Abstract
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► Pd deposition was performed by mixing Pd precursors with citrate-functionalized TiO2. ► Strong interaction of citrate with Pd led to well dispersed systems. ► Tuning the Ti/citrate molar ratio controls Pd particle size. ► Possible formation of highly intrinsically active Pd/TiO2 catalysts.
One-pot deposition of Pd onto TiO2 has been achieved through directly contacting palladium(II) salt with nanosized functionalized TiO2 support initially obtained by sol–gel process using titanium isopropoxide and citric acid. Citrate groups act as functional moieties able to directly reduce the Pd salt avoiding any further reducing treatment. Various palladium salts (Na2PdCl4 and Pd(NH3)4Cl2·H2O) and titanium to citrate (Ti/CA) ratios (20, 50, and 100) were used in order to study the effect of the nature of the precursor and of the citrate content on the final Pd particle size and catalytic properties of the as-obtained Pd/TiO2 systems. Characterization was performed using N2 adsorption–desorption isotherms, ICP-AES, FTIR, XRD, XPS, and TEM. The as-obtained hybrid Pd/TiO2 catalysts were tested in the selective hydrogenation (HYD) of an α,β-unsaturated aldehyde, i.e. cinnamaldehyde. Citrate-free Pd/TiO2-based catalysts present lower selectivity into saturated alcohol. However, citrate-functionalized Pd/TiO2 catalyst seems to control the selectivity, the particle size and dispersion of Pd NPs leading to high intrinsic activity.