LiBH 4 is an attractive material for hydrogen storage owing to its high hydrogen capacity of 13.8 wt% capacities. However, its high thermodynamic stability and sluggish kinetics limit its practical application as an onboard hydrogen storage medium. In this work, a synergetic effect of NbCl 5 and hexagonal BN (h-BN) on notably improving the dehydrogenation properties of LiBH 4 was investigated. It is found that the addition of NbCl 5 and h-BN co-dopants can significantly enhance the dehydrogenation kinetics of LiBH 4 , and the catalytic effect of co-dopant is better than that of NbCl 5 or h-BN dopant separately. The NbCl 5 /h-BN co-doped LiBH 4 can release 10.78 wt% hydrogen, which is about 13 times and 5 times more than that of the NbCl 5 doped LiBH 4 and h-BN doped LiBH 4 within 10 min at 400 °C, respectively. The major dehydrogenation temperature of NbCl 5 /h-BN co-doped LiBH 4 is reduced to 377 °C, much lower than that of ball-milled LiBH 4 (464 °C). The apparent activation energy ( E a ) of hydrogen desorption is reduced from 195.81 kJ/mol of LiBH 4 to 122.75 kJ/mol of NbCl 5 /h-BN co-doped LiBH 4 . The microstructural results reveal that the catalytic effect of NbCl 5 /h-BN co-dopant on improving the dehydrogenation kinetics of LiBH 4 could be ascribed to the in situ formed nano NbH@h-BN, which serves as the heterogeneous nucleation site to reduce the decomposition activation energy barrier of LiBH 4 and shortens the distance of the solid–liquid phase boundary movement of LiBH 4 decomposition.
Xiao-Shuang Cai,Hui-Xian Guo,Xiao-Juan Zhao,Jia-Ju Zhao,Hua-Min Liu,Sébastien Leveneur,Xue-De Wang
The cycloaddition of CO 2 to epoxidized molecules is an ecofriendly strategy for synthesizing aliphatic carbonates. In this study, heterogeneous catalytic synthesis of carbonated methyl oleate was performed. Influences of reaction parameters such as reaction temperature (403.15–443.15 K), pressure (1–3 MPa), concentration of functional groups (1.22–2.88 mol·L −1 ) and catalyst loading (0.025–0.042 g·mL −1 ) on the kinetics were evaluated. Gas-liquid mass transfer of CO 2 in the methylated oleic acid system was investigated, and a mathematical model was developed. The dissolution of CO 2 was found to be exothermic, and the dissolution capacity decreases with increasing temperature and decreasing pressure. The solubility of CO 2 follows an order of methylated form > epoxidized form > carbonated form. A high conversion rate (68.45 %) of epoxides was achieved in 6 h at 443.15 K and 3 MPa with a catalyst loading of 0.042 g·mL −1 . These results show a potential route for synthesizing aliphatic carbonates by combining methyl oleate with CO 2 .
CaO-doped γ-Al2O3 beads were prepared by an alginate assisted sol–gel method, followed by grafting with alkyl groups and impregnation of NbCl5 to construct multi-functionalized γ-Al2O3 beads for efficient catalytic conversion of glucose to 5-hydroxymethylfurfural (5-HMF). Doping with CaO improved the binding capacity of the catalyst with glucose and increased the Lewis acid amount. However, a high CaO content would cover the Lewis acid sites of γ-Al2O3, resulting in a lower isomeric conversion of glucose to fructose. When the C8–Ca(10%)–γ-Al2O3 catalyst was loaded with Nb2O5, intermediate fructose was consumed rapidly resulting in complete conversion of glucose, which indicated that conversion of glucose to 5-HMF involved the isomeric conversion of glucose to fructose followed by dehydration of fructose to 5-HMF. This was necessary to balance hydrophilic isomerization reactions with restraining the rehydration of 5-HMF by hydrophobic modification. This is similar to the reaction in which a medium with a certain amount of water was beneficial for glucose isomerization. Under the synergistic effect of Lewis acid provided by γ-Al2O3 and Brønsted acid offered by Nb2O5, C8–Ca(10%)–γ-Al2O3–Nb(3%), a glucose conversation rate of 100% and the highest yield of 5-HMF (68.4%) were achieved in the reaction medium with a dimethylsulfoxide/H2O (V/V) ratio of 4 : 1, a catalyst amount of 33 mg, a reaction temperature of 140 °C and a reaction time of 4 h.
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