Promoting effect of Mg in supported Mo/HBeta–Al2O3 catalyst for cross-metathesis of ethene and butene-2 to propene

Promoting effects of Mg in heterogeneous Mo/HBeta–Al₂O₃ catalyst have been carefully studied for cross-metathesis of ethene and butene-2 to propene. The catalyst shows good stability with Mg content in the range of 1–2 wt%. Such effect may be attributed to the elimination of weak acid sites through introduction of Mg which suppresses the side olefin oligomerization reaction, as evidenced from NH₃-TPD and ¹H MAS NMR results. Addition of more Mg content to 3 wt% may change the state and reducibility of Mo species, as indicated from the UV–vis, UV-Raman and H₂-TPR measurements. The increasing difficulty for the reduction of Mo(VI) species is closely related with the poor performance of 3 wt% Mg–4Mo/HBeta–30% Al₂O₃ catalyst in the metathesis reaction.     

EXAFS characterization of Ti/Al2O3 supports and Co/Ti/Al2O3 catalysts

The structure of Ti/Al₂O₃ supports (0–14 wt% Ti) and Co/Ti/Al₂O₃ catalysts (3 wt% Co) was examined by EXAFS. The results indicated that the Ti was present primarily as a highly dispersed surface phase. The Ti EXAFS results indicated that the Ti species were octahedrally coordinated. Evidence of Ti—Ti interactions was found for all loadings (2–14 wt% Ti) suggesting that the Ti surface species are present as small clusters of TiO₂.The Co EXAFS results showed evidence for several structurally different Co surface phases as a function of Ti loading. Evidence of a Co species interacting with the Ti surface phase was observed for the 3% Co/2% Ti-3%Co/6%Ti catalysts. At the highest loadings studied, 3%Co/8%Ti and 3%Co/14%Ti, evidence was found for a CoTiO₃-like phase.     

Fluoride modification of Mo/Al2O3 catalysts: Characterization of the changes induced in support and Mo phases

The characterization of fluoride-modified Mo/Al₂O₃ catalysts was performed in order to investigate on the effect that low levels of fluoridation of the alumina support (0-2.0 wt.%) cause on the support itself and on the supported Mo oxide and sulfide phases. Fluoride-modified Al₂O₃ supports and Mo/Al₂O₃ catalysts where characterized by nitrogen physisorption, scanning electronic microscopy (SEM-EDX), isoelectric point (IEP), Fourier transform infrared spectroscopy (FT-IR), infrared spectroscopy of adsorbed CO₂ (IR-CO₂), and temperature programmed reduction (TPR). The dispersion of the sulfided catalysts was estimated by dynamic NO chemisorption. The results indicate that the different hydroxyl types present on the alumina surface react to a different extent with fluoride and that it is the most basic hydroxyl groups that are titrated first.The consumption of the alumina OH by F⁻, inhibits, during the deposition of Mo, the formation of tetrahedral molybdenum oxide species in strong interaction with the support, leading to an increased number of polymeric octahedral Mo surface species. The NO adsorption results put in evidence a drop in the dispersion of the MoS₂ phase present in the sulfided samples.     

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al₂O₃–TiO₂–MgO and Al₂O₃–TiO₂–SiO₂ systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al₂TiO₅. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.     

Promoter effect of nickel in thiophene hydrodesulfurization as monitored by sulfur uptake and cyclohexane conversion

Hydrodesulfurization (HDS) activity and activation energy (ε′_TH) values were determined and compared with irreversible sulfur uptake (S_irr) by 5 Al₂O₃-supported (MoO_x, Ni and three NiMoO_x) catalysts and, in unsulfided form with the cyclohexane conversion activity. Synergy between Ni and Mo in catalytic activity and a correlation between HDS activity and the amounts of S_irr was found. Some explanations for the differences in catalytic behavior of the different samples are presented.     

Titania-supported mixed HPMoV polyoxometallates as precursors of hydrodesulfurization catalysts

HDS catalysts were prepared by loading H₃PMo₁₂O₄₀ or H₄PMo₁₁V₁O₄₀ polyoxometallates on TiO₂ (0.5 and 1.0 mmol (Mo+V)). Activity of the catalysts was tested in the HDS of thiophene. The activity of catalysts of low concentration was 2–3 times higher than the activity of those of high concentration. Temperature programmed reduction (TPR) and IR spectroscopy were used to determine the properties of the catalyst. TPR measurements proved that vanadium promotes and stabilizes HDS activity due to an increase in the Mo⁵⁺/Mo⁴⁺ ratio.     

The Effect of MoO3 Addition to V2O5/Al2O3 Catalysts for the Selective Catalytic Reduction of NO by NH3

The effect of MoO₃ addition to alumina supported vanadia catalysts on the catalytic activity for the selective catlaytic reduction of NO is investigated. Upon the addition of MoO₃, catalytic activity is enhanced and the particle size of V₂O₅ which is shown by the results of XRD and Raman spectroscopy is decreased. The MoO₃-V₂O₅/Al₂O₃ catalyst also exhibits more resistance to SO₂ deactivation than V₂O₅/Al₂O₃ does.     

FT-IR and FT-FIR studies of vanadium,molybdenum and tungsten oxides supported on different carriers

In the far IR region at low molybdenum loadings, Mo-SiO₂ catalysts present a pseudomolybdate or a polymolybdate species, while bulk-like MoO₃ appears at loadings close to the geometrical monolayer coverage. W-SiO₂ and V-SiO₂ spectra show bands close to those observed on the corresponding bulk oxides.In the case of TiO₂, Al₂O₃, ZrO₂ supported catalysts, a band is observed near 1000 cm^–1 which is assigned to the Mo=O stretching vibration of coordinatively unsaturated Mo ⁿ⁺ ions showing a stronger interaction with the support than one observed on silica.     

Reducibility of Mo species in Pt/MoO3 and PtMo/Al2O3 catalysis

Recucibility of Mo species in Pt/MoO₃ and PtMo/Al₂O₃ has been investigated by temperature-programmed reduction (TPR), temperature-programmed desorption of hydrogen (H₂-TPD) and temperature programmed electronic conductivity (TPEC) techniques. In Pt/MoO₃ at H₂ atmosphere, it was found by TPEC and TPR that, a slight amount of Pt could activate the transfer of the species and H atoms between H₂ and MoO₃, and thus accelerate the reduction of MoO₃. In PtMo/Al₂O₃, TPR and H₂-TPD revealed that the reduction of surface Mo species could also be facilitated by Pt. Two kinds of hydrogen molybdenum species were proposed on the surface of the catalyst after prereduction.     

Characterization of Fumed Alumina/Silica/Titania in the Gas Phase and in Aqueous Suspension

Fumed oxide alumina/silica/titania was studied in comparison with fumed alumina, silica, titania, alumina/silica, and titania/silica by means of XRD, ¹H NMR, IR, optical, dielectric relaxation, and photon correlation spectroscopies, electrophoresis, and quantum chemical methods. The explored Al₂O₃/SiO₂/TiO₂ consists of amorphous alumina (22 wt%), amorphous silica (28 wt%), and crystalline titania (50 wt%, with a blend of anatase (88%) and rutile (12%)) and has a wide assortment of Brønsted and Lewis acid sites, which provide a greater acidity than that of individual fumed alumina, silica, or titania and an acidity close to that of fumed alumina/silica or titania/silica. The changes in the Gibbs free energy (ΔG) of interfacial water in an aqueous suspension of Al₂O₃/SiO₂/TiO₂ are close to the ΔG values of the dispersions of pure rutile but markedly lower than those of alumina, anatase, or rutile covered by alumina and silica. The zeta potential of Al₂O₃/SiO₂/TiO₂ (pH of the isoelectric point (IEP) equals ≈3.3) is akin to that of fumed titania (pH(IEP_TiO2) ≈ 6) at pH > 6, but it significantly differs from the ζ of fumed alumina (pH(IEP_Al2O3) ≈ 9.8) at any pH value as well as those of fumed silica, titania/silica, and alumina/silica at pH < 6. The particle size distribution in the diluted aqueous suspensions of Al₂O₃/SiO₂/TiO₂ studied by means of photon correlation spectroscopy depends relatively slightly on pH in contrast to the titania/silica or alumina/silica dispersions. Theoretical calculations of oxide cluster interaction with water show a high probability of hydrolysis of Al–O–Ti and Si–O–Ti bonds strained at the interface of alumina/titania or silica/titania due to structural differences in the lattices of the corresponding individual oxides. Ab initio calculated chemical shift δ_H values of H atoms in different hydroxyl groups at the oxide clusters and in bound water molecules are in agreement with the ¹H NMR data and show a significant impact of charged particles (H₃O⁺ or OH⁻) on the average δ_H values of water droplets with (H₂O)_n at n between 2 and 48.     

不同磷含量对NiMoP/Al2O3加氢处理催化剂的影响

采用NiMoP浸渍液浸渍载体γ Al₂O₃制备了不同磷含量的NiMoP/Al₂O₃加氢处理催化剂。为了研究磷对该系列催化剂活性相结构的影响,用二苯并噻吩（DBT）和喹啉为模型化合物,考察了催化剂的加氢脱硫（HDS）和加氢脱氮（HDN）性能。结果表明,添加适当的磷能够提高催化剂的HDS和HDN活性,但是高含量的磷能显著的降低催化剂的催化性能。通过对催化剂进行XRD和HRTEM表征发现,添加磷能够增加MoS2的堆积层数以及Ⅱ型“Ni-Mo-S”相的相对含量,这是因为在制备过程中添加磷降低了活性组分与载体之间的相互作用。     

Catalytic oxidation of no to NO2 over Cr/TiO2 and Cu/TiO2 under oxidizing atmosphere

The catalytic activity of Cr/TiO₂ and Cu/TiO₂ for the oxidation of NO under an oxidizing atmosphere has been examined. Both catalysts had excellent ability for the oxidation of NO to NO₂ in the temperature range of 350–400°C.     

Evaluation of polymeric nanocomposites for the detection of toxic gas analytes

Four different metal oxide nanoparticles, copper oxide (CuO), aluminum oxide (Al₂O₃), nickel oxide (NiO), and titanium dioxide (TiO₂), were added to poly (2,5-dimethyl aniline) (P25DMA) during synthesis to create different polymer nanocomposites. These polymer nanocomposites were evaluated as potential sensing materials for six different gas analytes (acetaldehyde, acetone, benzene, ethanol, formaldehyde, and methanol). It was found that CuO did not incorporate into the P25DMA and only a small percentage of Al₂O₃ was incorporated. However, both NiO and TiO₂ were incorporated into the P25DMA at the same concentration as during the synthesis step. Overall, the type of metal oxide significantly affected the morphology of the sensing material and the amount of each analyte sorbed. For example, P25DMA doped with 5 wt% Al₂O₃ had high selectivity towards ethanol, whereas P25DMA doped with 20 wt% TiO₂ sorbed the most ethanol. However, P25DMA doped with 20 wt% TiO₂ also sorbed a high amount of formaldehyde, making P25DMA doped with 20 wt% TiO₂ less selective than P25DMA doped with 5 wt% Al₂O₃ towards ethanol with respect to formaldehyde.     

Calorimetric Characterization of Surface Reactivity of Supported Ga2O3 Catalysts

The surface properties of supported gallium oxide catalysts prepared by impregnation of various supports (γ-Al₂O₃, SiO₂, TiO₂, ZrO₂) were investigated by adsorption microcalorimetry, using ammonia and water as probe molecules. In the case of acidic supports (γ-Al₂O₃, ZrO₂, TiO₂), the acidic character of supported gallium catalysts always decreased in comparison with gallium-free supports; on very weakly acidic SiO₂, new acidic centers were created when depositing Ga₂O₃. The addition of gallium oxide decreased the hydrophilic properties of alumina, titania and zirconia, but increased the amount of water adsorbed on silica. The catalytic performances in the selective catalytic reduction of NO by C₂H₄ in excess oxygenwere in the order Ga/Al₂O₃>Ga/TiO₂>Ga/ZrO₂>>Ga/SiO₂. This order is more related to the quality of the dispersion of Ga₂O₃ on the support than to the global acidity of the solids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Elucidation of hydrodesulfurization mechanism on molybdenum‐based catalysts using 35S radioisotope pulse tracer methods

Elucidation of the hydrodesulfurization (HDS) mechanism on molybdenumbased catalysts using radioisotope tracer methods and reaction kinetics is reviewed. Firstly, to investigate the sulfidation state in Mo/Al₂O₃ and Co–Mo/Al₂O₃ catalysts, presulfiding of these catalysts has been performed using a ³⁵S pulse tracer method. Secondly, HDS of radioactive ³⁵Slabeled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts and cobaltpromoted molybdena–alumina catalysts in a pressurized flow reactor to estimate the behavior of sulfur on the working catalysts. Finally, sulfur exchange of a ³⁵Slabeled catalyst with hydrogen sulfide was performed to estimate the relationship between the amount of labile sulfur and catalytically active sites.     

Effect of H2S-uptake on the conversion of cyclohexene on Ru- and Pd-promoted molybdena-alumina catalysts

The effect of H₂S on the activity and selectivity of catalysts (Ru/Al₂O₃, Pd/Al₂O₃ and Ru and Pd promoted molydena-alumina) was different (on differnt catalysts and different conversions of cyclohexene). Ru-containing catalysts showed higher sulfur sensitivities than the Pd-containing ones. The sequence of catalysts by their H₂S uptake related to mass of catalyst was PdMo/Al₂O₃RuMo/Al₂O₃Mo/Al₂O₃>Pd/Al₂O₃Ru/Al₂O₃.     

Methodical aspects in the surface analysis of supported molybdena catalysts

Supported molybdena catalysts, with TiO₂, CeO₂ and Al₂O₃ supports, were studied by XPS and ISS. It was found that reliable results are obtained only when samples are calcined and transferred into the ultrahigh vacuum system without further contact with the ambient atmosphere (‘in situ calcination’). This applies also to catalysts that were previously calcined but had been stored in the ambient atmosphere. Supported Mo oxide becomes reduced under x‐ray irradiation during extended XPS data acquisition. A slight decrease of the Mo/support cation intensity ratio as a consequence of this reduction was detected by ISS in MoO₃/TiO₂ and MoO₃/CeO₂, therefore ISS analysis should be performed on freshly calcined samples without prior extended exposure to x‐rays. Because ISS spectra change rapidly due to sputtering, a correct analysis of the surface properties of the supported Mo catalyst requires extrapolation of the trend to the start of the experiment. It was established by this methodology that the surface of a 7% MoO₃/TiO₂ catalyst (5.3 Mo nm^?2) is completely covered by a monolayer of Mo oxide species, and no Ti cation is exposed. In a submonolayer MoO₃/CeO₂ catalyst the exposed support could be detected, as expected, whereas in an MoO₃/Al₂O₃ catalyst with an Mo oxide loading equal to the monolayer coverage a slight exposure of the Al support cation also was noted probably because of the high curvature of the smaller Al₂O₃ particles. Copyright © 2004 John Wiley & Sons, Ltd.     

Thermal behaviour of high surface area V2O5/TiO2 catalysts

Thermal analysis (TG and DTA) was employed for the characterization of V₂O₅/TiO₂ catalysts supported on high surface area TiO₂. The results obtained are consistent with a uniform spreading of vanadium oxide on TiO₂ surface for V₂O₅ content less than 15% by weight.The presence of V₂O₅ on the surface of TiO₂ affects the anatase-rutile phase transition lowering the temperature at which it occurs.DTA measurements, performed on catalysts after many months from the preparation, show the appearance of an exothermic peak in the range 280°–340°C. This signal has been related to the oxidation of V(IV) to V(V) on the catalyst surface.Catalysts characterization, performed by chemical analysis and FT-IR spectroscopy, has confirmed this interpretation.It has been suggested that a slow modification of the catalyst occurs, leading to an increase of the V(IV) content during the time.

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Zusammenfassung Zur Charakterisierung von V₂O₅/TiO₂-Katalysatoren auf hochoberflächigem TiO₂ Trägermaterial wurde die Thermoanalyse (TG und DTA) angewendet. Für einen V₂O₅-Gehalt von weniger als 15 Gew.% entsprechen die erhaltenen Ergebnisse einer gleichmäßigen Verteilung des Vanadiumoxides an der TiO₂-Oberfläche.Die Gegenwart von V₂O₅ an der Oberfläche von TiO₂ beeinflußt die Anatas-Rutil-Phasenumwandlung, indem sie die zugehörige Temperatur verringert.DTA-Messungen an Katalysatoren mehrere Monate nach ihrer Herstellung zeigten das Auftreten eines exothermen Peaks im Bereich 280°–340°C. Dieses Signal wurde der Oxidation von V(IV) zu V(V) an der Katalysatoroberfläche zugeschrieben.Diese Interpretation konnte durch eine Charakterisierung des Katalysatoren durch chemische Analyse und FT-IR-Spektroskopie bestätigt werden.Es wurde angedeutet, daß der Katalysator mit der Zeit einer langsamen Modifikation unterliegt, die zu einem Ansteigen des V(IV)-Gehaltes führt.

     

Increased promotion by deposition of Co acetylacetonate over sulphided Mo/TiO2 hydrodesulphurization catalyst

CoMo/TiO₂ catalysts prepared by deposition of Co acetylacetonate on presulphided Mo/TiO₂ catalyst in methanol exhibited higher promotion of hydrodesulphurization activity than catalysts prepared by conventional impregnation of Mo/TiO₂ by a solution of Co nitrate.     

High photocatalytic activity and stability for decomposition of gaseous acetaldehyde on TiO2/Al2O3 composite films coated on foam nickel substrates by sol-gel processes

A set of anatase titanium dioxide (TiO₂) films coated on foam nickel that modified by Al₂O₃ films as transition layer (indicated as TiO₂/Al₂O₃ films) were synthesized via sol-gel route. The bulk and surface properties of the TiO₂/Al₂O₃ films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO₂/Al₂O₃ films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing. The TiO₂/Al₂O₃ composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the onefold TiO₂ films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al₂O₃ transition layer, which concentrates the target substances around TiO₂ particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al₂O₃ modified foam nickel are 0.12 and 113.7 m²/g, respectively) to provide more sites for TiO₂ loading.