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Commercial non-functionalized (CNTs) and functionalized carbon nanotubes (CNT-COOH and CNT-NH2) were used as supports to synthesize vanadium-supported catalysts to be used in the gas phase partial oxidation of furfural towards maleic anhydride (MA). The CNTs and the VO2-V2O5/CNTs, so-called VO/CNT catalysts, were characterized by AAS, TGA, XRD, N2 adsorption isotherms at −196 °C, Raman, NH3-TPD and XPS. The surface area values, TGA and XRD results indicate that the larger thermal stability and larger dispersion of vanadium species is reached for the VO/CNT-NH2 catalyst. XPS indicates presence of surface VO2 and V2O5 species for the non-functionalized (CNT) and functionalized (CNT-COOH and CNT-NH2) catalysts, with a large interaction of the functional group with the surface vanadium species only for the VO/CNT-NH2 catalyst. The catalytic activity, evaluated in the range 305 °C to 350 °C, indicates that CO, CO2 and MA yield (%) and MA productivity are associated to the redox properties of the vanadium species, the oxygen exchange ability of the support and the vanadium–support interaction. For the reaction temperatures between 320 °C and 335 °C, the maximum MA yield (%) is found in the functionalized VO/CNT-COOH and VO/CNT-NH2 catalysts. This behavior is attributed to a decreased oxidation capability of the CNT with the functionalization. In addition, VO/CNT-NH2 is the more active and selective catalyst for MA productivity at 305 °C and 320 °C, which is related to the greater interaction of the surface vanadium species with the -NH2 group, which enhances the redox properties and stabilization of the VO2 and V2O5 surface active sites. Recycling at 350 °C resulted in 100% furfural conversion for all catalysts and a similar MA yield (%) compared to the fresh catalyst, indicating no loss of surface active sites. [ABSTRACT FROM AUTHOR]

An MCM-41-SO3H catalyst with 14 wt% S was successfully synthesized to be used in furfural production from xylose and hemicellulose in a biphasic n-butanol/water system. The precursor MCM-41 and the acid-functionalized MCM-41-SO3H catalyst were characterized by XRD, FTIR, TEM, N2 physisorption, ICP-MS, TPD-NH3, and XPS. The characterization results indicated that the sulfonic process partially decreased the ordered mesoporous structure and increased the acid strength of the initial MCM-41. The catalytic performance of the xylose conversion was evaluated in a batch-type reactor using different biphasic ecological and renewable n-butanol/water ratios (1:1, 1.5:1, 2:1, and 2.5:1) as dissolvent at 170 °C. The effect of the dissolvent mixture was clearly seen from the larger initial reaction rate and TOF values for the 1.5:1 ratio. This catalytic behavior indicated that a proper proportion of n-butanol/water dissolvent mixture enhanced the solubility of the substrate in the n-butanol-rich mixture and prevented the deactivation of acidic sulfonated surface groups. To achieve transformation of lignocellulosic raw material to value-added products, the MCM-41-SO3H catalyst was also used for the production of furfural. The recycling evaluation tests indicated that for the recovered catalyst submitted to a sulfonation process, the yield of furfural was closer to the fresh catalyst. [ABSTRACT FROM AUTHOR]

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed higher activity. The maximum benzyl alcohol conversions obtained were 93% and 97% using (TBA)5PMo10V2O40 and (TBA)5PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%. [ABSTRACT FROM AUTHOR]

Heterogeneous photocatalysis under visible light irradiation allows performing of selective oxofunctionalization of hydrocarbons at ambient temperature and pressure, using molecular oxygen as a sacrificial reagent and potential use of sunlight as a sustainable and low-cost energy source. In the present work, a photocatalytic material based on heterojunction of titanium dioxide and bismuth oxyiodide was used as photocatalyst on selective oxofunctionalization of cyclohexane and benzyl alcohol. The selective oxidation reactions were performed in a homemade photoreactor equipped with a metal halide lamp and injected air as a source of molecular oxygen. The identified oxidized products obtained from oxofunctionalization of cyclohexane were cyclohexanol and cyclohexanone. On the other hand, the product obtained from oxofunctionalization of benzyl alcohol was benzaldehyde. The yield obtained with BiOI/TiO2 photocatalysts was higher than that obtained with pure bismuth oxyiodide. The higher performance of this material with respect to pure BiOI was attributed to its higher specific area. [ABSTRACT FROM AUTHOR]