Kinetic analysis of Phenol Steam Reforming over Rh and Ni-Co based catalysts: identification of reaction’s pathway.

Great research efforts have been made during the last decades for the development and production of sustainable energy through renewable sources.Hydrogen has been considered a clean fuel and it can be produced from biomass,whose pyrolysis leads to the production of bio-oil that contains many components,which are the most renewable energy carriers.Phenol is the major component of the bio-oil and its catalytic steam reforming provides a promising technique for hydrogen production.The present work provides an extensive kinetic study of the mechanisms that occurs in the PSR,where the effect of temperature,space-time and partial pressure of the reactants(phenol and water)is investigated using two different catalysts over the same support.Due to the good metal-support interaction,Rh and Ni-Co active metals and γ-Al2O3 support have been selected and they were found to be appropriate catalysts with long-term stability for the hydrogen production via PSR,with Rh presenting the better performance in respect to transient metal-based catalysts.Identification of primary and secondary products revealed the reaction mechanism to be affected by the metal.On Rh, phenol is adsorbed with its aromatic ring in parallel with Rh,suggesting that the C-C bond activation is leading the reaction mechanism;on Ni-Co is observed the phenol dissociative adsorption producing phenoxyl and benzene species,suggesting the O-H and C-O bond activation happens first,followed by decomposition and reforming reactions.At lower temperatures,phenol dehydrogenation,dehydroxylation and decomposition were found to be the main reaction pathways,whereas at higher temperatures reforming and water gas shift reactions became enhanced.The excess of water was able to promote the WGS reaction.Time-on-stream studies at 500°C revealed Rh/γ-Al2O3 to have a good balance between stability,activity and selectivity.Oxidation of spent catalysts were also performed,in order to identify the type of carbonaceous deposits.