The present study is dedicated to the development of an original method for the measurement of the individual amounts Q(ASi) of the acid sites A(Si) (acidity of Lewis and Bronsted) present on three TiO2 based solids of increasing composition complexity: TiO2-P25, 6% WO3/TiO2-P25 and a sulfated 0.7 % V2O5/9% WO3/TiO2 NH3-SCR catalyst. The method is based on quantitative characterizations of the NH3 adsorption equilibrium (adsorption temperature T-a and pressure P-a) by the association of (a) the AEIR method providing the individual coverage theta(ASi)(T-a, P-a) of the adsorbed NH3 species on the AS(i) sites and (b) the total amount (in mu mol/g) of the adsorbed NH3 species: QTNH(3)(T-a, P-a) by using a mass spectrometer. For a solid having n types of AS(i) sites, the Q(ASi) values are obtained from the numerical solution of linear equation systems (with at least n equations) obtained considering that QTNH(3)(T-a, P-a) is equal to the sum of the contribution of each adsorbed NH3 species: Q(ASi) theta(ASi)(T-a, P-a).This imposes the measurement of at least n QTNH(3)(T-a, P-a) in a Ta range preventing the contribution of parallel surface processes (i.e NH3 oxidation). On TiO2-P25, n = 3 (two Lewis and one weak Bronsted acid sites) and the Q(ASi) amounts are obtained from three QTNH(3)(T-a, P-a) values. The others solids having two Lewis (L1 and L2) and two Bronsted (B1 and B2) acid sites impose a series of m measurements of QTNH(3)(T-a, P-a) with m>> n: the Q(ASi) are obtained by optimization between theoretical and experimental QTNH(3)(T-a, P-a) curves such as 109, 202, 70 and 130 mu mol/g for QL2, QL1, QB2 and QB1 respectively of 0.7 % V2O5/9% WO3/TiO2. It is shown that these four amounts of sites permit to conclude that the L2 Lewis acid site is the one forming the pivotal NH3ads-L2 species of the reaction by using nitrogen mass balances between the amounts of adsorbed NH3 species and the N-2 production in the presence of NO.

The adsorption of CO in the temperature range of 300–713 K on the PtSn particles of a reduced (H2, 713 K) 1.2%Pt-2.7%Sn/Al2O3 catalyst is studied by FTIR spectroscopy to reveal the geometric and electronic effects of Sn on the Pt sites. By comparison with a 1.2% Pt/Al2O3 it is shown that Sn (a) suppresses the Pt sites forming bridged CO species due to a geometric effect and (b) displaces the IR band of a linear CO species on Pt sites at 300 K from 2066 cm−1 to 2044 cm−1 due to an electronic effect. According to the AEIR method, the change in the IR band on the PtSn particles with the increase in Ta in isobaric condition (PCO = 1 kPa) provides the heats of adsorption of the linear CO species (named L1PtSn) at high (58 kJ/mol) and low (130 kJ/mol) coverages. By comparison with the values of the linear CO species on Pt particles (named LPt): 220 and 106 kJ/mol at low and high coverages, respectively, these values reveal the strong impact of the electronic effect of Sn on the heats of adsorption of CO. For Ta > 463 K there is a reconstruction of the PtSn particles due to the segregation of Sn as SnOx species associated with an enrichment of the surface in Pt. On the reconstructed PtSn particles, a new IR band is observed at 2057 cm−1 after adsorption of CO at 300 K ascribed to a new L2PtSn CO species. Its heats of adsorption are significantly higher than those of the L1PtSn species: 165 and 65 kJ/mol at low and high coverages. Moreover, successive reconstruction/H2 reduction at 713 K cycles leads to a sintering of the PtSn particles associated to the progressive increase in the heats of the L2PtSn CO species until a value at low coverage: 210 kJ/mol similar to that of the LPt species whereas at high coverage a significant difference exists between the two species (70 and 115 kJ/mol for L2PtSn and LPt, respectively). These data show that the impacts of Sn on the heat of adsorption of the linear CO species on the Pt sites are dependent on (a) the Pt/Sn surface ratio which changes with reconstruction and the particle size and (b) the coverage of the Pt sites. The comparison of the heats of adsorption of the L CO species on the fresh, reconstructed and aged PtSn particles with experimental and theoretical literature data reveals that they are consistent with some of them.

The combined dry-steam reforming (CDSR) of a model biogas (66 % CH4 + 34 % CO2) has been investigated under various feed compositions and reaction temperature conditions over a Ni-Rh/MgAl2O4 catalyst, with the objective to convert the excess of methane (compared to CO2) by steam reforming (SR). Methane, however, appeared to react preferentially with H2O rather than with CO2, leading to an inhibition of the dry reforming (DR) reaction in the presence of steam. CO2 and H2O adsorption and co-adsorption studies revealed that H2O was always adsorbed in much higher amounts than CO2 on the catalyst surface. A Temkin adsorption model applied to temperature-programmed adsorption experiments (TPAE) showed that two different strongly adsorbed CO2 and H2O species were present on the catalyst surface at moderate temperature, but only one of each remained adsorbed at temperatures relevant to the reaction conditions (600-800 degrees C). H2O was also shown to displace CO2 from the catalyst surface, confirming that they compete, at least partially, for the same adsorption sites. At high temperature, the surface coverage by the most strongly adsorbed H2O species was predominant. These results should contribute to the development of efficient catalytic processes for biogas valorization to produce syngas and hydrogen from renewable sources.

The presence of texture in Ti sheathed MgB2 cables, induced by the manufacturing process, have been evaluated using XRD pole figures. Drawn monofilamentary and rolled multifilamentary cables have been compared in order to determine the effect of different deformation degrees arising from the thermo-mechanical treatments. Finally, the critical current density of the cables (Jc) was evaluated using a SQUID magnetometer. We found that MgB2 {101-0} planes align with the AD direction after drawing, while after rolling, this alignment is not present. The Jc ratio between parallel and perpendicular field is larger for the monofilamentary than for multifilamentary wires, which may be correlated with the differences in the MgB2 texture between these samples.

The two first surface elementary steps of a gas/solid catalytic reaction are the adsorption/desorption at least one of the reactants leading to its adsorption equilibrium which can be or not disturbed by the others surface elementary steps leading to the products. The variety of the sites of a conventional catalyst may lead to the formation of different coadsorbed species such as linear, bridged and threefold coordinated species for the adsorption of CO on supported metal particles. The aim of the present article is to summarize works performed in the last twenty years for the development and applications of an analytical method named Adsorption Equilibrium InfraRed spectroscopy (AEIR) for the measurement of the individual heats of adsorption of coadsorbed species and for the validation of mathematical expressions for their adsorption coefficients and adsorption models. The method uses the evolution of the IR bands characteristic of each of coadsorbed species during the increase in the adsorption temperature in isobaric conditions. The presentation shows that the versatility of AEIR leads to net advantages as compared to others conventional methods particularly in the context of the microkinetic approach of catalytic reactions.

FTIR spectroscopy and volumetric measurements are used to study the adsorption of CO (mainly 1% CO/He) in the temperature range 300–713 K on a 1.2% Pt–2.7% Sn/Al2O3 solid reduced in H2 at 713 K leading from XRD to PtSn bimetallic particles. This reveals the changes in the adsorption properties of the Pt sites for CO adsorption by comparison with monometallic Pt/Al2O3 solids and the stability of the Pt–Sn bimetallic particles in the presence of CO. At 300 K, FTIR spectroscopy shows that the insertion of Sn leads to (a) the total disappearance of the Pt sites forming bridged CO species (ascribed to a geometric effect of Sn) and (b) a significant shift in the position of the IR band of linear CO species on Pt sites from 2066 to 2044 cm−1 on Pt and Pt–Sn particles, respectively, ascribed to different adsorbed species, namely LPt and L1Pt–Sn, respectively. Moreover, it is shown that the insertion of Sn is associated with the decrease in the amount (in µmol/g of platinum) of Pt adsorption sites for CO adsorption. The evolution of the IR band of the L1Pt–Sn CO species with the increase in Ta in isobaric conditions reveals a modification of the surface of the Pt–Sn particles for Ta > ≈  460 K ascribed to enrichment in Pt° due to a surface reconstruction. The Pt sites of the reconstructed surface are characterized by an IR band at 2057 cm−1 after adsorption of CO at 300 K ascribed to a linear CO species named L2Pt–Sn. The reconstructed surface is stable in the presence of CO in the range 300–713 K and disappears by hydrogen reduction at 713 K. Successive surface reconstruction/hydrogen reduction at 713 K cycles lead to an ageing of the Pt–Sn particles associated with a progressive decrease in the amount of Pt° sites on the freshly prepared and reconstructed Pt–Sn particles. It is shown that the reconstruction of the Pt–Sn particles is probably due to the formation of SnOx species via oxygen species coming mainly from the hydroxyls groups of the support.

The present study is a part of an experimental microkinetic approach (EMA) of the selective reduction of NOx to N-2 with NH3 in excess O-2 on V2O5/WO3/TiO2 catalysts (NH3-SCR process). In the temperature range of interest for NH3-SCR (T >=approximate to 473 K) and for three TiO2-based solids (sulfated and sulfate-free TiO2 supports and a sulfated 0.7% V2O5/9% WO3/TiO2 catalyst), FTIR spectroscopy and volumetric measurements with a mass spectrometer are used to study the impacts of the NH3H2O coadsorption on the coverages of (a) the molecularly adsorbed NH3 species and (b) the molecularly and dissociated H2O species on Lewis and Bronsted sites. Whatever the solid, it is shown that NH3 dominates the molecular coadsorption on the Lewis sites. However, this does not prevent the dissociative H2O chemisorption on a small amount of Lewis acidic sites, leading to an increase in the amount of OH groups. On the two sulfated solids, these OH groups increase the amount of adsorbed NH4+ species as compared to the NH3 adsorption equilibrium. For the sulfate-free TiO2 solid having weak Bronsted sites, the switch between the NH3 adsorption equilibrium to the NH3H2O coadsorption equilibrium is associated to the production of a small amount of NH3 due to the displacement of NH3ads-L species by H2O dissociation (competitive adsorption). It is shown that these experimental data are consistent with an original development of a competitive Temkin model (named Temkin-C), taking into account the individual heats of adsorption of NH3 and H2O species at different coverages in the absence of competition. The EMA and Temkin-C model developed in the present study can be applied to all solids having a significant IR transmission offering a method to study the surface acidity during realistic experimental conditions (in the presence of H2O), which is of interest for different catalytic processes such as NH3-SCR and alcohol dehydration.

The present study is a part of an experimental microkinetic approach of the selective reduction of NOx to N-2 with NH3 in excess of O-2 on V2O5/WO3/TiO2 catalysts (NH3-selective catalytic reduction (NH3-SCR) reaction). Water is always present either in the reactive gas mixtures representative of industrial processes or produced by the reaction. This suggests that H2O may modify the coverage of the pivotal adsorbed NH3 intermediate of the reaction by either a competitive adsorption or reactions (i.e., formation of NH4+). In the temperature range of interest for NH3-SCR (T >= approximate to 423 K), Fourier transform infrared spectroscopy and volumetric measurement using a mass spectrometer are used to study the impacts of the NH3-H2O coadsorption on the coverages of adsorbed NH3 (molecular adsorption) and H2O (molecular and dissociative adsorption) species on two sulfated solids: a 0.7% V2O5/9% WO3/TiO2 NH3-SCR catalyst and its TiO2 support. Regardless of the solid, it is shown that at the NH3-H2O coadsorption equilibrium, (a) NH3 dominates the adsorption on the Lewis sites (i.e., the introduction of NH3 at the H2O adsorption equilibrium displaces H2Oads-L species at the benefit of NH3ads-L species) and (b) the introduction of H2O at the NH3 adsorption equilibrium increases significantly the amount of adsorbed NH4+ species. This is ascribed to the H2O dissociation, which is operant on a small number of sites forming new Bronsted sites without a strong impact on the amount of Lewis sites. The surface composition of the solids has a limited impact on the coverages during the NH3-H2O coadsorption except on the fact that the NH4+ species is more stable on the NH3-SCR catalyst. In Part 6 of the present study (10.1021/acs.jpcc.8b05847), it is shown that the present experimental data are consistent with the mathematical formalism of a competitive Temkin model (named Temkin-C) developed without major approximations. The experimental procedure (present study) and the mathematical Temkin-C formalism (Part 6) can be applied for all solids having a significant IR transmission, thus offering a method to study the surface acidity during realistic experimental conditions (in the presence of H2O), which is of interest for different catalytic processes such as NH3-SCR and alcohol dehydration.

The present study is a part of an experimental microkinetic approach (EMA) of the selective reduction of NOₓ to N₂ with NH₃ in excess O₂ on V₂O₅/WO₃/TiO₂ catalysts (NH₃-SCR process). In the temperature range of interest for NH₃-SCR (T ≥≈ 473 K) and for three TiO₂-based solids (sulfated and sulfate-free TiO₂ supports and a sulfated 0.7% V₂O₅/9% WO₃/TiO₂ catalyst), FTIR spectroscopy and volumetric measurements with a mass spectrometer are used to study the impacts of the NH₃–H₂O coadsorption on the coverages of (a) the molecularly adsorbed NH₃ species and (b) the molecularly and dissociated H₂O species on Lewis and Bronsted sites. Whatever the solid, it is shown that NH₃ dominates the molecular coadsorption on the Lewis sites. However, this does not prevent the dissociative H₂O chemisorption on a small amount of Lewis acidic sites, leading to an increase in the amount of OH groups. On the two sulfated solids, these OH groups increase the amount of adsorbed NH₄⁺ species as compared to the NH₃ adsorption equilibrium. For the sulfate-free TiO₂ solid having weak Bronsted sites, the switch between the NH₃ adsorption equilibrium to the NH₃–H₂O coadsorption equilibrium is associated to the production of a small amount of NH₃ due to the displacement of NH₃ₐdₛ₋L species by H₂O dissociation (competitive adsorption). It is shown that these experimental data are consistent with an original development of a competitive Temkin model (named Temkin-C), taking into account the individual heats of adsorption of NH₃ and H₂O species at different coverages in the absence of competition. The EMA and Temkin-C model developed in the present study can be applied to all solids having a significant IR transmission offering a method to study the surface acidity during realistic experimental conditions (in the presence of H₂O), which is of interest for different catalytic processes such as NH₃-SCR and alcohol dehydration.

The present study is a part of an experimental microkinetic approach of the selective reduction of NOₓ to N₂ with NH₃ in excess of O₂ on V₂O₅/WO₃/TiO₂ catalysts (NH₃-selective catalytic reduction (NH₃-SCR) reaction). Water is always present either in the reactive gas mixtures representative of industrial processes or produced by the reaction. This suggests that H₂O may modify the coverage of the pivotal adsorbed NH₃ intermediate of the reaction by either a competitive adsorption or reactions (i.e., formation of NH₄⁺). In the temperature range of interest for NH₃-SCR (T ≥ ≈423 K), Fourier transform infrared spectroscopy and volumetric measurement using a mass spectrometer are used to study the impacts of the NH₃-H₂O coadsorption on the coverages of adsorbed NH₃ (molecular adsorption) and H₂O (molecular and dissociative adsorption) species on two sulfated solids: a 0.7% V₂O₅/9% WO₃/TiO₂ NH₃-SCR catalyst and its TiO₂ support. Regardless of the solid, it is shown that at the NH₃-H₂O coadsorption equilibrium, (a) NH₃ dominates the adsorption on the Lewis sites (i.e., the introduction of NH₃ at the H₂O adsorption equilibrium displaces H₂Oₐdₛ₋L species at the benefit of NH₃ₐdₛ₋L species) and (b) the introduction of H₂O at the NH₃ adsorption equilibrium increases significantly the amount of adsorbed NH₄⁺ species. This is ascribed to the H₂O dissociation, which is operant on a small number of sites forming new Bronsted sites without a strong impact on the amount of Lewis sites. The surface composition of the solids has a limited impact on the coverages during the NH₃-H₂O coadsorption except on the fact that the NH₄⁺ species is more stable on the NH₃-SCR catalyst. In Part 6 of the present study (10.1021/acs.jpcc.8b05847), it is shown that the present experimental data are consistent with the mathematical formalism of a competitive Temkin model (named Temkin-C) developed without major approximations. The experimental procedure (present study) and the mathematical Temkin-C formalism (Part 6) can be applied for all solids having a significant IR transmission, thus offering a method to study the surface acidity during realistic experimental conditions (in the presence of H₂O), which is of interest for different catalytic processes such as NH₃-SCR and alcohol dehydration.

The present experimental microkinetic approach is dedicated to the interpretation using the Temkin formalism of the experimental evolutions of (a) the coverage of adsorbed CO and hydrogen species and (b) the rate of the CH4 production during the increase in the temperature for x% CO/H-2 gas mixtures (x =1, 10(-2) and 10(-3), P-T = 1 atm) on a reduced 2.9% Pt/Al2O3 catalyst (Pt dispersion D approximate to 0.26). FTIR spectroscopy (a) shows that three adsorbed CO species: linear, bridged and threefold coordinated CO species (denoted L, B and 3FC respectively) are formed at 300 K and (b) provides the evolution of the coverage of the dominant L CO species (IR band at 2080 cm(-1) at 300 K) for the three CO/H-2 gas mixtures in the 300-740 K temperature range. These data support the development of a rigorous (without approximations) competitive adsorption model associated with a reaction based on the Temkin formalism (denoted Temkin-C.R model). This model provides (a) the theoretical coverages of the L CO and hydrogen species and (b) the theoretical rate of the CH4 production during the CO/H-2 reaction as a function of the partial pressures of the reactants and the reaction temperature which are compared to the experimental data. This shows that the L CO species which dominates the CO adsorption is not the active adsorbed species at the beginning of the CH4 production (T approximate to 475 K for 1% CO/H-2). It is shown that the active species is the 3FC CO species which represents 1/7 of the total amount of adsorbed CO species. These conclusions are consistent which literature data on Pt particles indicating that a small number of sites/adsorbed CO species are involved at the beginning of the CO/H-2 reaction. Moreover, as a contribution to the debate on the paradox of kinetics on heterogeneous surfaces, the Temkin-C.R model is compared to models based on the Langmuir formalism mainly used in kinetic studies. This reveals the clear advantage of the Temkin-C.R model for the representation of experimental data in large ranges of experimental conditions. (C) 2017 Elsevier Inc. All rights reserved.

The present study is dedicated to the development of a Temkin model for competitive chemisorption (denoted Temkin-C) which can be applied in large range of experimental conditions (partial pressures and temperatures). It is based on experimental data from the adsorption/reaction of x% CO/H-2 gas mixtures (x = 1, 10(-2) and 10(-3), total pressure 1 atm.) on a reduced 2.9% Pt/Al2O3 catalyst for two platinum dispersions (D approximate to 0.6 and 0.26) in the temperature range 300-740 K. FTIR spectroscopy (a) shows that three adsorbed CO species: linear, bridged and threefold coordinated CO species (denoted L, B and 3FC respectively) are formed at 300 K and (b) provides the evolution of the coverage of the dominant L CO species (IR band at 2080 cm(-1) at 300 K) for the three CO/H-2 gas mixtures in the 300-740 K temperature range. These data support the rigorous development of a Temkin-C model providing the theoretical coverage of the L CO and hydrogen species in the absence of the CH4 production. The comparison of the theoretical and experimental evolutions of the coverage of the L CO species shows that (a) the L CO species dominates the competitive chemisorption with the hydrogen species and (b) the heats of adsorption of the two species are not significantly modified by their co-adsorption. Moreover, in line with the debate dedicated to the paradox of kinetics on heterogeneous surface (briefly the catalytic activity of a heterogeneous surface can be well represented by assuming an homogeneous surface), the Temkin-C model is compared to models based on the Langmuir formalism currently used in the literature dedicated to kinetic studies. This reveals the clear advantage of the Temkin-C model for the representation of experimental data in large range of experimental conditions. In Part 2, the Temkin-C model is extended by considering that the L CO species is the adsorbed intermediate species of the CH4 formation from the CO/H-2 reaction at T > 500 K. (C) 2017 Elsevier Inc. All rights reserved.

The present article is dedicated to the adsorption of CO on reduced 2% Pd/Al2O3 and 2% Pd-x% Sn/Al2O3 (weight %, x = 2 or 5 wt %) in the 300–713 K temperature range to study the geometric and electronic effects of Sn on the palladium adsorption sites. Using Fourier transform infrared (FTIR) spectroscopy, it is shown that the insertion of Sn leads to (a) the total disappearance of the Pd sites forming bridged CO species (denoted as “B”), which are the dominant species on Pd0 particles and (b) a significant increase in the Pd sites forming linear CO species (denoted as “L”). This is ascribed to a geometric effect of Sn that dilutes the superficial palladium sites. The measurement of the individual heats of adsorption of the different adsorbed CO species by using two original temperature-programmed adsorption equilibrium methods (denoted AEIR and TPAE) allows the estimation of the electronic effect of Sn on the Pd sites. On 2% Pd/Al2O3, in parallel to the formation of two strongly adsorbed B CO species, two ...

The present article is dedicated to the measurement of the individual heats of adsorption of adsorbed NH3 species on WO3/TiO2 and V2O5/WO3/TiO2 (a catalyst for the selective catalytic reduction of NOx by NH3 on stationary sources, briefly NH3-SCR) model and commercial solids by using an original experimental procedure (adsorption equilibrium infrared spectroscopy, AEIR) developed in parts 1 [Giraud et al. J. Phys. Chem. C 2014, 118, 15664] and 2 [Giraud et al. J. Phys. Chem. C 2014, 118, 15677] for the adsorbed NH3 species on TiO, and V2O5/TiO2 solids. In agreement with the literature, Raman and Fourier transform infrared spectra indicate the presence of well-dispersed VxOy and WOz entities on the different solids. For NH3 adsorption at pressure P-a < 0.5 IrPa and temperature T-a in the range 300-673 K, the modifications of the V=O and W=O overtone IR bands indicate that these entities are involved in the adsorption of NH3, forming NH3ads-L, and NH4+ species on Lewis and Br-misted sites, respectively. For T-a = 300 K, it is shown that four adsorbed NH3 species are formed on the WOz- containing catalysts: two are adsorbed on Lewis sites, named NH3ads-L1 and NH3ads-L2, and two are adsorbed on Bronsted sites, named NH4+-1 and NH4+-2 ("1" and "2" indicate the increasing order of stability of the different species). Using the delta(as) IR band characteristic of the NH3ads-L (similar to 1600 cm(-1)) and NH4+ (similar to 1445 cm(-1)) species, it is shown that the AEIR method provides the individual heats of adsorption of the four adsorbed species at low and high coverages of their adsorption sites. For instance, on a model 0.5% V2O5/6% WO3/TiO2 catalyst the heats of adsorption of the two more stable species (which slightly change with the exact composition of the solid) at low and high coverages of the sites are 105 and 148 kJ/mol for NH3ads-L2 and 78 and 135 kJ/mol for the NH4+-2 species, respectively. These values indicate that the presence of WOz increases significantly the heat of adsorption of the NH4+ species, as compared to TiO2 and V2O5/TiO2, explaining that both NH3(ads-L2) and NH4+-2 species can be present in the experimental conditions of NH3-SCR.

The present study is a part of an experimental microkinetic approach of the removal of NOx from coal-fired power plants by reduction with NH3 on V2O5/WO3/TiO2 catalysts (NH3-selective catalytic reduction, NH3-SCR). It is dedicated to the characterization of the heats of adsorption of molecularly adsorbed H2Oads species formed on sulfate-free and sulfated TiO2 supports. Water, which is always present during the NH3-SCR, may be in competition and/or react (formation of NH4+) with the adsorbed NH3 species controlling the coverage of the adsorbed intermediate species of the reaction. Mainly, an original experimental procedure named adsorption equilibrium infrared spectroscopy (AEIR) previously used for the adsorption of NH3 species on the same solids is adapted for the adsorption of H2O. At T-a = 300 K and for P-H2O <= 1 kPa, three main H2Oads species are formed (associated with a minor amount of dissociated H2O species) on the two TiO2 solids. The species are identified by the positions of their IR bands in the 3750-3000 cm(-1) range. Considering the decreasing order of stability, they are (a) coordinated to strong (L-2) and weak (L-1) Lewis sites and denoted H2Oads-L2 and H2Oads-L1, respectively, and (b) hydrogen bonded to the H2Oads-L species and on O2-/OH sites of the solids (denoted H2Owads). The three species have a common well-defined delta H2O IR band at a position in the range 1640-1610 cm(-1) according to the total coverage of the surface. According to the AEIR method, the evolution of the intensity of this IR band during the increase in the adsorption temperature Ta in isobaric condition provides the evolution of the average coverage of the three species and then to their individual heats of adsorption as a function of their coverage. It is shown that there are no significant differences on the two TiO2 solids. In particular, the heat of adsorption of the H2Oads-L2 species varies from similar to 114 to 61 kJ/mol at low and high coverages respectively, indicating that it can be present in the experimental conditions of the NH3-SCR. In a forthcoming article, the competitive chemisorptions and reaction between adsorbed H2O and NH3 species are studied and modeled on the TiO2 supports and model and commercial V2O5/WO3/TiO2 catalysts.

Diffuse reflectance FT-IR spectroscopy (DRIFTS) is commonly used to investigate catalytic reactions. CO is a reagent of many reactions of interest for environmental catalysis and fuel and chemical synthesis, as well as being a surface probe to investigate the structure and oxidation state of metal-based particles by in situ and operando FT-IR spectroscopy. It is crucial to avoid IR signal distortion that may affect the IR spectrum in the region corresponding to adsorbed CO, which spans from ca. 2250 cm(-1) down to 1600 cm(-1). Such bands can appear in the DRIFTS spectra of silica-based solids when the temperature and/or the hydration level of the sample are modified. These bands are merely due to variations in the vibrations modes of the silica solids and are not related to adsorbed CO, Accurate correction of gas-phase CO signal during DRIFTS analyses can be obtained by collecting a subtrahend spectrum under identical reaction conditions over an inert material such as SiC. Spurious bands may otherwise arise if a subtrahend is collected at a different temperature. (C) 2015 Elsevier B.V. All rights reserved.

Fourier transform infrared spectroscopy (FTIR) in transmission and in diffuse reflectance (DRIFT) modes is used to characterize the adsorbed species formed during the adsorption of CO on EUROPT-1 (a 6.3% Pt/SiO2 catalyst) as a function of different experimental parameters such as the duration t(a) of the adsorption at 300K, the adsorption temperature T-a (300-673 K range) and pressure P-a (1-4 kPa range), the reduction temperature T-R in hydrogen (423, 523, 673 K) and the presence of H2O Whatever the experimental conditions the adsorption of CO on EUROPT-1 is dominated by linear CO species (denoted L CO) characterized by IR bands in the 2090-2040 cm(-1) range with a small contribution of bridged CO species (denoted B CO) with IR bands in the 1880-1830 cm(-1) range. It is shown that the intensity, shape and positions of the IR bands of the L CO are strongly dependent on the experimental conditions. Increasing the duration of adsorption 4, at 300K leads to an increase of the IR band intensity due to an activated reconstruction process. The presence of H2O leads to a shift of the L CO species IR band towards lower wavenumbers. Transmission and DRIFT modes provide similar qualitative data. However, the measurement of the heats of adsorption of the L CO species through the adsorption equilibrium infrared spectroscopy (AEIR) method, which is based on the quantification of the IR bands of adsorbed species, reveals the limitations of the DRIFT technique at high temperatures. Using transmission mode, it is shown that the heats of adsorption of the L CO species linearly vary which its coverage theta(L) from 90 kJ/mol to 250 kJ/mol at theta(L) = 1 and 0 respectively whatever (a) the reduction temperature and (b) the absence or the presence of H2O. These values are consistent with previous measurements on others Pt-o particles supported on different metal oxides. However the value at theta(L), = 0 is higher by about 30 kJ/mol, possibly due to the high Pt dispersion (D approximate to 0.9) of the reduced-reconstructed EUROPT-1. This study emphasizes that the use of CO to characterize supported Pt-o particles is not straightforward considering the different experimental parameters that may affect the Pt structure and IR band features of the adsorbed species. (C) 2015 Elsevier B.V. All rights reserved.

The present study is dedicated to the development of experimental procedures allowing the measurement of the individual heats of adsorption of adsorbed NH3 species on a sulfate-free TiO2 solid (P25 from Degussa). This solid has been selected because it is frequently used as support of V2O5- or/and WO3-TiO2 model catalysts for the understanding of the surface processes implicated in the selective catalytic reduction of NOx by NH3 (NH3-SCR). Two original analytical procedures denoted adsorption equilibrium infrared spectroscopy (AEIR) and temperature-programmed adsorption equilibrium (TPAE) (developed in previous works) were applied. These methods are based on (a) the experimental measurement of the change in the adsorption equilibrium coverage of the individual adsorbed species in isobar conditions and (b) the comparison of the experimental data to an adsorption model. It is shown that in the ranges of the ammonia partial pressures and reaction temperatures of the NH3-SCR process, only two adsorbed NH3 species on Lewis sites (Ti+delta) are detected on the solid dehydrated at 673 K. These species noted NH3ads.L1 and NH3ads.L2 are differentiated by their delta(s) NH3 IR bands at 300 K (1149 and 1228 cm(-1), respectively), whereas their delta(as) IR bands are at the same position (1596 cm(-1)). The AEIR and TPAE methods indicate that the heats of adsorption of the NH3ads.L1 and NH3ads-L2 species (noted E-L1(theta) and EL2(theta) accuracy +/- 5 kJ/mol) vary linearly with their respective coverages theta from E-L1(1) = 56 kJ/mol to E-L1(0) = 105 kJ/mol and from E-L2(1) = 105 kJ/mol to E-L2(0) = 160 kJ/mol. These values are compared to (a) isosteric heat of adsorption provided by the Clausius-Clapeyron method and (b) literature data using temperature-programmed desorption, microcalorimetry, and DFT calculations. Forthcoming artides show that the simplicity of the analytical procedures allows studying the impact of the presence of sulfate and VOx/WOy depositions over TiO2, on the nature and heats of adsorption of adsorbed NH3 species.