Ethanol steam reforming on Rh/Al2O3 catalysts

Ethanol steam reforming on Rh/Al2O3 catalysts has been the object of our research project. The mixture used for the research testing was prepared with a high water content (H2O/C2H5OH = 8.4 mol/mol) in order to simulate the composition of the ecological fuel product from vegetable biomass fermentation The experimental tests were carried out in a fixed bed reactor at a programmed temperature between 323 and 923 K. The maximum temperature (T = 923 K) is the standard working temperature of a molten carbonate fuel cell able to make direct use of the hydrogen produced for ethanol steam reforming. The reaction mechanism starts with the initial dehydrogenation and/or dehydration of the ethanol, followed by rapid conversion of the products into methane, carbon monoxide and carbon dioxide. The acid support (Al2O3) assists the dehydration of the alcohol, while all the other reactions are catalyzed by the Rh, although in different measures. For this reason, with increase in Rh content, there is also a progressive increase in the C-1 (CH4, CO, and CO2), while the Ct (ethylene, ethanol, and acetaldehyde) disappear gradually from the outlet gaseous stream. The acetaldehyde, that is produced by dehydrogenation, is formed during an intermediate stage, but rapidly decomposes to CH4 and CO when working at high temperatures. Traces of acetaldehyde and hydrogen in a ratio of 1:1 are also present in the reaction products when pure Al2O3 is used. However in this case the main product of the reaction is the ethylene obtained by dehydration on the acid sites of the Al2O3. Obviously the presence of the ethylene assists the formation of carbon whiskers very strongly, which after only a few hours can be easily seen on the depleted catalyst. Vice versa, in the presence of Rh at high temperatures (T = 923 K), coking does not occur and the catalyst maintains its activity for several hours transforming all the ethanol into C-1 and H-2.