Selective hydrogenation of cinnamaldehyde with PtFe_x/Al₂O₃@SBA-15 catalyst: Enhancement in activity and selectivity to unsaturated alcohol by Pt-FeO_x and Pt-Al₂O₃@SBA-15 interaction

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) was conducted over a series of FeO_x-doped Pt catalysts supported on a 15 wt% Al₂O₃@SBA-15 composite (15AS). It was found that the addition of FeO_x to the catalyst greatly improved its performance. With an optimal Fe/Pt molar ratio of 0.25, the PtFe_0.25/15AS catalyst reached a maximum reaction rate (defined as moles of converted CAL per gram of Pt per hour) of 13.93 mol g_Pt⁻¹ h⁻¹ with 76.9% selectivity to COL. Additionally, the PtFe_0.25/15AS catalyst afforded the highest TOF value (defined as moles of converted CAL per mole of Pt active sites per second) of 1.54 s⁻¹. X-ray photoelectron spectroscopy analyses and H₂ temperature-programmed reduction and CO diffuse-reflectance infrared Fourier-transformation spectroscopy studies reveal that there is strong interaction between Pt nanoparticles and Al₂O₃@SBA-15 composites and also between Pt and FeO_x, resulting in Pt species with a positive charge being dominant in PtFe_0.25/15AS catalysts. Therefore, Pt species with positive charges, together with FeO_x species, are beneficial for preferential adsorption and activation of carbonyl bonds of CAL, so that the activity and selectivity to COL were improved by PtFe_x/15AS catalysts (x represents the Fe/Pt molar ratio).