CO2 reactivity with Mg2NiH4 synthesized by in situ monitoring of mechanical milling

Influence of Synthesis Gas Components on Hydrogen Storage Properties of Sodium Aluminum Hexahydride

A systematic study of different ratios of CO, CO2, N2 gas components on the hydrogen storage properties of the Na3AlH6 complex hydride with 4 mol% TiCl3, 8 mol% aluminum and 8 mol% activated carbon is presented in this paper. The different concentrations of CO and CO2 in H2 and CO, CO2, N2 in H2 mixture were investigated. Both CO and CO2 gas react with the complex hydride forming Al oxy-compounds, NaOH and Na2CO3 that consequently cause serious decline in hydrogen storage capacity. These reactions lead to irreversible damage of complex hydride under the current experimental condition. Thus, after 10 cycles with 0.1 vol % CO + 99.9 vol %H2 and 1 vol % CO + 99 vol %H2, the dehydrogenation storage capacity of the composite material decreased by 17.2% and 57.3%, respectively. In the case of investigation of 10 cycles with 1 vol % CO2 + 99 vol % H2 gas mixture, the capacity degradation was 53.5%. After 2 cycles with 10 vol % CO +90 vol % H2, full degradation was observed, whereas after 6 cycles with 10 vol % CO2 + 90 vol % H2, degradation of 86.8% was measured. While testing with the gas mixture of 1.5 vol % CO + 10 vol % CO2 + 27 vol % H2 + 61.5 vol % N2, the degradation of 94% after 6 cycles was shown. According to these results, it must be concluded that complex aluminum hydrides cannot be used for the absorption of hydrogen from syngas mixtures without thorough purification.

Investigation of Catalyst Development from Mg2NiH4 Hydride and Its Application for the CO2 Methanation Reaction

In current study various aspects of catalyst development for the Sabatier type methanation reaction were investigated. It was demonstrated that starting from 330–380 °C Mg2NiH4 hydride heating under CO2 and H2 gas flow initiates hydride decomposition, disproportionation and oxidation. These reactions empower catalytic properties of the material and promotes CO2 methanation reaction. Detailed structural, colorimetric and thermogravimetric analysis revealed that in order to have fast and full-scale development of the catalyst (formation of MgO decorated by nanocrystalline Ni) initial hydride has to be heated above 500 °C. Another considerable finding of the study was confirmation that potentially both high grade and low grade starting Mg2Ni alloy can be equally suitable for the hydride synthesis and its usage for the promotion of methanation reactions.

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.