“Doing more with less”: Ni(II)@ORMOSIL, a novel sol-gel pre-catalyst for the reduction of nitrobenzene

Reduction of nitrobenzene with NaBH₄ using zero-valent iron nanoparticles (ZVI-NPs) and NiCl₂·6H₂O incorporated in organically modified hybrid silica matrices as ZVI@ORMOSIL and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H⁺ of the ORMOSIL matrix with Ni^II. Ni(II)@ORMOSIL is a pre-catalyst that undergoes reduction by NaBH₄ by an in-situ reaction and promotes nitrobenzene reduction by the unconsumed NaBH₄, leading to sparing use of the catalyst. Ni(II)@ORMOSIL undergoes color change from green to black in this process, returning to a green hue after washing and drying. Nitrobenzene reductions were examined in aqueous acetonitrile solvent mixtures, and the reduction cascade produced the reaction end-products with catalytic implications. Plausible mechanisms of ZVI@ORMOSIL and Ni(II)@ORMOSIL catalyzed reductions of nitrobenzene are discussed. This work is the first to report M(II)@ORMOSIL pre-catalysts for in-situ reduction of nitrobenzene, and expands the scope of the ORMOSIL series of catalysts for the reduction of polluting compounds. This approach enables the development of catalysts that use very low concentrations of transition metal cations.