Enhanced performance and selectivity of CO2 methanation over g-C3N4 assisted synthesis of NiCeO2 catalyst: Kinetics and DRIFTS studies. (9th August 2018)

• Record Type: Journal Article
• Authors: Yu, Yang; Chan, Yi Meng; Bian, Zhoufeng; Song, Fujiao; Wang, Juan; Zhong, Qin; Kawi, Sibudjing
• Is Part Of: International journal of hydrogen energy. Volume 43:Number 32(2018)
• Page Start: 15191
• Page End: 15204
• Publication Date: 2018-08-09
• Subjects: CO2 reduction -- CeNi catalyst -- g-C3N4-modification -- In-situ DRIFTS -- Kinetics; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2018.06.090
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: The hydrogenation of CO2 on CeNi catalyst modified with g-C3 N4 (CeNiCN) as a sacrificial and protective template was studied by in-situ DRIFTS and Kinetics experiments to investigate the influence of modification on the catalytic activity and selectivity to gain mechanistic insight. After modification, the catalyst showed higher catalytic activity and selectivity. H2 -TPR, CO2 -TPD, TEM and XPS confirmed that this modification could enhance the interaction of nickel and ceria and decrease the particle size of nickel, which is in favor of the dissociation of H2 and adsorption of CO2 . The in-situ DRIFTS experiments demonstrated that CO2 is adsorbed on ceria sites, forming carboxylate (CO2 δ− ), unidentate carbonate and bicarbonates, which, in turn, react with adsorbed and dissociated H on Ni to produce formate species. Furthermore, adsorbed methoxy species were observed, which are recognized to be intermediates in the methanation process. In-situ transient DRIFTS confirm that the adsorbed CO is not a reaction intermediate, but a by-product, which originates from the decomposition of weak-binding formate species on Ce 3+ sites. The unmodified catalyst has more weak-binding formate species, which are more inclined to decompose into CO accounting for the low selectivity. Furthermore, the adsorbed CO on Ce 3+ sites cannot react with the adsorbed hydrogen to produce methane. Kinetics studies are consistent with a Langmuir-Hinshelwood type mechanism in which the formation of bicarbonate is the rate-determining step (RDS). Graphical abstract: The reaction mechanism of CO2 methanation on Ni/CeO2 catalyst. Image 1 Highlights: Ce–Ni catalyst modified with g-C3 N4 was successfully synthesized. CO comes from the decomposition of weak-binding formate species on Ce 3+ sites. Adsorbed CO which isn't adjacent to Ni 0 can't get the dissociated H to produce CH4 . The formation of bicarbonate is the rate-determining step (RDS).