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Thermal conversion of CO 2 to value-added chemicals is challenging due to the extreme inertness of the CO 2 molecule and the low selectivity of products. We reported a defect-rich MgH 2 /Cu x O hydrogen storage composite from mechanochemical ball-milling for the catalytic hydrogenation of CO 2 to lower olefins. The defect-rich MgH 2 / Cu x O hydrogen storage composite achieves a C 2 = −C 4 = selectivity of 54.8% and a CO 2 conversion of 20.7% at 350 °C under a low H 2 /CO 2 ratio of 1:5, which increases the efficiency of H 2 utilization by offering lattice H − species for hydrogenation. Density functional theory calculations show that the defective structure of MgH 2 /Cu x O can promote CO 2 molecule adsorption and activation, while the electronic structure of MgH 2 is beneficial for offering lattice H − for CO 2 molecule hydrogenation. The lattice H − can combine the C site of CO 2 molecule to promote the formation of Mg formate, which can be further hydrogenated to lower olefins under a low H − concentration. This work for CO 2 conversion by a defect-rich MgH 2 / Cu x O hydrogen storage composite can inspire the catalysts design for the hydrogenation of CO 2 to lower olefins.

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This article presents a research study on the deposition process of Ca 2C induced by Synechocystis sp. PCC6803 in BG11 liquid medium with different Ca 2C concentrations and different pH. The changes of Ca 2C concentrations were measured by using atomic absorption method and the corresponding dynamical models were studied. Minerals and cells were analyzed by high resolution transmission electron microscope, selected area electron diffraction, scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction. The selected area electron diffraction patterns were analyzed by Digital Micrograph 3.7 software. The result showed that Ca 2C concentrations decreased faster in the experimental group. The changes of calcium carbonate precipitation were fitting to an exponential model. PH 7 and Ca 2C concentration of 1.5 g/L were most conducive to calcium carbonate precipitation in the corresponding gradient range. The result of high-resolution transmission electron microscopy showed that minerals in the experimental group differed obviously from that of the control group in the surface morphology, but both of them were calcites. It also showed that a certain number of minute calcites adhesion to the outer surfaces of S. PCC6803 cells. The result of scanning electron microscopy displayed that many sunken holes emerged on the surfaces of the prismatic calcium carbonate minerals. The results of X-ray diffraction proved that minerals induced by S. PCC6803 were calcites with preferential orientation. This article discusses the process of carbonate formation and the possible role played by S. PCC6803. It may be useful to further study the mechanism of microbial carbonates deposition in the field of geology.