Aqueous-phase hydrogenation of α-pinene catalyzed by Ni-B alloys loaded on a Janus amphiphilic carbon@silica nanomaterial

Abstract

A Janus amphiphilic carbon@silicon double-framework nanomaterial having an inner cavity, a hydrophobic N-doped carbon inner layer, and a hydrophilic silica outerlayer was prepared. Ni-B alloy nanoparticles were loaded on the amphiphilic carbon@silicon nanomaterial and used for catalyzing α-pinene hydrogenation in aqueous media. The hollow structure of the nanomaterial yielded a large specific surface area, which was beneficial for mass transfer and substrate enrichment, the doping of N atoms in the inner carbon skeleton allowed the attachment of additional metal nanoparticles, and the hydrophilic silica outer shell improved the stability and dispersion of the catalyst in the aqueous system. Crucially, in a water/oil two-phase reaction system, the amphiphilic nanocatalyst acted as a solid foaming agent, thus promoting the dissolution of H2 and substrate contact. Further, the synergy between Ni and B significantly improved the catalytic activity, and a kinetic study revealed the low activation energy for α-pinene hydrogenation over the prepared catalyst. DFT calculations indicate the transition states with low energy barriers. Further, the catalytic activity of our non-noble-metal nanocatalyst was comparable to that of noble metal Ru and Pd catalysts. Under mild conditions (80 °C, 1.0 MPa H2, 3 h), 99.0% α-pinene was converted to cis-pinane with 98.5% selectivity, and the developed amphiphilic Ni-B nanocatalyst also showed excellent recyclability as a result of the high dispersion and stability of the Ni-B nanoparticles on the carbon@silicon nanomaterial. The study provides a new green and efficient way for the deep processing and utilization of turpentine resources, and provides a guidance for the expansion of water-phase non-noble metal catalytic reaction types.