On the catalytic properties of mixed oxides obtained from the Cu-Mg-Al LDH precursors in the process of hydrogenation of the cinnamaldehyde

Catalytic hydrogenation of cinnamaldehyde (CNA) was investigated over oxidic materials obtained by the calcination of Cu-Mg-Al layered double hydroxide (LDH) precursors. A series of precursors with different Cu/Mg ratios (with a constant M 2+/Al 3+ ratio) were prepared by coprecipitation (under low supersaturation) and heated under reductive atmosphere until 623 K in order to avoid the formation of Cu-based spinels and to reduce the copper cations. The presence of Mg noticeably enhanced the selectivity of Cu-based catalysts with respect to the hydrogenation of the carbonyl group relative to the favoured hydrogenation of the CC bond. Moreover, the self-condensation of hydrocinnamaldehyde (HCNA) and the cross-condensation of hydrocinnamaldehyde with cinnamaldehyde were also observed especially when the basic sites of LDH structures are preponderant over hydrogenation species. Finally, all that reaction from CNA are of great interest for getting information about: (i) basic sites involved in condensation of CNA and HCNA; and (ii) active species for selective hydrogenation of CNA to cinnamyl alcohol (CNOL) which seem in strong interaction with the first ones.