A simple and convenient approach for preparing core–shell-like silica@nickel species nanoparticles: highly efficient and stable catalyst for the dehydrogenation of 1,2-cyclohexanediol to catechol
A simple and convenient approach denoted as gel-deposition–precipitation (G-D–P) for the preparation of core–shell-like silica@nickel species nanoparticles was studied systematically. Core–shell-like silica@nickel species nanoparticles consisted of a Si-rich core and a Ni-rich shell. The G-D–P process included two steps: one was the deposition–precipitation of nickel over the gelled colloidal silica particle, generating core–shell-like silica@nickel species nanoparticles, and the other was the aging period. It was found that the nickel phyllosilicate layer was formed mainly during the aging period and served as the protective cover to resist against aggregation of the nanoparticles, which could be utilized for regulating the dispersion of nickel over the silica@nickel species nanoparticles. In the present paper, the silica@nickel species nanoparticles were used as the catalysts for preparing catechol via dehydrogenation of 1,2-cyclohexanediol. Their catalytic activity and long-term stability were compared to those of a catalyst prepared by a conventional deposition–precipitation (D–P) approach. The higher activity and better stability of the title reaction over the silica@nickel species nanoparticles catalyst prepared by G-D–P than those over the catalyst prepared by D–P could be due to the higher dispersion of metallic nickel stabilized by the layers of nickel phyllosilicates. Moreover, it was found that the dehydrogenation of 1,2-cyclohexanediol to catechol was a structurally sensitive reaction.