dehydrogenated products.

Aerobic Oxygenation of Alkylarenes over Ultrafine Transition‐Metal‐Containing Manganese‐Based Oxides

“…Among the catalysts reported previously for the oxygenation of 1 a , nano‐sized hexagonal SrMnO 3 perovskite exhibited an excellent catalytic activity under relatively mild conditions (60–120 °C, 1 atm O 2 , no additives) . The oxygenation of 1 a using Ni‐MnO x was performed under the same reaction conditions as those reported for the SrMnO 3 ‐catalyzed oxygenation; the oxygenation of 1 a using Ni‐MnO x was completed more rapidly (within 1 h) than that using SrMnO 3 (within 8 h), which shows the effectiveness of Ni‐MnO x . Hereafter, we mainly utilized the most active Ni‐MnO x catalyst for further detailed investigations.…”

“…The Mn center is thought to accept an electron effectively by the SET mechanism from the n orbital of heteroatoms or the π orbital of aromatic rings . Alternatively, active oxygen species generated on the surface of the catalyst or oxygen atoms adjacent to the metal center are thought to abstract a hydrogen atom from weak C−H bonds directly by the HAT mechanism . To distinguish the predominant mechanism in the Ni‐MnO x ‐catalyzed oxygenation, the reactions of alkylarenes 4‐ethylanisole and 4‐isopropylanisole were conducted in the presence of Ni‐MnO x .…”

“…[16][17][18][19][20][21][22][23][24] In particular,t heir oxidation catalysis is of great interest, and thus numerousa erobic oxidation systemst hat use catalysts based on manganese oxide have been developed. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] As fora lkylarene oxygenation, several catalysts based on manganese oxide have also been reported to be highly effective (Table S2); [40][41][42][43][44] for example, Hara and colleagues reported recently that nanosized hexagonal SrMnO 3 perovskite exhibits ah igh catalytic performance for alkylarene oxygenation under relatively mild conditions (60-120 8C, 1atm O 2 ,n oa dditives). [43,44] In this study,w ep repared heterogeneous catalysts based on manganese oxide for alkylarene oxygenation and we considered the following factors.…”

Heterogeneously‐Catalyzed Aerobic Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid with MnO2

“…The use of Mn 2+ ‐ and Mn 3+ ‐containing manganese oxides (Mn 2 O 3 , Mn 3 O 4 , and MnO) led to extremely low yields of FDCA (0–5 % yield) and HMF conversions of 17–58 % (Figure S3) . The hexagonal SrMnO 3 catalyst, which exhibits high catalytic activity for the aerobic oxidation of various organic substrates, including alcohols and alkylarenes, was less effective than MnO 2 for the oxidation of HMF to FDCA with 58 % yield . Similarly, other metal‐oxide catalysts including Fe 2 O 3 , Fe 3 O 4 , FeO, Co 3 O 4 , CoO, NiO, CuO, and Cu 2 O were almost inactive, and the HMF conversion was moderate (16–40 %).…”

Catalytic Aerobic Oxidation of C(sp3)−H Bonds

“…The authors found that Au was superior to Pd or aAu-Pd alloy and that oxides provide ab etter support than graphite.O ther oxides tested were TiO 2 and CeO 2 .A th igher temperatures the support itself can catalyze oxidation. [91] Although they are typically employed at high temperatures,f or example in exhaust gas purification, they can also be employed at mild temperatures.Aporous [85] Aselectivity shift from ketone and alcohol towards epoxide was observed when the ring size increases.This shift in selectivity can be attributed to the inherent reactivity of the different rings.…”