Acquiring Clean and Highly Dispersed Nickel Particles (ca. 2.8 nm) by Growing Nickel-Based Nanosheets on Al2O3 as Efficient and Stable Catalysts for Harvesting Cyclohexane Carboxylic Acid from the Hydrogenation of Benzoic Acid

By growing nickel-based nanosheets on Al 2 O 3, a nickel catalyst present as clean uniform nickel particles ca. 2.8 nm in size was feasibly produced from the two-dimensional (2D) nanoprecursor predispersing strategy, and investigated for the hydrogenation of benzoic acid to cyclohexane carboxylic acid. A 98% yield of cyclohexane carboxylic acid and a 15–40-fold enhanced turnover frequency (TOF) value (31.4 s –1 ) were achieved with the catalyst. These values were superior to those achieved (yield = 28%–40%, time of flight TOF = 0.8–2.0 s –1 ) for traditional catalysts with larger nickel particles (ca. 5.2–6.8 nm); interestingly, the superior activity was re-examined, because of the well-maintained size of the catalyst after continuous catalytic recycling. The kinetic measurements further illuminated that the reaction activation energy could be clearly decreased by employing smaller nickel particles, which could be responsible for the dramatic TOF enhancements. These results also suggest that the hydrogenation with a nickel-based catalyst could be a structure-sensitive catalytic process.