Effect of Rhenium on the Catalytic Activity of Activated Carbon-Supported Nickel Applied in the Hydrogenation of Furfural and Levulinic Acid

This work evaluates the performance of activated carbon-supported Ni and Re catalysts in the hydrogenation of furfural and levulinic acid. The increase in Re content enhances Ni dispersion, decreases Ni reducibility and increases acidity. The Lewis acidity on the catalysts was attributed to unreduced Ni and Re species, while the Bronsted acidity, to Re–OH species formed in the presence of water. In the furfural hydrogenation, all the bimetallic catalysts were more selective to furfuryl alcohol (86–91%) than the monometallic materials. Low temperature and high pressures enhance selectivity to furfuryl alcohol. Concerning the conversion of levulinic acid to γ-valerolactone, the bimetallic catalysts also showed higher performance than the monometallic materials, with rates of levulinic acid conversion around four times superior. High temperature enhances levulinic acid conversion, and the selectivity to γ-valerolactone does not depend on pressure (> 97% for all conditions). The bimetallic catalyst containing 5.0 wt% Ni and 10.0 wt% Re was the most efficient one for both reactions. In this sense, we prepared this catalyst at different calcination temperatures (350 and 500 °C) and showed this is an important parameter for the catalyst stability. After four reuse cycles, in both reactions, the catalyst calcined at 350 °C lost considerable activity (loss of activity > 50%), while the catalyst calcined at 500 °C was considerably more stable. Catalyst deactivation was caused by leaching of the metallic active phase. The bimetallic Ni–Re/C catalysts calcined at high temperatures are promising materials for the hydrogenation of furfural and levulinic acid.