Influence of WO3 Content in Phosphated Tungsten-Zirconium Oxide Catalysts on the Catalytic Pathways of Glycerol Transformation

The catalytic performance of phosphate-stabilized WOx-ZrO2 compositions in gas-phase glycerol dehydration has been investigated. Results show that varying WO3 concentrations direct the process towards either acrolein or allyl alcohol formation. Catalysts with low WOx content exhibit strong Lewis acid sites (Zr4+ and W6+), where these metal ions likely function as redox sites, facilitating glycerol hydrogenolysis to produce allyl alcohol. Higher WOx concentrations (exceeding 20 wt %) lead to the shielding of some W6+ and Zr4+ sites by polytungstate surface complexes, which are strong Brønsted acid sites. This alteration promotes glycerol dehydration through the removal of two water molecules, thereby shifting the selectivity towards acrolein formation.

Tungsten-Based Catalysts for Environmental Applications

This review aims to give a general overview of the recent use of tungsten-based catalysts for wide environmental applications, with first some useful background information about tungsten oxides. Tungsten oxide materials exhibit suitable behaviors for surface reactions and catalysis such as acidic properties (mainly Brønsted sites), redox and adsorption properties (due to the presence of oxygen vacancies) and a photostimulation response under visible light (2.6–2.8 eV bandgap). Depending on the operating condition of the catalytic process, each of these behaviors is tunable by controlling structure and morphology (e.g., nanoplates, nanosheets, nanorods, nanowires, nanomesh, microflowers, hollow nanospheres) and/or interactions with other compounds such as conductors (carbon), semiconductors or other oxides (e.g., TiO2) and precious metals. WOx particles can be also dispersed on high specific surface area supports. Based on these behaviors, WO3-based catalysts were developed for numerous environmental applications. This review is divided into five main parts: structure of tungsten-based catalysts, acidity of supported tungsten oxide catalysts, WO3 catalysts for DeNOx applications, total oxidation of volatile organic compounds in gas phase and gas sensors and pollutant remediation in liquid phase (photocatalysis).

CuO modified vanadium-based SCR catalysts for Hg0 oxidation and NO reduction

The catalytic performance of Hg⁰ oxidation over vanadium-based SCR catalysts modified by different addition amounts of CuO was investigated. All catalysts were prepared by impregnation method and characterized. The 7% Cu/VWTi exhibited high Hg⁰ oxidation as well as a desired NO removal efficiency at 280-360 °C. The characterization revealed the enhancement of redox properties and well-dispersed active species results in the high catalytic performance after modification. The incorporation model showed that CuO in 7% Cu/VWTi was present in the monolayer dispersion, leading to the highest performance. Moreover, the effects of O₂, NO, SO₂, NH₃ and HCl were explored. It showed all flue gas except NH₃ could promote Hg⁰ oxidation. Fortunately, the inhibiting effect of NH₃ could be scavenged if the catalyst is installed at the downstream of the SCR reactor. In addition, the mechanism of Hg⁰ oxidation over Cu/VWTi was discussed.

Nano-sized mesoporous phosphated tin oxide as an efficient solid acid catalyst

Herein, we prepared a mesoporous tin oxide catalyst (mSnO2) activated with phosphate species by the adsorption of phosphate ions from a phosphoric acid solution onto tin oxyhydroxide (Sn(OH)4) surface. The phosphate content ranged from 3 to 45 wt%. The nonaqueous titration of n-butylamine in acetonitrile was used to determine the total surface acidity level. FTIR of chemically adsorbed pyridine was used to differentiate between the Lewis and Brönsted acid sites. Thermal and X-ray diffraction analysis indicated that the addition of phosphate groups stabilized the mesostructure of mSnO2 and enabled it to keep its crystalline size at the nanoscale. FTIR analysis indicated the polymerization of the HPO4 2- groups into P2O7 4-, which in turn reacts with SnO2 to form a SnP2O7 layer, which stabilizes the mesoporous structure of SnO2. The acidity measurements showed that the phosphate species are distributed homogeneously over the mSnO2 surface until surface saturation coverage at 25 wt% PO4 3-, at which point the acid strength and surface acidity level are maximized. The catalytic activity was tested for the synthesis of hydroquinone diacetate, where it was found that the % yield of hydroquinone diacetate compound increased gradually with the increase in PO4 3- loading on mSnO2 until it reached a maximum value of 93.2% for the 25% PO4 3-/mSnO2 catalyst with 100% selectivity and excellent reusability for three consecutive runs with no loss in activity.

Perlite: an inexpensive natural support for heterogenization of HBF4

Nano-perlite-fluoroboric acid (n-PeFBA) has been synthesized by immobilization of HBF₄ on perlite as a natural and cheap support to produce an efficient green heterogeneous reusable solid acid catalyst.

Expanded perlite: an inexpensive natural efficient heterogeneous catalyst for the green and highly accelerated solvent-free synthesis of 5-substituted-1H-tetrazoles using [bmim]N3 and nitriles

A versatile, green and highly accelerated protocol for preparing 5-substituted-1H-tetrazoles is reported using expanded perlite as a heterogeneous catalyst.