Support effects on structure and activity of molybdenum oxide catalysts for the oxidative dehydrogenation of ethane

The structural and catalytic properties of MoO₃ catalysts supported on ZrO₂, Al₂O₃, TiO₂ and SiO₂ with Mo surface densities, n_s, in the range of 0.5–18.5 Mo/nm² were studied for the oxidative dehydrogenation (ODH) of ethane by in situ Raman spectroscopy and catalytic activity measurements at temperatures of 400–540 °C. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO₄ and MoO₅, depending on the support) at low loadings to associated MoO_x units in polymolybdate chains at high loadings and ultimately to bulk crystalline phases for loadings exceeding the monolayer coverage of the supports used. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behaviour of the molybdena catalysts with monolayer coverage. The dependence of reactivity on the support follows the order ZrO₂ > Al₂O₃ > TiO₂ > SiO₂. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity.     

Understanding the activation mechanism induced by NOx on the performances of VOx/TiO2 based catalysts in the total oxidation of chlorinated VOCs

A previous investigation of the chlorobenzene combustion activity of VO_x/TiO₂, VO_x–WO_x/TiO₂ and VO_x–MoO_x/TiO₂ catalysts in the presence of NO pointed out the activation effect of NO. The suggested three-step mechanism based on catalytic performances data only was: (1) chlorobenzene is oxidized on the surface of the VO_x phase (as described by Mars–van Krevelen), (2) NO gets oxidized to NO₂, mainly on WO_x and MoO_x, and (3) the in situ produced NO₂ assists O₂ in the reoxidation of the VO_x phase thus speeding up the oxidation step of the Mars–van Krevelen mechanism. The latter effect macroscopically corresponds to the observed increase of chlorobenzene conversion. This contribution aims at validating this hypothetical mechanism by pointing out the favourable occurrence of an oxidation of NO to NO₂ on the WO_x and MoO_x phases and by pointing out the higher efficiency of NO₂ than O₂ to reoxidize the reduced VO_x sites. In addition, the present contribution clearly demonstrates that, in the absence of NO, the chlorobenzene total oxidation occurred following the Mars–van Krevelen mechanism. Moreover, a thorough characterization of the oxidation state of the vanadium proving that the improvement of the catalyst activity brought by the simultaneous presence of NO and O₂ is linked to the stronger reoxidation of the VO_x active phase. Furthermore, plotting all the catalytic activity data versus the mean vanadium oxidation level clearly depicts, for the first time, the strong dependence between them. Under a mean vanadium oxidation level of 4.82 the catalyst is inactive while above 4.87 the activity is stabilized at a high level of conversion independent of the vanadium oxidation level.     

Photocatalytic performance of nanometer-sized FexOy/TiO2 particle synthesized by hydrothermal method

The nanometer particles of two Fe_xO_y/TiO₂’s with high photocatalytic activities were obtained through hydrothermal treatment and impregnation method. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe_xO_y/TiO₂ attained through hydrothermal treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. In addition, it exhibited uniform anatase structure with particle size of below 50 nm. The FeO₃ component on the external surface of the TiO₂ anatase structure was identified in the Fe-loaded TiO₂ prepared through the impregnation method. In particular, the FT-IR spectroscopy revealed that the Fe_xO_y/TiO₂ particle attained through hydrothermal treatment had higher hydrophilic property compared to the other catalysts. Together with the Fe component, they absorbed wavelength of above 370 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe_xO_y/TiO₂ particle attained through hydrothermal method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. Despite the red shift in UV-Vis absorption, however, CHCl₃ decomposition on the Fe_xO_y/TiO₂ catalyst was not largely enhanced compared to pure TiO₂.     

Oxygen-deficient MoOx/Ni3S2 heterostructure grown on nickel foam as efficient and durable self-supported electrocatalysts for hydrogen evolution reaction

High-performance and ultra-durable electrocatalysts are vital for hydrogen evolution reaction (HER) during water splitting. Herein, by one-pot solvothermal method, MoO_x/Ni₃S₂ spheres comprising Ni₃S₂ nanoparticles inside and oxygen-deficient amorphous MoO_x outside in situ grow on Ni foam (NF), to assembly the heterostructure composites of MoO_x/Ni₃S₂/NF. By adjusting volume ratio of the solvents of ethanol to water, the optimized MoO_x/Ni₃S₂/NF-11 exhibits the best HER performance, requiring an extremely low overpotential of 76 mV to achieve the current density of 10 mA∙cm^‒2 (η₁₀ = 76 mV) and an ultra-small Tafel slope of 46 mV∙dec^‒1 in 0.5 mol∙L^‒1 H₂SO₄. More importantly, the catalyst shows prominent high catalytic stability for HER (> 100 h). The acid-resistant MoO_x wraps the inside Ni₃S₂/NF to ensure the high stability of the catalyst under acidic conditions. Density functional theory calculations confirm that the existing oxygen vacancy and MoO_x/Ni₃S₂ heterostructure are both beneficial to the reduced Gibbs free energy of hydrogen adsorption (|∆G_H*|) over Mo sites, which act as main active sites. The heterostructure effectively decreases the formation energy of O vacancy, leading to surface reconstruction of the catalyst, further improving HER performance. The MoO_x/Ni₃S₂/NF is promising to serve as a highly effective and durable electrocatalyst toward HER.     

Interaction between Pt and MoO3 dispersed over alumina

Pt–xMo/γ-Al₂O₃ catalysts of different molybdenum loading (2–20 wt.%) and with 1 wt.% of platinum were prepared by successive wet impregnation after intermediate calcination. The structure, morphology and surface were characterized by various methods. The DRS results indicate the presence of octahedral Mo⁶⁺ and tetrahedral Mo⁶⁺ phases. It also evidences the presence of polymeric MoO_x species, responsible for the formation of a well dispersed surface sublayer and bulk MoO₃ crystalline phase. XPS results after reduction and passivation of the 1Pt and 1Pt2Mo revealed the presence of residual chlorine, in the form of surface species such as [Pt(OH)_xCl_y]_s and [PtO_xCl_y]_sfavoring the formation of well dispersed platinum particles. The TPD and FTIR results are consistent with the existence of new active sites of Pt in the presence of molybdenum loading. For low Mo content there is a H₂ spillover effect. These results confirm the decoration model of Pt encapsulation by partially reduced Mo species as well as H₂ storage and backspillover due to the generation of a bronze compound.     

Catalysts for chlorinated VOCs abatement: Multiple effects of water on the activity of VOx based catalysts for the combustion of chlorobenzene

The influence of H₂O on the performances of VO_x/TiO₂, VO_x-WO_x/TiO₂ and VO_x-MoO_x/TiO₂ catalysts is investigated in the combustion of chlorobenzene. H₂O proves to influence in opposite manners the chlorobenzene conversion depending on its concentration and on the kind of catalysts. The overall influence of water is the sum of three effects, two negative: (1) the reduction of the vanadium phase dictated by its reducibility, itself influenced by the presence of WO_x or MoO_x, (2) the decrease of the number of strong Brönsted acid sites involved in the adsorption of the chlorobenzene and one positive (3) the retrieval of chlorine species from the surface through the production of HCl.     

Preparations and photocatalytic properties of magnetically separable nitrogen-doped TiO2 supported on nickel ferrite

A magnetically separable nitrogen-doped photocatalyst TiO_2−xN_x/SiO₂/NiFe₂O₄ (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO₂/NiFe₂O₄ (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO_2−xN_x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO₂/NiFe₂O₄ (SN) nanoparticles adhere to the surface of TiO_2−xN_x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO₂ coating round the surface of NiFe₂O₄ nanoparticles prevents effectively the injection of charges from TiO₂ particles to NiFe₂O₄, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity.     

Vanadium-containing catalysts for the selective oxidation of H2S to elemental sulfur in the presence of excess water

Various vanadium-containing catalysts were searched for the commercial application in the selective oxidation of H₂S to elemental sulfur at low temperatures (less than 250°C) in the presence of excess (more than 35 vol.%) water. In the test of binary oxides, it was found that TiVO_x was the only catalyst that could sustain its activity without deactivation at 230°C. The best catalytic activity (85–90% sulfur yield) was obtained when VO_x/TiO₂ was incorporated with other metals such as Fe, Cr and Mo. Reaction occurred via redox mechanism and the reoxidation of reduced vanadium was the rate-limiting step. A long-term deactivation observed during the reaction was due to slower reoxidation of reduced vanadium by oxygen than the reduction by H₂S. Catalytic activities of VO_x/SiO₂, VO_x/TiO₂ and V–Fe–Cr–Mo–O_x/TiO₂ were well correlated with their redox properties that were observed by TPR/TPO and XPS measurements.     

Tuning the selectivity of MoOx supported catalysts for cyclohexane photo oxidehydrogenation

The photocatalytic properties of sulphated MoO_x/γ-Al₂O₃ catalysts in cyclohexane oxidative dehydrogenation have been determined in a two-dimensional fluidized bed photoreactor and compared to those of sulphated MoO_x/TiO₂ catalysts. Photocatalytic tests on MoO_x/γ-Al₂O₃ at 8 wt% MoO₃ and various sulphate contents showed the selective (100%) formation of cyclohexene, without production of benzene, as instead found with MoO_x/TiO₂. These results show that the selectivity of photocatalytic cyclohexane oxydehydrogenation is dramatically influenced by the catalyst support.

Maximum cyclohexane conversion and cyclohexene yield of 11% were obtained for SO₄ content of 2.6 wt% at 120 °C. Physico-chemical characterisation of catalysts indicates the presence of both octahedral polymolybdate and sulphate species on alumina surface, as previously found for titania. Increasing sulphate load, thermogravimetry evidenced the presence of up to three sulphate species at different thermal stability. The lower activity observed at high sulphate content is likely due to polymolybdate decoration by sulphates.     

Catalytic activation of ceramic filter elements for combined particle separation, NOx removal and VOC total oxidation

The development of a catalytically active filter element for combined particle separation and NO_x removal or VOC total oxidation, respectively, is presented. For NO_x removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO₂–V₂O₅–WO₃ catalyst system was developed on a ceramic filter element. Different TiO₂ sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO₂-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m²/g. Selected TiO₂-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V₂O₅ and WO₃ precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO₂-impregnated filter element support was catalytically activated with a Pt/V₂O₅ system. Complete oxidation of propene with 100% selectivity to CO₂ was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm.     

Synthesis, characterization and photocatalytic activity of N-doped TiO2 modified by platinum chloride

Structures and photocatalytic performance of N-doped TiO₂ modified by platinum chloride (PtCl_x/N-TiO₂) was investigated. It was found that the PtCl_x/N-TiO₂ forms anatase structure of TiO₂ involving nitrogen, chloride species and platinum ions (+IV) as major species, and it exhibits higher photocatalytic activity than either N-TiO₂ or PtCl_x/TiO₂ for the decomposition of acetic acid or acetaldehyde in aqueous solutions under visible light irradiation (λ > 420 nm). An enhancement of the photocatalytic activity on PtCl_x/N-TiO₂ has been proposed as a Z-scheme mechanism for charge separation between platinum chloride and N-TiO₂.     

Conversion of N2O to N2 on TiO2(1 1 0)

In this study, we examine the interaction of N₂O with TiO₂(1 1 0) in an effort to better understand the conversion of NO_x species to N₂ over TiO₂-based catalysts. The TiO₂(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO₂(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti³⁺ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N₂O molecules adsorbed at 90 K on TiO₂(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N₂O molecules exposed to TiO₂(1 1 0) at 90 K decompose to N₂ via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N₂ ejection from the surface and vacancy oxidation. We propose that this channel involves N₂O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N₂O that decomposes at 170 K to liberate N₂ in the gas phase and deposit oxygen adatoms at non-defect Ti⁴⁺ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N₂O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti⁴⁺ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N₂O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N₂O at 90 K, and this charge transfer facilitates N₂O decomposition. Based on these results, it appears that the decomposition of N₂O to N₂ requires trapping of the molecule at vacancies and that the lifetime of the N₂O–vacancy interaction may be key to the conversion of N₂O to N₂.     

Enhanced high-potential and elevated-temperature cycling stability of LiMn2O4 cathode by TiO2 modification for Li-ion battery

The surface of spinel LiMn₂O₄ was modified with TiO₂ by a simple sol–gel method to improve its electrochemical performance at elevated temperatures and higher working potentials. Compared with pristine LiMn₂O₄, surface-modification improved the cycling stability of the material. The capacity retention of TiO₂-modified LiMn₂O₄ was more than 85% after 60 cycles at high potential cycles between 3.0 and 4.8 V at room temperature and near to 90% after 30 cycles at elevated temperature of 55 °C at 1C charge–discharge rate. SEM studies shows that the surface morphology of TiO₂-modified LiMn₂O₄ was different from that of pristine LiMn₂O₄. Powder X-ray diffraction indicated that spinel was the only detected phase in TiO₂-modified LiMn₂O₄. Introduction of Ti into LiMn₂O₄ changed the electronic structures of the particle surface. Therefore a surface solid compound of LiTi_xMn_2−xO₄ may be formed on LiMn₂O₄. The improved electrochemical performance of surface-modified LiMn₂O₄ was attributed to the improved stability of crystalline structure and the higher Li⁺ conductivity.     

SO2 resistant antimony promoted V2O5/TiO2 catalyst for NH3-SCR of NOx at low temperatures

To get the low temperature sulfur resistant V₂O₅/TiO₂ catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V₂O₅/TiO₂ catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V₂O₅/TiO₂ catalysts showed high catalytic activity for NH₃ selective catalytic reduction (NH₃-SCR) of NO_x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V₂O₅/TiO₂ > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V₂O₅/TiO₂ for maximum NO_x conversion, which also showed high resistance to SO₂ in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V₂O₅/TiO₂ and compared with commercial W(10%)V₂O₅/TiO₂ catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V₂O₅/TiO₂ catalyst with temperature was observed. SO₂ deactivation experiments were carried out for Sb(2%)/V₂O₅/TiO₂ and W(10%)/V₂O₅/TiO₂ at a temperature of 230 °C for 90 h, resulted Sb(2%)/V₂O₅/TiO₂ was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V₂O₅/TiO₂ than Sb(2%)/V₂O₅/TiO₂ catalyst.     

The structures of VOx/MOx and alkali-VOx/MOx catalysts and their catalytic performances for soot combustion

Vanadium oxides supported on γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ were studied on their molecular structures and reactive performances for soot combustion. To investigate the effect of different alkali metals on the structures and reactivities of supported-vanadium oxide catalysts, they were doped into the V₄/TiO₂ catalyst which had the best intrinsic activity for soot combustion in the selected supported vanadium oxide catalysts. The experimental results demonstrated that the catalytic properties of these catalysts depended on the vanadium loading amount, support nature, and the presence or the absence of alkali metals. The spectroscopic analysis (FT-IR and UV–vis) and H₂-TPR results revealed that the higher activity of alkali-promoted vanadium oxide catalysts could be related to the ability of alkali metal promoting the redox cycle of the active vanadyl species. TG results showed that adding alkali to V_m/TiO₂ catalyst was beneficial to lowering their melting points. Low melting points could ensure the good surface atom migration ability, which would improve the contact between the catalyst and soot. Due to the alkali metal components promoting the redox ability and the mobility of the catalysts, alkali-modified vanadium oxide catalysts could remarkably improve their catalytic activities for soot combustion. The catalytic activity order for soot combustion followed Li > Na > K > Rb > Cs in the catalyst system of alkali-V₄/TiO₂, and the reason why it followed this sequence was discussed.     

Hydroisomerization of n-heptane and dehydration of 2-propanol on bulk and supported WO2(Hx)ac on TiO2

Characterization by XPS–UPS and XRD of commercial bulk WO₂ enabled us to identify the presence of four to five layers of WO₃ on the sample surface with an equal amount of W⁵⁺, possibly W₂₀O₅₈ in the interface. The presence of these WO₃ and W₂₀O₅₈ on the WO₂ surface were not detected by XRD. Exposure of commercial bulk WO₂ to hydrogen at temperatures higher than 673 K results in the reduction of surface WO₃ to WO₂ and the formation of the bifunctional WO₂(H_x)_ac phase on its surface. A complete conversion of surface WO₃ to WO₂(H_x)_ac has been obtained following the exposure of the sample to hydrogen for at least 6 h at 773 K. A conversion of 52% of n-heptane at 573 K reaction temperature and a selectivity of 90% in isomerization products, mainly 2,3-MH and multibranched molecules were obtained. The isomerization products distribution is in agreement with the statistical and thermodynamic equilibrium of the methyl-shift mechanism. The stability of the active WO₂(H_x)_ac phase has been tested under prolonged exposure to hydrogen and the reaction mixture. Similar results were obtained in the case of bulk WO₃ and WO₃/TiO₂ systems. Dehydration and dehydrogenation of 2-propanol were studied on these systems at 393 K reaction temperature.     

Spectroscopic ellipsometry characterization of TiO2 thin films prepared by the sol–gel method

TiO₂ thin films were prepared on SiO₂/Si(100) substrates by the sol–gel process. XRD results indicate that the major phase of TiO₂ thin films is anatase. The surface morphology and cross-section are observed by FE-SEM. The surface of thin films is dense, free of cracks and flat. The average grain size is about 60–100 nm in diameter. The thickness of single layer TiO₂ thin films is about 60 nm, which increases with the concentration of solution. Ellipsometric angles ψ, Δ are investigated by spectroscopic ellipsometry. The optical constant and the thickness of TiO₂ thin films are fitted according to Cauchy dispersion model. The results reveal that the refractive index and the extinction coefficient of TiO₂ thin films in wavelength above 800 nm are about 2.09–2.20 and 0.026, respectively. The influences of processing conditions on the optical constants and thicknesses of TiO₂ thin films are also discussed.     

Synthesis of nanosized TiO2/SiO2 particles in the microemulsion and their photocatalytic activity on the decomposition of p-nitrophenol

Nanosized pure TiO₂ particles were prepared by hydrolysis of TTIP in the sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles. TiO₂/SiO₂ nanoparticles were also prepared from TEOS as a silicon source and TTIP as a titanium source. These particles were characterized by TEM, XRD, FT-IR, BET, TGA and DTA. From thermal analysis and XRD analysis, the anatase structure of pure titania appeared in the 300–600 °C calcination temperature range and the rutile structure was showed above 700 °C. However, no rutile phase was observed for the TiO₂/SiO₂ particles up to 800 °C. The crystallite size decreased and the surface area of TiO₂/SiO₂ particles monotonically increased with an increase of the silica content. From FT-IR analysis, the band for Ti–O–Si vibration was observed and the band intensity for Si–O–Si vibration increased with an increase of the silica content. The micrographs of TEM showed that the TiO₂/SiO₂ nanoparticles had a spherical and a narrow size distribution. In addition, TiO₂/SiO₂ particles showed higher photocatalytic activity than pure TiO₂ and the TiO₂/SiO₂ (90/10) particles showed the highest activity on the photocatalytic decomposition of p-nitrophenol.     

Effects of hydrothermal temperature and time on the photocatalytic activity and microstructures of bimodal mesoporous TiO2 powders

Bimodal nanocrystalline mesoporous TiO₂ powders with high photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate (TiO(C₄H₉)₄, TBOT) as precursor. The as-prepared TiO₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption–desorption measurements. The photocatalytic activity of the as-prepared TiO₂ powders was evaluated by the photocatalytic degradation of acetone (CH₃COCH₃) under UV-light irradiation at room temperature in air. The effects of hydrothermal temperature and time on the microstructures and photocatalytic activity of the TiO₂ powders were investigated and discussed. It was found that hydrothermal treatment enhanced the phase transformation of the TiO₂ powders from amorphous to anatase and crystallization of anatase. All TiO₂ powders after hydrothermal treatment showed bimodal pore-size distributions in the mesoporous region: one was intra-aggregated pores with maximum pore diameters of ca. 4–8 nm and the other with inter-aggregated pores with maximum pore diameters of ca. 45–50 nm. With increasing hydrothermal temperature and time, the average crystallite size and average pore size increased, in contrast, the Brunauer-Emmett-Teller (BET) specific surface areas, pore volumes and porosity steadily decreased. An optimal hydrothermal condition (180 °C for 10 h) was determined. The photocatalytic activity of the prepared TiO₂ powders under optimal hydrothermal conditions was more than three times higher than that of Degussa P25.     

Structure–reactivity relationships in VOx/TiO2 catalysts for the oxyhydrative scission of 1-butene and n-butane to acetic acid as examined by in situ-spectroscopic methods and catalytic tests

Different VO_x/TiO₂ catalyst have been catalytically tested and studied by in situ-spectroscopic methods (FT-IR, UV/vis, EPR) in the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid (AcOH). While 1-butene OHS follows the sequence butene → butoxide → ketone → AcOH/acetate with a multitude of side products also formed, n-butane OHS leads to AcOH, CO_x and H₂O only. Water vapour in the feed improves AcOH selectivity by blocking adsorption sites for acetate. The admixture of Sb₂O₃ was found to improve AcOH selectivity which is due to deeper V reduction under steady state conditions and lowering of surface acidity. VO_x/TiO₂ catalysts with sulfate-containing anatase are the most effective ones. Covalently bonded sulfate at the catalyst surface causes specific bonding of VO_x, stabilizes active V species and ensures their high dispersity.