Xiazhang Li

Hexene-1 isomerization catalyzed by alumina-supported triosmium clusters

Abstract Alumina-supported triosmium clusters, HO S 3 (CO) 10 OAl, were prepared by the reaction of [O S 3 (CO) 12 ] with surface OH groups of γ-Al 2 O 3 . The material was catalytically active for isomerization of hexene-1 to give cis - and trans -hewne-2, and infrared spectra of the catalyst under reaction conditions at 1 atm and 50 to 70 °C indicated that the osmium was present as HOs 3 (CO) 10  OAl. The reaction was promoted by hydrogen and was zero-order in hydrogen and in hexene-1 at partial pressures exceeding 0.1 atm. These results suggest that a supported triosmium cluster itself was the catalytically active species, and the effects of H 2 and D 2 in reactant mixtures and the characterization of the used catalyst by XPS indicate an insertion mechanism involving hydride ligands on the osmium. When the catalyst was treated at higher temperatures (> 120δC), the clusters broke up, giving ensembles consisting of three Os(II) carbonyl complexes. These are similar in their catalytic character to the clusters, as indicated by the kinetics of the isomerization reaction, but they are only half as active as the supported clusters at 70 °C.

Hexene-1 isomerization catalyzed by alumina-supported osmium complexes derived from [Os3(CO)12]

Abstract Supported osmium catalysts were prepared by the reaction of [Os 3 (CO) 12 ] with the surface −OH groups of γ-Al 2 O 3 to form HOs 3 (CO) 10 OAl. The catalyst was initially active for hexene-1 isomerization at 120 °C and 1 atm; the activity decreased rapidly, becoming almost constant after 2 h on stream in a flow reactor. Infrared spectra of the catalyst indicated that the decline in activity was accompanied by a breakup of the initial supported clusters [HOs 3 (CO) 10 OAl ] and the formation of mononuclear Os(II) carbonyl complexes, which are evidently present in ensembles of three complexes. The isomerization reaction catalyzed by this stable form of the catalyst was inhibited strongly and reversibly by CO. Hydrogen in the reactant stream increased the rate of the isomerization reaction, and we infer that hydride ligands on the osmium played a role in increasing the catalytic activity.

In situ fabrication of Ce1−xLaxO2−δ/palygorskite nanocomposites for efficient catalytic oxidation of CO: effect of La doping

Novel palygorskite (PG) supported Ce1−xLaxO2−δ nanocomposites were prepared by a facile in situ deposition method using hexamethylenetetramine as the precipitant. The textural and structural properties of the products were characterized by XRD, HRTEM, FT-IR, Raman, XPS and TPR techniques. The results indicated that the oxide particles with an average size of about 5 nm were loaded successfully onto the surface of PG rods and were uniformly dispersed. The catalytic activities of Ce1−xLaxO2−δ/PG (x from 0.1 to 0.9) for CO oxidation were investigated. La3+ doping was found to have critical effects on the CO oxidation activity. The best Ce1−xLaxO2−δ/PG nanocomposite was obtained when the x value was adjusted to 0.5, and the reaction rate was found to be three times higher than that of a commercial CeO2 catalyst. Adequate introduction of La3+ promotes the formation of non-stoichiometric Ce1−xLaxO2−δ and is responsible for the formation of oxygen vacancies and surface superoxide ions. However, when the doping ratio increases to 0.6 or higher, co-precipitation of La2O3 leads to decreased redox properties and CO oxidation activity.

Support effects in hexene-1 isomerization catalyzed by oxide-supported osmium complexes

Abstract Oxide-supported osmium was prepared from [Os 3 (CO) 12 ]and MgO, γ-Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , CeO 2 , Cr 2 O 3 , and ThO 2 . The samples were tested as catalysts for hexene-1 isomerization with vapor-phase reactant at 1 atm and 120 °C. The activities of the catalysts supported on MgO, Al 2 O 3 , and SiO 2 were approximately the same and at least an order of magnitude greater than those of the catalysts on the other supports. Infrared spectra indicate the presence of mononuclear osmium carbonyl complexes on the surfaces of all the used catalysts, and these are suggested to be the catalytic sites. The support effects may indicate differences in osmium-surface coordination, degree of coordinative unsaturation, or coverage by carbon.

Black phosphorus quantum dots/attapulgite nanocomposite with enhanced photocatalytic performance

Novel black phosphorus quantum dots/attapulgite (BPQDs/ATP) nanocomposites were prepared via a facile hydrothermal-deposition method. TEM showed that BPQDs dispersed evenly on the surface of ATP with uniform particle size about 5nm. UV-Vis revealed that the BPQDs/ATP composite showed wider visible light absorption range as compared with pure ATP. The photocatalytic activity was evaluated by degradation of bisphenol A (BPA). Results showed that BPQDs/ATP reached 90% degradation rate under solar light irradiation for 180min. The coherent heterostructure formed by BPQDs and ATP was responsible for the enhanced photocatalytic performance, due to the sensitization effect of BPQDs and the facilitation of charges separation.

Development of La1-xCexFeO3/attapulgite nanocomposites for photocatalytic reduction of NO at low temperature

A series of attapulgite (ATP) supported perovskite-type La1−xCexFeO3 (x = 0–0.5) nanocomposites were synthesized by a facile sol–gel method. The samples were characterized by X-ray diffraction, Transmission electron microscope, Ultraviolet–visible spectroscopy and Fourier-transform infrared spectroscopy. The photoactivity of the La1−xCexFeO3/ATP was evaluated via catalytic reduction of NOx with NH3 at low-temperature under visible light irradiation. The impact of the doping fraction of Ce on the NOx conversion was investigated. Results show that ATP provides a high surface area facilitating the dispersion of small nanoparticles as well as the gas adsorption, while incorporation of an appropriate amount of Ce leads to the formation of coherent heterostructure La1−xCexFeO3/CeO2 which benefits the separation of electron–holes. The highest conversion rate of NO reaches 80% at low temperature when the doping amount is 0.3.

Fabrication of γ-MnO2-Ce Pillared Montmorillonite for Low Temperature NH3-SCR

Abstract A series of γ-MnO2-Ce/MMT catalyst materials synthesized by homogeneous precipitation method was investigated for the selective catalytic reduction (SCR) of NOx with NH3. X-ray diffraction and specific surface areas were utilized for micro structure and layer spacing investigation. And NH3-TPD, Pyridoxine IR, H2-TPR and XPS were used to investigate Brønsted acid and Lewis acid, redox properties, atomic concentrations and element chemical state for as-prepared catalysts. The results showed that the γ-MnO2-Ce/MMT had superior NOx conversion compared to the bulk particles, among which 6 wt.% γ-MnO2-Ce/MMT displayed the best deNOx of 95.3% for the low temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) under the GHSV of 25,000 h−1, therefore it is a promising catalyst for low temperature NH3-SCR.

Surface modification of Sb-SnO2/potassium titanate composite and their performance for acrylic coatings

Abstract Sb-SnO2/potassium titanate (SSP) composites were synthesized by densely coating Sb-doped SnO2 on the surface of fibrous-like potassium titanate. X-ray diffraction demonstrated that Sb was successfully doped into the crystal lattice of SnO2. To improve the dispersion of SSP composites in the acrylic resin, the as-prepared SSP was modified with sodium stearate. Fourier transform infrared spectra, thermogravimetric analysis, and transmission electron microscopy confirmed that stearate radicals existed on the surface of SSP in the form of physical adsorption. The hydrophilic degree of modified SSP was largely improved by water contact angle measurements. The properties (surface resistivity and mechanical properties) of the conductive coatings prepared by adding the obtained composites were investigated in detail. The modified SSP coatings exhibit more superior electrical conductivity due to their better dispersion in the matrix compared with SSP. Moreover, the obtained composite coatings present high pencil hardness of 4H–5H and excellent adhesion force, flexibility, and impact resistance.

Z-Scheme Photocatalyst Constructed by Natural Attapulgite and Upconversion Rare Earth Materials for Desulfurization

The Er3+:CeO2/ATP (attapulgite) nanocomposites were prepared by a facile precipitation method. The samples were characterized by various measurements. XRD and TEM showed that Er3+:CeO2 nanoparticles were well-crystallized and loaded on the surface of ATP. The visible light was converted into ultraviolet light by Er3+:CeO2 as evidenced by upconversion photoluminance (PL) analysis. The mass ratio of Er3+:CeO2 to ATP on the desulfurization efficiency was investigated. Results showed that the desulfurization rate reached 87% under 4 h visible light irradiation when the mass ratio was 4:10. The mechanism was put forward as follows. Er3+:CeO2 and ATP formed Z-scheme heterostructure intermediated by oxygen vacancy, leading to the enhanced separation of photogenerated charges and preservation of high oxidation-reduction potential, both of which favored for the generation of radicals to oxidize sulfur species.

Preparation of rutile TiO2@avobenzone composites for the further enhancement of sunscreen performance

It is well known that organic avobenzone and inorganic TiO2 are applied to shield UVA and UVB, respectively. However, some of the disadvantages of the individual components are inevitable in sunscreens. Herein, avobenzone was coated on the surface of pretreated TiO2 for the preparation of a TiO2@avobenzone broad-spectrum sunscreen. The as-prepared products were characterized via XRD, FTIR, TG and SEM. The organic film-layer was evenly encapsulated on the surface of the pretreated TiO2 to assemble a core–shell structure. Subsequently, TiO2@avobenzone was applied to a formulation and the properties of the obtained emulsion were evaluated via droplet size distribution analysis, HPLC and an ultraviolet transmittance analyzer. The results show that TiO2@avobenzone possesses more excellent dispersity, lower degradation rate and higher SPF value as compared to the individual components in the formulated emulsion, and thus, TiO2@avobenzone could be used as a potential candidate for sunscreens.