Hydrogen production from ethanol on Rh/MgO based catalysts. The influence of rhodium precursor on catalytic performance

The influence of the metal precursor on the catalytic behaviour of Rh/MgO catalysts in steam reforming of ethanol was investigated. Rhodium nitrate and acetylacetonate, having different chemical properties, have been used as hydrophilic and hydrophobic precursors, respectively. More highly dispersed catalysts were obtained using Rh-nitrate, while catalysts prepared with Rh-acetylacetonate show higher stability being generally less affected by coke formation. Catalytic tests performed at molten carbonate fuel cell (MCFC) operative conditions (TR = 923K) clearly show a structure-sensitive reaction since the turnover frequency (TOF) significantly increases with the mean Rh particle size. Thermodynamic considerations on the basis of the outlet composition allowed to calculate the experimental equilibrium constant (Kexp) for (i) methane steam reforming (MSR), (ii) water-gas shift (WGS), (iii) methane pyrolysis and (iv) Boudouard reactions. By comparing Kexp with the equilibrium provided mass action ratios (Keq), we suggest that only WGS is fully equilibrated and that coke is formed mainly through methane pyrolysis.