Effect of HCl Treatment on Acidity of Pd/TiO2 for Furfural Hydrogenation

The acidity of supports can have a positive effect on their catalytic behaviors. Herein, the effects of HCl treatment of TiO2 on its acidic properties and catalytic activity were investigated. TiO2 was treated with various molar concentrations of HCl. Subsequently, Pd was deposited on the treated TiO2 via the deposition-precipitation method; here, the catalysts were denoted as Pd/xH-T, where X is the molar concentration of HCl. Evidently, the amount of strong acid in TiO2 increased with HCl treatment, whereas that in TiO2 treated with a high concentration (5 M) of HCl decreased. After Pd was supported, the amount of acid slightly decreased compared with that on the TiO2 support; however, the order of the acid amounts was similar. The strong acid density increased such that Pd/2H-T had the highest acid content, whereas Pd/5H-T had the lowest. The Pd/2H-T catalyst exhibited the highest selectivity for THFA (95.4%), thus confirming that the selectivity for THFA is correlated with the amount of strong acid. Thus, THFA selectivity is affected by the number of strongly acid sites.