Effect of the support material (TiO2) synthesis conditions in chemical vapor condensation on the catalytic oxidation for 1,2-dichlorobenzene over V2O5/TiO2

Abatement of dichloromethane with high selectivity over defect-rich MOF-derived Ru/TiO2 catalysts

The regulation of oxygen vacancies and Ru species using metal-organic frameworks was synergically adopted in a rational design to upgrade Ru/TiO₂ catalysts, which are highly active for the catalytic oxidation of dichloromethane (DCM) with less undesired byproducts. In this work, Ru/M-TiO₂ and Ru/N-TiO₂ catalysts were synthesized by the pyrolysis of MIL-125 and NH₂-MIL-125 incorporated with Ru, the existence of Ru nanoclusters and nanoparticles was detected by XAFS, respectively, and the catalytic performance was analyzed comprehensively. Complete oxidation of DCM was obtained at ∼290 °C over Ru/M-TiO₂ and Ru/N-TiO₂ catalysts, while Ru/N-TiO₂ showed quite less monochloromethane (MCM) and higher CO₂ yields, and better dechlorination capacity in oxidation. The distinction comes down to that the easier desorption of chlorine could be achieved over Ru⁴⁺ which act as the main activated adsorption sites for DCM in Ru/N-TiO₂, compared to oxygen vacancies that serve as the main dissociation sites in Ru/M-TiO₂. Additionally, Ru/N-TiO₂ exhibited superior stability and excellent resilience in moisture. An in situ DRIFTS experiment further indicated the different DCM catalytic degradation process as well as the reaction mechanism over the as-prepared catalysts.

Influence of zirconia addition in TiO2 and TiO2-CeO2 aerogels on the textural, structural and catalytic properties of supported vanadia in chlorobenzene oxidation

This paper studies the effect of the direct incorporation of ZrO₂ in TiO₂ and TiO₂-CeO₂ aerogel supports prepared by sol-gel route on the physico-chemical and catalytic properties of supported vanadia catalysts in the total oxidation of chlorobenzene. The obtained catalysts have been characterized by means of ICP-AES, N₂ adsorption-desorption at 77 K, XRD, XPS, H₂-TPR and NH₃-TPD. The results revealed that Zr-doped V₂O₅ based catalyst is beneficial for the improvement of catalytic properties in chlorobenzene total oxidation. In particular, in the absence of cerium groups, this beneficial effect is correlated with the better acidic properties or/and the stabilization of the V₂O₅ active phase in a higher oxidation state. However, in the case of cerium rich catalyst, this positive effect is much stronger thanks to the enhanced redox properties of V₂O₅/TiO₂-CeO₂-ZrO₂.

V2O5/TiO2 and V2O5/TiO2–SO42− catalysts for the total oxidation of chlorobenzene: one-step sol–gel preparation vs. two-step impregnation

This paper examines the effect of the preparation method of sulfated and unsulfated V₂O₅/TiO₂ catalysts on chlorobenzene total oxidation.

Synthesis of V-modified TiO2 nanorod-aggregates by a facile microwave-assisted hydrothermal process and photocatalytic degradation towards PCP-Na under solar light

Herein, novel V-modified titania nanorod-aggregates (VTNA), consisting of fine individual nanorods in radial direction, were fabricated via an efficient microwave-assisted hydrothermal (MWH) route. VTNA with high crystallinity and homogeneous mesopores were obtained by 30 min MWH processing at 190 °C; moreover, a mixed rutile–anatase phase appeared after vanadium doping. XPS analysis revealed that vanadium existed in the forms of V⁴⁺ and V⁵⁺ on the surface of MWV05 with V⁵⁺ being the dominant component, the content of which was approximately 3.5 times that of V⁴⁺. Vanadium implanting was achieved efficiently by doping 0.5 and 1 at% V using a rapid MWH process and contributed towards the dramatic improvement of the visible-light response, with E_g decreasing from 2.91 to 2.71 and 2.57 eV with the increasing V doping content. MWV05 exhibited optimal photocatalytic degradation activity of water-soluble PCP-Na under solar light irradiation. The enhanced photodecomposition was attributed to the red-shift in the TiO₂ band-gap caused by vanadium impregnation, efficient charge separation due to the V⁴⁺/V⁵⁺ synergistic effects and the free migration of charge carriers along the radial direction of the nanorods arranged in a self-assembled VTNA microstructure.

V-modified titania nanorod-aggregates were fabricated by microwave hydrothermal route. MWV05 exhibited optimal solar activity towards PCP-Na, due to red-shift by V-doping, carriers separation by V⁴⁺/V⁵⁺ synergistic effects and charge migration along the nanorods.

Dual degradation of gaseous 1,2-dichlorobenzene and PCDD/Fs using Ce doped VxOy/TiO2 immobilized on cordierite

The photocatalytic film Ce doped VxOy/TiO2 was loaded on cordierite honeycomb (CHC), and this composite was prepared by sol-gel and dipping method, with Ce, oxides of V and TiO2 as dopant and key substances, respectively. Using gaseous 1,2-dichlorobenzene to replace dioxin as target pollutant, dual degradation experiments at 140-280 °C were carried out (thermal decomposition and photodegradation), and the effects of preparation conditions on catalytic activity were investigated: doping amount of Ce, dipping time in the gel, the concentration of ammonium metavanadate (NH4VO3) solution, dipping time in NH4VO3 solution, sintering temperature. The gaseous samples were taken before and after the reactor and analyzed by gas chromatography. According to the results, the optimal preparation conditions were determined, and the corresponding removal rate was above 95% after 90 min of degradation at 280 °C. The composite was examined by ultrasonic to analyze the adhesive strength between the film and CHC, and further characterized by XRD and SEM. Furthermore, flue gas from waste incinerator was chosen as target pollutant, which contained PCDD/Fs, the industrial sidestream degradation experiment was carried out and showed excellent removal efficiency of the composite, the removal rate of PCDD/Fs reached ca. 90% after 90 min of degradation.

Characterization and Deactivation Study of Mixed Vanadium and Potassium Oxide Supported on Microemulsion-Mediated Titania Nanoparticles as Catalyst in Oxidative Dehydrogenation of Propane

The influence of potassium addition to the vanadia supported on the microemulsion-mediated TiO2 nanoparticles in propane oxidative dehydrogenation was studied. Raman spectroscopy demonstrated that the addition of potassium caused enhanced dispersion of vanadia species on the support surface. Also, potassium existence affects the H2 temperature programmed reduction maximum reduction temperature and shifted it to 520°C, which was in accordance with its lesser catalytic activity. Nevertheless, a propylene selectivity enhancement was observed by potassium addition. In spite of the fact that the catalytic performance loss was not severe in vanadia-supported TiO2 anatase, potassium addition led to improve the catalyst lifetime. After deactivation test, potassium-containing vanadia catalyst possessed lower surface area loss (i.e. from 52 to 49 m2 g−1). Average crystallite size of potassium-containing vanadia catalyst exhibited lower decrease than that of potassium-free vanadia catalyst after deactivation test. According to Raman spectra, deactivation phenomena had influenced the population of vanadia species so that monovanadates decreased and polyvanadates increased.

Titanium dioxide as a catalyst support in heterogeneous catalysis

The lack of stability is a challenge for most heterogeneous catalysts. During operations, the agglomeration of particles may block the active sites of the catalyst, which is believed to contribute to its instability. Recently, titanium oxide (TiO₂) was introduced as an alternative support material for heterogeneous catalyst due to the effect of its high surface area stabilizing the catalysts in its mesoporous structure. TiO₂ supported metal catalysts have attracted interest due to TiO₂ nanoparticles high activity for various reduction and oxidation reactions at low pressures and temperatures. Furthermore, TiO₂ was found to be a good metal oxide catalyst support due to the strong metal support interaction, chemical stability, and acid-base property. The aforementioned properties make heterogeneous TiO₂ supported catalysts show a high potential in photocatalyst-related applications, electrodes for wet solar cells, synthesis of fine chemicals, and others. This review focuses on TiO₂ as a support material for heterogeneous catalysts and its potential applications.