A DFT study for in-situ CO2 utilization realized by calcium-looping dry reforming of methane based on Ni/CaCO3

The calcium-looping dry reforming of methane (CaL-DRM) process couples CO2 capture and dry reforming of methane process using Ni/CaO dual-functional material. This process in-situ converts CO2 captured by CaO through reacting with CH4, catalyzed by Ni, to produce syngas. However, researches on reaction mechanism for CaL-DRM are rare. In this work, the fundamental reaction mechanism of calcium-looping dry reforming of methane is elucidated by density functional theory (DFT) analysis. The energy barriers for elementary reactions involved in various potential pathways were investigated to determine the primary reaction pathway. The DFT analysis shows two possible reaction pathways for the CaL-DRM, with the CH* assisted CaCO3 dissociation pathway being the more favorable one. Along this pathway, CH4 undergoes three dehydrogenation steps to form CH*. Then, CH* reacts with the CaCO3* to produce CHO* and CaCO2*, accompanying the cleavage of one C-O bond in the carbonate. Afterwards, CHO* dissociates into CO* and H*. Finally, another C-O bond in CaCO2* breaks, generating CO* and CaO. Notably, CH4 reduces the energy barrier for CaCO3 dissociation from 3.47 to 2.733 eV. Moreover, the perturbation of electron clouds around O in CaCO3* in the presence of CH or C, as evidenced in electron density differential results, highlights the effective activation of C-O bond by CH or C, thereby promoting CaCO3 decomposition. This work provides further support for the potential mechanism for in-situ CO2 utilization achieved through CaL-DRM.