Abstract
Catalytic reactions of industrial importance have attracted widespread attention among researchers. Among diverse industrial catalytic reactions, catalytic CO2 conversion reactions have gained more significance in recent days, owing to the increased concern on greenhouse effect and global warming issues caused by rising CO2 levels in Earth’s atmosphere. In specific, catalytic CO2 methanation reaction (Sabatier reaction) has emerged as a promising alternative to convert greenhouse CO2 to valuable stored renewable CH4 power. While Ni/ γ-Al2O3 catalyst has been conventionally employed for industrial CO2 methanation reaction, it suffers from poor catalytic activity at low temperatures and also suffers from considerable coking at high temperatures. In general, it has been shown from lab-scale packed bed experiments that by co-impregnating small quantities of Ru metal to Ni catalyst, the catalytic activity of Ni catalyst gets enhanced at low temperatures. However, to the best of our knowledge, no comprehensive validated kinetic model and detailed reaction mechanism explaining the synergy and the individual role of different constituent metals in the Ni-Ru/ γ-Al2O3 catalyst for CO2 methanation has been clearly established yet. We, in our current research aim to develop a workflow utilizing a combination of experimental and computational techniques to decipher the reaction mechanism and to develop a validated kinetic model for Ni-Ru/ γ-Al2O3 catalysed low temperature CO2 methanation reaction. The initial phase of the workflow deals with the catalyst structure estimation at different Ni and Ru metal loadings through a combination of lab-scale catalyst synthesis and characterization techniques. Subsequently, the catalytic CO2 methanation activity of the synthesized Ni-Ru/γ-Al2O3 catalysts at low temperatures is estimated with the help of lab-scale packed bed reactor experiments. Following the catalytic activity studies, we aim to decipher the important surface reaction intermediates participating in the CO2 methanation reaction using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments. The developed catalyst model from the experiments and the knowledge of the key active sites and surface species as deciphered from DRIFTS will be utilized in the Density Functional Theory (DFT) simulations to ascertain the adsorption energies of important reaction intermediates and activation energy barriers of different possible reaction steps. The final phase of the workflow deals with the development of the Microkinetic Model from the reaction energetic parameters as deciphered from the DFT simulations and estimation of plausible conversion and kinetically relevant steps in the Ni-Ru/γ-Al2O3 catalysed CO2 methanation reaction. The estimated plausible conversion from the MKM will then be validated against the conversion obtained from the packed bed experiments