Journal
APPLIED CATALYSIS A-GENERAL
Volume 511, Issue -, Pages 78-86Publisher
ELSEVIER
DOI: 10.1016/j.apcata.2015.12.002
Keywords
Epoxidation; Hydrogen peroxide; Supported catalyst; Hammett relationships; Manganese
Categories
Funding
- Dow Chemical Company
- NSF [CBET-0933667, DMR-0521267]
- NSF-NSEC
- NSF-MRSEC
- Keck Foundation
- State of Illinois
- Northwestern University
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Monomeric and dimeric complexes of Mn 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) were immobilized under reaction conditions onto solid supports to create heterogeneous catalysts for epoxidation with H2O2. These solid supports consist of activated carbon or silica grafted or co-condensed with benzoic or C3/C4 acids that function both as tethering points and as required co-catalysts. Immobilized catalysts were as much as 50-fold faster than the analogous soluble system, and an immobilized, dimeric Mn(tmtacn) complex with a solid benzoic acid co-catalyst gave the highest yields to epoxide. A Hammett study on the catalytic epoxidation of a series of styrenes showed weak increases in yield for more electron withdrawing p-substituents reactants for both immobilized complexes, which runs counter to previous observations with analogous homogeneous catalysts, and which appears to reflect a previously unappreciated tradeoff between the intrinsic epoxidation reactivity and strong catalyst inhibition by styrene oxides and glycols. Finally, these catalysts were tested with a variety of solid-co-catalysts, and were successfully utilized in the challenging epoxidation of divinylbenzene to industrially-useful divinylbenzene dioxide using a cascade of two catalyst charges. (C) 2015 Elsevier B.V. All rights reserved.
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