Shixue Zhou

A copper-based sorbent with oxygen-vacancy defects from mechanochemical reduction for carbon disulfide absorption

This work innovatively provides an efficient method to prepare a Cu-based sorbent with oxygen-vacancy (Ovac) defects via mechanochemical reduction of CuO for CS2 absorption. Crystalline structures based on XRD measurement show that mechanical force can lead to CuO reduction and Ovac defect generation during ball milling of CuO with Mg as a reducing agent. Sulfur content measurement shows that the prepared Cu-based sorbent with Ovac defects can realize efficient CS2 absorption at 150 °C with a breakthrough sulfur capacity of 10.7 wt%. Electronic structures based on first-principles calculation show that the Ovac defects can decrease copper coordination, increase the surface energy and electron density, and reduce the band gap by forming coordinatively unsaturated Cu, which benefit the chemisorption of CS2 molecules. Cu2O with Ovac defects, the main phase for CS2 absorption in the sorbent, can grab CS2 molecules by the trapping effect of its Ovac defects with a chemisorption distance of 1.53 A and an energy of −110.45 kJ mol−1, and offer electrons for breaking C–S bonds. This work paves a new pathway for the preparation of Cu-based sorbents with high performance for sulfur compound absorption.

Crystal structure and hydrogen storage behaviors of Mg/MoS2 composites from ball milling

The Mg/MoS2 composites were prepared by ball milling under argon atmosphere, and the effect of MoS2 on the crystal structure and hydrogen storage properties of Mg was investigated. It is found that 10 wt% of MoS2 is sufficient to prevent particle aggregation and cold welding during the milling process. The crystallite size of Mg will remain constant at slightly less than 38.8 nm with the milling process due to the size confinement effect of MoS2. The dehydrogenation temperature of MgH2 is reduced to 390.4-429.4 °C due to the crystallite size reduction. Through fitting by Johnson-Mehl-Avrami model, it is found that Mg crystal grows by three dimension controlled by interface transformation during the process of MgH2 decomposition. MoS2 has a weak catalyst effect on the decomposition of MgH2 and activation energy of 148.9 kJ/mol is needed for the dehydrogenation process calculated by the Arrhenius equation.

Solid-phase hydrogen in a magnesium–carbon composite for efficient hydrogenation of carbon disulfide

Desulfurization of syngas from coal gasification is an essential process in chemical synthesis to achieve high value-added utilization of coal. The hydrogenation conversion method is known for its high desulfurization degree in organic sulfur removal, but it is hindered by severe operating conditions, which leads to low safety and low efficiency. A Mg–carbon composite is synthesized by a reactive ball-milling method to store solid-phase hydrogen with high activity for CS2 hydrogenation. Without the presence of high-pressure gaseous hydrogen, CS2 in the stream is hydrogenated by the composite at 250 °C to yield CH4 and H2S, and the conversion achieved is over 91.8% in 300 min. First-principles calculations reveal that chemisorption structures can influence the reaction of CS2 with MgH2, in which horizontal chemisorption is in favor of the generation of gaseous H2S while vertical chemisorption can result in solid MgS. This new method of hydrogenation paves the way for organic sulfur compound removal at moderate temperatures without using a high-pressure hydrogen atmosphere.

Influence of aluminum location on hydrogen sorption kinetics of magnesium-based materials

Hydrogen storage materials from Mg–Al alloy and Mg+Al mixture were prepared by reactive milling under H2 atmosphere with carbonized anthracite as milling aid. The crystal structure of the materials and influence of Al location on hydrogen absorption/desorption kinetics were investigated. Results show that Mg partly got hydrided into β-MgH2 and γ-MgH2 during reactive milling. The average crystallite sizes of β-MgH2 in the as-milled Mg–Al alloy and Mg+Al mixture were calculated by Scherrer equation to be 10 nm and 17 nm, respectively. In the process of hydrogen desorption, the catalytic ability of Al in Mg crystal lattice was not as effective as that on particle surface. The apparent activation energies for hydrogen desorption of the two materials were estimated by Kissinger equation to be 112.2 kJ/mol and 63.7 kJ/mol, respectively. Mg17Al12 reacted with H2 to convert into MgH2 and elemental Al during static hydrogenation at 300°C. For the hydrogenated Mg+Al mixture, the obvious increase of crystallite size...

Enhancement of the hydrogen storage properties of Mg/C nanocomposites prepared by reactive milling with molybdenum

The effect of Mo on the morphology, crystal structure and hydrogen sorption properties of Mg/C composites prepared by reactive milling was studied. Transmission electron microscopic (TEM) observation shows that Mg/C composites prepared with the addition of Mo are of nanoscale with particle size about 20-120 nm after 3 h of milling under 1 MPa H2. MgH2 of tetrahedral crystal structure predominates in the materials with the geometric shape of oblique hexagonal prism. From X-ray diffraction (XRD) and hydrogen content studies, Mo and crystallitic carbon have a synergistic effect on promoting the hydrogenation rate in the reactive milling process. From differential scanning calorimetric (DSC) studies, the dehydrogenation peak temperature of the Mg/C materials with Mo is lowered to 299-340 °C.