Tham khảo tài liệu 'bioethanol part 15', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 270 Bioethanol due to the relatively complicated reaction networks involved originating from the increase of carbon atom. However the knowledge accumulated during the systematic explorations of the kinetic mechanisms occurring during MSR provides a valuable starting point for ESR researchers to expand upon. In recent years based on the observations obtained from both gas phase and sample surface several kinetic models have been proposed to simulate the mechanistic behaviors of various catalyst systems 128-132 which will facilitate better understanding of the reaction mechanisms. If the estimated values are in good consistency with the reported experimental results the assumed reaction pathways and ratedetermining step RDS will uncover the actual reaction mechanisms to a certain level. Furthermore the activation energy measured from this study provides the reference for molecular simulation. In addition the outcomes from this kinetic analysis will benefit the reactor design which can promote mass and heat transfer during reaction. Based on the TPD and DRIFTS results reported in 133 a possible reaction pathway for ethanol steam reforming over Co-based catalysts is proposed by our laboratories in . In Scheme 1 the reactant molecules EtOH and water diffuse from gas phase to the surface of the catalyst. The ethanol molecules adsorb dissociatively on the Co sites forming ethoxide species. Water on the other hand adsorbs on the support forming hydroxyl groups. The first H abstracted from ethanol can either form OH groups with the surface oxygen species or combine with hydrogen from H2O and form H2 Scheme 3 . Ethoxide species move to the interface of metal and oxide support and be oxidized by an additional hydrogen abstraction forming aceteldehyde Scheme 4 . Acetaldehyde molecules may lead to the formation of acetone through an aldol-condensation type reaction and acetone molecules are observed only in the gas phase. Acetaldehyde species have a short surface residence
