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Applied Catalysis A, General (v.325, #2)

Editorial Board (pp. co2).

Contents (pp. v-vi).

Jean-Claude Volta on the occasion of his retirement by J.C. Vedrine; J.-M. Millet; B.K. Hodnett (pp. 193-193).

Adventures with vanadium phosphate catalysts: Reflections on a long standing collaboration with J.C. Volta by Christopher J. Kiely; Graham J. Hutchings (pp. 194-197).

This short article provides reflections on a most productive collaboration between the authors and Dr. J.C. Volta as an appreciation to mark Jean Claude's retirement in 2006. The sole topic that we focused on during 15 years of intensive effort was a study of vanadium phosphate catalysts, a topic that all of us have found fascinating and challenging, as have many other scientists in the last 50 years. Aspects of the key research themes, in particular the role of amorphous VPO phases, are revisited.

Keywords: Keyword; Vanadium phosphate catalysts

Oxidation in catalytic membrane reactors by Jean-Alain Dalmon; Arquimedes Cruz-López; David Farrusseng; Nolven Guilhaume; Eduard Iojoiu; Jean-Christophe Jalibert; Sylvain Miachon; Claude Mirodatos; Amalia Pantazidis; Michael Rebeilleau-Dassonneville; Yves Schuurman; Andre C. van Veen (pp. 198-204).

This paper presents a series of applications of catalytic membrane reactors (CMR) to oxidation reactions like alkane activation (C2, C3 and C4) or total oxidation (WAO), using dense, microporous or mesoporous membranes. ▪This paper presents a series of applications of catalytic membrane reactors (CMR) to oxidation reactions. Four reactions were tested in our group. Alkane activation (C2, C3 and C4) or total oxidation (WAO) is implemented in various membrane reactor modes, using dense, microporous or mesoporous membranes. In some cases, a catalyst bed is associated with a membrane, whereas other applications use an intrinsically active membrane. Progresses in catalyst and membrane design, along with careful operational conditions led to overall higher performances when compared to conventional processes.

Keywords: Oxidation; Oxidative dehydrogenation; Wet air oxidation; Catalytic membrane reactors

Nucleation and growth of manganese oxides on metallic surfaces as a tool to prepare metallic monoliths by D.M. Frías; S. Nousir; I. Barrio; M. Montes; L.M. Martínez T; M.A. Centeno; J.A. Odriozola (pp. 205-212).

The use of austenitic stainless steel (AISI 304) as metallic substrate for catalytic devices is explored in this work as well as an alternative procedure to the washcoating of the active phase. Catalyst deposition on austenitic stainless steel takes advantage of the manganese concentration of this alloy by direct growing of the new catalytic phase on the monolith surface during the synthesis. Manganese oxide (OMS) is chosen as active phase and VOC abatement by total oxidation as catalytic test. It is possible to coat metallic monoliths by growing the catalytic phase, manganese oxide (OMS), in situ during the reflux synthesis of cryptomelane. This preparation strategy needs a proper metal surface modification but is possible to deposit a large amount of catalyst in a very adherent form. The metallic coating shows similar adherences to those found using Fecralloy substrates even thought, in the case of the monolith prepared by repeated washcoating on AISI 304, new phases seem to be produced showing quite higher activity in total oxidation of ethyl acetate.

Keywords: Metallic monoliths; Ethyl acetate oxidation; VOC abatement; Crytomelane; OMS

Magnetron sputter deposition for catalyst synthesis by H. Poelman; K. Eufinger; D. Depla; D. Poelman; R. De Gryse; B.F. Sels; G.B. Marin (pp. 213-219).

dc magnetron sputtering was applied to prepare a new type of supported vanadia/titania catalyst. Reactive sputtering of oxides onto inert carriers was developed using a rotating drum for overall exposure of the support. The catalytic performance of the deposited vanadia/titania catalysts for oxidative dehydrogenation (ODH) of propane proved very promising.

Keywords: dc magnetron sputtering; Vanadia-based catalysts; Propane oxidative dehydrogenation

HRTEM characterization of the nanostructural features formed in highly active Ni–Nb–O catalysts for ethane ODH by E. Heracleous; A. Delimitis; L. Nalbandian; A.A. Lemonidou (pp. 220-226).

In this work, we report an in-depth structural characterization of pure NiO and Ni–Nb–O mixed oxide catalysts (Nb/Ni=0–0.25), highly active and selective materials for ethylene production via ethane ODH, using high resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray analysis (EDS). This study led to the identification and investigation of the nanostructural features formed in the Nb-doped NiO catalysts and their relation with the excellent catalytic functionality of the Ni–Nb–O materials. It was found that low-temperature treatment of pure NiO leads to the formation of a non-stoichiometric oxidic phase with characteristic structural defects due to cationic deficiency, as demonstrated by microscopy results. On the Nb-doped oxides, two distinct structural phases, formed via the reaction of the Nb cations with the cationic vacancies, were identified: a NiO phase having Nb cations incorporated in the host lattice, which retains its initial cubic structure (Ni–Nb solid solution), and a highly distorted Nb-rich phase, precursor for the formation of the mixed NiNb₂O₆ crystal compound. The reduction of the structural defects in NiO via their interaction with the niobium ions was correlated with the extremely high selectivity of the Ni–Nb–O catalysts to ethylene in the ethane ODH reaction, since these vacancies lead to the formation of strong oxidizing electrophilic oxygen species (O⁻), responsible for the total oxidation of ethane to CO₂.

Keywords: Non-stoichiometric NiO; Ni–Nb–O mixed metal oxides; High-resolution transmission electron microscopy (HRTEM); Ethane oxidative dehydrogenation; Ethylene

Is BN an appropriate support for metal oxide catalysts? by G. Postole; A. Gervasini; M. Caldararu; B. Bonnetot; A. Auroux (pp. 227-236).

This article reports on the preparation of boron nitride supported metal oxide (In₂O₃, Ga₂O₃ and SnO₂) catalysts, their acid–base properties, and their activity for selective catalytic reduction of NO by C₂H₄. ▪Boron nitride supported metal oxide (In₂O₃, Ga₂O₃ and SnO₂) catalysts were prepared using a sol–gel method. The amounts of metal oxides (15–22wt.%) deposed on the BN support were close to the theoretical monolayer. The support and the catalysts were characterized by XRD, XPS, TG, IR, SEM, TPR and adsorption microcalorimetry measurements. A study of the interfacial bonding between the oxide phases and the support surface revealed that the bonding between BN and the guest oxide is the strongest for In₂O₃. The results of adsorption microcalorimetry experiments performed on the samples using NH₃ and SO₂ as basic and acidic probes show that acid sites are predominant on their surface, while no real basicity could be evidenced. The mean acid strengths of the surfaces were found to vary in the order: 13In/BN>17Sn/BN>19Ga/BN>BN when using acetylacetonate metallic precursors. The test reaction of selective reduction of NO by C₂H₄ in high oxygen atmosphere was chosen to compare our BN-supported oxide samples with the same oxides supported on conventional ceramic supports. The results showed that the mechanical and chemical properties of BN were altered by the deposition of the active guest oxide. Moreover, it was demonstrated that BN is a too inert support material for assisting these oxides to complete easily a NO_x reduction reaction mechanism.

Keywords: BN material; Ga; ₂; O; ₃; In; ₂; O; ₃; SnO; ₂; Support; Catalysts; Characterization; Acidity; Selective catalytic reduction; Nitrogen monoxide

The influence of tungsten on structure and activity of Mo–V–W-mixed oxide catalysts for acrolein oxidation by S. Endres; P. Kampe; J. Kunert; A. Drochner; H. Vogel (pp. 237-243).

For the partial oxidation of acrolein to acrylic acid, a series of catalysts with the general formula Mo₈V₂W_cO_x and a varying amount of tungsten (0≤ c≤5) was investigated. Catalysts were prepared starting from aqueous solutions of ammonium heptamolybdate, metavanadate and metatungstate, which were dried, employing spray drying and crystallisation followed by calcination. The resulting precursors and catalysts were characterised by XRD, SEM and TG/DTA–MS. Additionally, kinetic experiments were applied. Spray drying results in the formation of amorphous structures, whose temperature stability shows a tendency to rise with an increasing amount of tungsten. Spray dried samples in general show a better catalytic performance than crystallised ones. In TP-reactions the spray dried mixed oxides were investigated with regard to their catalytic properties: conversion of acrolein, yield and selectivity regarding the partial oxidation to acrylic acid. The best performance could be assigned to the minor tungsten doped catalysts. The oxygen pathways were investigated with the so-called steady state isotopic transient kinetic analysis (SSITKA). After the replacement of¹⁶O₂ against¹⁸O₂ in the feed gas, the rate of oxygen incorporation into the reactants and the isotopic distribution of the oxidation products were analysed depending on temperature and tungsten content. Tungsten doping has a significant influence on the amount of¹⁶O removed from the catalyst under¹⁸O₂. The amount of oxygen made available by the catalysts correlates with the catalysts’ activity.

Keywords: Catalysis; Oxidation; Acrolein; Molybdenum; Vanadium; Tungsten; Oxides; SSITKA

Sol–gel synthesis and characterization of transition metal based mixed oxides and their application as catalysts in selective oxidation of propane by Carlo Lucarelli; Pietro Moggi; Fabrizio Cavani; Michel Devillers (pp. 244-250).

In this work binary and ternary mixed oxides containing Nb, V, Mo and Sb were prepared by a modified hydrolytic sol–gel technique and tested as catalysts for the selective oxidation of propane. All systems were active in the ODH of propane, with the appearance in some cases of oxygenated products. The best results as concerns the selectivity to acrylic acid (about 20%) have been obtained on ternary Mo–Nb–V oxide systems in the presence of Nb–Mo–O and V–Mo–O crystalline phases.

Keywords: Nb–V–Mo–Sb–O catalysts; Mixed oxides; Sol–gel synthesis; Propane selective oxidation; Acrylic acid

Ionotropic alginate aerogels as precursors of dispersed oxide phases by Raluca Horga; Francesco Di Renzo; Françoise Quignard (pp. 251-255).

Ionotropic gelling of alginate, a natural block polysaccharide with carboxylic functions, allows to form hydrogel microspheres with 98% porosity and more than 10% cation content (w/w). Supercritical drying preserves the dispersion of the gel and the resulting aerogels have specific surface as high as 500m²g⁻¹. In this communication, it is shown that the thermal degradation of alginate aerogels allows to form aggregated nanocrystals of the mineral phase corresponding to the cation used in gelling. The aggregates of nanocrystals of carbonate and oxide retain the morphology of the parent gel particles and a significant fraction of their porosity.

Keywords: Nanoparticles; Transition metal oxides; Alginate; Polysaccharide; Aerogel; Copper oxide; Nickel oxide; Cobalt oxide; Calcium carbonate

Grafting of titanium alkoxides on high-surface SiO₂ support: An advanced technique for the preparation of nanostructured TiO₂/SiO₂ catalysts by M. Cozzolino; M. Di Serio; R. Tesser; E. Santacesaria (pp. 256-262).

The present paper reports and discusses results on the preparation, characterization and catalytic performances of silica-supported titania (TiO₂/SiO₂) catalysts. Samples were prepared by grafting titanium tetraisopropoxide (Ti-OPrⁱ)₄, dissolved in toluene, onto a silica surface in an N₂ atmosphere, followed by steam hydrolysis and calcination. The samples were characterized by chemical analysis, BET surface area measurements, X-ray diffraction (XRD), DR–UV–vis, FTIR and DRIFT spectroscopy analyses, TEM/EDX and NH₃-TPD. The results indicated that the grafting preparation method gives rise to very strong Si–O–Ti bonds, that are responsible for high titanium dispersion. In particular, at low Ti loading, titanium species in tetrahedric coordination resulted prevalent on the catalyst surface until the maximum surface monolayer coating reached (∼2.2Ti atoms/nm²). The degree of polymerization of Ti species increases with further TiO₂ load increases, giving rise to a large amount of octahedrical Ti-sites grafted on SiO₂. The effects on the catalytic activity of TiO₂/SiO₂ catalysts with increasing quantities of TiO₂ were also investigated. The catalytic results obtained in the epoxidation reaction of cyclooctene with cumene hydroperoxide showed the significant effect of titanium loading on the physicochemical and reactivity/selectivity properties of the silica-supported titania catalysts.

Keywords: Supported titanium oxide; Liquid-phase grafting preparation technique; TiO; ₂; dispersion; Epoxidation reaction

The dispersion of Keggin-type P/Mo polyoxometalates inside silica gel, and the preparation of catalysts for the oxidation of isobutane to methacrolein and methacrylic acid by N. Ballarini; F. Candiracci; F. Cavani; H. Degrand; J.-L. Dubois; G. Lucarelli; M. Margotti; A. Patinet; A. Pigamo; F. Trifirò (pp. 263-269).

Keggin-type P/Mo polyoxometalates (POM) were dispersed in a high-surface-area silica gel by means of a co-gelation procedure, in order to prepare catalysts for the gas-phase oxidation of isobutane to methacrolein and methacrylic acid. The aim was the dilution of the active phase, in order to favor the dispersion of the considerable reaction heat and limit the oxidative degradation of the desired products. However, the diluted heteropolyacid was less stable than the undiluted one, because of the exchange between P and Si as the heteroatom. When the gel was prepared in the presence of tetrapropylammonium hydroxide, the thermal decomposition of the latter generated the ammonium ion that replaced for protons in the cationic position of the POM. This enhanced the structural stability of the diluted POM at 350°C under reaction conditions. However, no improvement of the catalytic performance was obtained for the diluted catalysts as compared to the undiluted systems, because of the combustion of methacrylic acid, of the modification of the POM redox properties and of the considerable extent of POM decomposition.

Keywords: Isobutane oxidation; Methacrylic acid; Keggin heteropolycompounds; Polyoxometalates; Silica gel

Hydrothermal synthesis and structural characterisation of xTiO₂–(1− x)α-Fe₂O₃ mixed oxide nanoparticles by L. Diamandescu; M. Feder; D. Tarabasanu-Mihaila; F. Vasiliu (pp. 270-275).

xTiO₂–(1− x)α-Fe₂O₃ ( x=0.0–1.0) mixed oxide nanoparticles system has been synthesized by a hydrothermal route. X-ray diffraction, Mössbauer spectroscopy and electron microscopy have been used to study the structure, morphology and substitution in the nanosized samples. Experimental evidence for the solubility limits of Ti⁴⁺ in α-Fe₂O₃ lattice and of Fe³⁺ in TiO₂ structure is given.

Keywords: Catalytic materials; Hydrothermal synthesis; X-ray diffraction; Mössbauer spectroscopy; Transmission electron microscopy

Photo-oxidation of ethanol on mesoporous vanadium–titanium oxide catalysts and the relation to vanadium(IV) and (V) sites by Dilshad Masih; Hideaki Yoshitake; Yasuo Izumi (pp. 276-282).

Ethanol photo-oxidation was investigated over mesoporous, amorphous V+TiO₂ and V+TiO₂(anatase) catalysts. Under the UV+visible light, mesoporous V+TiO₂ generally exhibited faster photo-oxidation rates than V+TiO₂(anatase) catalysts did. V^IV doping directed preferable formation of acetic acid rather than predominant acetaldehyde formation. Under the visible light only, mesoporous V^IV–TiO₂ catalyst exhibited best reactivity among all V+TiO₂ catalysts. Ethanol dehydration reaction was preferred. Initial quicker water evolution may suggest greater oxidation capability compared to V+TiO₂(anatase) catalysts.

Keywords: Photocatalyst; Photocatalysis; Oxidation; Vanadium; Titania; Mesoporous; UV–vis

The role of crystalline structure of molybdenum oxide catalysts onto the activity and stability in sulfoxidation of thioethers by F. Bertinchamps; V. Cimpeanu; E.M. Gaigneaux; V.I. Pârvulescu (pp. 283-289).

Sulfoxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine and methyl-dodecyl-sulfure was carried out in liquid phase using H₂O₂ in dioxane (6 or 18wt%) and several molybdenum and mixed antimony–molybdenum oxides such as: Mo₈O₂₃, MoO₃-basal, MoO₃-iso, Sb₂MoO₆ and a mixture of Sb₂Mo₁₀O₃₁ and Sb₄Mo₁₀O₃₁ (Sb_xMo₁₀O₃₁) phases as catalysts. Both catalytic performances and catalysts stability (structural modifications and leaching) depended on characteristics of the structure. The less active catalysts exhibited a higher leaching. The most stable and thus active catalysts were those for which the leaching is compensated by structural changes going in the direction of the exacerbation of their crystallinity. In the investigated series the most effective were the Mo₈O₂₃ and Sb₂MoO₆.

Keywords: Sulfoxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine and methyl-dodecyl-sulfure; Mo; ₈; O; ₂₃; MoO; ₃; -basal; MoO; ₃; -iso; Sb; ₂; MoO; ₆; Sb; ₄; Mo; ₁₀; O; ₃₁; Catalysts stability; Leaching

Watching the crystallisation of complex oxides by in situ X-ray techniques by Andrew M. Beale; Lee M. Reilly; Gopinathan Sankar (pp. 290-295).

We report here the results from recent studies where in situ X-ray techniques have been employed to follow the structural evolution of complex oxide materials from amorphous precursors. Specifically we detail how combined X-ray absorption spectroscopy/X-ray diffraction (XAS/XRD) allowed us to obtain new insight into the heat-induced crystallization of industrially important bismuth molybdate catalysts (Bi₂O₃· nMoO₃ where n=3, 2 or 1 corresponding to the α, β and γ-phases) and nano-sized spinel (CoAl₂O₄) particles from amorphous zeolites. In addition we illustrate the power of the energy dispersive diffraction technique (EDXRD) to follow the evolution of bismuth molybdate phases in a real autoclave via low temperature (<150°C) hydrothermal treatment. Finally we illustrate how the results from a combined XAS/XRD and EDXRD study allowed us to propose a chemical reaction leading to the hydrothermal formation of γ-Bi₂MoO₆.

Keywords: In situ; XAS/XRD; EDXRD; Catalyst

Promoter role of V₂O₅ on vanadium supported Al_0.5Ga_0.5PO₄ catalysts during propane ammoxidation by M.A. Soria; S. Delsarte; E.M. Gaigneaux; P. Ruiz (pp. 296-302).

Vanadium (5wt%) was incorporated on the Al_0.5Ga_0.5PO₄ support by impregnation and the resulting catalyst, 5V/Al_0.5Ga_0.5PO₄ was characterized by BET surface area, pores distribution, X-ray diffraction, RAMAN spectroscopy and temperature-programmed reduction. Catalytic performances were measured on the propane ammoxidation. Crystalline V₂O₅ was observed on 5V/Al_0.5Ga_0.5PO₄ catalyst; in addition, the originally amorphous Al_0.5Ga_0.5PO₄ support crystallises in presence of vanadium. The presence of V₂O₅ on Al_0.5Ga_0.5PO₄ enhances the propane conversion and the selectivity to acrylonitrile.

Keywords: Vanadium; Propane ammoxidation; Acrylonitrile; Bimodal pores distribution

Selective oxidation of alkenes and alkynes catalyzed by copper complexes by Leonardo X. Alvarez; M. Lorraine Christ; Alexander B. Sorokin (pp. 303-308).

Benzoic esters of 2-cyclohexen-1-ol and propargylic alcohols were prepared by direct selective copper-catalyzed allylic and propargylic oxidation of alkenes and alkynes, respectively, using t-butyl peroxybenzoate as the oxidant. The high olefin and acetylene conversions as well as the high product yields were obtained although enantioselectivity of this oxidation was moderate (e.e.<68%). The reported optimized catalytic procedure is clean since the oxidation is carried out under mild conditions using stoichiometric amounts of oxidant and catalytic amounts of (CuOTf)₂C₆H₆ in combination with bisoxazoline ligands.

Keywords: Asymmetric oxidation; Allylic oxidation; Propargylic oxidation; Copper catalysts; Chiral bisoxazoline ligands

Chlorinated organics total oxidation over V₂O₅/TiO₂ catalysts prepared by polyol-mediated synthesis by S. Albonetti; G. Baldi; A. Barzanti; A.L. Costa; J. Epoupa Mengou; F. Trifirò; A. Vaccari (pp. 309-315).

Vanadia and titania/vanadia sols synthesized by the polyol method were used to prepare TiO₂-supported catalysts. Both the modification of the V₂O₅ sol with a low amount of water and the use of a TiO₂/V₂O₅ sol induced a reliable adhesion between the preformed active phases and the support, thus leading to stable catalysts. Despite the low amount of vanadium introduced in studied samples, V₂O₅/TiO₂/WO₃ catalysts were active in the o-DCB oxidation. The best results were obtained with 0.36-V₂O₅–TiO₂ catalyst, prepared by direct impregnation with colloidal TiO₂/V₂O₅-mixed oxides. The electroacoustic analysis indicated that the support does not show any particular electrostatic affinity for any studied sol; therefore, the higher ability of TiO₂/V₂O₅ sol to form stable vanadium active species may possibly be explained by a better chemical affinity with the support.

Keywords: Polyol-mediated synthesis; Catalytic total oxidation; V; ₂; O; ₅; /TiO; ₂; catalysts; Preformed oxide sols

Formation of structured silicalite-I/ZSM-5 composites by a self-assembly process by Leszek Gora; Bogdan Sulikowski; Ewa M. Serwicka (pp. 316-321).

The self-assembly method has been applied for the preparation of structured silicalite-I/ZSM-5 composites. The method has proven to be a controllable and reproducible approach for the preparation of a zoned, thin, oriented coating of silicalite-I on ZSM-5 crystals. b-Orientation of MFI crystals on the ZSM-5 crystals was boosted by pre-coating of the crystals using Ti-butoxide prior to the hydrothermal synthesis of silicalite-I.

Keywords: Silicalite-I/ZSM-5 composite; Self-assembly process; Adsorption isotherms

Influence of composition and preparation method on the activity of MnO_x/Al₂O₃ catalysts for the reduction of benzaldehyde with ethanol by N. Stamatis; K. Goundani; J. Vakros; K. Bourikas; Ch. Kordulis (pp. 322-327).

Two series of MnO_x/Al₂O₃ catalysts with varying Mn loading (0–1.2%, w/w Mn) prepared by equilibrium deposition filtration (EDF) and wet impregnation (WI) methodology were used for studying the influence of the composition and the preparation method on their activity for the reduction of benzaldehyde with ethanol. The prepared catalysts were characterized by BET measurements, X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy. It was found that following EDF methodology, the deposition of MnO_x species on the alumina takes place via adsorption of [Mn(H₂O)₆]²⁺ and [Mn–Ac]⁺ species on the negatively charged surface sites. On the contrary, following wet impregnation the deposition takes place mainly via precipitation in the step of the solvent evaporation. The extent of the interactions exerted between the support and supported phase is higher in the EDF samples. These interactions created during the impregnation step were detected by DRS after drying and calcination. Higher dispersion of the MnO_x phase is achieved when it is deposited on the γ-Al₂O₃ surface by the EDF than the WI method. The catalysts of the first series exhibited higher activity related well with the dispersion of MnO_x supported nano-particles.

Keywords: MnO; _x; /Al; ₂; O; ₃; catalysts; Supported manganese oxide catalysts; Equilibrium deposition filtration; MPVO reaction; Active sites

Catalytic properties of niobium and gallium oxide systems supported on MCM-41 type materials by I. Nowak; M. Misiewicz; M. Ziolek; A. Kubacka; V. Cortés Corberán; B. Sulikowski (pp. 328-335).

Novel MCM-41 modified catalytic materials were synthesized by impregnation of MCM-41 with niobium and gallium salts. A number of techniques, including nitrogen adsorption, X-ray diffraction, FT-IR and Raman spectroscopies, have been used to characterize a series of gallium and niobium-containing composite materials, aimed especially at the rationalization of the nature of oxides species formed. Generally, the presence of highly dispersed NbO_x and GaO_x moieties in the mesoporous materials could be deduced from this approach. It has been demonstrated that incorporation of gallium and niobium into the MCM-41 type silica matrix leads to formation of active and selective catalysts for the oxidation of hydrocarbons.

Keywords: Acid–base and epoxidation properties; MCM-41; Ga; ₂; O; ₃; Gallium–niobium interaction effect; Cyclization of acetonylacetone; Dehydration and dehydrogenation of 2-propanol; Oxidation of cyclohexene

Vanadium oxides supported on TiO₂-Sepiolite and Sepiolite: Preparation, structural and acid characterization and catalytic behaviour in selective oxidation of toluene by F.M. Bautista; J.M. Campelo; D. Luna; J. Luque; J.M. Marinas (pp. 336-344).

The synthesis of vanadium oxide systems (5–20wt% of V₂O₅) supported on TiO₂-Sepiolite (with titania loading around the theoretical monolayer, 12wt%) and on Sepiolite was carried out by the wet impregnation method. Materials were characterized by EDX, XRD, DR UV–vis, Raman,²⁹Si and¹H MAS NMR, TEM and nitrogen adsorption. Surface acid properties were evaluated through pyridine chemisorption. Their catalytic behaviour in the selective oxidation of toluene was studied. All solids exhibited the type IV isotherm, which corresponds to mesoporous solids. The decomposition of the Sepiolite into magnesium silicate and silica due to the effects of the vanadium incorporation process and calcination was not observed. The nature of the vanadium species depended on the support type and vanadium loading. Thus, in general, at the lowest vanadia loadings, isolated tetrahedral and polymetavanadate type species predominated. At higher loadings (15wt% or above), vanadium oxides were also presented as crystalline V₂O₅ nanoparticles and, especially in %V/Sepc systems, as pyro- and meta-magnesium vanadates. On the other hand, in relation to the supports, the vanadium systems exhibited new acid sites whose density and strength both depended on the vanadia species structures. The catalytic performance of the vanadium oxide systems in the selective oxidation of toluene was also influenced by the structure and nature of vanadia species. Thus, the species formed on TiO₂-coated Sepiolite support exhibited more activity in the formation of benzaldehyde (and benzoic acid) than the ones on Sepiolite. This formation is favoured by the polymeric vanadia species.

Keywords: TiO; _x; -Sepiolite supported vanadium oxide; Sepiolite supported vanadium oxide; TiO; _x; -Sepiolite; Sepiolite; Catalyst characterization (EDX/XRD/DR-UV–vis/Raman/; ¹; H,; ²⁹; Si MAS NMR/TEM) pyridine chemisorption; Toluene selective oxidation

Development of optimized Cu–ZSM-5 deNOx catalytic materials both for HC-SCR applications and as FCC catalytic additives by Vasilis G. Komvokis; Eleni F. Iliopoulou; Iacovos A. Vasalos; Kostas S. Triantafyllidis; Christopher L. Marshall (pp. 345-352).

Cu-exchanged ZSM-5 zeolites finely coated with CeO₂ nanoparticles were tested in this work as catalysts for the selective catalytic reduction (SCR) of NO with C₃H₆. The CeO₂ coated Cu/ZSM-5 shows lower maximum NO conversion activity compared to the non-coated Cu/ZSM-5 catalyst at relatively high temperatures (ca. 450°C) but the former catalyst is significantly more active at lower temperatures (ca. 350°C), especially at lower space velocities, both under dry and wet feed conditions. Under simultaneous addition of both SO₂ and water in the feed, the beneficial effect of the CeO₂ coating at lower reaction temperatures was retained only at low space velocities. The same Cu/ZSM-5 based samples were evaluated as fluid catalytic cracking (FCC) catalytic additives for the in situ reduction of NOx formed during regeneration of the coked FCC catalyst. The amounts of NO and CO emitted during regeneration of the spent FCC catalyst at 700°C in the presence of Cu/ZSM-5 based additives were compared with those obtained when a commercial CO promoter was used in the FCC catalyst inventory. All Cu/ZSM-5 additives exhibited significant NO reduction ability, which was further enhanced by increasing the Cu loading or the amount of additive in the FCC catalyst. The CeO₂-coated sample reached the highest deNOx performance (up to 78% NO reduction); however, all additives presented insufficient activity for CO oxidation. Simultaneous NO reduction and CO oxidation was achieved only when the CeO₂-Cu/ZSM-5 additive was promoted with Rh or when the non-promoted additives were combined with a commercial CO promoter. Preliminary studies suggested that the Rh-promoted CeO₂-Cu/ZSM-5 additives can be very effective for both NO reduction by CO and CO oxidation at certain O₂ concentrations, such as in the O₂-deficient zones of the FCC regenerator. Further studies are in progress in order to elucidate the reaction mechanism and optimize the additive's formulation.

Keywords: Cu–ZSM-5; NO reduction; FCC regenerator; CO oxidation; Rh–Ce promotion

Effect of nature and surface density of oxygen species on product distribution in the oxidative dehydrogenation of propane over oxide catalysts by Evgenii V. Kondratenko; Mikhail Yu. Sinev (pp. 353-361).

Catalytic performance of non-reducible (rare-earth/alkaline-earth oxides) and reducible (vanadium-based oxides) metal oxides in auto-thermal oxidative dehydrogenation (ODH) of propane differs strongly regarding to the ratio of C₃H₆/C₂H₄. In contrast to the latter materials, ethylene is the main olefin over the former ones. In order to elucidate factors influencing the catalytic performance, a kinetic analysis of the oxidative dehydrogenation (ODH) of propane was performed. In this analysis, the ODH reaction is assumed to occur via formation and further transformations of free propyl radicals. It was demonstrated that the overall reaction rate of these both processes is affected by both strength and density (surface concentration) of oxidising active sites. However, the ratio of propene-to-ethylene is mostly affected by the density of oxidising sites (DOS), and to much less extent by their strength. High DOS is essential for further ODH of propyl radicals to propene and, therefore, for suppression of concurrent cracking reaction channel yielding ethylene.

Keywords: Oxidative dehydrogenation of propane; Oxygen adsorption; Reaction mechanism; Kinetic modelling; Temporal analysis of products (TAP) reactor; Mechanism; Vanadia

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Applied Catalysis A, General (v.325, #2)