Selective hydrogenation of cinnamaldehyde with NixFe1-xAl2O4+δ composite oxides supported Pt catalysts: CO versus CC selectivity switch by varying the Ni/Fe molar ratios

Due to coexistence of two conjugated unsaturated functional groups in cinnamaldehyde (CAL), exploring efficient catalysts with desirable selectivity to highly value-added products is still challengeable for the selective hydrogenation of CAL. Herein, Ni x Fe 1- x Al 2 O 4+ δ spinel composite metal oxides (SCMOs) supported Pt catalysts were developed and proved to be active and selective for the selective hydrogenation of CAL. Moreover, the selectivity switch can be realized just by changing the Ni/(Fe + Ni) molar ratios in Ni x Fe 1- x Al 2 O 4+ δ SCMOs. As a result, the excellent cinnamyl alcohol (COL) selectivity (~92.2%) and hydrocinnamaldehyde (HCAL) selectivity (~80.7%) were achieved on Pt/FeAl 2 O 4+ δ and Pt/NiAl 2 O 4+ δ , respectively. Based on the kinetic investigation of further hydrogenation of semi-hydrogenated product, the reason for the selectivity switch with Pt/Ni x Fe 1- x Al 2 O 4+ δ was revealed. In combination with detailed characterization, the excellent COL selectivity on Pt/FeAl 2 O 4+ δ can be attributed to more Pt(1   1   1) facets and FeO x species which can facilitate the preferential activation of C O bonds; while the high HCAL selectivity on Pt/NiAl 2 O 4+ δ is owing to the fact that there are more low coordinated active sites and two neighbouring Pt sites.