Ethylbenzene oxidation by a hybrid catalysis system of reconstituted myoglobin and silica-protected PdAu nanoparticles under a hydrogen-oxygen mixed atmosphere

Abstract

C–H bond oxidation using molecular oxygen as a terminal oxidant is an important reaction in molecular conversions. This reaction is achieved by several enzymes such as cytochrome P450s in biological systems, whereas artificial catalytic systems for this reaction are limited. In this work, the oxidation of ethylbenzene was promoted by a hybrid catalysis system consisting of myoglobin reconstituted with manganese porphycene as an artificial peroxygenase in combination with PdAu nanoparticles encapsulated in hollow mesoporous silica spheres as a solid catalyst to produce hydrogen peroxide, respectively. Neither catalyst alone provides hydroxylated products. Favorable conditions for hydrogen peroxide generation and subsequent C–H bond hydroxylation are different from each other and require optimization of pH and salt concentration. The optimized conditions are found to be 0.5 atm of H2 and 0.5 atm of O2 at pH 8.5 in the presence of 10 mM NaCl. The total optimized turnover number of the hybrid catalysis system for ethyl benzene hydroxylation is 3.6, which is consistent with 97% of the turnover number value of the same reaction catalyzed by reconstituted myoglobin using 0.5 mM hydrogen peroxide under the hydrogen-oxygen mixed atmosphere. This finding indicates that the hybrid catalyst system operates without any negative effects for both catalytic reactions.