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A mesoporous alumina has been synthetized by a hydrothermal method describe by Ĉejka and al. who use as precursor an aluminium isopropoxide and subsequently calcining the precipitate obtained in nitrogen flow at 683 K for 6h. The structural and morphological study evidence that the alumina obtained is a thermal stable γ-Al2O3 phase up to 1073 K with a specific surface area value of 174 m2g-1. The study of the surface hydroxyl groups in the sample γ-Al2O3 phase calcined at 1073 K (hereinafter called ALMP1073) reveals the presence of three types of active OH groups absorbing at 3787, 3725 and 3690 cm-1 and that they are significantly acidic, but not enough to protonate pyridine., i.e, they can be considered as Lewis acid. Catalytic test in ethanol dehydration prove that the ALMP1073 sample is active and selective in the dehydration of ethanol to diethylether in the range 523-573 K, as well as in the dehydration of ethanol to ethylene in the range 623-723 K These data are consistent with those obtained by infrared spectroscopy. The ethoxy groups formed on the surface of γ-Al2O3 are proposed as intermediate species in the ethanol dehydration reaction for both diethylether and ethylene formation.

The adsorption of water, pyridine, CO and CO2 on a commercial γ-Al2O3 and a commercial amorphous silica alumina (ASA) cracking catalyst are reinvestigated by means of FTIR spectroscopy. It is concluded that the real active hydroxyl groups on γ-Al2O3 are those absorbing at 3790, 3770 and 3730 cm−1 and that they are significantly acidic. The strongest Lewis acid sites are identified as Nuclear Magnetic Resonance (NMR)-silent (or still undetected) tricoordinated Al3+, becoming tetracoordinated when interacting with basic adsorbates. More than one pyridine molecule may adsorb over such highly coordinatively unsaturated sites at high pyridine vapour pressure. It has also been confirmed that the existence of Bronsted acid sites sufficiently strong to protonate pyridine on ASA is its intrinsic property, not due to coadsorbed water. A “stuffed amorphous silica” model is proposed for low-alumina ASA, where part of Al3+ ions compensate the charge in-balance due to the substitution of Al for Si in a silica-like tetrahedral framework. Interstitial Al3+ occupy 4-, 5- or 6-coordination interstices in the amorphous silica-like framework as do alkali cations in “stuffed silicas” aluminosilicates. Such “interstitial” Al3+ ions when located accidentally in opened interstices exposed at the surface play the role of strong Lewis sites. When these ions are located near a silanol group, they increase the Bronsted acidity of the terminal silanols by neutralizing the negative charge produced by their dissociation when interacting with bases.

Serpentinite powdered samples from four different regions were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), SBET and porosity measurements, UV-Vis and Infrared Spectroscopy of the skeletal region and surface OH groups. SEM micrographs of the samples showed a prismatic morphology when the lizardite was the predominant phase, while if antigorite phase prevailed, the particles had a globular morphology. The few fibrous-shaped particles, only observed by SEM and weakly detected by XRD on MO-9C and MO13 samples, were characteristic of the chrysotile phase. All diffraction XRD patterns showed characteristic peaks of antigorite and lizardite serpentine phases, with crystallite sizes in the range 310&ndash, 250 &Aring, and with different degrees and types of carbonation processes, one derived from the transformation of the serpentine, generating dolomite, and another by direct precipitation of calcite. The SBET reached values between 38&ndash, 24 m2∙g&minus, 1 for the samples less crystalline, in agreement with the XRD patterns, while those with a higher degree of crystallinity gave values close to 8&ndash, 9 m2∙g&minus, 1. In the UV region all electronic spectra were dominated by the absorption edge due to O2&minus, &rarr, Si4+ charge transfer transition, with Si4+ in tetrahedral coordination, corresponding to a band gap energy of ca 4.7 eV. In the visible region, 800&ndash, 350 nm, the spectra of all samples, except Donai, presented at least two weak and broad absorptions centred in the range 650&ndash, 800 and 550&ndash, 360 nm, associated with the presence of Fe3+ ions from the oxidation of structural Fe2+ ions in the serpentinites ((MgxFe2+1&minus, x)3Si2O5(OH)4). The relative intensity of the IR bands corresponding to the stretching modes of the OH&rsquo, s groups indicated the prevalence of one of the two phases, antigorite or lizardite, in the serpentinites. We proposed that the different relative intensity of these bands could be considered as diagnostic to differentiate the predominance of these phases in serpentinites.

Ni-based catalysts, 13.5 Ni wt.%, with enhanced thermal stability and catalytic performance for CO2 methanation have been synthesized with different La2O3 loadings. Catalysts have been extensively characterised by: XRD, IR, H2-TPR, IPA-TPD, UV–vis-NIR, FE-SEM and tested in CO2 methanation. SiO2 addition to Al2O3 support decreases the activity for CO2 methanation, while lanthanum acts as suitable promoter by strongly increasing catalytic performances. Silica presence successfully inhibits the formation of crystalline perovskites phases, stabilizes support morphology, and allows the introduction of high La2O3 loadings, allowing a better control of acid-base properties. 37 % wt. La2O3 addition gives rise to even higher performances than those previously observed, i.e. 83 % CH4 yield at 573 K. Reaction orders for CO2 and H2 have been determined; La- addition is confirmed to be responsible for a reduction in the CO2 reaction order, suggesting a stronger CO2 adsorption and the possible role of these species as a reactant reservoirs.

10 % and 30 % wt.CuO/wtsupport CuO/Al2O3, CuO/ZnAl2O4 and CuO/MgAl2O4 were prepared through wet impregnation, starting from commercial supports (Sasol). The catalysts were characterized, before and after catalytic runs, by XRD, IR and UV–vis spectroscopies, SEM and energy dispersive X-ray spectroscopy, surface area and porosity measurements. The fresh CuO-containing powders are converted into supported Cu metal catalysts in an ethanol/nitrogen stream, and act as efficient dehydrogenation catalysts producing acetaldehyde yields in the range 65–90 % at 500−650 K. The best selectivity observed on Cu/ZnAl2O4 is apparently mostly associated to the low activity of the uncovered support surface in the dehydration reactions to diethyl ether and ethylene. These catalysts are progressively deactivated already at 623 K by carbon deposition on copper sites, which leaves almost intact the activity of the uncovered support surface for dehydration reactions. This effect is easily reversed by burning in oxygen at around 650 K. Increasing copper loading only produces some increase in acetaldehyde selectivity. At higher temperature, Cu particle sintering is also observed, but it not necessarily causes evident deactivation.

The conversion of ethanol over a commercial ZnAl2O4 has been investigated. The catalyst has been fully characterized by XRD, IR, UV–Vis-NIR, ICP-OES, EDX-FE-SEM, BET and porosimetry. The catalyst is active in converting ethanol. At low conversion, diethyl ether is the main product while at higher conversions acetaldehyde is the main product (max yield ~ 50%). Ethylene and ethyl acetate are coproduced. Acetone and propylene become relevant products at complete conversion. The mechanism of formation of the products is discussed based on infrared surface chemical data, thermodynamic and kinetic data. Two independent catalytic sites exist, one for dehydration, the other for dehydrogenation, similar to those of Zinc oxide, giving rise to two parallel reaction sequencies. Criteria for developing selective catalysts towards dehydrogenation products are briefly discussed.

Conversion of ethanol was investigated over four commercial aluminas prepared by different industrial procedures and one commercial silica-alumina. Characterization was performed by TEM, XRD, S BET and porosity measurements, and IR spectroscopy of the surface OH groups and of adsorbed CO and pyridine. Different features are attributed to different phases (γ-, δ-, θ-Al 2 O 3 ) and different impurities (Na + , Cl − ). Total conversion of ethanol with >99% selectivity to ethylene is achieved at 623 K over the purer Al 2 O 3 catalyst (Na 3+ sites in a tetrahedral environment located on edges and corners of the nanocrystals. Ethanol adsorbs dissociatively on Lewis acid-base pair sites but may also displace water and/or hydroxyl groups from Lewis acidic Al 3+ sites forming the active intermediate ethoxy species. Surface ethoxy groups are supposed to be intermediate species for both diethyl ether and ethylene production. Silica-alumina also works as a Lewis acid catalyst. The slightly lower activity on surface area basis of silica-alumina than aluminas attributed to the lower density of Lewis acid sites and the absence of significant basicity.

CO adsorption has been studied over Pd/Al 2 O 3 and Pt/Al 2 O 3 catalysts using IR spectroscopy in different conditions and after different pretreatments. The oxidation of CO by oxygen and water (water gas shift) has also been studied at 130–673 K. The spectra show that the most active species as oxidant for CO are dispersed Pt n + and Pd n + cations and PdO x species mainly “decorating” the defects of alumina crystals where they modify completely the behaviour of surface OH's and Lewis acid sites. Some of these species oxidize CO to CO 2 already below ∼200 K. These highly oxidized species escape detection by IR during reaction at 500–673 K, when only reduced sites are apparent due to their very strong interaction with CO. The data suggest that redox mechanisms could occur for both WGS and CO oxidation occurring on highly dispersed cationic species non detectable under reaction conditions.

The steam reforming of 1:2 phenol–ethanol mixture (ca. 80 gph + eth/N m3 in He) as a model of biomass gasification tar, has been investigated over Ni/Al2O3, Ni/MgO-Al2O3 and Ni/ZnO-Al2O3 catalysts. In this paper interest is focused over a 5% Ni-Al2O3 catalyst, that has been characterized in the unreduced and reduced states by IR of CO adsorbed at low temperature. The steam reforming reaction of ethanol and phenol has also been studied, separately, by IR spectroscopy. In spite of its low Ni content and the absence of alkali and alkali earth ions, this catalyst is actually active in the steam reforming of both ethanol and phenol. The reaction is, however, shifted to higher temperature than with catalysts containing higher Ni-loadings and also Mg and/or Zn ions. Ethanol steam reforming occurs at lower temperature than phenol steam reforming and does not seem to be much hindered by the presence of phenol. Phenol steam reforming in the presence of ethanol starts after, but is highly selective to COx and H2. At low temperature, however, alkylation of phenol mainly occurs over the 5% Ni-Al2O3 catalyst to give mostly o-ethylphenol. Active ethoxide, acetate and phenate species are observed on the surface.

The IR study of the interaction of NO 2 with ammonia-covered H-ZSM-5 zeolite shows a very fast reaction at room temperature between NO 2 and adsorbed ammonium ions. An adsorbed NO 2 species is also formed. In the presence of NO + NO 2 mixture ammonium ions are completely rapidly decomposed at 300–373 K. These data suggest some speculations on the mechanism of the reduction of NO x by ammonia on H-ZSM-5 catalysts.

Powders with composition (Al x Ga 1−x)2O3 (x = 0, 0.25, 0.50, 0.75, 1) have been prepared by coprecipitation from aluminum nitrate and gallium nitrate and have been charaterized after drying at 373 K and calcination at 673, 1073 and 1473 K, using XRD, DTA, FT-IR and diffuse reflectance UV-VIS and BET surface area and porosity measurements. At 373 K Al compounds are essentially amorphous and for the Ga0.75 Al0.25 sample a solubility of 12% of Al3+ in the diaspore type α-GaOOH has been calculated. In samples calcined at 673 and 1073 K for the Al-rich ones a poorly crystalline defective spinel-type phase γ -Al2O3 has been found while the Ga-rich materials are composed of the metastable corundum type phase α-Ga2O3 and the thermodynamically β -Ga2O3 at 673 and 1073 K respectively. Al3+ added to α-Ga2O3 tends to hinder the α→ β phase transition of gallium oxide. At 1473 K mixed oxides give rise the thermodynamically stable α-Al2O3 and β-Ga2O3 phases. Reciprocal solubilities of Ga and Al in their oxides have been calculated.

The vapor-phase cyclohexane oxidative dehydrogenation has been investigated over several catalysts. A typical catalyst for total oxidation, as Mn2O3, materials applied in the field of oxide hydrogenation reactions, as silica-supported vanadia- and niobia-based catalysts, V-, Fe-, and Ce-phosphates used for partial oxidation reactions and ZSM5 zeolite, protonic and Co exchanged, have been tested. Over almost all the catalysts, benzene is the main product obtained, although cyclohexene is obtained with high selectivity at low conversion on phosphate catalysts.

The steam reforming of ethanol/phenol mixture (168 gTOT/N m3, ethanol: phenol 2:1 mol), assumed as a model for tar mixtures, has been studied over Ni/Al2O3, Ni-Mg/Al2O3 and Ni-B/Al2O3 catalysts. The effects of reaction temperature and of the presence of sulphur have been investigated. Catalysts have been characterized by XRD, IR of adsorbed CO, TPR, UV–vis spectroscopies. IR studies of adsorbed water and phenol have also been performed. The addition of Magnesium shows an activating effect on Ni/Al2O3 but also increases sensitivity to sulphur poisoning. This has been associated to the formation of large Ni metal particles over the MgxAl2O3+x support surface formed by the penetration of Mg ions in the subsurface of alumina, and to the low activity of the surface of such a modified support in the conversion of the organic reactants. A possible role of Mg in a different, possibly more efficient, activation of water is envisaged. The addition of boron in small amounts reduces activity, mainly if boron is added to the support before impregnation of Ni. A slight positive effect in reducing the deactivation due to sulphur is observed when boron is added after nickel.

Several Fe–Ga mixed oxide samples denoted as Fe1 − xGax (x = 0, 0.10, 0.25, 0.50, 0.75, 0.90) have been synthesised by a conventional coprecipitation method at controlled pH, dried at 363 K for 24 hours and calcined at 673 K and 1073 K for 3 hours. All samples were characterised by X-ray diffraction, chemical analyses, thermogravimetry and differential thermal analysis (TG-DTA) and FT-IR and UV-VIS spectroscopies. It was found all materials formed a solid solution, α-(Fe,Ga)2O3, in the entire Fe/Ga compositional range until 673 K. Samples calcined at 1073 K gave rise to biphasic systems for x > 0.5 due to the different structure of β-Ga2O3 compared to α-Fe2O3. Surface acidity of samples was studied by pivalonitrile molecule adsorption on a pressed pellet of each material, and weak Lewis acidity was found in all cases, it not being possible to distinguish between both types of cation site on the surface, and Bronsted acidity that increased with increasing Ga content. Methanol molecules were also adsorbed, showing an increase of reactivity for those samples with very low Ga content.

Mn–Zr mixed oxide samples with the general formula Mn x Zr 1− x O y , where x =0,0.1,0.2,0.5,0.8,0.9,1, have been prepared by a conventional coprecipitation procedure and characterised by X-ray diffraction (XRD), TG-DTA analyses, FT-IR and UV–VIS-diffuse reflectance (DR-UV–VIS) spectroscopies, BET specific surface measurements and surface acidity by pyridine adsorption techniques. It was found that Mn stabilises the metastable phase tetragonal zirconia and gives rise to low-concentration solid solutions (up to about 10% of Mn), remaining as Mn(IV) within the structure. Their catalytic behaviour was tested by the phenanthrene combustion and the isopropanol oxidation reactions. All samples were found to be active in the total oxidation of phenanthrene at quite a low temperature of 523–673 K. They are also very active in the oxidation of isopropanol, giving rise to acetone with high selectivity at partial conversion and producing CO 2 with total selectivity at total conversion. These materials are relevantly more active than Mn–Ti catalysts and approach the activity of pure Mn oxides, but with higher thermal stability.

Ten zirconia powders have been characterized by XRD, FT-IR/FT-FIR and Raman skeletal spectroscopies and DR-UV electronic spectroscopy. The vibrational features of a yttria-stabilized cubic zirconia and of tetragonal, monoclinic and tetragonal + monoclinic pure zirconia mixtures have been discussed. Assignments for the vibrational features of cubic and tetragonal samples are proposed. The origin of very broad vibrational peaks in tetragonal zirconia is briefly addressed. The vibrational spectra provide evidence for the presence of trigonal oxide ions in the monoclinic phase only. The UV spectra show that monoclinic zirconia (where the coordination of zirconium is sevenfold) absorbs at lower energy than the cubic and tetragonal phases (where the coordination of zirconium is eightfold). However, it absorbs at higher energy than the perovskite SrZrO3 where Zr adopts octahedral coordination. The origin of the shifts of the corresponding absorption edges is discussed.

Several samples of iron chromium aluminium mixed oxides with different composition have been prepared by coprecipitation at controlled pH starting from the corresponding nitrate salts and following dried at 393 K and calcination at 673 K for 3 h and 1173 K for 3 h. The powders have been characterised by XRD, FT‐IR and DR UV‐Vis spectrocopies, DTA‐TG thermal analyses and measurements of BET surface area. It has been found alumina is soluble into a-FeCrO3 phase up to near 20%. These samples are stable at 1243 K with a relative high specific surface area. The g,q! a phase transition is shifted towards higher temperatures by increasing Al content, being not detectable when a-FeCrO3 phase is the main phase. Surface chromates species are identified by the different techniques used and their amount seem to depend directly on the specific surface area of each sample. # 1999 Elsevier Science S.A. All rights reserved.

Mn2O3–Fe2O3 powders have been prepared by a coprecipitation method. The pure compounds have been characterized as constituted of α-Fe2O3 (haematite) and α-Mn2O3 (bixbyite) while the mixed oxides are constituted of a mixture of haematite- and bixbyite-structure solid solutions. The observed reciprocal solubilities calculated from the XRD patterns approach the thermodynamic ones. α-Mn2O3 is more active than α-Fe2O3 as catalyst for both propane and propene oxidation. However, α-Mn2O3 is less active than Mn3O4 powder. Propene oxidation is in all cases very selective to CO2 while propane oxidation gives rise to significant amounts of propene on α-Fe2O3. Mn2O3–Fe2O3 powders are slightly more active than α-Mn2O3 as combustion catalysts. The selectivities to propene upon propane oxidation decrease with increasing Mn content.

The interaction of propane and propene and of C3, C2 and C1 oxygenates (propane-1-ol, propan-2-ol, allyl alcohol, acetone, propanal, acrolein, acrylic, propionoic, acetic and formic acids and CO2) on oxidized Co3O4 +x has been studied by FTIR spectroscopy, with the aim to collect data on the mechanism of hydrocarbon catalytic combustion. Propene is already oxidized to acrylate species at RT and burns completely starting from 473 K. Propane already gives rise to acetate, propanoate and acrylate species below 373 K. A reaction scheme for catalytic propane oxidation is proposed. The behaviour of Co3O4 +x combustion catalyst surfaces are compared with those of MgCr2O4 +x, previously investigated. In both cases nucleophilic oxygen species (lattice O2– anions at the oxidized surface) are thought to be involved in catalytic combustion, which occurs via overoxidation of adsorbed partially oxidized compounds.

Powders belonging to the Fe2O3–Al2O3 system prepared by a coprecipitation method have been characterized from the point of view of their solid-state and surface structure by X-ray diffraction (XRD), Fourier-transform (far) infrared (FTIR/FT-FIR), diffuse reflectance ultraviolet–visible (DR-UV–VIS) Spectroscopy, BET surface area and porosity and adsorption of probe molecules. In samples calcined at 673 K a disordered defective spinel-type phase, γ-FeAlO3, has been found, containing Fe3+ in octahedral sites and Al3+ in both octahedral and tetrahedral sites, both in the bulk and on the surface. Samples calcined at 1173 K are composed of mixtures of two saturated solid solutions with corundum–haematite-type structures. The surface of these biphasic materials is dominated by the higher reactivity of α-Fe2O3 with respect to α-Al2O3, although tetrahedral Al3+ is also found at the surface of the saturated solid solution of Fe2O3 in α-Al2O3. Al3+ added to Fe2O3 tends to stabilize the spinel-type phase and to hinder sintering, while Fe3+ added to Al2O3 accelerates the γ→α phase transition and sintering.

The thermal behaviour of seven different ‘pure’ TiO2(anatase) preparations, as well as of materials obtained by doping them with potassium sulfate and carbonate, silica, and the oxides of tungsten, molybdenum and vanadium has been investigated by TG-DTA, XRD, FTIR and surface-area measurements. Vanadia–titania catalysts prepared by impregnation of these supports have also been investigated by the same techniques. The temperature at which anatase sintering and phase transformation to rutile occur strongly depends on the morphology of the TiO2 preparation. The anatase phase is much less stable in high-area, highly porous materials than in low-area powders. Vanadium oxide speeds up the anatase-to-rutile transition. However, common catalyst additives like silica, tungsten oxide and alkali-metal carbonates and sulfates strongly slow down both anatase sintering and its transformation to rutile. These phenomena influence the formulation of additives for vanadia–titania (anatase) catalysts for both selective oxidation and reduction of NOx.

Mixed oxides of the general formula Fe2–xCrxO3 have been prepared by a coprecipitation–calcination procedure. The precursors contain a crystalline goethite-like phase and an amorphous trihydroxide phase if Cr is present. Calcnnation for 5 h at 673 K resulted in crystalline powders whose surface areas decrease from 102 to near 20 m2 g–1 with increasing Cr content. IR spectra suggest that the structure of these materials consists of a superstructure of the corundum-type lattice of haematite. In parallel with the decrease of surface area, the smallest slit-shaped pores arising from goethite-to-haematite topotactic decomposition progressively disappear. Cr is observed to form chromate species, some of which are exposed on the surface of the calcined materials. These species are thought to have a role in the catalytic combustion activity of these materials. The optical behaviour of the powders in the IR, visible and UV regions is discussed.

MoO3–TiO2 samples have been prepared from aqueous solutions of ammonium heptamolybdate and titania (by conventional impregnation and equilibrium adsorption) and by mechanically mixing both oxides (with and without further hydrothermal treatment). The samples have been characterized by X-ray diffraction, specific surface area assessment, Fourier-transform infrared (FTIR) and ultraviolet–visible diffuse refectance (UV–VIS DR) spectroscopies and temperature-programmed reduction (TPR). Surface properties have been studied following the adsorption of probe molecules by FTIR spectroscopy. Dispersed phases are formed preferentially in samples prepared by equilibrium adsorption and in physical mixtures submitted to hydrothermal treatment; in all other cases crystalline MoO3 is mainly formed. Dispersed phases are more easily reduced. They have been identified as surface molybdenyl species bonded to Ti cations through bridging oxygens, and their overall coordination depends on the degree of surface hydration. These species predominate quantitatively on the catalyst surfaces and have been found to be strong Lewis and Bronsted acids. They are also more easily reduced than bulk MoO3 under TRP conditions, and very active as oxidizing agents for methanol.

The surface chemistry of δ-Al2O3, NiAl2O4, and CoAl2O4 has been investigated comparatively by FT-IR spectroscopy using adsorbed carbon monoxide and pyridine as probe molecules. The surface OHs of the inverse spinel NiAl2O4 are very similar to those of δ-Al2O3 and other transitional aluminas while those of CoAl2O4 are different and resemble those of other normal spinels. Both carbon monoxide and pyridine adsorption provide evidence for the presence of tetrahedral Al3+ ions exposed on the surface of the inverse spinel NiAl2O4. On the normal spinel CoAl2O4 octahedral Al3+ ions predominate with respect to the tetrahedral ones, also present because of partial inversion. Ni2+ and Co2+ ions are also detected on the respective surfaces. Slight modifications to the literature criteria are suggested for the assignments of the IR bands to surface OHs and of adsorbed pyridine on aluminas.

The interaction of vanadia-titania catalyst with 1-butene, cis-2-butene, trans-2-butene, and isobutene has been investigated by FT-IR spectroscopy in the temperature range 150-673 K. The three normal butenes give at room temperature 2-butoxide species that can undergo at higher temperatures oxidative dehydrogenation to methyl ethyl ketone and later oxidative C-C bond cleavage to acetate species

The adsorption and transformation of propylene and of several O-containing C{sub 3} organic molecules (namely isopropyl alcohol, acetone, allyl alcohol, acrolein, and acrylic acid) on vanadia-titania in the temperature range 150-673 K have been investigated by IR spectroscopy. At low temperatures (150-200 K), propylene adsorbs as such through {pi}-bonding and reacts later to give an adsorbed species identified tentatively as an allyl radical. Alternatively, it undergoes addition by a surface OH group to given an isopropoxy species. At least two main surface pathways for propylene transformation are active, leading to surface species functionalized at C{sub 2} (isopropoxy species and acetone) and at C{sub 1} (acrolein and acrylates) as well as products arising from coupling of the allyl radical. The results are discussed in relation to literature data concerning the heterogeneously catalyzed selective oxidation of propylene carried out on vanadia-titania as well as on bismuth-molybdate-based catalysts.

Cu-Pd/Al2O3 bimetallic catalysts have been characterized by XRD, TEM, and EDX techniques. The surface structure has been investigated by FT-IR spectroscopy of low-temperature adsorbed CO in the reduced and in the oxidized state. Evidence has been provided of the formation of Cu-Pd alloy nanoparticles, both of the alpha-phase (disordered fcc) and of the beta-phase (ordered CsCl-type). IR spectra suggest that Cu likely decorates the edges while Pd mostly stays at the main faces. Part of copper disperses as Cu+ on the support even after reduction. The presence of copper seems to modify strongly the sate of oxidized Pd centers in oxidized high-Pd content materials. The redox chemistry of the system, where Pd is reduced more easily than Cu, appears to be very complex.

An IR study of syngas and methanol conversion has been performed over Cu–ZnO–Al 2 O 3 methanol synthesis catalyst, Ni–Al 2 O 3 methanation catalyst and Co–Al 2 O 3 Fischer Tropsch catalyst. The data, obtained at low pressure, provide unequivocal evidence of the existence of a way via oxygenated intermediates (formates, possibly dioxymethylene, methoxy groups) in the three cases. In the selectivity determining step, methoxy groups desorb associatively as methanol on Cu–ZnO–Al 2 O 3 . Methoxy groups are selectively hydrogenolyzed to methane over Ni–Al 2 O 3 . Over Co–Al 2 O 3 oxygenated surface species may be involved in the chain growth to give C 2+ compounds. It is possible that this mechanism coexists with the via -carbide all-metallic catalysis reported for methanation and FT synthesis, on the basis of studies performed on pure metals.

The X-ray diffraction (XRD) patterns and the Infrared, Raman and UV–visible spectra of CeO 2 ZrO 2 powders prepared by co-precipitation are presented. Raman spectra provide evidence for the largely predominant cubic structure of the powders with CeO 2 molar composition higher than 25%. Also skeletal IR spectra allow to distinguish cubic from tetragonal phases which are instead not easily distinguished on the basis of the XRD patterns. All mixed oxides including pure ceria are strong UV absorbers although also absorb in the violet visible region. By carefully selecting their composition and treatment temperature, the onset of the radiation that they cut off can be chosen in the 425–475 nm interval. Although they are likely metastable, the cubic phases are still pure even after heating at 1173 K for 4 h.

MnGa mixed oxides have been prepared by coprecipitation of the corresponding oxo-hydroxides as powders and have been characterized in relation to their structural and optical properties. The materials have been characterized by XRD, TG-DTA, skeletal IR and UV–visible–NIR spectroscopies. Large solubility of Mn in the diaspore type α-GaOOH oxo-hydroxide has been found. The spinel related structures of hausmannite Mn3O4 and of β-gallia present large reciprocal solubilities at least in a metastable form. At high temperature also bixbyite-type α-Mn2O3 solid solutions containing up to 20% at. Ga have been observed.

The conversion of ethane and cyclohexane in the presence of oxygen has been investigated on vanadia-silica (VS), niobia-silica (NS) and 1:1 vanadia-niobia-silica (VNS) catalysts. Vanadia-silica is an active catalyst for the production of ethylene from ethane and of benzene from cyclohexane. Selectivity to ethylene near 60% is obtained at near 10% ethane conversion near 820 K. Selectivity to benzene declines from above 70 to 40% when conversion of cyclohexane grows up to 40%. Cyclohexene is produced only after total oxygen conversion. Niobia-silica is much less active than vanadia-silica, and the selectivities to ethylene and to benzene grow by increasing conversion up to approach those obtained in the empty reactor at very high temperatures (above 900–1000 K). The vanadia-niobia-silica catalyst behaves quite like the vanadia-silica catalyst. Raman, UV-Vis and XRD characterization experiments show that V 2 O 5 particles are present both in vanadia-silica and in niobia-vanadia-silica. On the contrary niobium oxide is present as amorphous phase and traces of V-Nb mixed oxide are found in the V-Nb-silica catalyst.

Mn–Zr mixed oxide materials have been prepared by a sol–gel method from a Mn (III) precursor salt and a solution of zirconium acetate in acetic acid, being characterized from a structural and morphological point of view. Conventional solid state techniques show that as obtained powders are formed by mixtures of manganese and zirconium acetates and (hydro) oxides, which evolve to bixbyite, hausmannite, as well as tetragonal and monoclinic zirconia above 873 K. Zirconium enhances the formation of the non-thermodynamically stable manganese compounds instead of the thermodynamically stable ones. This effect was not observed in other samples previously prepared by coprecipitation. In general, mixed systems are thermally stable up to 1073 K due to the formation of a solid solution phase of 10% Mn into zirconia, and display higher specific surface areas than those prepared by the coprecipitation method. Their activities in the combustion of heavy aromatic molecules are higher than those of the pure manganese oxides, very likely due to a synergic effect of zirconium. Moreover, the catalytic properties of hausmannite and bixbyite phases for burning this type of hydrocarbons seem to be very similar.

The adsorption and the oxidation of ammonia over sub-monolayer TiO2-anatase supported chromium, manganese, iron, cobalt, nickel and copper oxides, has been investigated using FT-IR spectroscopy. These materials are models of catalysts active in the Selective Catalytic Reduction of NOx by ammonia (SCR process) and in the Selective Catalytic Oxidation of ammonia to dinitrogen (SCO process). For comparison, the adsorption of ammonia and hydrazine over the TiO2-anatase support has also been studied. CrOx TiO2 adsorbs ammonia both in a co-ordinated form over Lewis acid sites and in a protonated form over Bronsted acid sites, involving high-valence chromium (chromyl species). However, simple outgassing at r.t. causes the desorption of ammonia from Bronsted acid sites showing that they are very weak. All other catalysts do not present any Bronsted acidity. Co-ordinated ammonia gives rise to several oxidation products over Fe2O3 TiO2, CrOx TiO2, CoOx TiO2 and CuO TiO2, among which hydrazine is likely present. Other species have been tentatively identified as imido species, NH, nitroxyl species, HNO, and nitrogen anions,N−2. NiOx TiO2 and MnOx TiO2 appear to be even more active in ammonia oxidation, because the adsorbed species disappeared completely at lower temperature (473 K) than in the other cases. However, possibly just due to their excessive activity, no adsorbed species different from co-ordinated ammonia can be found in significant amounts over these surfaces. Based on these data, the mechanism of the SCR and SCO processes over these catalytic materials is discussed. In particular, it is concluded that Bronsted acidity is not a requirement for SCR and SCO activity.

Powders with composition SrxTiO2 +x(x= 0, 0.02, 0.11, 0.42 and 1) have been prepared by coprecipitation from strontium hydroxide and titanium isopropoxide and have been characterized after drying at 393 K, and after calcination at 773 and 973 K, using XRD, TG–DTA, BET surface area and porosity measurements, FTIR–FTFIR and FT-Raman skeletal vibrational characterization, diffuse reflectance UV–VIS spectroscopy and FTIR spectra of the hydroxy groups and of adsorbed pyridine nad CO2. Strontium was found to inhibit anatase crystallization, sintering and transformation to rutile. Strontium tended to be deposited at the surface of anatase and gave rise to a decrease of the surface acidity and an increase of surface basicity. Moreover, it shifted the absorption edge of anatase to higher energies. For x= 1, the truly cubic SrTiO3 pervoskite phase was produced at room temperature with high surface area. The surface of SrTiO3 was definitely basic, with only strontium and oxygen ions exposed at the surface, and hydrogen impurities in the bulk.

Monophasic powders constituting α-(Fe,Al)2O3 solid solutions have been prepared by a coprecipitation method and have been characterized, from the point of view of their solid-state and surface structures, by X-ray diffraction (XRD), Fourier-transform (far) infrared (FTIR/FT-FIR) and diffuse reflectance ultraviolet–visible (DR-UV–VIS) spectroscopy. BET surface area and porosity and adsorption of probe molecules. Their bulk and surface properties have been compared with those observed for pure α-Al2O3 and pure α-Fe2O3 as well as with biphasic materials constituting mixtures of two α-(Fe,Al)2O3 saturated solid solutions, with overall compositions external to the solubility limits of these phases. The maximum solubility of Fe2O3 in α-Al2O3 is near 11%, while the maximum solubility of Al2O3 in α-Fe2O3 does not exceed 7%, for samples calcined at 1173 K. Metastable solid-solution phases with higher solute concentrations can be obtained if the calcination temperature is limited to 673 K. Al3+ added to α-Fe2O3 tends to hinder sintering and stabilize the pore structure, while Fe3+ added to α-Al2O3 accelerates the γ→α phase transition and causes a reduction in the surface area. In spite of their structures, which forecast only octahedral cation coordination, tetrahedral Al3+ and Fe3+ rations are found, mainly at the surfaces of the solid solutions.

Anatase-to-rutile phase transition has been studied on high-area TiO2-anatase and bicomponent systems containing molybdena and, for comparison, cobalt oxide, copper oxide, vanadia and corresponding TiO2-rutile based systems, using TG–DTA, XRD and surface-area measurements. These materials were prepared by impregnation and (co)precipitation methods. Conversion to rutile and crystal size growth strongly depend on the minority phase oxide. It is found that, while Cu and V oxides speed up both phase transition and particle sintering, Mo and Co oxides inhibit them. Moreover, the rutile particles obtained by phase transition are always much larger than both the starting and residual anatase particles. A mechanism of rutile formation by coalescence and phase transformation of anatase particles is proposed.

The interaction of methane, ethane and ethylene, and of some C1 and C2 oxygenates on the surface of model oxidation catalysts (Co3O4 and Pd-TiO2) has been investigated by FT-IR spectroscopy. Oxidation of alkanes is observed on Co3O4 starting from near 673 K, and near 373 K on Pd-TiO2. Olefins are oxidized already at room temperatures. Attempts are made to propose a mechanism for these reactions.

FT Raman and FTIR/FTFIR skeletal spectra of different TiO2 powders, of both synthetic and commercial origin, and of Sr, Ba, Co and Ni metatitanates are reported and discussed in relation to the predictions of factor group analyses. The ability of vibrational techniques to show the presence of brookite impurities in both anatase and rutile, and of rutile in anatase, as well as to give morphological and surface information is emphasized. The spectra of SrTiO3, BaTiO3, NiTiO3 and CoTiO3 are also discussed in relation to their different structures (pervoskite and ilmenite-type).

Vanadia/titania samples have been prepared from two different titania supports (P-25 from Degussa and anatase from Tioxide) by impregnation with aqueous solutions of NH4VO3 and calcination at 723 K. A decrease in the specific surface area is observed on increasing the amount of vanadia; titania from Degussa being non-porous, only development of wide pores is observed upon supporting vanadia. However, while the unloaded Tioxide support shows pores with average diameters of 8 and 5 nm, these latter disappear upon incorporation of vanadia. The reactivity of the V2O5/TiO2 sample prepared using the P-25 support in olefin oxidation has been studied by FTIR spectroscopy in the temperature range 150–673 K. Ethylene and propene are adsorbed as such at low temperatures, become hydrated to alkoxy species at medium temperatures and later undergo oxidation to carbonyl compounds (acetaldehyde and acetone). Allylic oxidation of propene and oxidative breaking of the CC bonds is also observed.

Low-loaded vanadia-titania catalysts have been prepared by impregnation of titania P-25 (Degussa). The catalysts were characterized by X-ray diffraction, specific surface area and porosity assessment by nitrogen adsorption at 77 K. For very low vanadia contents the absence of surface acid Bronsted sites leads to dimerization on surface acid Lewis sites, whereas the presence of surface acid Bransted sites when the vanadia content is increased leads to oxidation to carbonyl and carboxylate species.

The C3 alcohols 1-propanol, 2-propanol and prop-2-en-1-ol (allyl alcohol) are catalytically oxidized in He/oxygen to the corresponding carbonyl compounds propanal, acetone and acrolein with high selectivities and yields over Mn 3 O 4 . The reaction occurs in the temperature range 400–550 K and yields far over 85% are obtained in the synthesis of acrolein and acetone. The reaction rate is faster for the secondary alcohol 2-propanol, than for the primary ones. The oxidation of the unsaturated allyl alcohol is faster than for the saturated one, 1-propanol. Selectivity is limited by overoxidation of the carbonyl compounds. IR studies show that the high yields obtained in carbonyl compounds production over this catalyst are mainly due to their very weak adsorption. The main factor limiting the selectivity to acetone and, mainly, propanal is their tendency to give enolate anions that further convert into acetaldehyde in both cases. Overoxidation of aldehydes to the corresponding car☐ylate species is a less efficient mechanism limiting selectivity. The selectivity/activity behavior is definitely different than that observed for stoichiometric alcohols oxidations with Mn(III) compounds and also than that observed on other catalysts. This difference is associated to the low surface acidity of the Mn 3 O 4 catalyst.

Crystalline phases have been coprecipitated from Al/Cr mixed-nitrate aqueous solutions with ammonium carbonate. These phases have been characte rized as probably layered hydroxycarbonates with the likely composition (NH 4 ) 2 (Al,Cr) 6 (OH) 14 (CO 3 ) 3 ·H 2 O, using XRD, FTIR and TG–DTA analyses. The calcination of these materials gives rise to amorphous mixed oxides where Cr is partly in the hexavalent state, while further calcination at 1173 K gives rise to polyphasic materials. Samples with Al: Cr atom ratio between 5:1 and 1:1 give rise to four phase materials with three corundum-type phases and a spinel-type phase. All these phases contain both Al and Cr.