Catalysts based on Rh(III)-hexamolybdate/γ-Al2O3 and their application in the selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde

Several catalysts based on [RhMo6O24H6]3− (RhMo6) heteropolyanion supported on γ-Al2O3 with different textural properties were prepared, characterized and tested in the liquid-phase hydrogenation of cinnamaldehyde. The characterization of pure and supported systems was carried out using several techniques including XRD, SEM-EDS microscopy, Raman microprobe, X-ray photoelectron spectroscopies and temperature programmed reduction (TPR). The catalytic performance was monitored by conversion of the starting cinnamaldehyde as a function of time: the initial activities represented as the turnover frequency (TOF), were measured considering the surface Rh atoms. The planar heteropolyanion RhMo6/(EI) based systems showed enhanced catalytic activity over the RhMo conventional catalyst obtained by successive impregnation of both transition metal ions (Rh(III) chloride and heptamolybdate). The selectivity for the RhMo6 systems was mainly toward HCAL unlike the conventional catalyst which showed selectivity toward CA. This study also showed a synergetic effect between Rh and Mo through which Rh promoted Mo reducibility.