Selective oxidation of 1-octanol over gold supported on mesoporous metal-modified HMS: The effect of the support

Selective oxidation of long chain alkanols (₊C₈₊) has deserved much less attention than that of more reactive benzylic or C ₁-C₄ aliphatic alcohols. Supported gold nanoparticles (NP) are active for the oxidation of alcohols under green chemistry conditions, and high surface supports are used to maximize and stabilize their dispersion. In this work, we investigate hexagonal mesoporous silicas (HMS), pure or modified with metal cations having redox properties (Ce, Fe), as supports of gold NP catalysts for the aerobic oxidation of 1-octanol under green process conditions. Two ways of support modification were used, say, by introducing the modifying cations during the HMS synthesis or by post-synthesis impregnation. Octanal was the main product on every catalyst under the conditions tested (80 C, oxygen flow at atmospheric pressure, solvent base-free heptane); the ester also formed but no acid was detected. Both the composition and the preparation method of the support influenced the activity and stability of the catalysts: the best performance was found on catalysts with post-synthesis impregnated supports, where additional phases of the corresponding oxides are detected by XRD (X-ray diffractometry). IR (infrared) studies of CO adsorption on the catalysts revealed that is due to the different nature of the Au NPs, which are smaller (or positively charged) and preferentially deposited on the modifier oxidic phase in these catalysts.