The effects of O2 on the combined capture and conversion of CO2 into methane by dual functional materials

Details

Supervisors

Debecker, Damien P.

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

With today’s increasing environmental concern, the urge is to develop sustainable ways to provide energy to the world population. Consequently, strategies for carbon dioxide abatement are of utmost importance in order to mitigate climate change while producing energy. This Master’s thesis focuses on Dual Functional Materials (DFMs), consisting of the combination of a catalyst phase and an adsorbing phase dispersed on a support material. The DFM technology aims to capture CO2 and subsequently convert it into value-added products such as CH4 upon addition of a reactive species (e.g. H2). The objective of this work is to study the effect of the O2 presence on DFM performances in CO2 adsorption and methanation. Two promising DFM types were synthesized by wet impregnation, a 5%Ru-6.1%Na2O/γ-Al2O3 sample (named RuNa2O/A) and a 5%Ru-5%NaAlO2/Boehmite one (RuNaAlO2/B). The effect of O2 on DFM performances in CO2 adsorption and methanation was analyzed by performing tests at 200 °C under three different experimental conditions for the capture step: only CO2, CO2 and 0.4% O2 or CO2 and 4% O2, all diluted in helium. The impact of O2 on the stability of DFM performances was also studied by performing 10 successive cycles of CO2 adsorption and methanation with and without O2. In order to highlight the different mechanisms occurring during adsorption and methanation, DRIFTS analyses were performed over both DFM types, in presence and absence of O2. Additionally, samples were characterized by XRD, H2 chemisorption, N2 physisorption, CO2-TPD and ICP-AES. The DRIFTS analysis confirmed for both samples that CO2 mainly adsorbed on the adsorbing phase and that a spillover effect of CO2 from the sorbent onto the Ru catalytic sites occurred during methanation. The presence of O2 resulted in significant differences in adsorption and methanation mechanisms for RuNa2O/A DFMs, whereas its impact seemed more limited for RuNaAlO2/B DFMs. This observation was confirmed by tests in adsorption and methanation, where the O2 impact was less pronounced for RuNaAlO2/B DFMs. However, RuNa2O/A DFMs were negatively affected by O2, demonstrating a lower CO2 adsorption in its presence. Furthermore, performances in CO2 adsorption and methanation of RuNa2O/A DFMs were relatively stable over 10 cycles, even though CO2 adsorption and CH4 production displayed a very slight decrease. The addition of O2 did not perturb the stability of the results, but CO2 adsorption and CH4 production both took lower values in this case. By comparing characterization studies and catalytic tests, potential correlations were established. Higher Ru dispersion after test was associated with higher H2 consumption. A more important amount of Ru atoms on the DFM surface (H2 chemisorption) as well as a lower basicity (CO2-TPD) seemed to result in a higher CH4 production. An increase of Ru dispersion after performing catalytic test detected by H2 chemisorption could also suggest that more CH4 will be produced under oxidizing conditions.