Intrinsic kinetics of CO2 methanation on low-loaded Ni/Al2O3 catalyst: Mechanism, model discrimination and parameter estimation. (March 2022)

• Record Type: Journal Article
• Authors: Quindimil, Adrián; Onrubia-Calvo, Jon A.; Davó-Quiñonero, Arantxa; Bermejo-López, Alejandro; Bailón-García, Esther; Pereda-Ayo, Beñat; Lozano-Castelló, Dolores; González-Marcos, José A.; Bueno-López, Agustín; González-Velasco, Juan R.
• Is Part Of: Journal of CO₂ utilization. Volume 57(2022)
• Publication Date: 2022-03
• Subjects: CO2 methanation -- Ni/Al2O3 catalyst -- Kinetic model -- Reaction mechanism -- H-assisted CO formation route; Carbon dioxide -- Periodicals; Carbon dioxide -- Environmental aspects -- Periodicals; Carbon dioxide mitigation -- Periodicals; Carbon dioxide; Carbon dioxide -- Environmental aspects; Carbon dioxide mitigation; Periodicals; 628.53205
• DOI: 10.1016/j.jcou.2022.101888
• Languages: English
• ISSNs: 2212-9820

Abstract

Graphical abstract: Highlights: CO2 methanation kinetics on low-loaded Ni/Al2 O3 catalyst is described based on DRIFTS and kinetic data. LHHW rate equations are deduced including the role of water, carbonyls and formates. Formates decomposition as RDS rate equation represents most accurately the kinetic performance. The participation of both carbonyls and formates in the CO2 hydrogenation is confirmed. Abstract: The mechanism and kinetic of CO2 methanation reaction of 9.5 % Ni/Al2 O3 catalyst is analysed under a wide range of operating conditions. Once the catalyst activity is stabilized, the influence of temperature, total pressure and space velocity is studied for kinetic characterisation. A data set comprising of 153 experimental runs has been used to develop a kinetic model capable to accurately predict the reaction rate. Ni/Al2 O3 catalyst shows an apparent activation energy of 80.1 kJ mol −1 in CO2 hydrogenation. Data obtained under differential mode adjust quite precisely to a power-law model with H2 O inhibition, with a water adsorption constant of 3.1 atm −1 and apparent orders of 0.24 and 0.27 for H2 and CO2, respectively. Based on DRIFTS results, we propose for the first time the H-assisted CO formation route, which is compared with the more conventionally reported carbonyl route, and describe the corresponding reaction rate LHHW equation, resulting in notable improvement for mean deviation ( D ) of 7.0 % in our model related to that based on the carbonyl route ( D = 20.1 %) usually suggested for catalysts with higher Ni loads around 20 %. The H-assisted CO formation route considers the formate species decomposition into carbonyls via H-assisted CO formation mechanism and further carbonyls hydrogenation into CHO as the rate determining step. Thus, the LHHW mechanism, in which carbonyls as well as formate species participate in CO2 methanation, is capable to reflect the kinetics of lowly-loaded Ni/Al2 O 3 catalyst with high accuracy under relevant process conditions (315−430 °C, 1−6 bar, H2 to CO2 molar ratios between 1–16 and, different reagents and products partial pressures).