Extended aging of Ru-Ni, Na2O/Al2O3 dual function materials (DFM) for combined capture and subsequent catalytic methanation of CO2 from power plant flue gas

Abstract

This study investigates the use of catalytic Ru and Ni combinations, intimately mixed with Na2O supported on γ-Al2O3 DFMs (dual function materials). We refer to these as dual function since one material – composed of an alkaline sorbent and catalytic component intimately dispersed on a high surface area carrier – can be used to capture CO2 from power plant flue gas and subsequently upgrade it to methane. The goal is to reduce the Ru content by combining it with catalytic Ni. Due to the presence of O2 in flue gas, Ni-only DFMs are not suitable candidates as they are oxidized and cannot be reactivated at temperatures below 550 °C. However, with the addition of small amounts of Ru, NiO can be reduced at DFM operating temperatures (∼300 °C, consistent with the exhaust temperature of natural gas flue gas), increasing catalytic sites for methanation. Several Ru + Ni combinations are investigated (0.5 % Ru, x% Ni, 6.1 % “Na2O”/Al2O3, x = 1, 5, 10, 20) for cyclic capture/methanation performance to identify an optimal formulation. 0.5 % Ru, 5 % Ni, 6.1 % “Na2O”/Al2O3 DFM is then aged in simulated, O2– and steam-containing natural gas flue gas. Aging over 60 cycles shows that there is steady deactivation in performance with XRD and STEM/EDS showing that the formation of inactive and stable NiAl2O4 is the primary cause for decreased methanation ability.