Direct and highly selective conversion of captured CO2 into methane through integrated carbon capture and utilization over dual functional materials

Abstract

Excessive atmospheric CO2 emission is regarded as one of the main factors causing global climate change. Thus, there is an urgent need to explore the possibility of CO2 capture and converting the captured CO2 to fuels or value-added products. Recently, an integrated carbon capture and utilization (ICCU) process performed in a single reactor under isothermal conditions draws intensive attentions due to the reduction of energy requirement for sorbent regeneration. However, from literature, normally a low loading of sorbent in dual functional materials (DFMs) was applied resulting in a very low CO2 capture capacity and consequent low CH4 yield in the ICCU process.Herein, we demonstrate the intermediate-temperature DFMs using inexpensive high-capacity MgO sorbent. The synthesized DFMs are a physical mixture of sorbent and Ru/CeO2 catalyst by the mass ratio of 2:1 allowing simultaneous regeneration of sorbent and conversion of CO2 in a single reactor at 300 ˚C. During the 1 st cycle of ICCU process, 10Ru/CeO2-MgO exhibits the best ICCU performance with the highest CH4 yield of 7.07 mmol g -1 and CO2 conversion of 89%. However, after 10 cycles of ICCU process, 5Ru/CeO2-MgO exhibits the highest CH4 yield (3.36 mmol g -1 ) and CO2 conversion (79%), which are much higher than that of 2.5Ru/CeO2-MgO (1.14 mmol g -1 and 39%) and 10Ru/CeO2-MgO (2.31 mmol g -1 and 69%). It is mainly attributed to that more oxygen vacancies are remained in 5Ru/CeO2-MgO resulted from the metal-support interaction.

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

“…Additionaly, CH 4 selectivity for many catalysts during CO 2 hydrogenation is high at temperatures that can coincide with those required for CO 2 desorption, thus rendering CH 4 as a preferable final product. The combination of these two processes, namely CO 2 adsorption and hydrogenation, in a single reactor can be realized via the development of novel dual-function materials (DFMs) that embody both adsorption and catalytic capabilities [19,20,25].…”

“…Lastly, Sun et al [25] employed a DFM consisting of a Ru supported on CeO2 nanorods methanation catalyst and an alkali nitrate promoted MgO sorbent mechanically mixed together ( Figure 11). It has been already reported by Wang et al [117] that the CO2 methanation mechanism over Ru/CeO2 follows a different pathway compared to Ru/Al2O3, with the oxygen vacancy catalyzed formate dissociation being the rate determining step in the former.…”

“…It was further noted that, although CH4 yield and CO2 conversion were higher for 10% Ru loading during the 1st cycle, the 5% Ru loaded catalyst showed better performance during the 10th cycle, probably due to the better preservation of the oxygen vacancies in the support. Lastly, Sun et al [25] employed a DFM consisting of a Ru supported on CeO 2 nanorods methanation catalyst and an alkali nitrate promoted MgO sorbent mechanically mixed together ( Figure 11). It has been already reported by Wang et al [117] that the CO 2 methanation mechanism over Ru/CeO 2 follows a different pathway compared to Ru/Al 2 O 3 , with the oxygen vacancy catalyzed formate dissociation being the rate determining step in the former.…”

“…It has been already reported by Wang et al [117] that the CO 2 methanation mechanism over Ru/CeO 2 follows a different pathway compared to Ru/Al 2 O 3 , with the oxygen vacancy catalyzed formate dissociation being the rate determining step in the former. Sun et al [25] performed the integrated CO 2 capture and methanation process in their DFM at 300 • C. CO 2 was initially captured in the form of MgCO 3 . Subsequently, during the methanation process, CO 2 was desorbed and activated by an oxygen vacancy in the CeO 2 nanorod support, forming a formate intermediate.…”

“…Schematic illustration for the CO 2 capture from the MgO sorbent phase and the conversion of captured CO 2 into CH 4 over the Ru/CeO 2 catalyst phase. Reproduced with permission from ref [25]…”