Oxidation catalysts based on ironporphyrin supported on diatomaceous earth.

The search for new and inventive catalysts that can mimetize certain reactions carried out by animal enzymes, such as by Cytochrome P450 and their synthetic models (for instance, synthetic porphyrins), is in the highlight for the last decades and equally important is the search for new matrices that can support these synthetic models. Not only the synthetic path to obtain the catalyst is important, but the conditions governing their optimal reaction pathways, such as pH or substrate concentration. Synthetic metalloporphyrins have been successfully used as biomimetic catalysts in many oxidation reactions. However, their high cost and the difficulties inherent to homogeneous catalysis have prevented their large-scale application. Catalyst heterogeneization aims to overcome these drawbacks in addition to mimicking enzyme site isolation, improving reaction selectivity. New matrices are essential to reach this target. Hybrid materials consisting of Diatomaceous Earth (DE) amino-functionalized with aminopropyltriethoxysilane (DE-APTES), followed by grafting with [meso-tetrakis(pentafluorophenyl) porphinato]iron(III), (DE-APTES-FeTFPP), have been here studied. The UV–Vis spectrum exhibited a Soret band at 416 nm, characteristic of ironporphyrin located in a confined space (the amount of FeFFPP per gram of DE was 20.0 mg/g). Leaching studies of FeTFPP from DE and DE-APTES confirmed that ironporphyrin was entrapped and not just adsorbed on the silica surface. IR spectroscopy confirmed that FeTFPP was grafted onto DE-APTES via the amine groups (amine band at 1570 cm-1). DE displayed typical quartz and cristobalite crystalline phases and amorphous porous silica, the intensity of its characteristic reflection at 2Ɵ = 22º decreasing in the presence of FeTFPP; the ironporphyrin influenced the organization of the material, as confirmed by SEM analysis. Tests using DE-APTES-FeTFPP as catalysts in the epoxidation of cyclooctene, showed complete selectivity to the epoxide. The degradation of caffeine, confirmed the ability of DE as a promising natural support for ironporphyrin catalysts. Caffeine degradation was influenced by pH, substrate and catalyst concentration.