Triphenylphosphine-Based Covalent Organic Frameworks and Heterogeneous Rh-P-COFs Catalysts.

The synthesis of phosphine-based functional covalent organic frameworks (COFs) has attracted great attention recently. Herein, we present two examples of triphenylphosphine-based COFs (termed P-COFs) with well-defined crystalline structures, high specific surface areas, and good thermal stability. Furthermore, rhodium catalysts with these P-COFs as support material show high turnover frequency for the hydroformylation of olefins, as well as excellent recycling performance. This work not only extends the phosphine-based COF family, but also demonstrates their application in immobilizing homogeneous metal-based (e.g., Rh-phosphine) catalysts for application in heterogeneous catalysis.

Stabilizing the active phase of iron-based Fischer-Tropsch catalysts for lower olefins: mechanism and strategy.

Fischer-Tropsch synthesis of lower olefins (FTO) is a classical yet modern topic of great significance in which the supported Fe-based nanoparticles are the most promising catalysts. The performance deterioration of catalysts is a big challenge due to the instability of the nanosized active phase of iron carbides. Herein, by in situ mass spectrometry, theoretical analysis, and atmospheric- and high-pressure experimental examinations, we revealed the Ostwald-ripening-like growth mechanism of the active phase of iron carbides in FTO, which involves the cyclic formation-decomposition of iron carbonyl intermediates to transport iron species from small particles to large ones. Accordingly, by suppressing the formation of iron carbonyl species with a high-N-content carbon support, the size and structure of the active phase were regulated and stabilized, and durable iron-based catalysts were conveniently obtained with the highest selectivity for lower olefins up to 54.1%. This study provides a practical strategy for exploring advanced FTO catalysts.

Immobilization of Carbonylcobalt Catalyst by Poly(4-vinylpyridine) (P4VP) through N→Co Coordination Bonds: The Promotional Effect of Pyridine and the Reusability of Polymer Catalyst.

A carbonylcobalt catalyst, immobilized by poly(4-vinylpyridine) (P4VP) through N→Co coordination bonds, has been prepared by solvothermal method. It has been revealed that the pyridine fragments in the polymer catalyst act not only as promoters to improve the catalytic performance of the carbonylcobalt catalyst for alkoxycarbonylation of ethylene oxide to methyl 3-hydroxypropanoate but also as stabilizers to enhance the reusability of the polymer catalyst. Furthermore, the polymer catalyst could be easily separated by filtration and reused with only a slight loss of catalytic efficiency.

Selective hydrogenolysis of raw glycerol to 1,2-propanediol over Cu-ZnO catalysts in fixed-bed reactor.

The catalytic properties of Cu-ZnO catalysts for glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) were tested in a fixed-bed reactor at 250 °C and 2.0 MPa H2. The relation between composition, surface properties, and catalytic performance of glycerol hydrogenation of Cu-ZnO catalysts was studied using nitrogen adsorption (BET methods), XRD, H2 temperature-programmed reduction, and N2O chemisorptions. It was found that there was a close link between the surface CuO amount of Cu-ZnO catalyst and the reactivity for glycerol hydrogenation. The Cu-ZnO catalyst (Cu/Zn = 1.86) which had the highest surface Cu amount showed the best catalytic activity for glycerol hydrogenolysis. Furthermore, Cu-ZnO catalyst presented good stability and remarkable catalytic activity for glycerol hydrogenolysis to 1,2-PDO using raw glycerol derived from the fat saponification as feedstock.

[Synthesis and properties of nano-rutile TiO2 photocatalysts].

Nano-rutile TiO2 photocatalysts with bigger specific surface area were prepared by a hydrolysis method at 323 K, and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), ultraviolet-visible diffuse reflection spectroscopy (UV-Vis DRS), infrared spectroscopy (IR) and photoelectrochemical (PEC). The ultraviolet (UV) and visible light photocatalytic activities of as-prepared rutile and anatase TiO2 nano-photocatalysts with almost same specific surface areas were evaluated by methyl orange (MO) as mode compound to photocatalytic reaction. The results of the photocatalytic experiment shows that when rutile and anatase have the similar specific surface area of approximately 95 m2.g-1, the UV light photocatalytic activity of rutile is comparable to that of anatase, while rutile shows significantly higher visible light photocatalytic activities than anatase. The photoelectrochemical experiment shows that the order of photocurrent densities of the catalysts from weak to strong is in accordance with the order of UV light photocatalytic activities of the catalysts from low to high under UV light irradiation.

Mechanistic insights into the Brust-Schiffrin two-phase synthesis of organo-chalcogenate-protected metal nanoparticles.

New insights into the formation chemistry of chalcogenate-protected metal nanoparticles (NPs) synthesized via the well-known Brust-Schiffrin two-phase method are presented here. On the basis of Raman, NMR, and surface plasmon resonance characterizations, it is concluded that, before the formation of any metal-chalcogen bonds, metal nucleation centers/NPs are first formed inside the inverse micelles of the tetrabutylammonium bromide in the organic solvent, where the metal ions are reduced by NaBH(4). The ensuing formation of the metal-chalcogen bonds between the naked metal NPs inside the micelles and the organo-chalcogen ligands in the organic solvent is the mechanism by which the further growth of the metal core can be controlled. This proposed mechanism is further examined in the formation of Ag and Cu NPs.

The structure and catalytic activity of anatase and rutile titania supported manganese oxide catalysts for selective catalytic reduction of NO by NH3.

The structure and catalytic properties of anatase and rutile supported manganese oxide catalysts prepared by impregnation method have been studied by using X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), H(2) temperature-programmed reduction (H(2)-TPR) and BET surface area measurements combined with activity testing of selective catalytic reduction (SCR) of NO by NH(3). It has been shown that the manganese oxide loadings on the two TiO(2) supports exert great influences on the SCR activity. For the rutile supported manganese oxide catalysts, increasing manganese oxide loading leads to the increase of reducibility of dispersed manganese oxide species and the rate constant k, which reaches a maximum around 9.6 × 10(-6) mol g(Mn)(-1) s(-1) at 0.5 mmol Mn per 100 m(2) TiO(2). When the manganese oxide loading is beyond this value, the existence of amorphous MnO(x) multiple layers will certainly reduce the ratio of manganese oxide species exposed on the surface and the reducibility of dispersed manganese oxide species, resulting in the rapid decrease of rate constant k. The LRS and XPS results have revealed that for the anatase supported manganese oxide catalysts manganese oxide species exist in Mn(+4) as a major species with Mn(+3) species and partially undecomposed Mn-nitrate as the minor species. Under the SCR reaction conditions, Mn(+3) species on anatase are oxidized to Mn(+4) species, inserting in the surface of anatase and promoting the anatase-to-rutile transformation in the surface layers of the anatase support. Since these Mn(4+) cations are actually dispersed on the support with a rutile shell-anatase core structure and its concentration is very near to that of MnO(x)/TiO(2) (R) catalyst, the relation between the rate constant k and the MnO(x) loading on the anatase support is similar to that on the rutile support, and that the rate constant k values for anatase and rutile supported manganese oxide catalysts are very close at the same MnO(x) loading.

Designing a capsule catalyst and its application for direct synthesis of middle isoparaffins.

A catalyst in the form of a capsule catalyst was prepared by coating HZSM5 membrane on a preshaped Co/SiO2 catalyst pellet. The capsule catalyst with HZSM5 membrane exhibited excellent selectivity for light hydrocarbon synthesis, especially for isoparaffin synthesis from syngas (CO + H2). Long-chain hydrocarbon formation was totally suppressed by the zeolite membrane. The modification of membrane and core catalyst significantly improved the catalytic properties of these new kinds of capsule catalysts.