Integrated capture and conversion of CO2 into methane using NaNO3/MgO + Ru/Al2O3 as a catalytic sorbent

Abstract

Catalytic sorbents are prepared by physically mixing NaNO3/MgO sorbents and Ru/Al2O3 catalysts and the ability of the composite materials to capture and convert CO2 to methane in a combined capture and conversion cycle is evaluated. The catalytic sorbents are prepared using two preparation methods: i) packing the two components in two separate beds and ii) packing as a single bed after mixing and pelletization of the two components. The catalytic sorbents prepared as two separate beds are more effective, showing an elevated CO2 sorption capacity of 3.24 mmol CO2/g and methane production capacity of 2.21 mmol CH4/g. Mixing and pelletizing the two components together is found to significantly decrease the CO2 sorption capacity of the catalytic sorbent. CO2 methanation reaction pathways are also investigated over 1% Ru/Al2O3 catalysts and 5% NaNO3/1% Ru/Al2O3 catalysts via combination of kinetic studies elucidating the apparent CO2 and H2 reaction orders combined with insitu FTIR measurements. For 1% Ru/Al2O3, it is hypothesized that carbonyl species are reaction intermediates and formate species are spectator species, while for the 5% NaNO3/1%Ru/Al2O3 catalyst, both carbonyl species and formate species are potentially reaction intermediates for the methanation reaction. Hypothetical reaction mechanisms and rate laws are proposed for the two types of catalysts as well.