Influence of composition and preparation method on the activity of MnOx/Al2O3 catalysts for the reduction of benzaldehyde with ethanol Original Research Article

Two series of MnOx/Al2O3 catalysts with varying Mn loading (0–1.2%, w/w Mn) prepared by equilibrium deposition filtration (EDF) and wet impregnation (WI) methodology were used for studying the influence of the composition and the preparation method on their activity for the reduction of benzaldehyde with ethanol. The prepared catalysts were characterized by BET measurements, X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy. It was found that following EDF methodology, the deposition of MnOx species on the alumina takes place via adsorption of [Mn(H2O)6]2+ and [Mn–Ac]+ species on the negatively charged surface sites. On the contrary, following wet impregnation the deposition takes place mainly via precipitation in the step of the solvent evaporation. The extent of the interactions exerted between the support and supported phase is higher in the EDF samples. These interactions created during the impregnation step were detected by DRS after drying and calcination. Higher dispersion of the MnOx phase is achieved when it is deposited on the γ-Al2O3 surface by the EDF than the WI method. The catalysts of the first series exhibited higher activity related well with the dispersion of MnOx supported nano-particles.