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CuO-ZnO-Al 2 O 3 catalysts with different Cu/Zn/Al atomic ratios were obtained by thermal decomposition of hydroxycarbonate precursors. The hydroxycarbonate precursors, prepared by coprecipitation at pH = 8, depending on the Cu/Zn/Al atomic ratios contain malachite Cu 2 CO 3 (OH) 2 , zincian-malachite Cu 2-x Zn x CO 3 (OH) 2 , aurichalcite Zn 5-x Cu x (CO 3 ) 2 (OH) 6 , hydrozincite Zn 5 (CO 3 ) 2 (OH) 6 , and an hydrotalcite-like: Cu 6-x Zn x Al 2 (CO 3 ): 2 (OH) 16 . Upon calcination, well interdispersed oxidic phases are obtained. In the ternary Cu/Zn/Al catalysts, the aluminium-containing phase was found to be amorphous and, regardless of the composition, only CuO and ZnO oxides are identified by X-ray diffraction analysis. The reduction process in H 2 was studied by XPS and XAES. The reduction of the Cu(II) species leads to the formation of both Cu(I) (Cu 2 O) and Cu(0) species. The reduction process is much slower for the alumina-containing samples compared to the binary CuO/ZnO specimen. Alumina and ZnO play an important role in the stabilization of Cu(II) and Cu(I) chemical states at low temperature. Upon reduction at high temperature, alumina plays a key role by preventing the sintering process of the Cu(0) particles.

Cobalt–zinc manganites at rather low Co content ( x =Co/(Co+Zn)=0, 0.01, 0.05, 0.10) were prepared by thermal decomposition of carbonate precursors obtained by coprecipitation at constant pH. Precursors were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA-DTA) and magnetic susceptibility measurements. For all samples, a single rhodochrosite-like phase, Co x Zn y Mn (1− x − y ) CO 3 , was formed, as detected by XRD. Magnetic analysis confirmed that cobalt and manganese were present as Co 2+ and Mn 2+ in the rhodochrosite crystal lattice. The carbonate monophasic precursors were decomposed at 723 and 973 K in air and Co–Zn–Mn based spinel-like solid solutions were obtained at both temperatures. The DRS and magnetic susceptibility data suggested that after calcination cobalt was mainly present as Co 3+ ions in the octahedral sites of the spinel together with Mn 3+ ions. The catalyst reducibility in H 2 was studied by temperature-programmed reduction (TPR). The cobalt containing catalysts reduced almost as the pure ZnMn 2 O 4 suggesting that cobalt does not show a detectable influence on the spinel reducibility. Preliminary results of the catalytic activity for the reduction of NO by hydrocarbons in absence of oxygen are presented.

In this work the results of a TPR and XPS investigation of CoxOy–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N2 at 723 K for 24 h of single‐phase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co2+[Co3]2O4 (Co3O4) spinel phase. The copper‐containing catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co 1-x 2+ Cu x 2+ [Co3+]2O4 and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N2 formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu+Co3+O2 compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO2 phase was the main component. A further addition of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N2‐calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.

Copper-zinc manganites with general formula CuxZn1−xMn2O4 (x=0, 0.01, 0.05, 0.10) were prepared by thermal decomposition of carbonate precursors obtained by coprecipitation at constant pH. Precursors were characterised by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA-DTA) and FT-IR spectroscopy. For all samples a single rhodochrosite-like phase, CuxZnyMn1−x−yCO3, with Cu2+, Zn2+ and Mn2+ in solid solution was detected by XRD. Precursors were decomposed in air at 723 and 973 K giving spinel-like solid solutions, as evidenced by XRD and measurements of magnetic susceptibility. X-ray photoelectron spectroscopy (XPS) showed that Cu2+ and Mn3+ are present at the surface of the spinel structure and that the spinel surface is enriched in copper at higher calcination temperature. As evidenced by temperature programmed reduction (TPR), the presence of copper markedly enhances the reducibility of CuxZn1−xMn2O4 spinels with respect to ZnMn2O4. Preliminary results of the catalytic activity of copper-zinc-based manganites for the reduction of NO by hydrocarbons are presented.

The recently reported interesting behavior of the EPR spin intensity as freshly prepared CuZSM-5 is dehydrated has been confirmed, and the interpretation offered in explanation has been tested by extending the data. Magnetic susceptibility and optical diffuse reflection spectroscopy have been used to show that the anomalous EPR data correspond to changes in symmetry rather than disproportionation of [CuOH]+ into Cu+ and Cu2+O- as H2O is removed, as previously suggested. Moreover, the relatively small negative Weiss constants suggest that antiferromagnetic coupling through the supposedly EPR silent conventional bridge species, [Cu2+−O2-−Cu2+]2+, cannot be responsible for the relatively large changes in observed EPR spin intensity on dehydration. EPR measures selectively individual paramagnetic species and ignores those of low symmetry, while magnetic susceptibility integrates over all magnetic species in the sample. The changes in the EPR intensities were much larger than those observed by magnetic suscept...

Different mixed oxides containing Cu, Zn, Cd and Cr were obtained by heating hydroxycarbonate precursors at various temperatures and in different atmospheres, and characterized by using X-ray diffraction (XRD), infrared, diffuse reflectance spectroscopy, thermogravimetry, and BET and copper surface area analysis. The reduction process and the phase evolution during reduction of the mixed oxides was followed by temperature-programmed reduction and XRD. The mixed oxides were activated in an H 2 /N 2 flow and then tested as catalysts in the vapour-phase hydrogenation of γ-butyrolactone (GBL) and a solution of maleic anhydride (MA) in GBL (60:40 w/w). Depending on composition, heating temperature and atmosphere, the samples contained different phases, such as CuO, CdO, Cr 2 O 3 , CuCrO 2 , CuCrO 4 , α-CdCrO 4 , cubic and tetragonal CuCr 2 O 4 , and cubic Cu Zn and Cu Cd spinel-type phases. The partial substitution of Cu 2+ ions with Zn 2+ or Cd 2+ ions stabilizes the cubic form of the spinel-type phases, which form via intermediate chromate phases. The final product of reduction in all cases is metallic copper. Cubic CuCr 2 O 4 is more reducible than the corresponding tetragonal phase, which reduces to metallic copper through the intermediate formation of CuCrO 2 . The presence of zinc or cadmium promotes or inhibits, respectively, the copper reducibility both in CuO and in the copper chromite spinel. In the hydrogenation of GBL, the Cu/Cr catalysts obtained by calcination show similar behaviours, with a small increase in activity as a function of the copper content. At the lower temperatures investigated the main products are tetrahydrofuran (THF) and n-butanol, while at 548 K significant amounts of ethanol are observed, favoured by increasing copper content. On the other hand, the Cu/Cr catalyst obtained by heating under a reduced oxygen atmosphere, for which only tetragonal CuCr 2 O 4 is detected before reduction, shows a decrease in catalytic activity. Partial substitution of the Cu 2+ ions gives rise to a decrease in GBL conversion, with a considerable deactivation when Cd 2+ ions are present. Decreasing the H 2 /C 4 molar ratio gives rise to a decrease in activity for all samples, without any significant change in the trend observed. With the MA/GBL solution, the partial substitution of Cd 2+ ions for Cu 2+ ions also gives rise to considerable deactivation. For the other catalysts, the main products at the lower temperatures are GBL and succinic anhydride (SA), while at 548 K overhydrogenation and hydrogenolysis reactions predominate. The presence of Zn 2+ ions gives rise to an increase in yield in GBL, due to an increase in the hydrogenation activity toward SA, but the consecutive transformation of GBL at high temperature to low cost by-products is not inhibited. On the other hand, the presence in the Cu/Cr catalyst of only CuCr 2 O 4 increases the yield in GBL, as a consequence of a strong inhibition of the overhydrogenation and/or hydrogenolysis reactions of GBL. With the MA/GBL solution, similar behaviours are observed when the H 2 /C 4 molar ratio decreases. At the same time, however, the lack in the carbon balance increases and a displacement towards high temperature of the maximum yield in GBL is found.

The oxidative dehydrogenation of 1-butene has been studied over catalysts with the scheelite structure and general formula Bi[sub 1-x/3]Me[sub y][V[sub 1-x]Mo[sub x-y]Fe[sub y]]O[sub 4] with x = 0.45; y = 0, 0.10, or 0.15; Me = Fe or Bi. Experiments were carried out in a pulse microreactor in the temperature range 473-673K. The trend of total conversion with catalyst composition is similar to that found previously for the same catalyst composition is similar to that found previously for the same catalysts in propene oxidation. Moreover, the total conversion was identical in the presence and in the absence of gaseous oxygen in the pulse (first pulse with 1-butene alone). On the other hand, the production of butadiene was markedly different from that of acrolein in the propene reaction for the catalyst in which the cationic vacancies were completely filled with bismuth ions (y = 0.15, Me = Bi). This finding points to a differing importance of the cationic vacancies depending on whether the selective reaction occurs with oxygen insertion. Also the oxidation to isomerization ratios and the reduction-oxidation properties changed with catalyst composition. The results are discussed in terms of participation of cationic vacancies and iron ions in the steps ofmore » the allylic oxidation. 39 refs., 7 figs., 4 tabs.« less

Different mixed oxides containing Cu, Zn, Cd and Cr were obtained by heating hydroxycarbonate precursors at various temperatures and in different atmospheres, and characterized by using X-ray diffraction (XRD), infrared, diffuse reflectance spectroscopy, thermogravimetry, and BET and copper surface area analysis. The reduction process and the phase evolution during reduction of the mixed oxides was followed by temperature-programmed reduction and XRD. The mixed oxides were activated in an H 2 /N 2 flow and then tested as catalysts in the vapour-phase hydrogenation of γ-butyrolactone (GBL) and a solution of maleic anhydride (MA) in GBL (60:40 w/w). Depending on composition, heating temperature and atmosphere, the samples contained different phases, such as CuO, CdO, Cr 2 O 3 , CuCrO 2 , CuCrO 4 , α-CdCrO 4 , cubic and tetragonal CuCr 2 O 4 , and cubic Cu Zn and Cu Cd spinel-type phases. The partial substitution of Cu 2+ ions with Zn 2+ or Cd 2+ ions stabilizes the cubic form of the spinel-type phases, which form via intermediate chromate phases. The final product of reduction in all cases is metallic copper. Cubic CuCr 2 O 4 is more reducible than the corresponding tetragonal phase, which reduces to metallic copper through the intermediate formation of CuCrO 2 . The presence of zinc or cadmium promotes or inhibits, respectively, the copper reducibility both in CuO and in the copper chromite spinel. In the hydrogenation of GBL, the Cu/Cr catalysts obtained by calcination show similar behaviours, with a small increase in activity as a function of the copper content. At the lower temperatures investigated the main products are tetrahydrofuran (THF) and n-butanol, while at 548 K significant amounts of ethanol are observed, favoured by increasing copper content. On the other hand, the Cu/Cr catalyst obtained by heating under a reduced oxygen atmosphere, for which only tetragonal CuCr 2 O 4 is detected before reduction, shows a decrease in catalytic activity. Partial substitution of the Cu 2+ ions gives rise to a decrease in GBL conversion, with a considerable deactivation when Cd 2+ ions are present. Decreasing the H 2 /C 4 molar ratio gives rise to a decrease in activity for all samples, without any significant change in the trend observed. With the MA/GBL solution, the partial substitution of Cd 2+ ions for Cu 2+ ions also gives rise to considerable deactivation. For the other catalysts, the main products at the lower temperatures are GBL and succinic anhydride (SA), while at 548 K overhydrogenation and hydrogenolysis reactions predominate. The presence of Zn 2+ ions gives rise to an increase in yield in GBL, due to an increase in the hydrogenation activity toward SA, but the consecutive transformation of GBL at high temperature to low cost by-products is not inhibited. On the other hand, the presence in the Cu/Cr catalyst of only CuCr 2 O 4 increases the yield in GBL, as a consequence of a strong inhibition of the overhydrogenation and/or hydrogenolysis reactions of GBL. With the MA/GBL solution, similar behaviours are observed when the H 2 /C 4 molar ratio decreases. At the same time, however, the lack in the carbon balance increases and a displacement towards high temperature of the maximum yield in GBL is found.

Iron–zinc manganites at different Fe content [x = Fe/(Fe + Zn) = 0, 0.01, 0.05, 0.10] were prepared by thermal decomposition of carbonate precursors obtained by coprecipitation at constant pH. Precursors were characterized by diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA-DTA) and magnetic susceptibility measurements. All samples are made by a single rhodochrosite-like phase, FexZnyMn(1−x−y)CO3, in which besides Zn2+ and Mn2+, only 5% of the total iron was Fe2+, the remaining 95% surprisingly being Fe3+ ions. The carbonate monophasic precursors were decomposed at 723 and 973 K in air and solid solutions of iron in the zinc manganite spinel-like phase were obtained at both temperatures. Zinc manganite, ZnMn2O4, is a ‘normal’ spinel in which the Zn2+ ions occupy the tetrahedral sites and Mn3+ ions the octahedral sites of the crystal lattice. When iron is loaded, it is present as Fe3+ ions in the octahedral sites of the spinel together with Mn3+ ions. The catalyst reducibility in H2 was studied by temperature-programmed reduction (TPR). The iron-containing catalysts resulted to be slightly more resistant towards reduction than pure ZnMn2O4, suggesting that Fe3+ ions play a stabilizing effect on the spinel structure. Results of a Mossbauer investigation on the iron chemical state and its coordination symmetry are extensively reported. Some preliminary results of the catalytic behaviour for the reduction of NO by hydrocarbons are presented.

Preparation and characterization of both iron-zinc manganites at different iron content (x = Fe/(Fe + Zn) = 0, 0.01, 0.05, 0.10) and their carbonate precursors are reported. In particular, structural properties and the iron chemical state were investigated. Precursors, obtained by coprecipitation at constant pH, were in all cases monophasic and made by a rhodochrosite-like, FexZnyMn(1-x-y)CO3, phase. Mössbauer spectroscopy proved that, surprisingly, Fe3+ was 95% of total iron. A hypothesis about the charge compensation mechanism in the rhodochrosite-like structure is given. The carbonate precursors were decomposed in air at 723 and 973 K, leading at both temperatures to monophasic iron-zinc manganites characterized by a distorted spinel-like structure with tetragonal symmetry. In such a structure, trivalent Mn3+ ions and bivalent Zn2+ ions are perfectly ordered in the octahedral and tetrahedral sites of the crystal lattice, respectively, as expected for a ‘normal’ spinel. Mössbauer investigation revealed that iron is present as trivalent ions in the octahedral sites and that no iron extra-phases were formed. Moreover, three doublets corresponding to octahedral Fe3+ ions were detected, likely related to different distributions of Fe3+/Mn3+ cations in the next-nearest coordination sphere.

Publisher Summary This chapter presents a comparative study of nitric oxide (NO) and nitrous oxide (N2O) selective catalytic reduction on copper and iron-containing ZSM-5 catalysts. A comparison between the activities of H-ZSM-5, H-[Fe]-ZSM-5, Cu-[Fe]-ZSM-5, Cu-ZSM-5, and Fe-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO and N2O by propane (C3H8) in the presence of oxygen is discussed. The results show that for the NO reduction the order of activity is Cu-[Fe]-ZSM-5 ≈ Cu-ZSM-5 > Fe-ZSM-5 > H-[Fe]-ZSM-5 ≈ H-ZSM-5. For the N2O reduction, the order of activity changed as follows: H-[Fe]-ZSM-5 > Fe-ZSM-5 > Cu-[Fe]-ZSM-5 ≈ Cu-ZSM-5 > H-ZSM-5. Catalytic results for the N2O decomposition are also presented.

Temperature-Programmed Reduction (TPR) has been critically tested by carrying out experiments at different operating conditions on both copper-based catalysts and pure copper oxides (CuO, Cu 2 O). In this work we give experimental evidence that, even if interference caused by mass transfer limitations or dispersion is removed, the reduction profiles are markedly affected by artefacts when an inadequate combination of the typical TPR operating variables is used. Furthermore, an attempt of tracing back to the artefacts origin is also effected.

The oxidation state of a molybdena-γ-Al2O3 (8%) catalyst was varied by reduction with either H2 or CO under carefully controlled conditions. The decomposition of cyclopropane was studied and correlations were sought between surface chemistry and catalytic function. Temperatures between 50 and 130 °C and a pulse reactor were employed. In every case propylene, ethylene, and n-butenes were produced in proportions depending upon the extent of reduction. When cyclopropane was reacted over a catalyst reduced with D2, deuterated propylenes were formed in increasing percentages with higher extents of reduction. Similar results were obtained when the catalyst was first thoroughly reduced with D2, then reoxidized and finally reduced to different extents with CO. When mixtures of cyclopropane-d0 and -d6 were co-isomerized, the products were readily equilibrated. Methylcyclopropane reacted much faster than cyclopropane, yielding both isomerization and metathesis products. No trace of isobutane was detected. A small portion of the first cyclopropane to contact the catalyst reacted to form ethylene and the methylene carbene. Otherwise the data were consistent with a proton-catalyzed ring opening followed by metathesis on coordinatively unsaturated Mo (IV) ions occurring through a carbene mechanism. The results are discussed in terms of current literature.

Supported copper oxide on γ-alumina (2,4, or 10% Cu atoms per 100 A1) was subjected to cycles of reduction (by hydrogen) and oxidation (by oxygen). From the hydrogen consumed, from the water released and from the oxygen used in the oxidation step it was possible to deduce the molar fractions of Cu 0 , Cu 1+ and Cu 2+ present, as a function of the extent of reduction. At low copper loadings (2 or 4%) Cu 1+ is preferentially formed. The reduction to Cu 0 is thermodynamically favorable, but kinetically hindered. The role of the support and of the surface configuration is discussed.

Small amounts of gallium ions were added to y-alumina and their influence on the structural properties of the system Co-(Mo)/y-Al203 was studied. It is shown that, due to the presence of Ga3+ ions, a "surface" spinel CoAl204 is formed with a larger amount of Co2+ in tetrahedral sites as compared to the spinel formed on gallium-free alumina. A decrease of the segregated Co304 is also observed. A possible effect of gallium ions on molybdenum is discussed. It is also reported that different preparation methods (single or double impregnation) lead to the formation of different surface species. Cobalt aluminate, molybdate monolayer, and Co3O4, depending on the Co content, are formed on doubly impregnated specimens. Cobalt aluminate and cobalt molybdate are the main species formed on singly impregnated specimens. Finally brief consideration is given to how the Co and Mo species, present in the oxide form, change in the sulfided form.

Copper and zinc hydroxycarbonates with Cu Zn atomic ratios of 100 0 , 92 8 , 85 15 , 77 23 , 67 33 , and 50 50 were prepared by the coprecipitation method. The samples with the ratios 100 0 , 92 8 and 85 15 were monophasic with the monoclinic P2 1 a malachite structure, whereas the richer zinc samples contained in addition to the malachite phase the orthorhombic B2212 aurichalcite, whose concentration was very low in the 77 23 specimen but increased continuously with zinc content. The amount of aurichalcite in the biphasic powders has been estimated by means of quantitative X-ray diffraction and differential thermal analysis. With only those X-ray reflections belonging to the malachite structure taken into account, the unit cell constants for all the solid solution hydroxycarbonates have been determined, showing that as a whole the cell volume of malachite decreases continuously with increasing zinc content. This result is related, as shown also by DTA measurements and thermochemical literature data, to an increasing stability of compounds richer in zinc, to increasing covalent effects, and/or to less octahedral site distortion around the metal atoms when zinc substitutes for Cu2+ ions in the malachite lattice. Magnetic susceptibility and thermogravimetric measurements together with diffuse reflectance spectra are also presented and discussed.

X-ray photoelectron spectroscopy has been applied to the study of the surface composition and the redox behaviour of multicomponent oxide catalysts having the scheelite structure and general formula Bi 1−x 3 □ x 3−y Me y (V 1−x Mo x−y Fe y )O 4 (Me = Fe or Bi, □ = cation vacancies), before and after exposure to hydrogen, propene, and a propene + oxygen mixture. The results point to a different reactivity toward the various reactants. By interaction with hydrogen, an extensive reduction is obtained with considerable change of the catalyst surface composition. The reduction behaviour depends on the sample composition, the iron-containing catalysts being reduced at low temperature (140 °C). As regards propene treatment, a preferential reactivity of bismuth with propene has been found, regardless of the sample composition. Bismuth is reduced at low temperature (175 °C) with ensuing migration to the surface. Under conditions leading to the catalytic oxidation of propene, a high surface stability is exhibited by these compounds. The catalysts remain oxidized and the surface composition reflects that of the bulk. A correlation with the catalytic properties has also been made on the basis of the different mobility of the oxygen ions among the samples examined.

When cyclopropane was isomerized using a microcatalytic pulse technique over a reduced molybdena-γ-alumina catalyst (0.3 to 1.5 e Mo ), the resulting propene underwent secondary reactions including polymerization, metathesis to ethene and butenes, and hydrogenation (in H2 carrying gas) to propane, ethane, and butane. Isotope exchange also occurred when D2 or cyclopropane-d6 was used. Complementary tracer studies were also made with propene-d0 and D2 using a static recirculation system. The kinds of sites required for the several reactions were classified and estimates made of their concentrations using strongly adsorbed (poison) molecules as probes. Small amounts of CO and NO were effective poisons for hydrogenation and exchange, but not for isomerization or metathesis in these experiments, but some poisoning of isomerization by CO was observed in pulse experiments. H2O, pyridine, and NH3 were less selective, but all of the reactions tested were poisoned. CO2 and N2O were ineffective and O2 appeared to selectively reoxidize the active hydrogenation sites. From the data obtained, it could be estimated that the site concentrations utilized for these reactions were much lower than the measurable parameters such as anion vacancies, Mo4+ or Mo3+ centers, etc; they amounted to no more than a few percent of the Mo present and may have corresponded to multiplet vacancies. The chemisorption of NO and of CO correlated with both the extent of reduction and the vacancy concentration as did hydrogenation and exchange, and these same molecules, when chemisorbed, effectively poisoned these reactions.

The purpose of this research was to study the best conditions for the synthesis of the double oxides Li5AlO4 and Li3AlO3 in the solid state starting from the simple oxides, and to determine their heats of formation.

An infra-red investigation has been carried out of CO adsorbed onto Ni2+/η-Al2O3 and Ni2+/γ-Al2O3 catalysts. These contain a “surface spinel” phase in which nickel ions are present both in octahedral and tetrahedral sites. Their relative concentrations are primarily determined by the atmosphere (damp or dry) in which the preparation at 600°C has been carried out. Upon CO adsorption four bands appear in the 2250–2150 cm–1 region due to molecules linked to coordinatively unsaturated surface cations. The relative intensities are related to the preliminary treatment of the sample and are therefore discussed in terms of the possible surface configurations and of the relative amounts of tetrahedral and octahedral sites occupied. The infra-red spectrum of CO adsorbed on hydrogen reduced samples has also been investigated and the importance of the preliminary treatment on the reducibility has been confirmed.

The ESR spectra of CoO-Al2O3, MoO3-Al2O3 and CoO-MoO3-Al2O3 were investigated in the oxidized state and after reduction with H2 + H2S (sometimes followed by a further treatment with H2) or by H2. All Co-containing samples produce signals at 1200 Oe (for γ-Al2O3) which shift to 1750 and 4300 Oe after treatment at 1300 °C (formation of α-Al2O3). The signals are assigned to Co2+ in tetrahedral sites in the support: they are not affected by sulfiding or reduction. If no Mo is present, reduction leads to the formation of an extremely broad and strong signal ascribed to cobalt metal: it is eliminated by the presence of Mo. In the absence of Co and in the oxidized state Mo-containing samples develop a weak signal at g = 1.93, assigned to traces of Mo5+ in free MoO3; in the presence of Co this signal disappears. Pretreatment of Mo-containing samples with H2 + H2S leads first to a hundredfold enhancement of the signal which, however, disappears after application of longer reduction times or higher temperatures. No signal connected with Mo3+ could be found. Finally, H2 after H2 + H2S treatments produced a signal at g = 2.16 if Co was present; it is assigned to either Co+ or Co2+ (low spin). A catalyst model is proposed containing two solid states. State I is the support with Co2+ and Mo6+ in its subsurface layers. Its fate after reduction is uncertain but Co2+ is not changed. State II is a separate system of compounds, Co3O4, MoO3 or CoMoO4 depending on the composition. Treatments with H2 + H2S lead, respectively, to Co + CoS, MoS2 or CoS + MoS2 (CoMo2S4).

The limits of solubility of NiO in ZnO at different temperatures of calcination have been determined by means of lattice parameter and magnetic measurements. The limits have been estimated as less than 0.5, from 0.5 to 1.0, and from 1.0 to 1.5 Ni atoms per 100 Zn atoms for the firing temperatures of 1000, 1200, and 1300°C, respectively.

Small amounts of gallium ions were added to y-alumina and their influence on the structural properties of the system Co-(Mo)/y-Al203 was studied. It is shown that, due to the presence of Ga3+ ions, a "surface" spinel CoAl204 is formed with a larger amount of Co2+ in tetrahedral sites as compared to the spinel formed on gallium-free alumina. A decrease of the segregated Co304 is also observed. A possible effect of gallium ions on molybdenum is discussed. It is also reported that different preparation methods (single or double impregnation) lead to the formation of different surface species. Cobalt aluminate, molybdate monolayer, and Co3O4, depending on the Co content, are formed on doubly impregnated specimens. Cobalt aluminate and cobalt molybdate are the main species formed on singly impregnated specimens. Finally brief consideration is given to how the Co and Mo species, present in the oxide form, change in the sulfided form.

Presentation des resultats spectrometriques XPS pour le systeme catalytique CuO-ZnO prepare a partir de Cu 2 CO 3 (OH) 2 ou de (Cu, Zn) 5 (CO 3 ) 2 (OH) 6 . Etude de la chimie de surface

Summary It is shown that when transition metal ions (Mn, Co, Ni and Cu ions) are supported on γ- and η-Al 2 O 3 , at 600°C, two reactions occur concurrently: one leads to the formation of a spinel and the other to a segregation of an oxide. The factors which effects both reactions are discussed. It is also shown how the addition of small amounts of foreign ions, such as Zn 2+ , Ga 3+ and Ge 4+ , affects the interaction between the transition ions and the aluminas. Simple catalytic tests show how the catalytic activity is influenced by the type of compound which is formed on the aluminas surface.