Ion induced promotion of activity enhancement of mesoporous manganese oxides for aerobic oxidation reactions

• We report synthesis of cation promoted mesoporous manganese oxides.
• Enhanced catalytic activity was observed due to cation promotion.
• Aerobic oxidations of alcohols and 1,3,5-trimethylbenzene were performed.
• Promoted materials displayed more basicity and accessible lattice oxygen.
• The developed process was less expensive, base free, and environmentally benign.

Inverse micelle templated mesoporous manganese oxide (University of Connecticut mesoporous material, UCT-1) and ion promoted mesoporous manganese oxides (UCT-18-X, X = Mg2+, Ca2+, K+, Na+ and Cs+) having trace amount of alkali metal ions as promoters with tunable porosity and crystallinity were synthesized. The synthesis was based on the use of inverse micelles as soft templates and unique NOx chemistry as established for recently discovered UCT materials. The materials were tested for selective aerobic alcohol oxidation and the catalytic activity followed the order of UCT-1 < UCT-18-Mg < UCT-18-Ca < UCT-18-K < UCT-18-Na < UCT-18-Cs. The catalytic activity was correlated to the promoter ion induced increase in basicity of the materials. The retention of an amorphous structure, low reducibility, and the effects of lattice oxygen are other key factors responsible for the enhanced catalytic activity. The UCT-18-Cs catalyst was found to oxidize various alcohols to corresponding aldehydes and ketones selectively (100% selectivity) with very high conversion (as high as 100%). The UCT-18-Cs also exhibited solvent free green oxidation of 1.3.5-trimethylbenzene to yield 3,5-dimethylbenzoic acid and (3,5-dimethylphenyl)methyl ester with >90% conversion and 90% selectivity for the acid and 9% selectivity for the ester.

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