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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]

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]