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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; Chemisorption of probe molecules such as hydrogen and carbon monoxide on the surface of Pt particles is the most common chemical technique used to estimate the crucial parameters of metal catalysts, namely the dispersion (D), the particle size (d), and the metallic specific surface area (SPt). However, it remains a controversy concerning the stoichiometry of adsorbate per surface metal atom, leading to an inaccurate estimation of D, d, and SPt. A model describing the statistics of the surface atoms and sites on perfect cuboctahedron clusters was developed to assess values of D, d, and SPt, assuming the most favorable adsorption sites based on density functional theory (DFT) calculation of the literature. This model successfully predicted the experimental values of D, d, and SPt determined from H or CO chemisorption data, and it allowed providing a set of simple equations for the accurate determination of these parameters from chemisorption experiments on Pt.

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 relationship between acidity, surface structure and catalytic activity for a series of WOx/Al2O3 catalysts was investigated. The catalysts, containing up to 4.1 atom W/nm2, were prepared by incipient wetness impregnation and studied by N2 physisorption, XRD, in situ Raman and infrared spectroscopy. The W phase was essentially present as surface species. Polymeric W surface species appeared above 1.4 atom W/nm2; their abundance increased with W surface density. Lutidine and CO adsorption measurements, followed by infrared spectroscopy, evidenced the presence of relatively strong Bronsted acid sites. The development of these acid sites was similar to that of the abundance of polymeric W surface species. Similar evolution with W surface density was also observed for the activity for 2-propanol dehydration, an acid-catalyzed reaction, indicating a direct relationship between the abundance of polymeric W surface species, that of relatively strong Bronsted acid sites and the catalytic activity of WOx/Al2O3 catalysts.

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.

International audience; The preparation of binary materials based on Ta2O5-ZrO2 by a sol-gel method and with a wide range of compositions is reported (Ta2O5 nominal content from 4 to 74% w/w). Materials were characterized by X-ray diffraction, and infrared and Raman spectroscopy. Their acidic characteristics were evaluated from the model reaction of 2-propanol dehydration and the adsorption of CO at 77 K and 2,6-dimethylpyridine at 373 K, both followed by infrared spectroscopy. Increasing tantalum content brings about a development of a surface TaOx phase followed by a progressive formation of aggregates of amorphous Ta2O5. Increased stabilization of tetragonal zirconia was also observed with increasing Ta loading. The surface area, number and strength of Bro¨nsted acid sites, and the catalytic activity in the 2-propanol dehydration increase with the increase in tantalum content up to ca. 50% w/w Ta2O5. A surface area of 103 m2 g-1 was obtained for a solid with a Ta2O5 content of 53% w/w after calcination at 873 K. The abundance of Bro¨nsted acid sites, determined by lutidine adsorption, and their strength, determined by CO adsorption at 77 K, correlated with the catalytic activity in the 2-propanol dehydration.

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 development of the acidity and the relationship between acidity, catalytic activity, and the surface structure for niobium oxide supported on zirconia were investigated for a series of solids. The catalysts were active for 2-propanol dehydration only above a threshold in Nb loading. The acidity was studied by infrared spectroscopy of adsorbed 2,6-dimethylpyridine as a probe molecule, and the onset of activity was correlated with that of the formation of relatively strong Brønsted acid sites. The variation in the abundance of these sites also correlated with the catalytic activity. Raman, IR, and UV spectroscopy results indicated that the active sites were related to polymeric Nb surface species. These results were compared to those previously reported for the WOx/ZrO2 catalysts

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

Electrospray ionization (ESI) time-of-flight mass spectrometry has been used to investigate the pH-dependence of phosphomolybdates in solution from pH = 1.7 to 10.2. Mass spectra are reported for the first time for H2Na2P2Mo5O232–, PMo9O313–, PMo10O343–, and PMo11O373–. The pH dependence of phosphomolybdate species as measured by electrospray is compared with measurements reported for combined potentiometry—31P NMR. The pH ranges of most species are similar (±1 pH unit) when measured by these two methods, although some differences are observed. Protonation and solvation of phosphomolybdate species measured by ESI differ from those observed by 31P NMR. However, the core phosphomolybdate species are measured correctly by ESI.

Electrospray-ionization (ESI) time-of-flight mass spectrometry has been used to investigate the pH-dependent behavior of phosphotungstates in solution from pH = 2.7 to 8.0. Mass spectra are reported for the first time for H3PW11O394–, H4PW11O393–, and H5PW11O392–. The pH dependence of phosphotungstate species as measured by electrospray is compared with that measured by 31P NMR. The pH ranges of species are similar (±1 pH unit) when measured by these two methods. Protonation and solvation of phosphotungstate species measured by ESI differ from those observed by 31P NMR. However, the core phosphotungstate species are measured correctly by ESI.

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.

A series of WO 3 /ZrO 2 catalysts with tungsten (W) loadings varying from 0.5 to 11A wt.% WO 3 was prepared by incipient wetness impregnation. The surface coverage of these catalysts was monitored by ion scattering spectroscopy (ISS) and low-temperature CO adsorption. Comparable values for the surface coverage were obtained from ISS and CO adsorption. The surface coverage as determined by these two independent techniques increased from zero to 51 ± 3% as the W loading increased from zero to 4.5 wt% WO 3 , and leveled off at ∼54 ± 3% with further increases in W loadings. For catalysts with W loadings

A series of Mo/TiO 2 catalysts was prepared by equilibrium adsorption from aqueous solutions of (NH 4 ) 6 Mo 7 O 24 by varying the pH of the solution from 9.8 to 4. The Mo loading increases from 0.8 to 3.6 wt.% as the pH of preparation decreases. The surface coverage of the calcined catalysts was monitored by CO 2 chemisorption and ion scattering spectroscopy (ISS) measurements. Carbon dioxide uptake was determined in a standard BET system from the adsorption isotherms by extrapolating to zero pressure. Coverage measurements from ISS were obtained by monitoring the changes of the ISS Ti signal with Mo addition. Additional information about the dispersion of the Mo phase of these catalysts was obtained from x-ray photoelectron spectroscopy (XPS) measurements The XPS results evidenced the presence of a highly dispersed Mo phase. Carbon dioxide chemisorption results for Mo/TiO 2 catalysts indicated that the Mo coverage increases linearly from 0.16 to 0.93 with increasing Mo loading from 0.6 to 3.6 wt.%. These results were consistent with those determined by ISS measurements and are in good agreement with the predicted values for monolayer dispersion. These findings are in contrast with those obtained for alumina-supported catalysts, where the CO 2 chemisorption method has been show to overestimate the surface coverage. The origin of the apparent suitability of the CO 2 chemisorption method for monitoring the surface coverage of TiO 2 -based systems is discussed.

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 selection of an appropriate internal standard (IS) for quantification by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is critical for the successful application of quantitative MALDI. Selection of the IS depends on the chemical similarity of the analyte and IS and the mass separation of the analyte and IS as a function of instrumental peak resolution. For the quantification of bovine insulin, a series of internal standards including horse heart cytochrome C, bovine insulin chain B, des-pentapeptide human insulin, and des-octapeptide porcine insulin was investigated. Des-pentapeptide human insulin was found to be the most appropriate internal standard (relative standard deviation of the standard curve slope = 2.99%, correlation coefficient = 0.988 in the range of 0.5-0.4 μmol/L). Two methods for measuring of the MALDI signal intensity were evaluated, direct peak integration following subtraction of a linear background and non-linear least squares curve fitting. The results obtained with these methods were equivalent.

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.

Absolute surface coverages (θ) of a series of tungsten-alumina catalysts prepared by the equilibrium adsorption method were determined by ion scattering spectroscopy (ISS) and low-temperature CO adsorption. The θCO values for the W catalysts were very similar to those obtained with the ISS method, for a given W loading. A linear increase in W coverage with increasing W loading, reaching ~55% coverage for the 13.1% W solid, was observed. The calculated W cross-sections (22.0- 24.5A2/W) were in agreement with other reports in the literature. Due to the inherent limitations of each method, the combined use of ISS and low-temperature CO adsorption is recommended for estimating absolute surface coverages in tungsten-alumina catalysts.

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.

A chromium-substituted silicoaluminophosphate molecular sieve (CrAPSO-11) and a Cr-supported SAPO-11 molecular sieve (Cr/SAPO-11) were studied by XPS and reduction-oxidation (redox) cycles. The distribution of oxidation states as well as the average oxidation state for chromium were determined for both preparations. The XPS results showed that two chromium 2p doublets (Cr(VI) and Cr(III)) were necessary to curve fit the experimental data. Comparison of curve-fitting results for the two oxidic samples (O 2 , 773 K) revealed a significantly higher percentage of Cr(III) species in the Cr/SAPO-11 catalyst. The difference between the two samples remained following reduction (H 2 , 773 K). For the CrAPSO-11 sample, Cr(VI) showed a higher stability towards reduction, compared to chromium supported on conventional supports. This result suggests the incorporation of Cr(VI) into the silicoaluminophosphate framework, as mentioned in the literature. For the Cr/SAPO-11 solid, Cr(III) was extremely stable towards oxidation at 773 K. Due to the redox characteristics and the XPS results, the formation of chromia species on this catalyst is suggested.

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

The surface coverage of a series of rhenium-alumina catalysts prepared by equilibrium adsorption was determined by ion scattering spectroscopy (ISS) and infrared spectroscopy (IR). The coverage results were compared with those determined from previously published CO 2 chemisorption data. The ISS results show an almost linear increase in Re coverage with increasing Re loading, reaching ∼30% coverage for a loading of ∼6.5 wt.% Re. The near-linearity of the coverage with increasing Re content indicates a uniform build-up of the surface species. The Re cross-sections calculated from the corresponding surface coverages (24.8-30.5 A 2 /Re) were comparable with those previously reported for the Re/Al 2 O 3 system. The surface coverage determined from IR was shown to depend on the extent of dehydroxylation of the samples. Following pretreatment at 500°C, the coverage values for high loading catalysts were comparable with those obtained from ISS. However, the IR method yielded increasingly higher coverage values with decreasing Re loading. The Re cross-section values estimated from the corresponding surface coverages indicate an increased overestimation of the coverage with decreasing loading. As expected, the CO 2 chemisorption method consistently leads to an overestimation of the Re surface coverage.

The redox chemistry and the changes that occurred within the solids were studied for an excessively exchanged and a nearly stoichiometric CoZSM-5 zeolite as a function of pretreatment, reduction, and reoxidation conditions. Both gravimetric and volumetric techniques were used to determine this chemistry and the stoichiometry of the processes, which became reversible after the first couple of oxidation/reduction cycles. The catalyst was examined in its several states by diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscoy (XPS), and both the Faraday and Gouy magnetic susceptibility methods. With the excessively exchanged sample, it was found that Co3O4 formed after pretreatment with O2 and that Co metal was produced on reduction with either CO or H2 at 773 K in amounts corresponding to only a portion of the Co2+ originally present. The stoichiometric sample showed evidence for the presence of Co3+, but crystalline Co3O4 was not detectable. However, two different ...

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.

The surface coverage of a series of Mo/Al2O3 catalysts prepared by the equilibrium adsorption method was measured by CO2 chemisorption, low-temperature CO adsorption and ion scattering spectroscopy (ISS). Comparable values were obtained from ISS and CO adsorption. The results correspond to Mo cross-sections of 22.2 A2 Mo−1 (CO) and 20 A2 Mo−1 (ISS). The Mo coverages obtained by CO adsorption and ISS were compared with those estimated from CO2 chemisorption. The resuls indicated that, irrespective of the approach used to measure the coverage from CO2 chemisorption (volumetric method or from the decrease of the IR peaks attributed to bicarbonate and ‘free’ carbonate species), the CO2-based method signficantly overestimates the coverage.

X-ray photoelectron spectroscopy (XPS, ESCA) was used to determine the tungsten oxidation states in a 5 wt.% WO 3 /TiO 2 catalyst reduced in hydrogen in the temperature range 400-700 o C. Because, in the region of interest, W 4f overlaps with the Ti 3p energy level, a multiple analysis procedure including deconvolution, non-linear least-squares curve fitting and factor analysis was used to analyze the data. Deconvolution was better able to resolve the peaks in the W 4f region and thus elucidate the positions of the tungsten components for each reduction temperature. It was shown that there is a maximum of three W 4f doublets. The W 4f 7/2 peaks of these components were located at 35.5, 33.3 and 31.1 eV and they were assigned to W +6 , W +4 and W o , respectively. Factor analysis verified the presence of three spectral tungsten components X-ray diffraction verified the presence of W o on reduction at 675 o C. Non-linear least-squares curve fitting, using the positions from deconvolution, was able to determine the distribution of tungsten oxidation states as a function of reduction temperature: W +6 steadily decreased with increasing reduction temperature, W +4 initially appears at 408 o C and goes through a maximum around 580 o C; W o was first detected following reduction at 550 o C and was the only species present for reduction temperatures higher than 665 o C. From the distribution, it is proposed that, unlike the molybdenum systems, tungsten undergoes a more simplifed reduction process in which only one intermediate oxidation state (presumably W +4 ) is detected

A series of W/TiO 2 catalysts was prepared by incipient wetness impregnation with W loadings varying from 1.64 to 28.4 wt.% WO 3 . The coverage of the TiO 2 surface by W species was monitored by ion scattering spectroscopy (ISS). The results indicated that the W coverage increased from 21.6% for the 1.64 wt.% WO 3 /TiO 2 catalyst to ∼85% for catalysts with W loadings ≥10.3 wt.% WO 3 . These values agreed with those predicted from monolayer-like dispersion. The relatively constant coverage for W loadings >10.3 wt.% WO 3 was taken as an indication of multilayer or WO 3 formation. These results were consistent with Raman and x-ray photoelectron spectroscopy (XPS) data previously obtained in our laboratory

Two series of Mo/Al2O3 catalysts were prepared by equilibrium adsorption and incipient wetness impregnation methods. The effect of preparation method on the surface coverages of the calcined catalysts was investigated by the combined use of CO2 chemisorption, low temperature CO adsorption and ion scattering spectroscopy (ISS). For a given Mo loading, the CO2 and CO adsorption results showed little difference between the two preparation methods. As previously noted, the CO2 chemisorption method overestimated the Mo surface coverage. In contrast to the adsorption methods, the ISS technique gave different Mo surface coverage values for a given Mo content of the two series of catalysts. This apparent discrepancy was attributed to different repartition of the Mo phase between the internal and external surfaces which can only be detected by ISS. This interpretation is supported by the observed agreement between the coverage values measured from ISS and low temperature CO adsorption for presumably uniform catalysts obtained by the equilibrium adsorption method.

The interaction of Mo with zirconia has been investigated by infrared spectroscopy (IR) and carbon dioxide chemisorption. Quantitative analysis of the IR results indicated that Mo interacts preferentially with the most basic hydroxyl group (high frequency band at 3775 cm−1). An approximately 79% decrease in the 3775 cm−1 band is observed vs. 21% for the low frequency band at 3673 cm−1, with increasing the Mo loading up to 1 wt%. The relative decrease of the IR band at 3775 cm−1 was identical to that measured for the CO2 uptake. The Mo cross-sections estimated from CO2 chemisorption results were much higher than those typically reported for the Mo system. It was concluded that, as previously reported for the Mo/Al2o3 system, CO2 chemisorption overestimates the surface coverage of Mo/ZrO2 catalysts.

International audience; The development of Brønsted acidity and the relationship between acidity, catalytic performance and structure of niobium oxide were investigated for a series of samples prepared by calcination of niobic acid at temperatures between 423 and 823 K. All solids were active for propan-2-ol dehydration. The Brønsted acidity was monitored by adsorption of lutidine and CO followed by FT-IR. Low temperature CO adsorption measurements showed that all solids exhibit essentially the same medium Brønsted acid strength. A direct relationship between the abundance of Brønsted acid sites monitored by lutidine adsorption followed by desorption at 523 K and propan-2-ol dehydration activity was observed.

The author`s research on oxidation state/catalytic activity correlation involves a three-prong attack on the problem. First, the authors acquire XPS spectra as a function of the reduction temperature over the range of interest. Second, the authors determine the number and amounts of oxidation states using data analysis protocols, to be discussed herein. Third, the authors correlate catalyst activity with the appearance and amounts of specific oxidation states.

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.

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al2O3 catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm−1) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO2 chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO2 chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO2 chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO2.

Methodology for the quantitation of the distribution of oxidation states in reduced catalysts is reviewed. The adopted approach is based on the curve fitting the x-ray photoelectron spectroscopy (ESCA, XPS) envelope using a non-linear least squares curve fitting (NLLSCF) routine. The procedure was applied to the study of the reduction of Mo/TiO 2 and Mo/Al 2 O 3 catalysts. The distribution of Mo oxidation states obtained by ESCA was corrobrated by chemical measurements and correlated with catalytic activity. The limitations of the NLLSCF approach are discussed. It is shown that the uncertainties inherent in curve fitting methods can be minimized by the used of factor analysis. This data analysis technique provides an independent estimate of the number, positions, and shapes of components required to describe the Mo 3d envelopes in the reduced catalysts.

Principal component analysis (PCA) and target testing (TT) were performed on a series of reduced 2.5 wt.% Cr/Al2O3 catalysts to determine the number, positions, shapes and relative spectral compositions (i.e. Cr oxidation states) in Cr 2p spectra as monitored by ESCA. The results from PCA indicated the presence of only two abstract components. The abstract factors were transformed through iterative TT into real spectroscopic components that were attributed to Cr6+ and Cr3+. These factor analysis results were used in addition to non-linear least-squares curve fitting to provide a detailed description of changes in the Cr 2p envelope during reduction of the Cr/Al2O3 catalysts. Only two components were necessary to reproduce the original data.

Ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS, ESCA) were used to study the dispersion of the vanadium phase and the coverage of Al2O3 by vanadium. A series of V/Al2O3 catalysts was prepared by equilibrium adsorption with vanadium loadings varying from 1.9 to 6.7 wt.% V. By monitoring the ISS Al/O intensity ratio the surface coverage of the catalysts was determined. The surface coverage increases from 15 to 33% with increasing the loading from 1.9 to 3.5 wt.% V. The results are consistent with a model of a uniform monolayer vanadium phase. For higher vanadium loadings the surface coverage appears to level off, suggesting the formation of a multilayer vanadium phase.