Green and Efficient Hydrogenation of 2-Ethyl-2-Hexenal to 2-Ethylhexanol over Ni/TiO₂ in Isopropanol and Its Kinetics

The effect of solvents on the catalytic performance of the Ni/TiO2 catalyst for the liquid-phase hydrogenation of 2-ethyl-2-hexenal to 2-ethylhexanol was investigated. Using water as a solvent, the hydrogenation rate of 2-ethyl-2-hexenal was reduced because of the incompatibility between water and organic material. Using nonpolar cyclohexane as a solvent, the hydrogenation of 2-ethyl-2-hexenal was neither promoted nor hindered while polar solvents ethanol, 2-butanol, cyclohexanol, and isopropanol improved the selectivity of 2-ethylhexanol. Especially using isopropyl alcohol as a solvent, the catalytic performance of Ni/TiO2 was the highest. In addition, too high a Ni loading, calcination temperature, and reduction temperature led to the aggregation and growth of the Ni grain, which was not conducive to the hydrogenation reaction. Therefore, the conversion of 2-ethyl-2-hexenal was 100.0% and the selectivity of 2-ethylhexanol was 96.4% under suitable catalyst preparation and reaction conditions in isopropanol. After five cycles, the catalytic performance of the catalyst did not decrease significantly. The kinetics study showed that the hydrogenation of 2-ethyl-2-hexenal to 2-ethylhexanal in isopropanol and the hydrogenation of 2-ethylhexanal to 2-ethylhexanol in isopropanol were first-order irreversible reactions.