An Efficient Acetalization Method for Biomass-Derived Furfural with Ethanol Using gamma-Al2O3-Supported Catalysts

In this paper, the mono and bimetallic catalysts of Rh, Pt and Ni supported on gamma-Al2O3 were tested for the selective acetalization of furfural to produce furfural diethyl acetal in a mixture containing furfural diluted in ethanol. Ni1.5Rh1.5/gamma-Al2O3 exhibited the highest catalytic activity among all the tested catalysts, with an 85% furfural conversion and 100% furfural diethyl acetal selectivity at 100 degrees C and 30 min of reaction. Catalyst characterization showed that Ni1.5Rh1.5/gamma-Al2O3 presented particle sizes smaller than 1.2 nm, and the active metals were partially oxidized (Rh-III and Ni-II). A direct correlation between conversion and weak acidity of mono and bimetallic catalysts was obtained. Interestingly, despite exhibiting strong acidity, gamma-Al2O3 alone was little active in the process, which evidenced the role of the metal in acetalization of furfural into ethanol. In-situ DRIFTS experiments indicated that furfural is easily adsorbed onto these small particles as Ni delta+-(eta(1)-O,C-FFR) and Rh delta+-ethoxide species and rapidly transforms into furfural diethyl acetal and water. The catalyst was recycled four times, with a loss in catalytic activity of approximately 19%. The Ni1.5Rh1.5/gamma-Al2O3 catalyst was also successfully applied in the condensation of a variety of biomass derivatives.