Nickel Nanoparticles for Liquid Phase Toluene Oxidation – Phenomenon, Opportunities and Challenges.

Effective oxidative transformation of toluene into valuable products was achieved under solvent‐free reaction conditions with as‐prepared nickel nanoparticles as heterogeneous catalysts in liquid phase. The crystalline structure and size of the as‐prepared nanoparticles were confirmed by X‐ray diffractometry (XRD) and dynamic light scattering (DLS). The catalytic implications of the different crystalline forms (face‐centred cubic: fcc; hexagonal close‐packed: hcp) of these nanocatalysts were investigated. The product selectivity of toluene oxidation was found to vary depending on the crystalline forms of the catalyst. Fcc nanocatalysts showed remarkable chemoselectivity (83 mol %) for the product benzyl alcohol and were readily reusable. In contrast, the hcp Ni phase showed reasonable reusability but lower chemoselectivity (29 mol %) compared to its fcc counterpart. Moreover, the simple organic solvents used had a remarkable effect on the crystal structure and phase purity of the Ni nanocrystals, which also affected the catalytic process. [ABSTRACT FROM AUTHOR]