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Catalysts based on tungsten oxide supported on silica and containing up to 2.5 W atoms nm–2 were studied for the purpose of establishing quantitative relationships between the nature and abundance of surface species, acidity, and catalytic activity. Synthesis conditions that maximize the formation of amorphous WO3 were adopted to assess its influence on the overall acidity and activity. The results were compared to those of conventionally prepared catalysts. The catalysts’ structure was characterized by FTIR, Raman, and UV spectroscopies. The acidity of the solids was monitored by adsorption of 2,6-dimethylpyridine followed by FTIR, and their catalytic activity was tested for the reaction of propan-2-ol dehydration. A methodology for quantitation of W species (WOx surface species, amorphous or crystalline WO3 particles) detected following calcination at 673 or 773 K was developed. For both calcination temperatures, surface W species were first formed with initial W addition. Their abundance increased with...

International audience; Ring-opening reactions of decalin and MCH were studied over monofunctional acid (WO3/Al2O3) and metal (Ir/Al2O3) catalysts containing, respectively, up to 5.3 at. W/nm(2) and 1.8 wt% Ir. The catalysts were characterized by X-ray diffraction, Raman spectroscopy, low-temperature CO adsorption followed by infrared spectroscopy, and H-2 chemisorption. A reaction network was proposed for both molecules and used to determine the kinetic parameters. Kinetic modeling allowed relating characterization results and catalytic performance. For WO3/Al2O3 catalysts, ring contraction precedes ring opening of both molecules. The evolution of ring contraction activity was consistent with the development of relatively strong Bronsted acid sites. Ring opening occurs according to a classic acid mechanism. For Ir/Al2O3 catalysts, only direct ring opening was observed. Ring opening proceeds mostly via dicarbene mechanism. Analysis of products indicated that monofunctional metal catalysts are better suited than acid solids for upgrading LCO. (C) 2011 Elsevier Inc. All rights reserved.

International audience; The present paper investigates the development of Ir-based catalysts supported on tungstated aluminas for the ring opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of tungstated aluminas WOx/Al2O3 containing up to 6.0 at.W/nm(2) was prepared. Ir-based catalysts containing 1.2 wt% were obtained by impregnation of these solids. The performance of Ir/WO3/Al2O3 catalysts for methyl cyclohexane ring opening was found to be similar to that observed over the corresponding zirconia-based system indicating that the metal-acid balance (and not the nature of the support) is the key parameter for optimum performance. (C) 2010 Elsevier B.V. All rights reserved.

The present paper is the second part of a systematic study of the influence of W and Ir loading on the activity of Ir/WO 3 /ZrO 2 –SiO 2 catalysts for the ring-opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of Si-stabilized tungstated zirconias, WO x /ZrO 2 –SiO 2 , containing up to 3.5 atom W/nm 2 , was prepared. Ir-based catalysts containing up to 1.2 wt% were obtained by impregnation of these solids. Characterization of the metal dispersion and catalyst acidity was described in a previous article. The objective of the present study was to determine the best metal/acid balance for optimal performance of Ir/WO x /ZrO 2 –SiO 2 catalysts in the ring-opening reaction of MCH. Monofunctional (acid WO x /ZrO 2 –SiO 2 or metal Ir/ZrO 2 –SiO 2 ) and bifunctional (Ir/WO 3 /ZrO 2 –SiO 2 ) catalysts were examined. Based on the analysis of the yields and products distributions, a reaction network was proposed, and kinetic data (e.g., activation energies, initial rates) were calculated. Correlations between characterization results obtained earlier (e.g., acidity, dispersion) and catalytic performance are also reported. The monofunctional acid catalysts WO x /ZrO 2 –SiO 2 showed a low selectivity for ring opening. The ring-contraction activity developed for W surface density above a threshold value of 1 atom W/nm 2 . This was attributed to the appearance and the development of a relatively strong Bronsted acidity monitored by infrared measurements. MCH ring contraction and C5 naphthene ring opening occur according to a classic acid mechanism. For low conversions, the monofunctional metal catalysts Ir/ZrO 2 –SiO 2 exhibited significant selectivity for ring opening that decreased with increasing conversion. Because of the lack of ring-contraction products, the observed activity was attributed to the direct ring opening of the MCH. Ring opening and cracking occur according to a dicarbene mechanism. The study of MCH conversion on Ir/WO x /ZrO 2 –SiO 2 catalysts indicated that MCH ring contraction to alkylcyclopentanes occurs before ring opening. The best yields for ring opening were obtained with the 1.2% Ir/WO x /ZrO 2 (1.5 atom of W/nm 2 ). Further increases in W surface density led to a decrease in the indirect ring-opening yield, attributed to a decrease in Ir dispersion. For bifunctional metal/acid catalysts, analysis of the mechanism is less straightforward. The activation energy for C6 ring contraction and indirect C6 ring opening is a function of the metal/acid ratio. For high ratios, indirect ring opening occurs essentially over metallic sites. A decrease in the metal/acid ratio enhances the contribution of acid mechanism.

The oxidation of dibenzothiophene by an oxygen/aldehyde system, using heterogeneous (unsupported and alumina-supported oxides) and homogeneous (acetate salts) catalytic systems based on Mn, Co and Ni, was examined. In all instances, Co- and Mn-based systems were the most active catalysts. In contrast, a markedly lower activity was measured for Ni(II) acetate whereas NiO and the alumina-supported NiO were inactive. The study indicates that involvement of homogeneous catalysis cannot be excluded when using the supported catalysts.

This paper is the first part of a systematic study of the influence of W and Ir loading on the activity of Ir/WO 3 /ZrO 2 –SiO 2 catalysts for the ring-opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of Si-stabilized tungstated zirconias, WO x /ZrO 2 –SiO 2 , containing up to 3.5 at W/nm 2 was prepared. Ir-based catalysts containing up to 1.2 wt% were obtained by impregnation of these solids. The acidity of Si-stabilized tungstated zirconias, ZSiW x , was monitored by low-temperature CO adsorption followed by infrared (IR) spectroscopy. The results indicated the development of strong and relatively strong Bronsted acidity with increasing W surface density above a threshold of 1 atom W/nm 2 . The study of the Ir-doped solids showed that the texture, structure, and acidity of the ZSiW x solids were not affected by Ir deposition. The characterization of the metallic function was performed by hydrogenation of toluene and by CO adsorption at ambient temperature, followed by IR spectroscopy. Both methods indicated a low and constant Ir dispersion for the y Ir/ZSiW0 ( y = 0.3 , 0.6, 1.2) series. For a given Ir loading (1.2Ir/ZSiW x ), a progressive decrease in the dispersion of Ir metal with increasing W surface density was observed.

International audience; The relationship between the acidity, catalytic activity, and surface structure for tungsten oxide supported on zirconia was investigated for a series of solids prepared by equilibrium adsorption on monoclinic zirconia. The catalysts were active for propanol dehydration only above a threshold in W loading. The acidity was studied by infrared spectroscopy of adsorbed probe molecules (2,6-dimethylpyridine and CO), and the onset of activity was correlated with that of the formation of relatively strong Bronsted acid sites. The variation in the abundance of these sites correlated with the catalytic activity. Lewis sites were present but could not be directly associated with the activity. Raman, IR, and UV spectroscopy results indicated that the active sites were related to polymeric W surface species.

A series of NbOx=ZrO2 catalysts containing up to 2.67 wt% Nb (ca. 80% nominal surface coverage) was prepared by incipient wetness impregnation from niobium oxalate and oxalic acid solution. The structure of the catalysts was monitored by X-ray diffraction and Raman spectroscopy. The results indicated the presence of a surface Nb phase. No evidence for the formation of crystalline Nb2O5 species was found. The development of the acidity as a function of Nb loading was monitored by adsorption of a

Synthetic nylon-6 single molecular mass oligomers were studied by matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometry. These oligomers, considered as model compounds for the study of nylon-6 polymers, gave good mass spectrometric results using both MALDI and ESI. In spite of the gentle nature of both techniques, the MALDI and ESI spectra showed evidence of end-group cleavage from the oligomer chains. MALDI-MS was found to give similar fragmentation patterns for all of the oligomer samples. An increase in doubly charged ion signals with increasing oligomer mass was observed in the ESI mass spectra, as was end-group fragmentation. Signals from oligomer clusters were observed in ESI-MS for the dimer, tetramer and hexamer, most likely due to non-covalent bonding among the low-mass oligomer molecules.

Electrospray ionization mass spectrometry (ESI-MS) was applied for the characterization of inorganic polyphosphates [orthophosphate, pyrophosphate, tripolyphosphate, trimetaphosphate, and tetrapolyphosphatel. The high selectivity of ESI-MS allows the detection of different polyphosphate species without preseparation by ion chromatography or capillary electrophoresis. Furthermore, ESI-MS does not require the incorporation of UV-absorbing chromophores into the analytical method for the detection of phosphates, unlike conventional UV-chromatographic methods. Limits of detection by ESI-MS were estimated to range from approximately 1 to 10 ng/mL. The quantification of polyphosphate samples as single-component and multicomponent mixtures was investigated. Linear signal response for single-component samples ranged from the limit of detection to approximately 10 microg/mL Quantification of polyphosphate in streamwater is demonstrated using the standard addition method. The effect of multi-polyphosphate components and salts on signal response was also studied. For concentrations less than 2.0 microg/mL, signal response from a tetrapolyphosphate sample was comparable to those obtained from tetrapolyphosphate-tripolyphosphate mixtures. Signal response obtained from tetrapolyphosphate in the presence of tripolyphosphate or NH4NO3 at higher concentrations (approximately 50 microg/mL and 35 microg/mL, respectively) was significantly lower relative to single-component standards (approximately 40%-70%).

The enhancement of the (M + H) + static secondary ion mass spectrometry (static SIMS) signal intensity resulting from pretreatment of silver sample substrates with aqueous halide acids was studied. Surface coverage experiments with silver halide surfaces prepared by aqueous halide acid treatment and electrodeposition indicated that the presence of silver halides alone could not account for the observed enhancement. Deuterium exchange studies showed that protons are adsorbed on the substrate during the acid treatment. It is likely that these protons are responsible for the improvement of static SIMS signal intensity by promoting the formation of (M + H) + species.

A series of Nb2O5/TiO2 catalysts were prepared by incipient wetness impregnation of TiO2 with aqueous solutions of niobium oxalate/oxalic acid. Eight different catalysts with Nb loadings of 0.48–8.5 wt.% Nb were prepared. Analysis of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra of Nb2O5/TiO2 catalysts shows the presence of monomeric, dimeric and trimeric NbxOy clusters at all loadings. This indicates that polymeric Nb oxide species are present even at loadings well below that corresponding to monolayer coverage (∼4.5 wt.% Nb). Moreover, it was found that the degree of aggregation of the niobia active phase increases with Nb loading. The tetrameric Nb oxide cluster was the largest fragment detected for amorphous Nb2O5. For Nb2O5/TiO2 catalysts the tetrameric Nb cluster was first detected in the 2.8 wt.% Nb catalyst. It is concluded that bulk-like Nb2O5 is present in catalysts containing ≥2.8 wt.% Nb (i.e. ≥60% theoretical coverage). Copyright © 2000 John Wiley & Sons, Ltd.

XPS and metathesis activity studies were performed on oxidic allyl‐based Mo/SiO2 catalysts (0.5 wt% Mo) and the oxidic catalyst following photoreduction to various extents. XPS results and average oxidation state measurements from the amount of CO2 formed during photoreduction, indicated that controlled photoreduction of the oxidic catalyst, in CO atmosphere, produces a mixture of Mo6+ and Mo4+ oxidation states with Mo4+ in abundances ranging from 0 to 100%. Propene metathesis activity studies were performed on the oxidic and photoreduced allyl‐based Mo/SiO2 catalysts. The results indicated that metathesis activity appears on photoreduction and increases linearly with increasing abundance of Mo4+ present on the catalyst. The linear relationship between the % propene conversion and the % Mo4+ present on the catalyst is consistent with the proposed uniformity of the Mo species and with the hypothesis that the active site (or active site precursor) is associated with Mo4+.

Electrospray time-of-flight mass spectrometry was used to study dilute (10(-3) M) solutions of tungstate, vanadate and perrhenate oxyanions under acidic and basic conditions. The electrospray mass spectra of tungstate and vanadate solutions indicate the presence of protonated monomeric oxyanions in basic solution (pH approximately 10) and protonated polymeric species in acidic solutions (pH approximately 4). Monomeric perrhenate was the only species detected in both acidic and basic perrhenate solutions. For all three systems, the core metalate species detected by electrospray were consistent with reported speciation in aqueous solutions. Copyright 2000 John Wiley & Sons, Ltd.

Two series of molybdena–alumina catalysts were prepared. The first series was prepared by the incipient wetness procedure (1.7–8.8 wt.% Mo) (series IW). A second series was obtained using the equilibrium adsorption (1.3–8.2 wt.% Mo) (series EA) method. X-ray photoelectron spectroscopy (XPS) was used to study the distribution of Mo oxidation states. The average Mo oxidation state estimated from XPS agreed with that obtained by measuring the O 2 consumption on reoxidation, for a given catalyst. The chemisorption of oxygen at −78°C and the isomerization of 1-butene were performed as probes for assaying the number of coordinatively unsaturated sites created by the reduction process. These studies were conducted in order to study possible changes in Mo speciation or distribution, relevant to catalytic reactions, which may occur as a result of the specific features of the preparation method (EA vs. IW). The results showed that for both series of solids, the reducibility of the molybdenum species increases as the metal loading increases, in agreement with the literature. For catalysts with similar loading, the IW series showed a higher degree of reduction with a concomitant increase in the relative abundance of Mo(IV) species attributed to paired double-bonded Mo(IV) entities (as in MoO 2 ). The reducibility data were consistent with the catalytic results and the oxygen chemisorption results. IW preparations (with similar Mo loading) were more active towards the isomerization of 1-butene and chemisorbed larger amounts of oxygen than their EA counterparts. The differences in reducibility can be ascribed to a nonuniform repartition of the molybdenum species between the external and internal surfaces of the alumina, for the IW preparations. Another possible explanation may stem from a decoration effect of the molybdenum species by Al(III) ions. The latter may arise from dissolution of the alumina, which is favored on the EA series due to the long contact time between the solution of the Mo promoter and the support.

Surface and chemical characterization were performed on a manganese-substituted silicoaluminophosphate molecular sieve (MnAPSO-11), and on a manganese-supported silicoaluminophosphate molecular sieve (Mn/SAPO-11). For comparison purposes, the characterization process was also carried out over the parent SAPO-11 molecular sieve. Different characterization techniques were used: XPS, redox cycles, 31 P MAS NMR, and acidity measurements. The transformations of n -butane were carried out over the corresponding platinum promoted solids (Pt/MnAPSO-11, Pt/Mn/SAPO-11 and Pt/SAPO-11). Platinum dispersion was measured by H 2 chemisorption. XPS results indicated that manganese was better dispersed on the MnAPSO-11 solid than on the supported Mn/SAPO-11 catalyst. Redox cycles showed a strong difference between the H 2 (or O 2 ) consumed by each solid. The Mn/SAPO-11 consumed nearly three times as much H 2 (or O 2 ) per Mn atom as the MnAPSO-11 solid. 31 P MAS NMR results showed an increase in the intensity of the side bands, probably due to an anisotropic paramagnetic shift caused by a stronger dipolar interaction between the 31 P and the paramagnetic Mn(II) ions on the MnAPSO-11 sample, when compared with the Mn/SAPO-11 solid. These results suggest a better dispersion of the manganese species on the MnAPSO-11 solid, which would facilitate the above mentioned 31 P –Mn(II) interaction, in agreement with the XPS results. Acidity was measured by pyridine chemisorption at different temperatures. A larger number of (moderate+strong) Bronsted acid sites was found for the MnAPSO-11 solid compared with the SAPO-11 and Mn/SAPO-11 samples. The addition of platinum decreased the acidity. The Pt dispersions were 83%, 68% and 54% for the Pt/SAPO-11, Pt/Mn/SAPO-11 and Pt/MnAPSO-11 solids, respectively. The catalytic results indicate higher yields for the production of isobutane and isobutene over the Pt/MnAPSO-11. A severe decrease in the yield of formation of hydrocarbons with less than four carbon atoms (undesirable side reaction) was also observed for the Pt/MnAPSO-11 system compared with the Pt/SAPO-11 and Pt/Mn/SAPO-11 systems. An ensemble effect is suggested as responsible for the differences observed in the yield of formation of hydrocarbons with less than four carbon atoms. The higher yield and selectivity observed for the formation of isobutane (iso-C4) and isobutene (iso-C4) hydrocarbons over the Pt/MnAPSO-11 solid, was accounted for in terms of the largest number of (moderate+strong) Bronsted acid sites found on this solid. The catalytic and characterization results suggest the incorporation of manganese into the molecular sieve structure for the substituted MnAPSO-11 solid.

The isomerization and metathesis of cyclopropane were carried out over a series of reduced molybdena–alumina catalysts (1.7–13 wt% Mo). The distribution of Mo oxidation states was determined by XPS. The average Mo oxidation state estimated from XPS agreed with that obtained by measuring the O 2 consumption on reoxidation for a given catalyst. A good correlation was found between the catalytic activity for the isomerization reaction and the relative intensity of the XPS peak attributed to paired double-bonded Mo (IV) species (as in MoO 2 ). The results indicate a direct relationship between these Mo (IV) species and the coordinative unsaturated sites involved in the formation of metallocyclobutane. The latter is reportedly the intermediate required for the isomerization reaction to take place.

The surface coverage of a series of WO3/TiO2 catalysts prepared by incipient wetness impregnation was monitored by CO2 chemisorption. The coverage of the TiO2 support increases from 31±2% for the 3.3 wt% WO3/TiO2 catalyst to ca. 86±2% for catalysts with W loadings ≥10.3 wt% WO3. The leveling off of the surface coverage for the high-loading catalysts has been attributed to the formation of W multilayers or bulk WO3. The surface coverage values obtained by CO2 chemisorption were consistent with those measured previously using ion scattering spectroscopy. The apparent suitability of CO2 chemisorption for monitoring the surface coverage of TiO2-supported catalyst systems, in contrast to previous results for Al2O3-supported systems, will be discussed.

International audience; Ring-opening reactions of decalin and methylcyclohexane (MCH) over bifunctional catalysts (1.2Ir/WO3/Al2O3) were investigated. A series of catalysts containing up to 5.3 at. W/nm(2) and 1.2 wt.% Ir was prepared. The acidity of the solids was monitored by low-temperature CO adsorption followed by infrared spectroscopy. Characterization of the Ir metal phase was performed by H-2 chemisorption and X-ray diffraction. The activity and product selectivity patterns obtained for the decalin ring-opening reaction were compared with those observed for MCH. For both naphthenes, ring contraction precedes ring opening, suggesting a similar ring-opening mechanism. Kinetic modeling based on the proposed reaction network allowed the determination of the activation energies and initial rates. Based on the yields and products distribution obtained for the decalin reaction, the potential for improvement of the cetane number is discussed. (c) 2012 Elsevier Inc. All rights reserved.

The objective of this work is to undertake a detailed study of the Mo/C system. This will include (a) study of the adsorption of Mo oxyanions from aqueous solutions of ammonium heptamolybdate onto activated carbon and (b) characterization of a series of Mo/C catalysts obtained by the equilibrium absorption method, using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy. The structural information thus obtained will be used to evaluate the Mo speciation proposed earlier. 35 refs., 6 figs., 2 tabs.

X-ray photoelectron spectroscopy (XPS or ESCA) measurements were performed on a photoreduced Mo allyl-based Mo/SiO{sub 2} catalyst (1.7 wt % Mo). Photoreduction was carried out in CO at room temperature for increasing lengths of time. Factor analysis, deconvolution, and curve fitting were used to determine the number and positions of components present in the series of XPS Mo 3d spectra obtained for the oxidic and photoreduced Mo/SiO{sub 2} catalyst. The results indicated the formation of a single oxidation state Mo{sup x+} (Mo 3d{sub 3/2} binding energy at 232.1 eV) after 2 h of photoreduction and the appearance of Mo{sup 4+} as in MoO{sub 2} (Mo 3d{sub 3/2} binding energy at 230.2 eV) with continued photoreduction. Average oxidation state studies indicated that the species designated as Mo{sup x+} should also be assigned to Mo{sup 4+} but in an environment different than that of MoO{sub 2}. 36 refs., 6 figs., 2 tabs.

Series of rhenium catalysts were prepared by equilibrium adsorption on unmodified alumina and alumina containing F and Mg additives. The uptake of perrhenate on alumina was dependent on the pH and the concentration of nitrate in the impregnation solution. Uptake of perrhenate at pH 6.5 on F modified alumina decreased with increasing F loading; for Mg-modified aluminas, perrhenate uptake at pH 9.3 increased with increasing Mg content. A correlation was observed between perrhenate uptake and the isoelectric point (IEP) of the modified supports. These data are interpreted on the basis of electrostatic attractions which occur between perrhenate ions in solution and alumina surfaces. Competition between nitrate and perrhenate for adsorption sites satisfactorily accounts for the effect of nitrate on perrhenate adsorption.

The oxidative decomposition of dimethyl methyiphosphonate (DMMP) has been studied over Cu-substituted hydroxyapatite catalysts in a flow reactor in the temperature range 373-773 K. By substitution of a portion of the Ca 2+ by Cu 2+ in the hydroxyapatite lattice, the catalytic activity was markedly increased. The composition Cu 2 Ca 8 (PO 4 ) 6 (OH) 2 , herein called Cu2-HA, had the highest activity among these catalysts. All the catalysts showed 100% conversion at the beginning of the reaction, but became deactivated after a period of time. Only CO 2 and H 2 O were produced during the "protection period" of the 100% conversion. With deactivation, CO 2 formation decreased and methanol and dimethyl ether appeared as products. A phosphorus-containing product was not detected in the gas phase. Some condensate of phosphoric acid appeared in the outlet of the reactor after deactivation. Several analytical methods revealed that carbonaceous compounds did not remain on the surface after 773-K oxidative regeneration, but the phosphorus compounds that had accumulated during the reaction were not eliminated. The catalytic activity of Cu-substituted hydroxyapatite was compared to that of conventional supported Pt catalysts. This study suggested that easily made and cheap Cu-substituted hydroxyapatite catalysts could be used as successful alternatives to conventional adsorbents and catalytic systems based on supported noble metals devised for protection against nerve gases in warfare.

In order to investigate the combined effect of a promoter and a detached support species on a supported metal catalyst, alkali promotion of Rh on the decorative support La[sub 2]O[sub 3] was investigated by X-ray photoelectron spectroscopy, X-ray diffraction, H[sub 2] and CO chemisorption, ethane hydrogenolysis, and cyclopropane hydrogenation. Previously, decorating lanthana moieties have been found to partially suppress ethane hydrogenolysis and cyclopropane hydrogenation on Rh/La[sub 2]O[sub 3]. The major effects of alkali promotion of Rh/La[sub 2]O[sub 3] on these reactions were a decline in apparent activation energy for ethane hydrogenolysis and a moderate additional suppression of cyclopropane hydrogenation activity. Alkali promotion of the more active Rh/SiO[sub 2] reference catalyst, which is not decorated by support entities, resulted in a much more significant suppression of these reactions. For Rh/La[sub 2]O[sub 3], alkali promotion appeared to block sites and/or pathways for hydrogen spillover. In addition, Rb inhibited the Rh-catalyzed decomposition of carbonate species on the lanthana support. No additional effect of alkali promotion was indicated on the [minus]1-eV shift of Rh 3d[sub 5/2] binding energy observed on Rh/La[sub 2]O[sub 3] relative to Rh/SiO[sub 2]. This is consistent with the lack of a Rh 3d[sub 5/2] binding energy shift observed for Rb-promotionmore » of Rh/SiO[sub 2]. The Rb 3p[sub 3/2] binding energy was shifted to the same extent as Rh in Rb/Rh/La[sub 2]O[sub 3], suggesting that the chemical environment for Rb differs between SiO[sub 2]-supported and La[sub 2]O[sub 3]-supported systems or, more likely, that the binding energy shifts observed for this system are just due to differences in the binding energies for the reference carbon on SiO[sub 2] vs on La[sub 2]O[sub 3]. 44 refs., 4 figs., 7 tabs.« less

Samples containing 8% Mo and l5% W supported on magnesium- and fluoride-modified aluminas were prepared by incipient wetness impregnation and examined in the dried and calcined states using X-ray photoelectron spectroscopy (XPS, ESCA). The presence of fluoride as an additive decreased the dispersion of the Mo and W phases for dried samples. The opposite effect was observed for dried Mg-modified samples. The effects of F and Mg addition largely disappeared when the samples were calcined. The results are interpreted in terms of the interactions between Mo and W species and the basic hydroxyl groups of the alumina.

A series of titania supported cobalt catalysts (0.5-6%) were prepared by incipient wetness impregnation, and were characterized by ESCA, XRD, and hydrogen chemisorption. After calcination at 400 C, a surface CoTiO[sub 3]-like phase was the main species present in the 0.5 and 1% cobalt catalysts. For higher cobalt loadings, discrete Co[sub 3]O[sub 4] particles were formed in addition to surface CoTiO[sub 3]. ESCA indicates that after reduction the cobalt metal particle size (6-13 nm) increases with increasing cobalt loadings, but does not vary with reduction temperature (400-500 C). Hydrogen chemisorption was found to be activated and suppressed. The extent of hydrogen chemisorption suppression increases with increasing reduction temperature and decreasing cobalt particle size. The turnover frequency (based on cobalt dispersion derived from ESCA) for benzene and CO hydrogenation decreases with increasing reduction temperature and decreasing cobalt particle size. The decline in activity correlates with the extent of suppression of H[sub 2] chemisorption. The results were interpreted in terms of a decrease in the fraction of exposed surface cobalt due to site blocking by reduced TiO[sub 3] moieties.

The objective of this work is to undertake a detailed study of the Mo/C system. This will include (a) study of the adsorption of Mo oxyanions from aqueous solutions of ammonium heptamolybdate onto activated carbon and (b) characterization of a series of Mo/C catalysts obtained by the equilibrium absorption method, using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy. The structural information thus obtained will be used to evaluate the Mo speciation proposed earlier. 35 refs., 6 figs., 2 tabs.

International audience; Tungstated zirconias consist typically of WOx species deposited on zirconia support. Additives like Si can be added to stabilize the catalyst surface area. The aim of this work is to identify the location of the Si (surface or bulk) as a function of W addition. Zirconia doped with 1.2 wt% Si remained purely tetragonal and exhibited a high specific surface area (150 m(2)/g) following calcination at 1023 K. Infrared quantification of the silanol band at 3745 cm(-1) indicated that Si is essentially present at the surface. The Si-29 NMR chemical shift of the zirconia is characteristic of isolated silicium. This result is corroborated with infrared by the absence of the structural band ascribed to Si-C-Si vibrations. NMR and infrared results indicated that W addition brings about a progressive evolution of the Si environment towards that of silica-like species. These results can be tentatively explained by a ligand enhanced dissolution of the support on W deposition. Si leached from the surface will then aggregate, forming small SiO2-like domains on the zirconia. (c) 2009 Elsevier B.V. All rights reserved.

35-2 FIELD Section Title:Chemistry of Synthetic High Polymers 45, 67 Laboratoire Catalyse et Spectrochimie, ENSICAEN, CNRS, Universite de Caen, Caen, Fr. FIELD URL: written in English; A series of WOx/TiO2 catalysts contg. between 0.6 and 3.4 W at./nm2 was prepd. by pore vol. impregnation using ammonium metatungstate soln. on crystd. TiO2. Characterization of the solids by X-ray diffraction and Raman and IR spectroscopy indicated that the W phase was present essentially as a surface W species. The results also suggested an increased degree of condensation of the W phase with increasing W surface d. The most condensed W species was characterized by a ?(W=O) vibration at 1017 cm-1. The IR or Raman bands attributed to sp. surface species of the solids were correlated with the abundance of relatively strong Bronsted acid sites and isopropanol dehydration activity. A direct correlation was obsd. between propene formation rate and the area of the band at 1017 cm-1, attributed to the most condensed W species. Furthermore, the abundance of this species appeared to be directly related to that of Bronsted acid sites capable of retaining lutidine following desorption at 573 K. The behavior of the WOx/TiO2 system was compared with that reported for the corresponding WOx/ZrO2 solids. Higher intrinsic activity (activity per W atom) was obsd. for WOx/TiO2 system. [on SciFinder(R)]

X-ray photoelectron spectroscopy (XPS, ESCA) valence band spectra were used to infer information about the molybdenum phase in standard Mo compounds such as sodium molybdate and ammonium heptamolybdate and in Mo/Al[sub 2]O[sub 3] catalysts prepared by equilibrium adsorption and incipient wetness impregnation methods. ESCA valence band measurements can distinguish between tetrahedrally coordinated Mo (sodium molybdate) and octahedrally coordinated Mo (ammonium molybdate). Mo ESCA valence band results show that Mo/Al[sub 2]O[sub 3] catalysts prepared by equilibrium adsorption at pH 2.2 and Mo/Al[sub 2]O[sub 3] catalysts prepared by incipient wetness impregnation contain primarily octahedral Mo. 31 refs., 7 figs.

ESCA, Mössbauer spectroscopy, XRD, and CO chemisorption were used to study the reduction and sulfidation reactions of a series of 1 to 24 wt % Fe/Al2O3 catalysts. The speciation and particle size of the active phase were correlated with CO hydrogenation activity data. Two phases were previously identified in all oxidic catalysts: Fe2O3 and Fe+3 in solid solution with the alumina support. The Fe2O3 phase was found to reduce to Fe0 and sulfide to Fe1- xS. For the reduced and sulfided catalysts, Mössbauer was able to identify two iron species which were detected as a single solid solution species in the oxidic catalysts. The two species were found to differ by their location in the alumina support. One species is incorporated within the alumina matrix [Fe+2(A)] and the other species [Fe+2(B)] is present at the alumina surface. Both ESCA and CO chemisorption indicate that the Fe particle size increases with increasing iron loading. The turnover frequency (TOF) for CO hydrogenation appears to be a function of the extent of reduction and particle size of the metallic iron phase.

The distribution of Mo oxidation states in reduced Mo/Al{sub 2}/Al{sub 2}O{sub 3} catalysts (8 wt % MO) has been determined by ESCA. The results show that Mo oxidation states ranging from +6 to 0 produced on reduction in the range 500-900{degrees}C. The Mo 3d binding energy values obtained for various Mo oxidation states were the same as those reported in an earlier study of Mo/TiO{sub 2} catalysts. The full widths at half-maxima for all Mo 3d peaks were larger than those for the corresponding Mo/TiO{sub 2} system. The average Mo oxidation state estimated from ESCA for a reduced catalyst agrees with that obtained by measuring the O{sub 2} consumption on reoxidation. The benzene hydrogenation activity was measured for all reduced catalysts. Significant conversion occurs only for reduction temperatures {ge} 600C. The onset of catalytic activity coincides with Mo{sup 2+} formation. However, the comparison of the distribution of Mo oxidation states determined by ESCA with the catalytic activity indicates that Mo metal is the most active species.

The surface coverage of a series of rhenia–alumina catalysts prepared by equilibrium adsorption was determined by low‐temperature CO adsorption. The results show a linear increase in the coverage of the Re oxide on the alumina support up to 24% with increasing Re loading from 0 to ca. 5.6 wt%. This is consistent with a uniform build‐up of the surface species. The coverage values measured by this method agreed very well with those obtained by ion scattering spectroscopy.

A series of Mo/Al 2 O 3 catalysts was prepared by using an equilibrium adsorption method. The dispersion of the molybdenum phase and coverage of the alumina surface by Mo species as a function of Mo loading were monitored by ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS, ESCA). By modeling changes in the ISS Mo/Al intensity ratio as a function of molybdenum coverage, It is shown that, for Mo/Al 2 O 3 catalysts prepared by equilibrium adsorption, coverage of the alumina surface should be complete at a loading of 47×10 13 Mo atoms/cm 2 for calcined catalysts

Two series of silica supported cobalt catalysts were prepared by incipient wetness impregnation, one by varying the calcination temperature (200-400{degree}C, 3 wt % Co) and the other by changing the cobalt loading (1-10 wt % Co). Examination by ESCA, XRD, and H{sub 2} chemisorption showed that Co{sub 3}O{sub 4} is the dominant phase. The cobalt phase is reduced to cobalt metal at 400{degree}C. The cobalt particle sizes obtained from ESCA correlated well with those derived from H{sub 2} chemisorption and XRD line broadening. The turnover frequency of Co/SiO{sub 2} for CO hydrogenation was invariant with cobalt dispersion in the range of 6-20% dispersion.

The adsorption of perrhenate, permanganate, molybdate, tungstate, and chromate on alumina was studied at pH 4.5. The effect of nitrate in the impregnation solution on the adsorption of these ions was examined as well as the effect of washing the freshly prepared catalysts. The uptake of perrhenate and permanganate decreased with increasing nitrate in the impregnation solution; the uptake of molybdate, tungstate, and chromate was unaffected. Washing the catalysts almost completely removed perrhenate, permanganate, and chromate, but allowed a significant amount of molybdate and tungstate to remain on the alumina. It is concluded that tungstate and molybdate adsorb on two types of surface sites, producing loosely and tightly bound surface species. From the amounts of molybdate and tungstate adsorbed, and from EXAFS results from washed and unwashed Mo/Al2O3 samples, both loosely and tightly bound molybdate and tungstate are polymeric in nature. The results are discussed in terms of electrostatic and surface reaction models.

The acidity of catalytic systems based on tungsten oxide or niobium oxide supported on titania was compared. Two series with metal contents up to 3.6 atom nm � 2 were prepared by incipient wetness impregnation of the titania support with ammonium metatungstate or niobium oxalate solutions. Characterization of both systems by X-ray diffraction and Raman spectroscopy studies did not show evidence of bulk metal oxide formation. The acidity was monitored by adsorption of 2,6-dimethylpyridine (2,6-lutidine) followed by infrared spectroscopy. The catalytic activity was tested for the reaction of isopropanol dehydration. At a reaction temperature of 403 K, WOx/TiO2 catalysts were inactive for a surface density of W � 1.2 W atom nm � 2 . Above this loading, the activity increased progressively with increasing W content. Similar evolution was observed for the abundance of relatively strong Bronsted acid sites (i.e. able to retain lutidine at 573 K). In contrast, NbOx/TiO2 catalysts were essentially inactive at this reaction temperature and a higher reaction temperature (473 K) was required to reach a comparable catalytic activity. No threshold of Nb loading for the development of catalytic activity was observed. Similar behavior was evidenced for the abundance of medium strength Bronsted acid sites (able to retain lutidine at 523 K). For both systems, a direct correlation between the catalytic activity and the abundance of Bronsted acid sites was observed. # 2005 Elsevier B.V. All rights reserved.

X-ray photoelectron spectroscopy (XPS or ESCA) was used to monitor changes in the amount of organic and pyritic sulfur, and inorganic sulfur present on coal surfaces following hydrochloric and nitric acid treatments. The results show that after treatment with HCl the oxidized sulfur was totally removed from the surface. Subsequent leaching with HNO 3 decreased the atomic abundance of sulfide forms on the coal surface.

The distribution of Mo oxidation states in reduced Mo/Al2O3 catalysts (8 wt% Mo) was determined by ESCA. The results showed that Mo oxidation states ranging from +6 to 0 are produced on reduction between 200°C and 900°C. The catalytic activity of the reduced Mo/Al2O3 catalysts for propene hydrogenation and propane hydrogenolysis was measured as a function of the reduction temperature. The variation of catalytic activity of the reduced catalysts was compared with the distribution of Mo oxidation states obtained from ESCA. The results indicated that Mo oxidation states ≤ +4 are required for propene hydrogenation. Propane hydrogenolysis required a more severe reduction pretreatment. The catalytic activity correlated with the change in the abundance of Mo metal. This suggested that Mo metal is the most active species for propane hydrogenolysis.

The adsorption of perrhenate, permanganate, molybdate, tungstate, and chromate on alumina was studied at pH 4.5. The effect of nitrate in the impregnation solution on the adsorption of these ions was examined as well as the effect of washing the freshly prepared catalysts. The uptake of perrhenate and permanganate decreased with increasing nitrate in the impregnation solution; the uptake of molybdate, tungstate, and chromate was unaffected. Washing the catalysts almost completely removed perrhenate, permanganate, and chromate, but allowed a significant amount of molybdate and tungstate to remain on the alumina. It is concluded that tungstate and molybdate adsorb on two types of surface sites, producing loosely and tightly bound surface species. From the amounts of molybdate and tungstate adsorbed, and from EXAFS results from washed and unwashed Mo/Al2O3 samples, both loosely and tightly bound molybdate and tungstate are polymeric in nature. The results are discussed in terms of electrostatic and surface reaction models.

The use of solid-state mass spectrometry for studying polymers is evaluated. Structural differences between polymers can be obtained by laser mass spectrometry by observing fingerprint-like spectra in the range m/z

High-surface-area supported nickel-silicon alloys were prepared by treating Ni/Al2O3 with silane (SiH4) at 300–400°C in flowing hydrogen. Microbalance studies indicated that the supported nickel-silicon alloys were easily decomposed, compared with alloys prepared by bulk melting. However, the decomposed alloys were difficult to reduce, indicating formation of an interaction species. ESCA and ISS studies indicate that silane treatment brings about considerable shielding of the nickel surface which coincides with a drastic decrease in CO hydrogenation activity.

The isoelectric point (IEP) of γ-alumina was modified by the addition of various amounts of fluoride. The modified aluminas were used as supports for molybdenum catalysts prepared by equilibrium adsorption at pH = 6.5. Also, the adsorption of molybdate on supports containing various amounts of fluoride was studied as a function of pH. The amount of molybdenum adsorbed on the fluoride-modified aluminas was found to decrease as the IEP of the carrier decreased. An electrostatic model is used to interpret the results.

Catalysts were prepared by subliming Mo(CO)6 onto partially dehydroxylated (PDA) and exhaustively dehydroxylated (DA) alumina made from the same parent preparation (American Cyanamid Aero 100PHF). The chemisorption of NO and CO on these materials was studied using volumetric, Chromatographic, and spectroscopic techniques. ESCA data indicated that metallic Mo crystals formed on Mo(CO)6DA whereas on PDA both Mo4+ and some lower valence state, Mo2+ or Mo0, were present. NO chemisorbed on both preparations at 195 K without releasing either N2O or N2. The chemisorption on the PDA preparations was over tenfold higher than that on the DA-supported catalysts under these conditions, but on raising the temperature to 300 K the difference was reduced to a factor of 2. Moreover, redox chemistry occurred at this higher temperature as evidenced by the release of N2O and N2; this was quantified. The amounts of NO actually chemisorbed under these conditions correlated well with the integrated IR band intensities. These data suggest that lower valence states are oxidized to Mo4+ at 300 K and that the observed IR bands stem from Mo4+(NO)2, irrespective of the initial catalyst. Infrared spectra from residual CO remaining on decomposition of Mo(CO)6 on DA and PDA at increasing temperatures up to 473 K showed bands which could be attributed to residual Mo(CO)6 and/or to subcarbonyl species formed during decomposition. By 573 K, no residual bands could be observed. On adding-back CO at 300 K to the PDA preparation, bands at 1989 and 2170 cmt−1 appeared, suggesting the presence of Mo4+ and residual Mo0. Spectra from similar experiments with the DA preparation demonstrated that chemisorbed Mo(CO)6 was reforming and possibly some subcarbonyl species; there was scant evidence for any higher valence states. The results are discussed in terms of the current literature.

A method is described for the use of X-ray photoelectron spectroscopy (ESCA) for quantitatively determining the distribution of species in supported metal catalysts. The method can determine the distribution of metal species for catalysts which contain both discrete metal oxide and metal surface phases with differing dispersions. The utility of the method is illustrated for a series of CoAl2O3 catalysts containing Co3O4 and both tetrahedrally and octahedrally coordinated Co2+ surface phases. The determination of the distribution of Co species for a series of CoAl2O3 catalysts by the present method is consistent with results from studies using other techniques.

A series of Mo/Al/sub 2/O/sub 3/ (molybdenum/alumina) catalysts was prepared by incipient wetness impregnation at various pH's (4.0, 5.4, 7.1, and 11.0) using a fixed amount of Mo (8% Mo). The effect of pH on the state and dispersion of Mo species in the dried, calcined, and reduced catalysts was investigated by the combined use of two surface sensitive techniques: X-ray photoelectron spectroscopy (XPS, ESCA) and ion scattering spectroscopy (ISS). The surface properties were correlated to thiophene hydrodesulfurization activities for the various catalysts. A tentative interpretation of the influence of pH of the Mo impregnating solution on the surface structure of Mo/Al/sub 2/O/sub 3/ catalysts at various stages of their preparation is proposed. 8 figures, 1 table.

Two series of La/alumina and CoLa/alumina catalysts have been characterized by several bulk and surface sensitive techniques. The chemical state and dispersion of the La and Co phases have been determined. The results were compared with the CO hydrogenation activity and selectivity of supported Co/alumina catalysts.