Kinetics, Model Discrimination, and Parameters Estimation of CO₂ Methanation on Highly Active Ni/CeO₂ Catalyst

Abstract

The reaction kinetics of CO2 methanation over a highly active 8.5% Ni/CeO2 catalyst was determined in a fixed-bed reactor, in the absence of heat- and mass-transfer limitations. Once the catalyst activity was stabilized, more than 120 kinetic experiments (with varying values of reaction temperature, total pressure, space velocity (GHSV), and partial pressure of products and reactants) were performed. From initial reaction rates, an apparent activation energy of 103.9 kJ mol–1 was determined, as well as the effect of reactants (positive) and water partial pressures (negative) on CO2 methanation rate. Three mechanistic models reported in the literature, in which CO2 is adsorbed dissociatively (carbon and formyl routes) or directly (formate route), were explored for modeling the entire reaction kinetics. For that, the corresponding rate equations were developed through the Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach. In agreement with DRIFTS experiments, formate route, in which the hydrogenation of bicarbonate to formate is considered to be the rate-determining step, reflects the kinetic data accurately, operating from differential conversion to thermodynamic equilibrium. In fact, this mechanism results in a mean deviation (D) of 10.38%. Based on previous own mechanistic studies, the participation of two different active sites has been also considered. Formate route on two active sites maintains a high fitting quality of experimental data, providing kinetics parameters with a higher physical significance. Thus, the LHHW mechanism, in which Ni0 sites as well as oxygen vacant near to Ni-CeO2 interface participate in CO2 methanation, is able to predict the kinetics of Ni/CeO2 catalyst accurately for a wide range of operational conditions.

Progress in reaction mechanisms and catalyst development of ceria-based catalysts for low-temperature CO2methanation

“…6IV). Recently, Onrubia-Calvo et al 122 step, in good line with the kinetic data and the results of in situ DRIFTS.…”

“…6IV). Recently, Onrubia-Calvo et al 122 performed 124 kinetic experiments to establish a kinetic model that reflects the intrinsic CO 2 methanation activity over Ni/CeO 2 catalyst. They found the formate Langmuir–Hinshelwood–Hougen–Watson mechanistic model, which considered the hydrogenation of bicarbonate to formate as rate-determining step, in good line with the kinetic data and the results of in situ DRIFTS.…”

Double-Edged Sword Effect of Classical Strong Metal–Support Interaction in Catalysts for CO2 Hydrogenation to CO, Methane, and Methanol

“…The Sabatier reaction, also known as CO 2 methanation (CO 2 + 4H 2 → CH 4 + 2H 2 O, Δ H 298 K = −165.0 kJ mol –1 ) is a highly exothermic process that is favored at low temperatures (<400 °C). − The reaction is considered to be one of the promising technologies for power-to-gas because it can be conducted at moderate temperatures and ambient pressure, and the produced CH 4 can be injected into the existing natural gas grid for transportation or locally used. , Ni and Ru supported on reducible oxides are the most active catalysts for CO 2 methanation; important examples of these are discussed in this section. Ni-based materials are the most extensively studied catalysts because of their relatively low price. − …”

Efficient CO2 methanation using nickel nanoparticles supported mesoporous carbon nitride catalysts

“…The oxides of alkaline-earth metals are also the more abundant oxides used for this purpose, especially the oxides of Ca, Ba, and Mg 47 , 48 . For nickel-based catalysts, the strong interaction between Ni and support, the perfect metal dispersion on the support surface, and catalyst morphology are important factors that affect the conversion efficiency of the catalyst 49 , 50 . The good dispersion of nickel on the support is usually achieved by using micro or mesoporous supports that have good structural properties and have the ability for modifier addition 51 .…”