Search

Cu-Co/X-MMT (X = Na, SiO2) catalysts were prepared via impregnation method using Na-MMT and SiO2-MMT (montmorillonite pillared by SiO2) as the support and copper nitrate and cobalt nitrate as precursors. In addition, the citric acid was introduced during the preparation of Cu-Co/SiO2-MMT to obtain Cu-Co/SiO2-MMT-Ac catalyst. The catalysts were characterized by XRD, TEM, H2-TPR, XPS and N2 adsorption–desorption at low temperature. The results showed that the acidity and specific surface area of SiO2-MMT were larger than those of Na-MMT, thus resulting in dimethyl ether (DME) conversion and H2 yield of Cu-Co/SiO2-MMT higher than those of Cu-Co/Na-MMT during steam reforming of DME (SRD). However, for Cu-Co/SiO2-MMT, there was a large amount of methanol in the carbon-containing product due to the large particle size of Cu. The Cu particle size of Cu-Co/SiO2-MMT-Ac was decreased significantly due to the introduction of citric acid, thus accelerating the steam reforming of methanol reaction and enabling the timely conversion of the intermediate product methanol of SRD, resulting in the increasing DME conversion and H2 yield. Therefore, Cu-Co/SiO2-MMT-Ac was expected to be a potential catalyst for SRD. [ABSTRACT FROM AUTHOR]

In this study, a novel polyoxometalates-based metal-organic frameworks (POMOFs) microsphere, that is [Ni(phen)H2O]·V2O6 (phen is o-phenanthroline), have been successfully fabricated by one-pot simple hydro(solvent)thermal reaction through regulating different solvent ratios (H2O/EtOH). The experimental results show that the solvent effect has a significant effect on the micro-morphology and the catalytic activity of the materials. The dual-function in electrocatalytic hydrogen evolution and catalytic reduction of Cr6+ of the as-prepared POMOFs microspheres have been also studied. The POMOF(V,Ni)_3 catalyst prepared in the medium of pure ethanol have the best catalytic activity, in which the overpotential of 159 mV for the electrode is comparable to that of MoS2-based electrode material, and the rate constant k reaches 0.14 in the process of catalytic reduction of Cr6+. In this study, a novel polyoxometalates-based metal-organic frameworks (POMOFs) microsphere [Ni(phen)H2O]·V2O6 have been successfully fabricated by one-pot simple hydro(solvent)thermal reaction through regulating different solvent ratios. The dual-function in electrocatalytic hydrogen evolution and catalytic reduction of Cr6+ of the as-prepared sample have been also studied. [ABSTRACT FROM AUTHOR]

In this study, a novel polyoxometalates-based metal-organic frameworks (POMOFs) microsphere, that is [Ni(phen)H2O]·V2O6 (phen is o-phenanthroline), have been successfully fabricated by one-pot simple hydro(solvent)thermal reaction through regulating different solvent ratios (H2O/EtOH). The experimental results show that the solvent effect has a significant effect on the micro-morphology and the catalytic activity of the materials. The dual-function in electrocatalytic hydrogen evolution and catalytic reduction of Cr6+ of the as-prepared POMOFs microspheres have been also studied. The POMOF(V,Ni)_3 catalyst prepared in the medium of pure ethanol have the best catalytic activity, in which the overpotential of 159 mV for the electrode is comparable to that of MoS2-based electrode material, and the rate constant k reaches 0.14 in the process of catalytic reduction of Cr6+. In this study, a novel polyoxometalates-based metal-organic frameworks (POMOFs) microsphere [Ni(phen)H2O]·V2O6 have been successfully fabricated by one-pot simple hydro(solvent)thermal reaction through regulating different solvent ratios. The dual-function in electrocatalytic hydrogen evolution and catalytic reduction of Cr6+ of the as-prepared sample have been also studied. [ABSTRACT FROM AUTHOR]

Anthocyanins are major pigments in plants. Methylation plays a role in the diversity and stability of anthocyanins. However, the contribution of anthocyanin methylation to lower coloration is still unclear. We identified two homologous anthocyanin O-methyltransferase (AOMT) genes from purple-lowered (PsAOMT) and red-lowered (PtAOMT) Paeonia plants, and we performed functional analyses of the two genes in vitro and in vivo. The critical amino acids for AOMT catalytic activity were studied by site-directed mutagenesis. We showed that the recombinant proteins, PsAOMT and PtAOMT, had identical substrate preferences towards anthocyanins. The methylation activity of PsAOMT was 60 times higher than that of PtAOMT in vitro. Interestingly, this vast difference in catalytic activity appeared to result from a single amino acid residue substitution at position 87 (arginine to leucine). There were significant differences between the 35S::PsAOMT transgenic tobacco and control lowers in relation to their chromatic parameters, which further confirmed the function of PsAOMT in vivo. The expression levels of the two homologous AOMT genes were consistent with anthocyanin accumulation in petals. We conclude that AOMTs are responsible for the methylation of cyanidin glycosides in Paeonia plants and play an important role in purple coloration in Paeonia spp. [ABSTRACT FROM AUTHOR]

Nitrilase can catalyze nitrile compounds to generate corresponding carboxylic acids. Nitrilases as promiscuous enzymes can catalyze a variety of nitrile substrates, such as aliphatic nitriles, aromatic nitriles, etc. However, researchers tend to prefer enzymes with high substrate specificity and high catalytic efficiency. In this study, we developed an active pocket remodeling (ALF-scanning) based on modulating the geometry of the nitrilase active pocket to alter substrate preference and improve catalytic efficiency. Using this strategy, combined with site-directed saturation mutagenesis, we successfully obtained 4 mutants with strong aromatic nitrile preference and high catalytic activity, W170G, V198L, M197F, and F202M, respectively. To explore the synergistic relationship of these 4 mutations, we constructed 6 double-combination mutants and 4 triple-combination mutants. By combining mutations, we obtained the synergistically enhanced mutant V198L/W170G, which has a significant preference for aromatic nitrile substrates. Compared with the wild type, its specific activities for 4 aromatic nitrile substrates are increased to 11.10-, 12.10-, 26.25-, and 2.55-fold, respectively. By mechanistic dissection, we found that V198L/W170G introduced a stronger substrate-residue π-alkyl interaction in the active pocket and obtained a larger substrate cavity (225.66 ų to 307.58 Å3), making aromatic nitrile substrates more accessible to be catalyzed by the active center. Finally, we conducted experiments to rationally design the substrate preference of 3 other nitrilases based on the substrate preference mechanism and also obtained the corresponding aromatic nitrile substrate preference mutants of these three nitrilases and these mutants with greatly improved catalytic efficiency. Notably, the substrate range of SmNit is widened. IMPORTANCE In this study, the active pocket was largely remodeled based on the ALF-scanning strategy we developed. It is believed that ALF-scanning not only could be employed for substrate preference modification but might also play a role in protein engineering of other enzymatic properties, such as substrate region selectivity and substrate spectrum. In addition, the mechanism of aromatic nitrile substrate adaptation we found is widely applicable to other nitrilases in nature. To a large extent, it could provide a theoretical basis for the rational design of other industrial enzymes. [ABSTRACT FROM AUTHOR]

• The 3D Co/NCNS/CNT nanocomposite is prepared by the carbonization of MOF. • The Co/NCNS/CNT can effectively adsorb and catalyze the lithium polysulfides. • Co/NCNS/CNT serves as the separator coating in Li-S battery with high performance. Lithium sulfur (Li-S) battery is regarded as one of the most promising next generation high-energy storage systems. However, the shuttle effect and sluggish redox kinetics of lithium polysulfides always compromise the cycling performance of Li-S batteries. Herein, an effective strategy is presented to fabricate high-performance Li–S batteries using a 3D network-like nanocomposite of Co/NCNS/CNT, which is obtained via the well-distributed composition of the carbon nanotubes (CNTs) (in situ formed and added) with nitrogen-doped carbon nanosheets (NCNS) as well as Co nanoparticles from carbonization of the nitrogen-rich bio-MOF-100 nanosheets at an inert atmosphere. Owing to good sulphiphilicity, excellent conductivity and high catalytic activity from Co-N x and Co nanoparticles, Co/NCNS/CNT nanocomposite could effectively adsorb and catalyze the fast conversion of lithium polysulfides. When serving as the separator coating for Li-S cells, the cell shows excellent performances with an initial capacity of 972.4 mAh/g at 2C under a sulfur loading of 2.0 mg/cm2, and excellent cycling stability with the capacity decay of 0.05% per cycle during the 1000 long-term cycles. Furthermore, even at a high sulfur loading of 5 mg/cm2, the specific capacity of 522.1 mAh/g (2.61 mAh/cm2) can be maintained after 500 cycles at 1 C, thus providing a promising path toward advanced Li–S batteries. [ABSTRACT FROM AUTHOR]