Optimization of the Zr-loading on siliceous support catalysts leads to a suitable Lewis/Bronsted acid sites ratio to produce high yields to gamma-valerolactone from furfural in one-pot

The study for the production of gamma-valerolactone from furfural in one-pot has been carried out using ZrO2 supported on silica spheres. The catalysts synthesized were characterized by XRD, UV-vis, HR-TEM, N-2 adsorption, IR, pyridine adsorption-IR and NH3-TPD in order to determine their physicochemical characteristics. Both, Lewis and Bronsted acid sites are necessary to produce gamma-valerolactone from furfural, because they are involved in different steps of the reaction. Accordingly, a reaction mechanism has been proposed. Lewis acid sites of ZrO2 interacting with the -OH surface groups of the siliceous spheres can generate Bronsted acid sites in the supported Zr catalysts, which are absent in both pure ZrO2 and the silica spheres. Then, by controlling the amount of Zr in the supported catalysts, the relative amount of Lewis and Bronsted acid sites can be optimized to obtain the highest yields to gamma-valerolactone. The Zr-loading of the optimal supported catalyst was ca. 7 wt% Zr, which reached a gamma-valerolactone yield of 72.4 % after 8 h at 180 C using 2-propanol as a solvent and hydrogen donor.