CoxFe1-xAl2O4+δ composite oxides supported Pt nanoparticles as efficient and recyclable catalysts for the liquid-phase selective hydrogenation of cinnamaldehyde
Abstract CoxFe1-xAl2O4+δ composite oxides were prepared using a sol-gel method with glucose as hard template. Pt nanoparticles supported on CoxFe1-xAl2O4+δ were employed for the liquid-phase selective hydrogenation of cinnamaldehyde (CAL) to yield the desired cinnamyl alcohol (COL). The activity increased with the x value; while the selectivity to COL almost kept above 90% despite of different x values. Upon investigation of kinetic behaviour with Pt/Co0.5Fe0.5Al2O4+δ as a model catalyst, the initial activity (in terms of TOF, defined as the converted CAL molecules per surface Pt atoms per second) of 4.1 s−1 was furnished. As for the selectivity to COL, it almost kept around 95% at whatever CAL conversions despite of the reaction temperatures. Pt/Co0.5Fe0.5Al2O4+δ catalyst can also be recycled for at least 10 times without obvious loss in activity or selectivity toward COL. This suggests that the active sites on the Pt/Co0.5Fe0.5Al2O4+δ catalyst preferentially adsorb and activate CAL via the terminal carbonyl groups. XPS analyses, H2-TPR, and CO-IR studies reveal that the intimate contact of Pt nanoparticles with FeOx or CoOx plays an important role in determining the catalytic performance of the Pt/CoxFe1-xAl2O4+δ catalysts. The Pt δ+/Pt0 ratio increased with the x value so that the Pt/CoAl2O4 was the most active among the Pt/CoxFe1-xAl2O4+δ catalysts.