Hydrogen production by ethanol steam reforming over Rh nanoparticles supported on lanthana/silica systems

The aim of the present work was to investigate Rh nanoparticle catalysts supported on La2O3–SiO2, with different contents of La2O3, in the ethanol steam reforming reaction. The size of Rh particles was determined by both XPS, applying the Davis model, and CO chemisorption measurements. Particle sizes between 1.2 and 3 nm were estimated with these techniques. The catalyst with 15 wt.% of La2O3 was the most stable one under the different reaction conditions under study, i.e. 773 K and water to ethanol molar ratios of 3 and 5. In order to explain the deactivation observed in the other catalysts, the samples used in the reaction were characterized by XPS, TEM and in situ Raman spectroscopy. The TEM results allowed a direct visualization of the carbon deposits that presented different degrees of catalyst coverage. The surface of the most stable catalyst was not fully covered by carbon while the Rh/La2O3(40)–SiO2 sample, which deactivated partially, exhibited a carbon layer uniformly distributed over the surface. The oxidation of the carbon deposits was analyzed using in situ Raman spectroscopy. Results were in agreement with those obtained by TEM microscopy. DRIFTS experiments under reaction conditions suggested that the direct decomposition of ethoxy species would produce hydrogen, CO, and CHx species, which could result in carbon formation.