Catalytic behavior of YBa2Cu3O7-x in the partial oxidation of ethanol to acetaldehyde

The partial oxidation of ethanol to acetaldehyde was performed over YBa₂Cu₃O_7-x in a flow reactor. The catalytic characteristics of YB₂Cu₃O_7-x were compared with those of an individual oxide comprising the YBa₂Cu₃O_7-x . The structural change of YBa₂Cu₃O_7-x and the other catalysts after the reaction was measured by means of XRD and XPS, and it was found that the high oxidation state of copper in YBa₂Cu₃O_7-x was responsible for the higher activity and the higher selectivity for acetaldehyde.     

Corrosion behavior of high-temperature superconductor YBa2Cu3-yAgyO7-x in the presence of water

Because of the presence of water vapor, YBa₂Cu₃O_7-x degrades easily in the atmosphere and thus very difficult to put it to practical use. When Cu is partially substituted with Ag, however, there is not much a decrease in the critical temperature (T_c) : T_c is 89 K compared with 91 K without substitution. Moreover, partial substitution of Ag increases density, hardness, and superconducting particle size and above all improves considerably its stability in water. In this study YBa₂Cu₃O_7-x and YBa₂Cu_3-yAg_yO_7-x as a result of a partial substitution of Ag for Cu were synthesized by pyrophoric method. We investigated their stabilities in water by XRD, SEM, and EPMA after immersing samples in distilled water for 3 hours. We can see that YBa₂Cu_2.94Ag_0.06O_7-x was the largest particle size and anticorrosion behavior.     

Ammoxidation of toluene over Y-Ba-Cu-Co-O perovskites

Ammoxidation of toluene over the perovskites YBa₂Cu₃O_6.1, YBa₂Cu₂CoO_6.7 and YBaCuCoO_4.9 was investigated at 400 °C. At low partial pressures of O₂ benzonitrile was selectively formed, while CO₂ was the main product at high pressures of O₂. Systematic differences in activity were observed for the three phases and are related to the crystal contents of Cu and Co. At low O₂ pressures, Cu-sites are active for nitrile formation, while Co-sites give CO₂. At high O₂ pressures, the activity for CO₂ of Cu-sites increases more than that of Co-sites due to filling of near-surface oxygen vacancies.     

Treatment of exhaust gases from a methanol fueled vehicle over perovskite oxide catalysts

As a study on the treatment of exhaust gases from a methanol-fueled vehicle, catalytic oxidation of formaldehyde and methanol on perovskite-type oxides was performed. La_0.8Sr_0.2MnO₃, La_0.8Sr_0.2CoO₃, YBa₂Cu₃O₇ (superconductor), and ErBa₂Cu₃O₇ (superconductor) were used as catalysts. La-based catalysts were prepared by a citrate method and calcined at 650°C, 800°C, and 900°C, respectively. The catalytic activity of La-based catalysts increased with the increase in the surface area that was dependent on the calcination temperature. Superconductive oxides were also prepared by a citrate method and calcined at 920°C. The catalytic activity of ErBa₂Cu₃O₇ was found to be better than that of YBa₂Cu₃O₇. For La-based perovskite calcined at 650°C, the catalytic activity of La_0.8Sr_0.2MnO₃ was higher than La_0.8Sr_0.2CoO₃. Calcining at 800°C and 900°C, however, the catalytic activity of LLa_0.8Sr_0.2 CoO₃ was higher than La_0.8Sr_0.2MnO₃.     

The influence of inter-granular coupling on the magnetic susceptibility and critical current density of YBa2(Cu1−xAgx)3O7−δ superconductors prepared by ethylene glycol assisted solvothermal approach

Series of YBa₂(Cu_1−xAg_x)₃O_7−δ (0≤x≤0.09) powders were prepared by ethylene glycol assisted solvothermal approach. X-ray diffraction verified the formation of single phase crystal structure for all the investigated samples, implying the complete solubility of the silver ions into YBa₂Cu₃O₇. The partial substitution of the Ag atoms into the Cu sites caused a decrease of the lattice constant (c) and an increase of the lattice constants, a, and, b, to preserve the orthorhombic crystal structure of YBa₂Cu₃O₇. The scanning electron microscopy depicted that the incorporation of silver ions into copper sites adjusts the random orientations of the YBCO grains and suppresses the formation of grain boundary. The AC magnetic susceptibility measurement revealed that the superconducting performance of the YBa₂Cu₃O₇ is preserved at all Ag concentrations. The critical current density, J_c, measurement revealed that the addition of the Ag into the YBCO caused a strong pinning force is established due to the strong coupling among the grains instead of the weak Josephson junctions and in turn a remarkable increase of the zero field J_c from 2.7 MA/cm² to 9.1 MA/cm² was achieved.     

Comparative studies on direct conversion of methane to methanol/formaldehyde over La–Co–O and ZrO2 supported molybdenum oxide catalysts

The selective oxidation of methane with molecular oxygen over MoO_x/La–Co–O and MoO_x/ZrO₂ catalysts to methanol/formaldehyde has been investigated in a specially designed high-pressure continuous-flow reactor. The properties of the catalysts, such as crystal phase, structure, reducibility, ion oxidation state, surface composition and the specific surface area have been characterized with the use of XRD, LRS, TPR, XPS and BET methods. MoO_x/La–Co–O catalysts showed high selectivity to methanol formation while MoO_x/ZrO₂ revealed the property for the formation of formaldehyde in the selective oxidation of methane. 7 wt MoO_x/La–Co–O catalyst gave 6.7 methanol yield (ca. 60 methanol selectivity) at 420°C and 4.2 MPa. On the other hand, the maximal yield of formaldehyde ca. 4 (47.8 formaldehyde selectivity) was obtained over 12wt MoO_x/ZrO₂ catalyst at 400 °C and 5.0MPa. 7MoO_x/La–Co–O catalyst showed higher modified H₂-consumption than 12MoO_x/ZrO₂ catalyst. The reducibility and the O^–/O^2– ratio of the catalysts may play important roles on the catalytic performance. The proper reducibility and the O^–/O^2– ratio enhanced the production of methanol in selective oxidation of methane. [MoO₄]^2– species in MoO_x/ZrO₂ catalysts enable selective oxidation of methane to formaldehyde.     

Catalytic Oxidation of CO Gas over Nanocrystallite Cu x Mn1−x Fe2O4

The catalytic oxidation of CO over nanocrystallite Cu _x Mn_(1−x)Fe₂O₄ powders was studied using advanced quadruple mass gas analyzer system. The oxidation of CO to CO₂ was investigated as a function of reactants ratio and firing temperature of ferrite powders. The maximum CO conversion was observed for ferrite powders which have equal amount of Cu²⁺ and Mn²⁺ (Cu_0.5Mn_0.5Fe₂O₄). The high catalytic activity of Cu_0.5Mn_0.5Fe₂O₄ can be attributed to the changes of the valence state of catalytically active components of the ferrite powders. The firing temperature plays insignificant role in the catalytic activity of CO over nanocrystallite copper manganese ferrites. The mechanism of catalytic oxidation reactions was studied. It was found that the CO catalytic oxidation reactions on the surface of the Cu _x Mn_1−x Fe₂O₄ was done by the reduction of the ferrite by CO to the oxygen deficient lower oxide then re-oxidation of this phase to the saturated oxygen metal ferrite again.     

A thermogravimetric study of the partial oxidation of methanol for hydrogen production over a Cu/ZnO/Al2O3 catalyst

The partial oxidation of methanol for the production of hydrogen was investigated in both a fixed-bed microreactor and in a thermogravimetric analyzer (TG-FTIR) from 180 °C to 250 °C using a commercial Cu/ZnO/Al₂O₃ catalyst. In the microreactor, a hot spot in the undiluted catalyst bed of 4 K and 32 K was observed at 180 °C and 220 °C, respectively. Methanol conversion was strongly accelerated between 180 °C and 220 °C. In the TG-FTIR experiments, the reduced copper was completely oxidized to cuprite, Cu₂O, with increasing time-on-stream in the presence of oxygen and methanol (O₂/MeOH = 0.5) at 180 °C. The selectivity to formaldehyde increased in the same manner as the catalyst was oxidized to cuprite. In contrast, at 250 °C the catalyst remained completely reduced for the same O₂/MeOH ratio. Two main reaction pathways are proposed explaining the influence of the copper oxidation state on the product distribution.     

Orthorhombic YBCO-123 ceramic oxide superconductor: Structural,resistive and thermal properties

Two YBa₂Cu₃O_7-x materials (YBCO-I sintered at 1000?°C, and YBCO-II sintered at 960?°C and following special cooling programs) belonging to the orthorhombic system were obtained. YBCO-I has a complete volume texture, while for YBCO-II it is only on sample surface. On heating in air (with 10?K?min^?1 in the temperature range 20–1000?°C), two endothermic processes are recorded on DSC curves (of YBCO-II) and they are due to oxygen diffusion from O1 to O5 sites, and then to the release into the environment; second endothermic effect is attributed to the decomposition reaction. Different behaviour is encountered on heating in argon: an endothermic process in two steps; continuous mass decrease (oxygen loss) during argon cooling is recorded on the thermogravimetric curve. In argon atmosphere, the obtained material shall correspond to the chemical composition: YBa₂Cu₃O_6.77, while in air atmosphere, the maximal composition than may be obtained is: YBa₂Cu₃O_6.88. The barrier energies from Arrhenius plots of resistivity vs. temperature (91–93?K) show 2D (YBCO-I) and 3D (YBCO-II) behaviour for the thermally activated flow of melted vortex lattice, below the critical temperature.     

Microstructural and electrical characterization of bulk YBa2Cu3O7−δ ceramics

The value of critical current density at 77 K in “zero” applied field (J_c) characterizing the superconducting state for YBa₂Cu₃O_7−δ ceramics is closely related to the microstructure.The interrelationships between the microstructural factors such as pore volume fraction, oxygen content, average grain size, are complex. However, these factors also influence the normal state resistivity measured at room temperature (ρ₃₀₀). We demonstrate how the current carrying cross section influences Jc and ρ₃₀₀ in a similar way. Data, reported for two classes of YBa₂Cu₃O_7−δ: small grain porous ceramics and larger-grain denser ceramics, reveal an approximate linear relation between ρ_300 K and J_c. Extrapolation of this relation to a fully dense small grain YBa₂Cu₃O_7−δ ceramic yields values of ρ₃₀₀ = 0.4 mΩ cm and J_c = 10³ A cm⁻².     

Wetting and spreading of Ca-Y-Ba-Cu-O solution on Y2O3 and CaSZ crucible in growing Y1-xCaxBa2Cu3O7-δ single crystal

Sizable and uniform Y_1-xCa_xBa₂Cu₃O_7-δ single crystals are of significant importance to study high-temperature superconductivity. However, the severe liquid loss resulting from intrinsic wetting property during top-seeded solution-growth (TSSG), makes it difficult to obtain such crystals. Here the reactive wetting performance of the Ca-Y-Ba-Cu-O solution on two types of crucibles was studied. It was identified that the spreading process on the Y₂O₃ crucible is characterized by forming double-layer of Y₂BaCuO₅ and YBa₂Cu₃O_7-δ, while that on the CaSZ crucible (Ca-stabilized ZrO₂) produces the BaZrO₃ layer with CuO phase. In the former case, the liquid has a low energy interface with the top layer of YBa₂Cu₃O_7-δ, leading to strong spreading and creeping behaviors. Conversely, due to a high interfacial energy between solution and BaZrO₃, the CaSZ crucible has a low wettability, particularly beneficial to solve the liquid loss problem. Consequently, with negligible liquid creeping out of CaSZ crucibles, we succeeded in growing a series of homogeneous Y_1-xCa_xBa₂Cu₃O_7-δ single crystals with an acceptable size up to a × b × c = 11.2 × 11 × 4.8 mm³. Moreover the wetting modes of solution on various kinds of crucibles for TSSG in growing doped YBa₂Cu₃O_7-δ single crystals were also elucidated. Most importantly, the understanding gained from this work is broadly applicable for producing other desirable doped-crystals.     

Photocatalytic decomposition of N2O on Cu+/Y-zeolite catalysts prepared by ion-exchange

Insitu characterization of Cu⁺/Y-zeolite catalysts and their photocatalytic reactivities for the decomposition of N₂O into N₂ and O₂ have been investigated by means ofin situ photoluminescence, XAFS, and ESR techniques along with an analysis of the reaction products. It was found that Cu(I) ions included within the nanopores of Y-zeolite exist as the [Cu(I)--Cu(I)] dimer species as well as the isolated Cu(I) monomer species, their ratio being much dependent on the SiO₂/Al₂O₃ ratio of Y-zeolite. UV irradiation of these Cu⁺/Y-zeolite catalysts in the presence of N₂O led to the photocatalytic decomposition of N₂O into N₂ and O₂ at temperatures as low as 275 K. The electronically excited state of Cu(I) ion (3d⁹4s¹ state) plays a vital role in the photocatalytic decomposition of N₂O into N₂ and O₂. The photocatalytic reactivity of these Cu⁺/zeolite catalysts was found to be strongly affected by the local structure of the Cu(I) ions which could easily be modified by changing the SiO₂/Al₂O₃ ratio of Y-zeolite. The isolated linear 2 coordinated Cu(I) monomer species formed on Y-zeolite having a moderate SiO₂/ A1₂O₃ ratio exhibited a high photocatalytic reactivity for the direct decomposition of N₂O into N₂ and O₂, clearly showing the importance of the coordinative unsaturation of the active sites.     

Comparison of the catalysed decomposition of hydrogen peroxide over superconducting and insulating barium cuprates—kinetics of decomposition over Y2BaCuO5

Catalytic activities of two non-conducting cuprates (Ba₂Cu₃O₅, Y₂BaCuO₅) and a superconducting cuprate YBa₂Cu₃O_7–δ, prepared by two different methods, were compared using H₂O₂ solution. The two non-conducting barium cuprates were found to be about two orders of magnitude more active than the superconducting perovskite-like YBa₂Cu₃O_7–δ. The near coincidence of the kinetic curves for the catalysed decomposition of H₂O₂ over YBa₂Cu₃O_7–δ, prepared either from the perovskite-like Ba₂Cu₃O₅ and Y₂O₃ or from its components, proves that Ba₂Cu₃O₅ is essential in the formation of YBa₂Cu₃O_7–δ. First-order kinetics were observed for the catalysed decomposition of H₂O₂ solution over the non-perovskite Y₂BaCuO₅ at the initial stages of the reaction, similar to that of the superconducting perovskite catalyst. A tentative scheme of the possible catalytic reactions for the decomposition of H₂O₂ solution over the insulator Y₂BaCuO₅ is given.     

Steam Reforming of Methanol Over Cu/CeO2 Catalysts Studied in Comparison with Cu/ZnO and Cu/Zn(Al)O Catalysts

A series of Ce_1-xCu_xO_2- mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce_1-xCu_xO_2- mixed oxides indicated that Cu²⁺ ions were dissolved in CeO₂ lattices to form a solid solution by calcination at 773K when x < 0.2. A TPR (temperature-programmed reduction) investigation showed that the CeO₂ promotes the reduction of the Cu²⁺ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu²⁺ species in the Ce_1-xCu_xO_2- mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu²⁺ species which dissolved into the CeO₂ lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO₂. The Ce_1-xCu_xO_2- mixed oxides were reduced to form Cu/CeO₂ catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/AL₂O₃ catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO₂ (over 97%) and H₂. A 3.8wt% Cu/CeO₂ catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513K (W/F = 4.9 g h mol^-1), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/AL₂O₃ (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO₂ catalysts may be due to the highly dispersed Cu metal particles and the strong metalsupport interaction between the Cu metal and CeO₂ support. Slow deactivations were observed over the 3.8wt% Cu/CeO₂ catalyst at 493 and 513K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773K followed by reduction in H₂ at 673K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature-programmed oxidation) method, the amounts of coke on the 3.8wt% Cu/CeO₂ catalyst were 0.8wt% at 493K and 1.7wt% at 513K after 24h on stream.     

A 31P-NMR study of peroxo species formed during oxidation of cyclohexene with hydrogen peroxide in tri-n-butylphosphate catalyzed by heteropolyacids

In the oxidation of cyclohexene with H₂O₂in monophasic tri-n-butylphosphate (TBP) solution catalyzed by Keggin-type 12-heteropolyacids, i.e., H₃PMo_12-xW _x O₄₀(x=0–12), several peroxo species were observed by ³¹P-NMR spectroscopy in lower field than the original heteropolyacids. Their composition varied regularly with that of the starting catalyst. The P-containing peroxo species formed was deduced as [PM₄O₈(O₂)₈]^3-(M = Mo, W). The peroxo species formed more easily with a decrease in the W content, x of H₃PMo_12-xW_xO₄₀. It was further indicated from the reactivity with cyclohexene and the comparison with catalytic performance that W-rich peroxo species were catalytically more active than Mo-rich peroxo species for the oxidation of cyclohexene in this reaction system.     

Highly Active CNT-Promoted Cu–ZnO–Al2O3 Catalyst for Methanol Synthesis from H2/CO/CO2

With types of in-house-synthesized multi-walled carbon nanotubes (CNTs) and the nitrates of the corresponding metallic components, highly active CNT-promoted Cu–ZnO–Al₂O₃ catalysts, symbolized as Cu _i Zn _j Al _k -x%CNTs, were prepared by the co-precipitation method. Their catalytic performance for methanol synthesis from H₂/CO/CO₂ was studied and compared with the corresponding CNT-free co-precipitated catalyst, Cu _i Zn _j Al _k . It was shown experimentally that appropriate incorporation of a minor amount of the CNTs into the Cu _i Zn _j Al _k could significantly increase the catalyst activity for methanol synthesis. Under the reaction conditions of 493 K, 5.0 MPa, H_2/CO/CO₂/N₂ = 62/30/5/3 (v/v), GHSV = 8000 h^-1, the observed CO conversion and methanol formation rate over a co-precipitated catalyst of Cu₆Zn₃Al₁-12.5%CNTs reached 36.8% and 0.291 mol CH₃OH s^-1 (m²-surf. Cu)^-1, which was about 44 and 25% higher than those (25.5% and 0.233 mol CH₃OH s^-1 (m²-surf. Cu)^-1) over the corresponding CNT-free co-precipitated catalyst, Cu₆Zn₃Al₁. Addition of a minor amount (10–15 wt%) of the CNTs to the Cu₆Zn₃Al₁ catalyst was found to considerably increase specific surface area, especially Cu surface area of the catalyst. H₂-TPD measurements revealed that the CNTs and the pre-reduced CNT-promoted catalyst systems could reversibly adsorb and store a considerably greater amount of hydrogen under atmospheric pressure at temperatures ranging from room temperature to 573 K. This unique feature would be beneficial for generating microenvironments with higher stationary-state concentration of active hydrogen adspecies on the surface of the functioning catalyst, especially at the interphasial active sites since the highly conductive CNTs might promote hydrogen spillover from the Cu sites to the Cu/Zn interphasial active sites, and thus be favorable for increasing the rate of the CO hydrogenation reactions. Alternatively, the operation temperature for methanol synthesis over the CNT-promoted catalysts can be 15–20 degrees lower than that over the corresponding CNT-free contrast system. This would contribute considerably to an increase in equilibrium CO conversion and CH₃OH yield. The results of the present work indicated that the CNTs could serve as an excellent promoter.     

A comparative study of (Ce) and (Gd) doping influence on the superconducting properties of YBCO ceramics

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa_2-xRE_xCu₃O_7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature T_C and the critical current density J_C.The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa_2-xRE_xCu₃O_7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature T_C was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of T_C for YBa_2-xRE_xCu₃O_7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density J_C was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.     

Development of New Cu0–ZnII/Al2O3 Catalyst Supported on Copper Metallic Foam for the Production of Hydrogen by Methanol Steam Reforming

Copper metallic foam with thermal conductive properties, manufactured by S.C.P.S., has been investigated as a support for catalysts to improve thermal exchange inside the reactor for the endothermic steam reforming of methanol. Thus, we have developed a procedure for the in situ preparation of a Cu⁰–Zn^II/Al₂O₃ catalyst onto the copper metallic foam. The foam-based Cu⁰–Zn^II/Al₂O₃ catalyst shows an activity three times as high as commercial catalysts for a conversion of 74% of methanol into hydrogen.     

Radiation shielding and structural features for different perovskites doped YBa2Cu3Oy composites

The increased demand for ionizing radiation in various fields led to the search for new shielding substances. In this study, five samples of perovskite oxides (BaTiO₃, SrTiO₃, BaTiO₃–SrTiO₃, and PbZr_0.2Ti_0.8O₃) doped YBa₂Cu₃O_y ceramics were prepared to explore their structure and ability for exploitation in the radiation shielding field. The structural properties were explored by using the XRD technique. The XRD results showed an orthorhombic structure for all prepared ceramics. The crystallite size reduces gradually from 96.19 to 66.63 nm with adding different perovskite oxides into the composites. The density shows a variation from about 5.89 to 6.23 g/cm³. The mass attenuation coefficient (MAC) was defined experimentally (MAC)_exp and theoretically (MAC)_the to check its validity. The maximum relative difference between (MAC)_exp and (MAC)_the is 7.83%. YBa₂Cu₃O₇/(PbZr_0.2Ti_0.8O₃)_2% and YBa₂Cu₃O₇/(BaTiO₃–SrTiO₃)_2% samples showed superior gamma shielding properties and mass stopping power (MSP) for charged particles, respectively, while the pristine YBa₂Cu₃O₇ sample has a better fast neutron removal cross-section (Σ_R). From the obtained results, it can be seen a slight variation in shielding properties, indicating the ability to use the different ceramic samples as radiation shielding materials.     

Selective oxidation of hydrogen sulfide containing excess water and ammonia over Bi-V-Sb-O catalysts

We investigated the selective oxidation of hydrogen sulfide to elemental sulfur and ammonium thiosulfate by using Bi₄V_2-xSb_xO_11-y catalysts. The catalysts were prepared by the calcination of a homogeneous mixture of Bi₂O₃, V₂O₅, and Sb₂O₃ obtained by ball-milling adequate amounts of the three oxides. The main phases detected by XRD analysis were Bi₄V₂O₁₁, Bi_1.33V₂O₆, BiSbO₄ and BiVO₄. They showed good H₂S conversion with less than 2% of SO₂ selectivity with a feed composition of H₂S/O₂/NH₃/H₂O/He=5/2.5/5/60/27.5 and GHSV=12,000 h^-1 in the temperature ranges of 220–260 ‡C. The highest H₂S conversion was obtained for x=0.2 in Bi₄V_2-xSb_xO_11-y catalyst. TPR/TPO results showed that this catalyst had the highest amount of oxygen consumption. XPS analysis before and after reaction confirmed the least reduction of vanadium oxide phase for this catalyst during the reaction. It means that the catalyst with x=0.2 had the highest reoxidation capacity among the Bi₄V_2-xSb_xO_11-y catalysts.