Preparation of solid acid catalyst SO42−/TiO2/γ-Al2O3 for esterification: A study on catalytic reaction mechanism and kinetics

Sulfurized nano zero-valent iron prepared via different methods: Effect of stability and types of surface corrosion products on removal of 2,4,6-trichlorophenol

Sulfurization improves the stability and activity of nano zero-valent iron (nZVI). The sulfurized nZVI (S-nZVI) were prepared with ball milling, vacuum chemical vapor deposition (CVD) and liquid-phase reduction techniques and the corresponding products were the mixture of FeS₂ and nZVI (nZVI/FeS₂), well-defined core-shell structure (FeS_x@Fe) or seriously oxidized (S-nZVI(aq)), respectively. All these materials were applied to eliminate 2,4,6-trichlorophenol (TCP) from water. The removal of TCP was irrelevant with the structure of S-nZVI. Both nZVI/FeS₂ and FeS_x@Fe showed remarkable performance for the degradation of TCP. S-nZVI(aq) possessed poor mineralization efficiency to TCP due to its bad crystallinity degree and severe leaching of Fe ions, which retarded the affinity of TCP. Desorption and quenching experiments suggested that TCP removal by nZVI and S-nZVI was based on surface adsorption and subsequent direct reduction by Fe⁰, oxidation by in-situ produced ROS and polymerization on the surface of these materials. In the reaction process, the corrosion products of these materials transformed into crystalline Fe₃O₄ and α/β-FeOOH, which enhanced the stability of nZVI and S-nZVI materials and was conductive to the electron transferring from Fe⁰ to TCP and strong affinity of TCP onto Fe or FeS_x phases. All these were contributed to high performance of nZVI and sulfurized nZVI in removal and minerazilation of TCP in continuous recycle test.

Catalytic Esterification of Levulinic Acid into the Biofuel n-Butyl Levulinate over Nanosized TiO2 Particles

Levulinic esters, synthesized by the esterification of biomass-derived levulinic acid with various alcohols, is an important chemical that plays an essential role in the fields of biomass fuel additives, organic synthesis, and high value-added products. In the present work, the catalytic esterification of levulinic acid with n-butyl alcohol was selected as a typical model reaction to investigate the catalytic performance of an inexpensive commercial catalyst, titanium oxide nanoparticles. The influences of reaction time, reaction temperature, and catalyst loading on the conversion of levulinic acid to n-butyl levulinate were systematically examined through single-factor experiments. Additionally, the optimization of the reaction conditions was further investigated by a Box-Behnken design in response to the surface methodology. The desired product, n-butyl levulinate, with a good yield (77.6%) was achieved under the optimal conditions (reaction time of 8 h, reaction temperature of 120 °C, and catalyst dosage of 8.6 wt.%) when using titanium oxide nanoparticles as catalysts. Furthermore, it was found that addition of water to the catalytic system facilitated the reaction process, to some extent. This study reveals that the nanosized TiO₂ material_, as an efficient solid acid catalyst, had good catalytic performance and stability for the esterification of levulinic acid after six consecutive uses.

A mesoporous SnO–γ-Al2O3 nanocomposite prepared by a seeding-crystallization method and its catalytic esterification performances

A mesoporous SnO–γ-Al₂O₃ nanocomposite was synthesized by a seeding-crystallization method and investigated in catalytic esterification of pentaerythritol and stearic acid to produce pentaerythrityl tetrastearate.

Significantly Enhanced Photoluminescence Performance of NixSy(NiS and Ni9S8)/ZnO Nanorods by a Hydrothermal Method

This paper reports on a near zero band gap semiconductor, Ni_xS_y, which significantly enhances the photoluminescence (PL) performance of ZnO nanorods. The structural, morphological, and optical properties of the composites were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible spectroscopy (UV-vis), PL spectrometry, etc. The PL patterns at an excitation wavelength (λ_ex) of 325 nm revealed that the 10% Ni_xS_y/ZnO nanorod (10NZNR) composites displayed the highest emission intensity in the region of 420-630 nm. The relationship between the emission intensity of ZnO and the concentration of Ni_xS_y demonstrated that the PL intensity of NZNRs initially increased (<10%) and then declined with an increase in Ni_xS_y content (>10%). According to PL spectra at different excitation wavelengths and PL excitation (PLE) spectra, the visible emission of Ni_xS_y/ZnO nanorod (NZNR) composites can only be excited by light with energy greater than that of the band gap. Studies of the morphological structures and PL behaviors of NZNR composites have illustrated that Ni_xS_y considerably enhances the visible emission of ZnO by regulating its morphology and structure. An appropriate mechanism by which Ni_xS_y enhances the PL performance of ZnO has been proposed.

Dehydration of glucose/fructose to 5-hydroxymethylfurfural (5-HMF) over an easily recyclable sulfated titania (SO42−/TiO2) catalyst

An efficient SO₄²⁻/TiO₂ catalyst was developed which demonstrated a maximum of ∼75% and ∼37% yield of 5-HMF in the presence of fructose and glucose, respectively. Brønsted/Lewis acidic ratio of catalyst played a crucial role in the yield of 5-HMF.