Understanding the Effect of Water on CO2 Adsorption

Carbon capture from large sources and ambient air is one of the most promising strategies to curb the deleterious effect of greenhouse gases. Among different technologies, CO₂ adsorption has drawn widespread attention mostly because of its low energy requirements. Considering that water vapor is a ubiquitous component in air and almost all CO₂-rich industrial gas streams, understanding its impact on CO₂ adsorption is of critical importance. Owing to the large diversity of adsorbents, water plays many different roles from a severe inhibitor of CO₂ adsorption to an excellent promoter. Water may also increase the rate of CO₂ capture or have the opposite effect. In the presence of amine-containing adsorbents, water is even necessary for their long-term stability. The current contribution is a comprehensive review of the effects of water whether in the gas feed or as adsorbent moisture on CO₂ adsorption. For convenience, we discuss the effect of water vapor on CO₂ adsorption over four broadly defined groups of materials separately, namely (i) physical adsorbents, including carbons, zeolites and MOFs, (ii) amine-functionalized adsorbents, and (iii) reactive adsorbents, including metal carbonates and oxides. For each category, the effects of humidity level on CO₂ uptake, selectivity, and adsorption kinetics under different operational conditions are discussed. Whenever possible, findings from different sources are compared, paying particular attention to both similarities and inconsistencies. For completeness, the effect of water on membrane CO₂ separation is also discussed, albeit briefly.

Catalysis effect on CO2 methanation using MgH2 as a portable hydrogen medium

The feasibility of the reduction of CO2 to CH4 employing MgH2 in the presence and absence of cobalt as a catalyst was investigated for the first time, exploring different non-independent reaction conditions such as the grade of microstructural refinement, the molar ratio MgH2 : CO2, reaction time and temperature. For the un-catalyzed process a methane yield of 44.6% was obtained after 24 h of thermal treatment at 400 °C employing a molar ratio of 2 : 1, through a methanation mechanism that involves the direct reduction of CO2 and the generation of CH4via C as an intermediary. For the MgH2 catalyzed process a methane yield of 78% was achieved by heating at 350 °C for 48 h, 4 : 1 being the optimal molar ratio. The global mechanism corresponds to a Sabatier process favored by Co as an active catalyst, together with the reverse water gas shift reaction followed by methanation of CO in the presence of steam. On account of the fact that it was proved that the use of the catalyst allows lowering the operational temperature without collapsing the methane yield, this research provides interesting insight into a thermochemical method for CO2 reduction to CH4 employing a solid hydrogen storage medium as an H2 source.

Enhancing CO2 chemisorption on lithium cuprate (Li2CuO2) at moderate temperatures and different pressures by alkaline nitrate addition

Reaction mechanism description of CO₂ capture on alkaline (Li, Na and K) nitrate-containing Li₂CuO₂ at moderate temperatures.

CO2 chemisorption in Li2CuO2 microstructurally modified by ball milling: study performed with different physicochemical CO2 capture conditions

Lithium cuprate (Li₂CuO₂) was obtained by a solid state reaction and a subsequent ball milling process. Then, the samples were characterized (structurally and microstructurally) and evaluated as CO₂ captors.

Steam treatment of a hollow lithium phosphate catalyst: enhancing carbon deposition resistance and improving the catalytic performance of propylene oxide rearrangement

The reaction mechanism of propylene oxide rearrangement on a hollow lithium phosphate catalyst in the presence of steam.

Influence of the precursor on the porous structure and CO2 adsorption characteristics of MgO

MgO is promising for CO₂ capture. The effect of precursor source on the porous structure and CO₂ adsorption of MgO was investigated. The adsorption performance of MgO could be enhanced through the regulation of precursor source and its morphology.

Water steam effect during high CO2 chemisorption in lithium cuprate (Li2CuO2) at moderate temperatures: experimental and theoretical evidence

Li₂CuO₂ is able to chemisorb high quantities of CO₂ in the presence of water steam at low temperatures.