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.

Consideration of Photoactivity of TiO2 Pigments via the Photodegration of Methyl Orange under UV Irradiation.

Developing a rapid and reliable method for measuring the photoreactivity of TiO2 pigments is of great importance for industrial application. The photoactivity of industrial TiO2 pigments were evaluated via the photodegradation of a model azo dye, methyl orange (MO), in the present work. The TiO2 pigments were characterized by Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The photoactivity test results showed that the anatase TiO2 pigment was responsible for accelerating MO degradation, while the rutile pigment acted as a stabilizer, and effective UV absorber retarded the photodegradation of MO. It was found that the photodegradation of MO was driven mainly by photoholes (h+) and hydroxyl radicals (•OH), in the presence of TiO2 pigment with high photoactivity. With the help of the degradation intermediates during the photodegradation process and the calculated data, the preliminary degradation mechanism including azo bond cleaving, h+ oxidation, and hydroxylated products' generation for MO was also elucidated. The photoactivity of TiO2 pigments can be rapidly evaluated in this work, which would be an efficient approach for assessing the product quality control and the end-use performance of TiO2 pigments.

Titanate Nanotubes-Based Heterogeneous Catalyst for Efficient Production of Biomass Derived Chemicals.

The development of efficient heterogeneous catalytic system to convert plentiful biomass to renewable bio-chemicals is urgent need. Titanate nanotubes-based materials obtained from hydrothermal treatment have been reported as low-cost and efficient catalytic materials in chemical syntheses for bio-based chemicals production with interesting catalytic performance. This mini-review expressly revealed the significance and potential of using titanate nanotubes based material as sustainable and environmentally benign solid catalysts/supports for synthesis of various bio-based chemicals, including glycerol-derived solketal, jet fuel range alkanes precursors, biomass-derived esters, aldehydes, aromatic compounds and so on. From the current knowledge on titanate nanotubes-based material via hydrothermal method here summarized, the future lines of research in the field of catalysis/supports for bio-based chemicals production are outlined.

Titania Nanotubes-Bonded Sulfamic Acid as an Efficient Heterogeneous Catalyst for the Synthesis of n-Butyl Levulinate.

The titania nanotubes-bonded sulfamic acid (TNTs-NHSO3H) catalyst was designed and successfully fabricated by the post-synthesis modification method. The as-prepared catalyst was characterized by a variety of characterization techniques, including Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and thermogravimetry-differential thermal gravimetry (TG-DTG). The crystal structure of the TNTs still maintained during the modification process. Although the BET surface area was decreased, the amount of Brønsted acid sites can be efficiently fabricated on the TNTs. The catalytic activity of TNTs-NHSO3H was examined for the synthesis of n-butyl levulinate (BL) from levulinic acid (LA) and furfuryl alcohol (FA). A relatively high selectivity (99.6%) at 99.3% LA conversion was achieved for esterification of levulinic acid owing to the strong Brønsted acidity sites. And also, the TNTs-NHSO3H catalyst exhibited a higher reactivity for alcoholysis of FA and the yield of BL reached 90.4% with 100% FA conversion was obtained under the mild conditions.

Highly-selective solvent-free catalytic isomerization of α-pinene to camphene over reusable titanate nanotubes.

Titanate nanotubes, prepared by the hydrothermal reconstitution and modification with hydrochloric acid, were tested as solid acid catalysts in the isomerization of α-pinene under solvent free conditions. The results showed that titanate nanotubes have better catalytic properties than titanium dioxide nanoparticles, and the camphene was the main product for α-pinene isomerization. The effects of several reaction variables, such as reaction temperature, catalyst dosage, and reaction time, on the conversion of α-pinene and the selectivity to camphene were examined. The highest conversion was up to 97.8% with selectivity to camphene of 78.5% under the mild reaction conditions, and the catalyst also showed outstanding reusability after four runs. It is proposed that appropriate surface acidic sites and opened nanotubular structures are mainly responsible for the excellent catalytic performance of titanate nanotubes materials.

Selective oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran over VPO catalysts under atmospheric pressure.

Vanadium phosphate oxide (VPO) heterogeneous catalysts with different V/P molar ratios were prepared and used for selective oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to produce 2,5-diformylfuran (DFF) in the liquid phase. It was found that the VPO catalyst with V/P molar ratio 0.25 exhibited the best catalytic performance. Then the VPO catalyst was utilized to catalyze the oxidation of HMF in a batch reactor under different conditions, in terms of type of solvent (water and organic), reaction time and temperature. A high DFF yield of 83.6% with HMF conversion of 100% was obtained under atmospheric pressure.

Titanate nanotubes-bonded organosulfonic acid as solid acid catalyst for synthesis of butyl levulinate.

In this study, titanate nanotubes-bonded organosulfonic acid (TNTs-SO3H) was prepared and employed as an efficient heterogeneous catalyst for esterification of levulinic acid with n-butanol. Two reaction products pseudo n-butyl levulinate (pseudo-BL) and n-butyl levulinate (BL) were detected by GC-MS. The catalyst showed 86.8% conversion of levulinic acid with 99.7% selectivity towards n-butyl levulinate. TNTs-SO3H exhibited strong acidic sites and high stability even after seven cycles of usage and would be well expected to be a potential candidate for alkyl levulinate production.

Photocatalytic degradation of carbofuran in TiO2 aqueous solution: kinetics using design of experiments and mechanism by HPLC/MS/MS.

The photocatalytic degradation kinetics of carbofuran was optimized by central composite design based on response surface methodology for the first time. Three variables, TiO2 concentration, initial pH value and the concentration of carbofuran, were selected to determine the dependence of degradation efficiencies on independent variables. Response surface methodology modeling results indicated that the degradation efficiency of carbofuran was highly affected by the initial pH value and the concentration of carbofuran. Then nine degradation intermediates were detected by HPLC/MS/MS. The Frontier Electron Densities of carbofuran were calculated to predict the active sites on carbofuran attacked by hydroxyl radicals and photoholes. Point charges were used to elucidate the chemisorption pattern on TiO2 catalysts during the photocatalytic process. By combining the experimental results and calculation data, the photocatalytic degradation pathways of carbofuran were proposed, including the addition of hydroxyl radicals and the cleavage of the carbamate side chain.