Description:
Sorption Enhanced Steam Methane Reforming (SESMR) provides a promising method for the production of high purity hydrogen by in-situ CO 2 capture. Ni-doped CaO (Ni-CaO) which combines catalytic and adsorption active sites can effectively improve the hydrogen production performance of SESMR reactions. It is difficult to determine the enhancement mechanism of Ni-CaO in SESMR simply by experiments. In this study, the reaction mechanisms of SESMR promoted by Ni in the presence of CaO were investigated by density functional theory (DFT) calculations. The possible reaction pathway was determined by analyzing the activation barriers along the seven possible reaction pathways in SESMR reaction. The SESMR reaction promoted by CaO was also studied as a comparison to clarify the catalysis of Ni. The results show that the SESMR reaction is more prone to proceed along with the CH 4 progressive dehydrogenation mechanism (path 1), which starts with first process of O-assisted methane cleavage from CH 4 to CH (CH 4 →CH 3 →CH 2 →CH). Subsequently, the dehydrogenation of CH leads to C, followed by successive oxidation to form CO. Finally, CO is oxidized to CO 2 by the direct oxidation path (CO→CO 2 ). The presence of Ni atoms allows the SESMR reaction rate limiting step to change from CH dissociation (on CaO surface) to CH 2 dissociation (on Ni-CaO surface). In comparison with the activation barrier of CH dissociation (3.215 eV), the SESMR reaction of the Ni-CaO surface is easier to occur with lower activation barrier of 2.448 eV. Besides, Ni reduces the adsorption energy of CH 4 (-0.106 eV) and H 2 O (-1.32 eV) as well as increases the adsorption energy of H 2 (-0.047 eV). Therefore, the calculation result reinforces the comprehension on the mechanism of Ni-CaO on SESMR and Ni improving CH 4 conversion rate and H 2 productivity efficiency