Experimental Microkinetic Approach of De-NOx by ... - ACS Publications

Subscriber access provided by UNIV OF LOUISIANA

C: Surfaces, Interfaces, Porous Materials, and Catalysis x

3

Experimental Microkinetic Approach of De-NO by NH on VO/WO/TiO Catalysts. 5. Impacts of the NH-HO Coadsorption on the Coverage of Sulfated TiO Based Solids 2

5

3

2

3

2

2

Francois Giraud, Julien Couble, Christophe Geantet, Nolven Guilhaume, Stéphane Loridant, Sébastien Gros, Lynda Porcheron, Mohamed Kanniche, and Daniel Bianchi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b05846 • Publication Date (Web): 10 Oct 2018 Downloaded from http://pubs.acs.org on October 10, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

1

Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 5. Impacts of the NH3-H2O Coadsorption on the Coverage of Sulfated TiO2 Based Solids

AUTHOR NAMES François Giraud,1,2 Julien Couble1, Christophe Geantet,1 Nolven Guilhaume,1 Stephane Loridant,1 Sébastien Gros,2 Lynda Porcheron,2 Mohamed Kanniche,2 and Daniel Bianchi1*

AUTHOR ADDRESS 1

University of Lyon, Institut de Recherche sur la Catalyse et l’Environnement de Lyon

(IRCELYON), UMR 5256 CNRS, Université Claude Bernard Lyon I, Bat. Chevreul, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne-France.

2

EDF- Fluid Dynamics, Power Generation and Environment Department, 6 Quai Watier,

78401, Chatou-France.

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2 ABSTRACT: 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 (NH3SCR 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 either by a competitive adsorption or/and reactions (i.e., formation of NH4+). In the temperature range of interest for NH3-SCR (T≥≈ 423 K), FTIR 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. Whatever 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 Brønsted 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 NH3SCR catalyst. In Part 6 of the present study it is shown that the present experimental data are consistent with the mathematical formalism of a competitive Temkin model (named TemkinC) 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.


Page 2 of 47

Page 3 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3 Text 1. INTRODUCTION The present study is a continuation of an experimental microkinetic approach (abbreviation EMA) of the catalytic reduction of NOx (NO and NO2) into N2 and H2O by NH31 (named NH3-selective catalytic reduction: NH3-SCR) considering the experimental conditions of flue gas denitrification in coal-fired power plants (T≥ 473 K). Stationary sources use mainly x% V2O5/y% WO3/sulfated-TiO2 (weight %) catalysts with x and y in the ranges 0.7-2 and 9-13 respectively.2,3 The aims of applying EMA to NH3-SCR reaction are (a) the identification of the surface elementary steps controlling the rate of the reaction, in particular the nature and the coverage of the pivotal adsorbed NH3 species allowing the reduction of NOx and (b) the measurements of the kinetic/thermodynamic parameters of interest. Previous works have been dedicated to the characterization of the adsorbed NH3 species on different solids involved in the catalyst preparation, from sulfate free and sulfated TiO2 supports to model and commercial NH3-SCR catalysts.4-6 The originality of these works was the measurements (using the AEIR method)7-10 of the individual heats of adsorption of the different adsorbed species formed by the non dissociative adsorption of NH3 in the 300-713 K range (a) two molecularly adsorbed NH3 species on different type of acidic Lewis sites whatever the solid composition (named NH3ads-L1 and NH3ads-L2 in the increasing order of stability)4-6 and (b) two adsorbed NH4+ species on different types of Brønsted sites for WO3 or/and V2O5 containing solids (named NH4+-1 and NH4+-2 in the increasing order of stability).6 These studies have shown that the individual coverages of the different adsorbed species are consistent with the Temkin model, which considers an increase in the heat of adsorption with the decrease in the coverage. These data constitute new contributions to the debate on the pivotal adsorbed species of the NH3-SCR reaction on V2O5/WO3/TiO2 catalysts, which is considered to be either NH3ads-L or NH4+ species as summarized in different review



4 articles.11, 12 For instance Centi and Perathoner12 focused on the fact that two equations of the reaction rate based on the Langmuir formalism of two Eley-Rideal kinetic mechanisms (see eqs 21.3 and 21.4 in ref 12) can fit the same type of experimental data. The two mechanisms are different by the nature of the pivotal adsorbed species considered to be (a) either NH3 adsorbed on the Lewis sites (NH3ads-L species) in competition with H2O in line with Forzatti et al.13, 14 or (b) NH3 adsorbed on the Brønsted sites (NH4+ species) without competition with H2O in line with Topsøe et al.15, 16 Considering our recent works,4-6 these rate equations do not take into account the facts that (a) they are two types of NH3ads-L and NH4+ species and (b) the coverages of these adsorbed NH3 species are consistent with the Temkin adsoption model. The high partial pressures of H2O due to the coal combustion suggests that the coverages of the NH3ads-L and NH4+ species can be modified in the presence of H2O (and therefore the amount of intermediate species of the NH3-SCR) due to processes such as (a) a competitive chemisorption between NH3 and H2O on the same sites in line with Forzatti et al.13, 14 and (b) reactions leading to total/partial transformation of NH3ads-L into NH4+ species supporting the mechanism of Topsøe et al.15, 16 This shows that the NH3-H2O coadsorption constitutes a key point of the debate on the pivotal adsorbed species of the NH3-SCR reaction and its EMA must be performed before that of the N2 production from NH3-SCR on x% V2O5/y% WO3/TiO2 catalysts. As a first step of the NH3-H2O coadsorption study, a previous work has been dedicated to the measurement of the heats of adsorption of molecularly adsorbed H2O species on the Lewis sites of sulfate free and sulfated TiO2 solids using the adsorption equilibrium infrared spectroscopy method (abbreviation AEIR).17 Whatever the solids and in agreement with literature data,17 in parallel to the dissociative H2O adsorption forming hydroxyl groups (detected even in the presence of H2O traces at high temperatures), three molecularly adsorbed species are present at 300 K for adsorption pressure PH2O in the range 0.2-2 kPa: two


Page 4 of 47

Page 5 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5 strongly adsorbed species on the two types of Lewis sites (named H2Oads-L1 and H2Oads-L2 in the increasing order of stability) and a weakly adsorbed species (named H2Owads) hydrogen bonded to the H2Oads-L species and/or O2-/OH groups of the surface. It has been shown that the individual heats of adsorption of the three adsorbed species increase with the decrease in their coverages according to the Temkin formalism.17 The present EMA of the NH3-H2O coadsorption is an extension of these previous works.4-6,17 In a first step the heats of adsorption of the adsorbed H2O species formed on a sulfated 0.7% V2O5/9% WO3/TiO2 model NH3-SCR catalyst are measured via the AEIR method. Then for this catalyst and its TiO2 support, the impacts of the NH3-H2O coadsorption on the coverages of the adsorbed species (NH3ads-L, NH4+, H2Oads and OHads) are studied for experimental conditions relevant to the NH3-SCR reaction (i.e., Ta≥≈ 423 K). The EMA of surface processes includes a modeling of the experimental data based on plausible kinetic mechanisms. In Part 6,18 the experimental coverages of the different adsorbed NH3 and H2O species are compared to theoretical coverages from a Temkin model for competitive adsorption (named Temkin-C). The mathematical formalism of this model has been developed in recent works dedicated to the CO and H2 coadsorption (non dissociative and dissociative adsorption respectively) on the Pt sites of a Pt/Al2O3 catalyst for experimental conditions allowing or not the CO/H2 hydrogenation.19,20 As compared to early works,21,22 the Temkin-C model has been developed without major mathematical approximations. This leads to an accurate representation of experimental data in broad ranges of experimental conditions.19, 20 The present EMA of the NH3-H2O coadsorption on TiO2 based solids has a second intrinsic interest: the comparison of the surface acidity of a solid in the absence and in the presence of H2O via the change in the amounts of adsorbed NH3 species on the Lewis and Brønsted sites. In particular, it is shown in Part 6,18 that the Temkin-C model provides a quantitative approach of the water-tolerant Lewis sites on metal oxides as qualitatively



6 discussed in literature.23-25 In this context, it is well known that NH3 can be dissolved in liquid H2O at room temperature forming NH4+ species. The contribution of a similar process via the presence at 300 K of physically like adsorbed H2O species,17 is prevented by the adsorption temperature used in the experiments: Ta ≥ 423 K.

2. EXPERIMENTAL SECTION 2.1 Solids and Pretreatment Procedures The NH3-H2O coadsorption has been studied on two sulfated solids (compositions in weight %) (a) a TiO2 support: TiO2-DT51 (≈ 80 m2/g, 100% anatase, 0.56% of S) from Millenium Inorganic Chemical and (b) a model 0.7% V2O5/9% WO3/TiO2 catalyst obtained by deposition of V2O5 on a 9% WO3/TiO2 sulfated solid from Millennium Inorganic Chemical (DT52, pure anatase, 85 m2/g, 1.35% S) using an incipient wetness method with an aqueous solution of ammonium metavanadate dissolved in the presence of oxalic acid (see more details in refs 5 and 6). This catalyst (80 m2/g, 1.34% S) mimics commercial catalysts for NH3 adsorption.6 Similarly to literature data, the composition was indicated as V2O5 and WO3 even if the species formed on the supports are well-dispersed VxOy (with small x values) and WOz groups with limited interactions with the sulfates groups as shown by Raman and IR spectroscopy.5,6 Before NH3 and/or H2O adsorption, the solids were treated in the different analytical systems as follows: O2 (713 K, 10 min)→ He (713 K, 5 min)→ He (adsorption temperature Ta). The same sample of solid was used to perform a series of experiments and it was pretreated as above before each experiment. 2.2 IR Cell in Transmission Mode The FTIR characterizations have been performed using a Nicolet-6700 FTIR spectrometer equipped with a home made small path length (≈ 2.2 mm) and internal volume (≈ 2 cm3) stainless steel IR cell reactor in transmission mode using CaF2 windows and


Page 6 of 47

Page 7 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


7 described in more detail previously.26 Briefly, it allowed in-situ treatments, at atmospheric pressure, of a compressed disk of solid (Φ= 1.8 cm, m≈ 40-80 mg), in the temperature range of 293-800 K with controlled gas flow rates (range of 150-2000 cm3/min) selected using different valves and purified by different traps in particular cool traps for H2O impurities (i.e., 77 K for helium).4-6 The thermal inertia of the IR cell led to a slow cooling rate: ≈ 1 h from 713 K to ∼300 K. This was associated with the dissociative (at high temperatures) and molecular adsorption (at T< 473 K) of tiny traces of H2O having an impact on the IR bands of isolated OH groups (range 3800-3600 cm-1) before adsorption.17 Similarly to previous studies,4-6,17 for the quantification of the IR bands of the adsorbed species (i.e., AEIR method), the IR spectrum of the solid at the same temperature before adsorption was subtracted. Otherwise, the spectra result from the overlap of the IR bands of the solid and the adsorbed species. This allows showing the impact of the NH3 and/or H2O adsorption on the IR bands of the solid such as those of (a) the isolated OH groups and (b) the SO4 groups for the sulfated solids.4-6 In particular, the ν(S=O) IR band of the SO4 groups at ≈ 1375 cm-1 after pretreatment27-30 is a very sensitive indicator (position and intensity) of the coverage of the surface via long range interactions between sulfate groups and adsorbed species.5,6,17 2.3 Development of the AEIR Method to Study the NH3-H2O Coadsorption This method7-10 allows measuring the individual heats of adsorption of coadsorbed species formed by a gas X (i.e., NH3 on TiO2 based solids)4-6 by studying the evolution of the intensity of the IR bands characteristic of each adsorbed species Xads (i.e., NH3ads-L and NH4+ species) during the increase in Ta under isobaric conditions Pa (see Supporting Information). This provides the isobaric evolutions of the experimental coverage of each adsorbed species Xads with Ta (θXads= f(Ta), see eqs ES1 and ES2). The curves θXads= f(Ta) are compared to a theoretical adsorption model (often the Temkin model: eq ES3) considering localized adsorbed species for the adsorption coefficient (eq ES4) to obtain the individual heats of



8 adsorption of each adsorbed species. Moreover, for the adsorption of NH3 and H2O on different TiO2 based solids,4-6,17 it has been shown that an IR band common to two (NH3) or three (H2O) adsorbed species can be used for the determination of their individual heat of adsorption (eqs ES5 and ES6) considering their respective contributions xi to the common IR band at the lowest adsorption temperature. The AEIR method has been developed to study the NH3-H2O coadsorption by following the evolutions of the IR bands of the adsorbed species during the increase in the Ta using x% NH3/y% H2O/He gas mixtures (x and y in the range 0.1-0.5 and 0.2-1 respectively, the amount of H2O was fixed by an evaporator/condenser system). Moreover, to provide more experimental data on the surface processes of NH3-H2O coadsorption, the evolutions of the IR bands obtained after adsorption equilibrium using either x% NH3/He or y% H2O/He have been studied during the switch x% NH3/He (or y% H2O/He)  x% NH3/y% H2O/He under isothermal conditions (Ta≥ 473 K). In Part 6,18 these different experimental data are compared to theoretical curves from a competitive adsorption model based on the Temkin formalism (named Temkin-C) developed in recent works.19,20 2.4 Volumetric Measurements on the NH3-H2O Coadsorption Using Mass Spectrometry To support the exploitation of the IR spectra, transient experiments using a mass spectrometer (MS) have been performed to reveal how the amounts of adsorbed species at the adsorption equilibrium with either NH3 or H2O are modified by the NH3-H2O coadsorption. The setup4-6,31 provided the molar fractions of the gases at the outlet of a quartz microreactor containing the solid (weight in the range of ≈0.2-0.5 g) during switches of controlled gas flow rates at the atmospheric total pressure. In isothermal condition at Ta, these data allowed us determining, for each gaseous reactant, the rates of either formation (i.e., desorption) or consumption (i.e., adsorption) with time on stream: R(t), (eqs ES7 and ES8 respectively) and thus the total amount of each reactant either consumed or produced during the experiment at


Page 8 of 47

Page 9 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9 Ta. For instance, the MS experiments provided the total amounts of NH3 or/and H2O either adsorbed (Qads) or desorbed (Qdes) (a) at the adsorption equilibrium in the absence of coadsorption using the switch He x% NH3/z1%Ar/ He (or y% H2O/ z2%Ar/ He) and (b) then at the coadsorption equilibrium after the switch x% NH3/z1%Ar/ He (or y% H2O/ z2%Ar/ He)  x% NH3/y% H2O/z3% Ar/ He. Argon in the different gas mixtures was used as a tracer (i.e. time 0 for the adsorption and coadsorption processes).

3. RESULTS AND DISCUSSION 3.1 Individual Heats of Adsorption of NH3 and H2O Adsorbed Species on the Solids. The EMA of the NH3-H2O coadsorption requires knowing the nature and heats of adsorption of the adsorbed NH3 and H2O species in the absence of competition. This was the aims of previous works for different sulfate free and sulfated TiO2 based solids (without and with VxOy and/or WOz groups).4-6,17 The natures of the adsorbed species formed by NH3 and H2O have been determined by assignment of the IR bands observed at the adsorption equilibrium in the Ta range 300-713 K using accepted literature data (see references cited in refs 4-6, 17). For each adsorbed species, a selection of characteristic IR bands has been discussed4-6,17 for quantitative application such as the measurement of their individual heats of adsorption according to the AEIR method.4-6,17 This selection is also used in the present study and briefly summarized for the two sulfated solids (see more detail in Supporting Information). For the NH3 species adsorbed on the Lewis sites (named NH3ads-L), their asymmetric deformation IR band δas at ∼ 1605 cm-1,32-35 leads to the conclusions (eqs ES3ES5) that the two solids have two groups of Lewis sites L1 and L2 in the increasing order of strength, forming NH3ads-L1 and NH3ads-L2 species having significantly different (a) heats of adsorption at low: E(0), and high: E(1) coverages according to the Temkin model and proportions xi on the surface at saturation of the Lewis sites as shown in Table 1.5-6



Page 10 of 47

10 Solid

TiO2- DT51* 0.7% V2O5/9% WO3/TiO2*

NH3ads-L1 E1(1) E1(0) (kJ/mol)

(kJ/mol)

(kJ/mol)

(kJ/mol)

56 59

102 97

110 100

150 142

NH4+-1 E1(1) E1(0) 0.7% V2O5/9% WO3/TiO2*

NH3ads-L2 E2(1) E2(0)

NH4+-2 E2(1) E2(0)

(kJ/mol)

(kJ/mol)

(kJ/mol)

(kJ/mol)

57

90

75

135

Proportion x1 x2 0.65 0.65

0.35 0.35

Proportion x1 x2 0.65

0.35

Table 1: Heats of adsorption at different coverages Ex(θ) of the adsorbed NH3 species and their contributions to the intensity of their common characteristic IR bands at 300 K. (* ref 6) On 0.7% V2O5/9% WO3/TiO2 strong Brønsted sites are also present on the surface leading to the formation of NH4+ species. As discussed by different authors,36-38 the IR spectrum of adsorbed NH4+ species depends on interactions with others surface sites/groups of the surface (see Supporting Information for more details). The IR band selected for application of the AEIR method6 was their asymmetric deformation IR band δas at ∼ 1450 cm1 34,35

.

Equations ES3-ES5, leads to the conclusions that two groups of Brønsted sites form

NH4+-1 and NH4+-2 species having different (a) heats of adsorption at low: E(0), and high: E(1) coverages according to the Temkin model and (b) proportions xi on the surface as shown in Table 1.5-6 On TiO2-DT51, the Brønsted sites lead to NH4+ species of low stability (heats of adsorption not measured).5 The individual heats of adsorption of molecularly adsorbed H2O species on TiO2DT51 and a sulfate free TiO2 support have been measured17 using their δH2O IR band of at ∼ 1630 cm-1 at 300 K. The AEIR method indicates (using eqs ES3, ES4 and ES6) that three species are present with different heats of adsorption consistent with the Temkin model and proportion xi (Table 2):17 (a) a weakly adsorbed species (named H2Owads) corresponding to H2O molecules H-bonded to strongly adsorbed H2O species and/or O2-/OH sites of the surface and (b) two chemisorbed H2O species named H2Oads-L1 and H2Oads-L2 on the two groups of Lewis sites of the solids.17 Similar measurements for the adsorbed H2O species on 0.7%


Page 11 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


11 V2O5/9% WO3/TiO2 are presented below to study the impacts of the surface composition on the nature and stability of the different adsorbed H2O species. It is shown that there are strong similarities between the two sulfated solids. Solids

TiO2-DT51* 0.7% V2O5/9% WO3/TiO2**

H2Owads E1(1) E1(0) kJ/mol kJ/mol 45 50 45 52

H2Oads-L1 E1(1) E1(0) kJ/mol kJ/mol 54 60 56 61

H2Oads-L2 E2(1) E2(0) kJ/mol kJ/mol 61 114 58 117

Proportion xwads x1 x2 0.35 0.4

0.30 0.26

Table 2: Heats of adsorption at different coverages Ex(θ) of the molecularly adsorbed H2O species and their contribution to the intensity of the δH2O IR bands at 300 K according to the composition of the solids.* from ref 17 and ** present study.

3.2 Heats of Adsorption of the Adsorbed H2O Species on 0.7% V2O5/9% WO3/TiO2. Similarly to sulfate free and sulfated TiO2 supports,17 FTIR spectra recorded during the cooling stage in helium after the pretreatment procedure (see Figure S1) indicate that traces of H2O are adsorbed leading to the increase in the IR bands of the isolated OH groups formed by dissociative chemisorption (main IR band at 3642 cm-1 with two small shoulders at 3682 and 3575 cm-1 respectively) while molecular adsorption at Ta≤ ≈500 K leads to the appearance and then the increase in small IR bands at ≈ 1610, 3387 and 3262 cm-1 (Figure S1) ascribed to molecular adsorption of H2O on the strongest Lewis sites (deformation: δH2O, stretching vibration and overtone 2 δH2O respectively, see ref. 17 and references therein). However, these spectra are not representative of a homogenous surface composition of the sample because the H2O adsorption is limited by the inlet molar flow rate of the H2O traces in the IR cell (the adsorption proceeds according to a breakthrough curve).17 This is also the situation during the switch He → 0.25% H2O/He at 300 K (see Figure S2) until the adsorption equilibrium is reached after ta ≥ 3 min leading to spectrum a in Figure 1 which is very similar to that observed in the same experimental conditions on TiO2-DT51.17 This indicates that the


0.35 0.34


12 surface composition of the solids (presence or not of VxOy/WOz groups) has no significant impact on the type of adsorbed H2O species at 300 K. The IR bands of spectrum a in Figure 1 are ascribed as follows (ref 17 and references therein): (a) the IR band at 1630 cm-1 is the δH2O IR band of molecularly adsorbed H2O species (named H2Oads), (b) the broad IR band in the range 3650-3000 cm-1 is due to hydrogen bonds (named H-bonds) between H2Oads species and/or with O2-/OH groups of the surface and (c) the IR band at 3686 cm-1 (observed at 3690 cm-1 on TiO2-DT51) is ascribed to dangling hydrogen (abbreviation d-H) which correspond to OH bonds of H2Oads species not involved in H-bond. a

1374 A

j 3647

a 3380

Absorbance

Absorbance

0.2

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 47

3265

3686

j

0.2

1369

3647

1348

3686

a f 3800

3600

3400 -1 3200

Wavenumber (cm )

3700

3600

1287

f

3500

Wavenumber (cm-1)

a

1630 0.2 1617

a j

1800

1600 Wavenumbers (cm-1)

1431 1400

Figure 1: Evolution of the IR bands on 0.7% V2O5/9% WO3/TiO2 during the increase in Ta for 0.25% H2O/He: (a)-(i) Ta= 300, 330, 353, 398, 448, 523, 573, 623 and 673 K. Spectrum (j) is recorded in helium at 673 K after spectrum (i). Inset A: Evolution of the IR band of the free OH groups during the increase in Ta for 0.25% H2O/He: (a)-(f) 300, 323, 343, 373, 423 and 483 K.

The IR band of the sulfate groups situated at 1381 cm-1 before H2O adsorption (Figure S1) is broadened and shifted below 1300 cm-1 due to long range interactions with the H2Oads species. This shift leads to the detection of a small and broad IR band at 1431 cm-1 present as


Page 13 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


13 a shoulder of the ν(S=O) IR band before H2O adsorption as observed by Lietti et al,39 on model and commercial V2O5/WO3/TiO2 catalysts. Figure 1 gives the evolution of the IR spectra with the increase in Ta in isobaric condition using 0.25% H2O/He. Similarly to TiO2-DT51, the δH2O IR band of the H2Oads species decreases and shifts progressively from 1630 cm−1 at 300 K to 1617 cm−1 for Ta≥ 448 K: it is still detected, although weak, at 673 K (Figure 1, spectrum i). Similarly to TiO2-DT51, the increase in Ta leads to the appearance and then the increase in the ν(S=O) vibration of the SO4 groups associated to a shift to higher wavenumbers: i.e 1348 and 1369 cm-1 at Ta= 398 and 673 K respectively (Figure 1, spectra d and i). These modifications are due to the decrease in long range interactions with the decrease in the coverage of the H2Oads species. Note that at 673 K, the difference of position of the ν(S=O) IR band at the H2O equilibrium: 1369 cm−1 (Figure 1, spectrum i) and after desorption in helium 1374 cm−1 (Figure 1, spectrum j) indicates that the small amounts of adsorbed H2Oads and OH groups disturb the totality of the sulfate groups (as observed for NH3ads‑L2 species)6 consistent with long range interactions. In the 3800−3000 cm−1 range (inset A, Figure 1) the increase in Ta leads to (a) the decrease and disappearance at 373 K in the d-H IR band at 3686 cm−1 (indicating that it is due to H2Owads species)17 allowing the detection of the IR band of the isolated OH groups at 3647 cm-1 and (b) the strong decrease in the broad IR band below 3600 cm−1 due to H-bond of the weakly adsorbed H2Owads species. At Ta> 473 K only strongly adsorbed H2O species on the Lewis sites (H2Oads‑L species) are present and similarly to TiO2-DT51, they are associated with the two well-defined IR bands at 3385 and 3264 cm−1 (stretching vibration, see references in ref 17) overlapping the remaining broad H-bond IR band. Note that, at 673 K, the higher intensity (factor ≈ 2.2) in the IR band of the isolated OH groups at 3647 cm-1 in the presence of H2O (spectrum i) than in helium (spectrum j) is due to the adsorption equilibrium of dissociated adsorbed H2O species.



14 Similarly, to TiO2-DT51,17 the δH2O IR band has been selected for the measurement of the heats of adsorption via the AEIR method (see more detail on this choice in ref 17) using its evolutions with Ta for PH2O= 250 Pa (Figure 1). Note that in Part 618 it is shown the IR band of the isolated OH groups (≥ 3600 cm-1) can be used for the estimation of the heats of adsorption of dissociated H2O species. A Absorbance

1

0.8 a 0.6

1634

d

a 0.2

1800

1700

1600

Wavenumber (cm-1)

B 0.4

0.02

1/A

Coverage of the H2Oahs species

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 47

0.015

0.2 0

0 200

300

400 500 Temperature (K)

2

1/Pa (kPa-1)

600

4

700

6

800

Figure 2: Individual heats of adsorption of the molecularly adsorbed H2O species on 0.7% V2O5/9% WO3/TiO2 by using the AEIR method.  and  evolutions of the experimental coverages (eq. ES1) during the first cooling stage and the second heating stage in 0.2% H2O/He respectively considering the δH2O IR band; (a) theoretical coverage from eqs ES3, ES4 and ES6 considering three adsorbed H2O species: H2Owads, H2Oads-L1 and H2Oads-L2 with the heats of adsorption and contributions to the IR band at 300 K indicated in Table 2. Inset A: Evolution of the δH2O IR band with the increase in PH2O: (a)-(d) PH2O= 200, 400, 610 and 810 Pa. Inset B: Determination of the area of the δH2O IR band at saturation of the sites: AM, by using eq. ES2 with the data in inset A.

Due to the presence of weakly adsorbed H2O species the saturation of the sites is not obtained at 300 K for Pa= 250 Pa as shown by the increase in the IR band with the increase in Pa in inset A of Figure 2. This allows estimating the area AM of the IR band at saturation of the sites via eq. ES2 as shown in inset B of Figure 2. Thus, the evolution of the area of the


Page 15 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15 δH2O IR band in Figure 1 provides that of the average coverage of the H2Oads species versus Ta as shown by the dark square symbols in Figure 2. Similarly, the red circle symbols give the evolution of the coverage during the second heating stage in 0.25% H2O/He (after the experiment in Figure 1, the solid is cooled to 300 K in 0.25% H2O/He before a new heating) showing the good repeatability of the experimental data. Curve a in Figure 2 fitting the experimental data is obtained from eqs ES3, ES4 and ES6), which considers that the δH2O IR band at 300 K is due to the contribution (xi, i= 1, 2 and 3) of three molecularly adsorbed species (H2Owads, H2Oads-L1 and H2Oads-L2) with different heats of adsorption increasing linearly with the decrease in their coverages (Temkin model) as indicated in Table 2. The heats of adsorption of the three H2Oads species on the model catalyst are not significantly different from those on TiO2-DT51,17 indicating that the surface composition has a limited impact as observed for the NH3ads‑L1 and NH3ads‑L2 species (Table 1).

3.3 Theoretical Coverages of the NH3 and H2O Adsorbed Species on the NH3-SCR Catalyst in the Absence of Coadsorption. Taking into account the heats of adsorption of NH3 and H2O species adsorbed on 0.7% V2O5/9% WO3/TiO2, those implicated in the NH3-H2O coadsorption in the temperature range of the NH3-SCR: Ta> 473 K, can be identified considering their coverages in the absence of coadsorption. Figure 3 shows the theoretical coverages of the adsorbed species for 0.1% NH3/He and 0.25% H2O/He considering (a) the Temkin model (eq ES3) for localized adsorbed species (eq ES4) and (b) the heats of adsorption reported in Tables 1 and 2. At Ta≥ 473 K, NH3ads-L2 (curve a) and a fraction of NH3ads-L1 (curve b) are both present on the surface: i.e., their coverages are of (a) ≈1 and 0.2 at Ta= 473 K and (b) 0.71 and 6 10-3 at Ta= 573 K respectively. However, the amounts of NH3ads-L1 and NH3ads-L2 at each temperature must take into account that at 300 K at saturation of the Lewis sites, their ratio is NH3ads-L1/NH3ads-L2 ≈ 2



16 (Table 1). Similarly, curves c and d in Figure 3 show that NH4+ads-2 and a fraction of NH4+ads-1 species are present on the surface after NH3 adsorption for Ta≥ 473 K: i.e., their coverages are (a) 0.75 and 0.08 at Ta= 473 K and (b) 0.4 and ≈ 0 at Ta= 573 K respectively. PNH3= 100 Pa PH2O= 250 Pa

1

Coverage of the adsorbed species

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 47

0.8 g

e

f

c

a

0.6 d

b

NH3ads-L2

0.4

NH3ads-L1

0.2

NH4+-2 NH4+-1 H2Oads-L2

H2Oads-L1 H2Owads

0

200

473

300

400

500

Temperature (K)

600

700

800

Figure 3: Theoretical coverages according to the Temkin model (see Supporting Information) of the adsorbed NH3 and H2O species on 0.7% V2O5/9% WO3/TiO2 in the absence of competition using 0.1% NH3/He and 0.25% H2O/He and considering the individual heats of adsorption in Tables 1 and 2 measured by the AEIR method.4-6,17

Curves e, f and g in Figure 3 display the coverages of the H2Oads-L2, H2Oads-L1 and H2Owads species respectively for 0.25% H2O/He. At Ta≥ 473 K only the H2Oads-L2 species may contribute to the NH3-H2O coadsorption: the coverage of the H2Owads and H2Oads-L1 species are ≈ 0 above Ta= 400 K and 450 K respectively, whereas the coverages of the H2Oads-L2 species are 0.51 and 0.17 at Ta= 473 K and 573 K respectively. Finally, Figure 3 leads to the conclusion that at Ta≥ 473 K the NH3-H2O coadsorption using PNH3= 100 Pa and PH2O= 250 Pa on the sulfated 0.7% V2O5/9% WO3/TiO2 catalyst concerns (a) the two NH3ads-L and the H2Oads-L2 species on the Lewis sites and (b) the two NH4+ species formed on the Brønsted sites. Moreover, the dissociative adsorption of H2O forming OH groups (Figure 1) which has been observed at high temperatures even in the presence of H2O traces17 (Figure S1) must be


Page 17 of 47

17 taken into account during NH3-H2O coadsorption. This point is particularly considered in Part 618 with the support of the Temkin-C model.

3.4 FTIR Study of NH3-H2O Coadsorption on the Model 0.7%V2O5/9%WO3/TiO2 Catalyst. Figure 4 shows the evolutions of the IR bands of the adsorbed species on the catalyst during the increase in Ta in the range of 423-700 K for 0.1% NH3/0.25% H2O/He.

Absorbance Absorbance

A

Absorbance

3651

0.02

a e

d

3654

1800

3164

a

1377

c

1358

b 3616

3800

0.2

3253

3647 3390

3700 0.1

3600

g 3600

g

3400

Wavenumber (cm-1)

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.04 1666

a g

1337

3200

1428

1607

a 1604

1317 1700

1700

1600

1600

a g 1415 1500 1400 Wavenumbers (cm-1)

1300

Figure 4: IR spectra at different temperatures Ta of the 0.7% V2O5/9% WO3/TiO2 catalyst after coadsorption equilibrium of 0.1% NH3/0.2% H2O/He: (a)-(f) Ta= 423, 473, 523, 573, 623 and 698 K; g: in helium at 698 K after the pretreatment procedure. Inset A: IR bands of the isolated OH groups of the solid: (a) in helium at 423 K before coadsorption; (b)-(d) at the NH3-H2O coadsorption equilibrium at 423, 473 and 698 K and (e) in helium at 698 K.

At 423 K the IR bands of spectrum a are ascribed as follows (see ref 6 and references therein): (a) 1607 cm-1 is the δas IR band of NH3ads-L (note the absence of the δH2O IR band observed at ≈ 1617 cm-1 in Figure 1), (b) 1666 (broad shoulder) and 1428 cm-1 are the δs and δas IR bands of NH4+ and (c) 1317 cm-1 is the ν(S=O) IR band shifted from 1379 cm-1 before adsorption and broadened due to long range interactions with the adsorbed species. Note that



Page 18 of 47

18 the impacts of these interactions during either adsorption of NH3,5-6 and H2O17 or their coadsorption (Figure 4) prevent studying if the SO4 groups are involved as adsorption sites. In the 3800-3100 cm-1 wavenumber range, the OH IR band observed at 3651 cm-1 before adsorption (spectrum a in inset A of Figure 4) is not detected at the coadsorption equilibrium (spectrum b inset A of Figure 4). Note that the absence of OH groups in spectrum b cannot exclude a dissociative adsorption of H2O in the presence of NH3 because if new OH groups are formed they can be involved in (a) the formation of NH4+ species according to the adsorption equilibrium: M-OH + NH3g ↔ MO-+ NH4+

(1)

(where M is either Ti, or/and V or/and W) and (b) H-bonds with the different adsorbed NH3 species. The IR bands in the 3500-3100 cm-1 range (Figure 4) correspond to the overlapping stretching bands of the NH3ads-L and NH4+ species5-6 (these IR bands may also overlap a small and broad IR band due H-bonds between OH/O2- groups and the adsorbed NH3 species). Increasing Ta leads to the decrease in the IR bands (Figure 4 spectra a-f) of the adsorbed NH3 species associated with a shift to lower wavenumbers (a) for the NH3ads-L species from 1607 to 1604 at 423 K and 573 K respectively and (b) for the NH4+ species from 1428 to 1415 cm-1 at 423 and 623 K respectively. The ν(S=O) IR band increases progressively and shifts to higher wavenumbers with the increase in Ta due to the decrease in the coverages of the different adsorbed NH3 species (decrease in the long range interactions). At 698 K, its intensity and position are significantly different from that observed after the pretreatment procedure (compare spectra f and g in Figure 4) due to the presence of adsorbed NH3ads-L2 and NH4+-2 species (see Figure 3). In the range 3800-3100 cm-1, the increase in Ta leads to (a) the decrease in the IR bands of the NH3ads-L and NH4+ species such as 3390, 3253 and 3164 cm-1 (see references in ref 6) in parallel to those in the range 1800-1300 cm-1 and (b) from Ta ≈ 440 K, the appearance and then increase in the IR bands of the isolated OH groups (compare


Page 19 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


19 spectra b, c and d in the inset A of Figure 4). This can due to the decrease in the coverages of (a) the NH4+ species (eq 1) and (b) the NH3ads-L species leading to a decrease of the H-bonds with the isolated OH groups. At 698 K, spectra d and e in inset A of Figure 4 show that the intensity of the IR band at 3647 cm-1 (free OH groups) is slightly higher in the presence of NH3-H2O than after the pretreatment procedure. However, the remaining fraction of the NH4+-2 species (spectrum f in Figure 4 is consistent with curve c in Figure 3) must decrease the amount of free OH groups (eq 1) suggesting that H2O dissociation is operant during the NH3-H2O coadsorption. Considering this dissociative H2O chemisorption, the absence of OH IR band at the NH3-H2O coadsorption equilibrium at 423 K (spectrum b, inset A Figure 4) can be due to the coverage of the NH4+ species. Moreover, curves c and d in Figure 3 show that the coverages of the NH4+-1 and NH4+-2 species are of ≈ 0.31 and ≈ 0.92 respectively at 423 K for PNH3= 100 Pa indicating that the OH adsorption sites forming the NH4+-1 and NH4+-2 species are mainly partially and almost totally occupied respectively. Assuming that the heats of adsorption of the NH4+ species are not modified by the coadsorption, this indicated that the dissociative H2O adsorption in the presence of NH3 forms mainly OH groups for the NH4+-2 species which contributes mostly to the increase in the IR bands at 1428 and 1666 cm-1. Finally, the IR spectra of the NH3-H2O coadsorption on the model NH3-SCR catalyst (Figure 3) appear very similar to those observed on this solid during the isobaric adsorption of 0.1% NH3/He,6 suggesting that the competitive adsorption on the Lewis sites is dominated by the NH3ads-L species. However, this does not prevent the dissociative H2O chemisorption. Experiments have been performed to obtain more data on these processes on 0.7% V2O5/9% WO3/TiO2 and TiO2-DT51 to take into account the surface composition on the NH3-H2O coadsorption. These experiments performed using FTIR spectroscopy and volumetric measurements, consist in studying how the adsorption equilibriums obtained with either 0.1% NH3/He or 0.25% H2O/He are disturbed by the coadsorption using 0.1% NH3/0.25% H2O/He.



20 3.5 Experimental Approach of NH3-H2O Coadsorption on the Model NH3-SCR Catalyst. Impacts of H2O on the NH3 Adsorption Equilibrium Studied by FTIR Spectroscopy. After, subtraction of the spectrum of the solid before adsorption, Figure 5 compares at Ta= 473 K and 573 K, the IR spectra of the adsorbed species on the 0.7% V2O3/9% WO3/TiO2 solid at (a) the adsorption equilibrium after the switch He  0.1% NH3/He (spectra a and b respectively) and (b) the coadsorption equilibrium after the switch 0.1% NH3/He  0.1% NH3/0.25% H2O/He (spectra c and d). 3647

3253

0.01

Absorbance

d

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

b 3654

3201 3166

3324 3382

c

1428 c

c

d

a 3700 3600

a

0.1 3654 3800

b

3647

d 3600

3400

3200 -1

Wavenumber (cm )

1606

0.1

a

a, c 1666

1800

1700

b, d

1422

b

1600 1500 Wavenumbers (cm-1)

Figure 5: Comparison of the IR spectra of 0.7% V2O5/9% WO3/TiO2 at two temperatures at the NH3 and NH3-H2O adsorption and coadsorption equilibrium respectively: (a) and (b) in 0.1% NH3/He at 473 and 573 K respectively; (c)-(d) in 0.1% NH3/0.25% H2O/He at 473 and 573 K respectively (The IR spectra in the extended presentation of the inset have been shifted according to the Y axis to facilitate the presentation).

It can be observed that whatever Ta the presence of H2O (a) does not modify strongly the intensity of the δas-NH3ads-L IR band at 1606 cm-1 (slight decrease) confirming that the competitive NH3-H2O coadsorption on the Lewis sites is dominated by the NH3ads-L species and (b) increase the intensities of the δas-NH4+ (≈ 1425 cm-1) and δs-NH4+ IR bands (1666 cm-


Page 20 of 47

Page 21 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21 1

) indicating that H2O favors the NH4+ species. Moreover, the intensity of the IR bands in the

3500-3100 cm-1 range (inset A Figure 5 showing spectra without subtraction of the spectrum of the solid before adsorption) increases with the addition of H2O in agreement with the overlap of the IR bands of the NH3ads-L (not strongly modified) and the NH4+ species (increased). At each temperatures the intensity of the IR band of the free OH groups (37003600 cm-1) is higher in the presence of H2O (Figure 5) indicating that H2O dissociation is operant during NH3-H2O coadsorption. Note that the intensity of the OH IR band results from different adsorption equilibriums such as (a) the H2O dissociation, (b) the formation of NH4+ species (eq. 1) and (c) the H-bonds with the NH3ads-L species. Figure 5 permits some quantifications of the impact of the NH3-H2O coadsorption on the NH4+ species using the area ANH4+(Ta) of the half δas-NH4+ IR band at 1422-1428 cm-1 (see justifications of this quantification in ref 5 in relation with the presence of the ν(S=O) IR band). For instance, the increases in the δas-NH4+ IR band due to the presence of H2O are of factors ≈ 2.9 and ≈ 3.7 at 473 K and 573 K. The intensity of an IR band of an adsorbed Xads species at Ta (AXads(Ta)) is proportional to its amount on the surface sample according to: AXads(Ta)= α Ns θXads(Ta)

(2)

where α is a proportional factor (independent on the coverage and including the IR absorption coefficient of the Xads species), θXads(Ta) is the coverage of the Xads species at Ta (depending on the heats of adsorption, the adsorption pressure and Ta) and Ns is the amount of sites which adsorbs Xads. Equation (2) shows that in the absence of competitive adsorption on the same sites, the increase in the δas IR band of the NH4+ species by the introduction of H2O can be due to the increases of (a) the amount of the OH adsorption sites (Ns) or/and (b) the coverages of the NH4+ (i.e., by an increase in their heats of adsorption if their coverage are 473 K on 0.7% V2O5/ 9% WO3/TiO2 studied by FTIR, the modification of the NH3 adsorption equilibrium on TiO2DT51 by H2O at Ta= 473 K and Ta> 473 K studied by FTIR, and the modification of the H2O adsorption equilibrium on TiO2-DT51 by NH3 at Ta= 473 K and Ta>473 K studied by FTIR. This information is available free of charge via the Internet at http://pubs.acs.org

ACKNOWLEDGMENTS: The authors from IRCELYON would thank the financial support of the EDF- Fluid Dynamics, Power Generation and Environment Department during the Ph.D thesis of F.G



42 REFERENCES (1) Forzatti, P. Environmental Catalysis for Stationary Applications. Catal. Today 2000, 62, 51−65. (2) Shang, X.; Li, J.; Yu, X.; Chen, J.; He, C. Effective Regeneration of Thermally Deactivated Commercial V-W-Ti Catalysts. Front. Chem. Sci. Eng. 2012, 6, 38−46. (3) Nova, I.; dall’Acqua, L.; Lietti, L.; Giamello, E.; Forzatti, P. Study of Thermal Deactivation of a De-NOx Commercial Catalyst. Appl. Catal., B 2001, 35, 31−42. (4) Giraud, F.; Geantet, C.; Guilhaume, N.; Gros, S.; Porcheron, L.; Kanniche, M.; Bianchi, D. Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO2/TiO2 Catalysts: Part 1- Individual Heats of Adsorption of Adsorbed NH3 species on a Sulfate-free TiO2 Support using adsorption isobars. J. Phys. Chem. C 2014, 118, 15664−15676. (5) Giraud, F.; Geantet, C.; Guilhaume, N.; Loridant, S.; Gros, S.; Porcheron, L.; Kanniche, M.; Bianchi, D. Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 2. Impact of Superficial Sulfate and/or VxOy Groups on the Heats of Adsorption of Adsorbed NH3 Species. J. Phys. Chem. C 2014, 118, 15677−15692. (6) Giraud, F.; Geantet, C.; Guilhaume, N.; Loridant, S.; Gros, S.; Porcheron, L.; Kanniche, M.; Bianchi, D. Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 3. Impact of Superficial WOz and VxOy/WOz Groups on the Heats of Adsorption of Adsorbed NH3 Species. J. Phys. Chem. C 2015, 119, 15401−15413. (7) Dulaurent, O.; Bianchi, D. Adsorption Isobars for CO on a Pt/Al2O3 Catalyst at High Temperatures using FTIR Spectroscopy: Isosteric Heat of Adsorption and Adsorption Model. Appl. Catal. A 2000, 196, 271−280. (8) Derrouiche, S.; Gravejat, P.; Bianchi, D. Heats of Adsorption of Linear CO Species Adsorbed on the Au° and Ti+δ Sites of a 1% Au/TiO2 Catalyst Using in Situ FTIR Spectroscopy under Adsorption Equilibrium. J. Am. Chem. Soc. 2004, 126, 13010−13015. (9) Derrouiche, S.; Bianchi, D. Heats of Adsorption Using Temperature Programmed Adsorption Equilibrium: Application to the Adsorption of CO on Cu/Al2O3 and H2 on Pt/Al2O3. Langmuir 2004, 20, 4489−4497. (10) Dulaurent, O.; Chandes, K.; Bouly, C.; Bianchi, D. Heat of Adsorption of Carbon Monoxide on Various Pd Containing Solids using In-situ Infrared Spectroscopy at High Temperatures. J. Catal. 2000, 192, 273−285.


Page 42 of 47

Page 43 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


43 (11) Busca, G.; Lietti, L.; Ramis, G.; Berti, F. Chemical and Mechanistic Aspects of the Selective Catalytic Reduction of NOx by Ammonia over Oxide Catalysts: A review. Appl. Catal. B. 1998, 18, 1−36. (12) Centi, G.; Perathoner, S. Selective Catalytic Reduction (SCR) Processes on Metal Oxides. Chap. 21 in Metal Oxides Chemistry and Application, Ed. Fierro, J. L. G, CRS press, Taylor & Francis, 2006. (13) Svachula, J.; Ferlazzo, N.; Forzatti, P.; Tronconi, E.; Bregani, F. Selective Reduction of NOx by NH3 over Honeycomb DeNOxing Catalysts. Ind. Eng. Chem. Res. 1993, 32, 1053−1060. (14) Forzatti, P.; Lietti, L. Recent Advances in de-NOxing Catalysis for Stationnary Applications. Heter. Chem. Rev. 1996, 3, 33−51. (15) Topsøe, N. Y. Mechanism of the Selective Catalytic Reduction of Nitric Oxide by Ammonia Elucidated by in Situ On-Line Fourier Transform Infrared Spectroscopy. Science 1994, 265, 1217−1219. (16) Topsøe, N. Y.; Topsøe, H.; Dumesic, J. H. Vanadia/Titania Catalysts for Selective Catalytic Reduction of Nitric Oxide by Ammonia: 1. Combined Temperature Programmed in situ FTIR and On-Line Mass Spectroscopy Studies. J. Catal. 1995, 151, 226−240. (17) Giraud, F.; Couble, J.; Geantet, C.; Guilhaume .N; Puzenat, E.; Gros, S.; Porcheron, L.; Kanniche, M.; Bianchi, D. Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 4. Individual Heats of Adsorption of Adsorbed H2O Species on Sulfate-Free and Sulfated TiO2 Supports. J. Phys. Chem. C 2015, 119, 16089−16105. (18) Giraud, F.; Couble, J.; Geantet, C.; Guilhaume .N; Loridant, S.; Gros, S.; Porcheron, L.; Kanniche, M.; Bianchi, D. Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 6. NH3-H2O coadsorption on TiO2 based solids and competitive Temkin model. J. Phys. Chem. C 2018, submitted. (19) Couble, J.; Bianchi D. Experimental Microkinetic Approach of the CO/H2 Reaction on Pt/Al2O3 using the Temkin Formalism. 1. Competitive Chemisorption between Adsorbed CO and Hydrogen Species in the Absence of Reaction. J. Catal. 2017, 352, 672–685. (20) Couble, J.; Bianchi D. Experimental Microkinetic Approach of the CO/H2 Reaction on Pt/Al2O3 using the Temkin Formalism. 2. Coverages of the Adsorbed CO and Hydrogen species during the Reaction and Rate of the CH4 Production. J. Catal. 2017, 352, 686–698. (21) Corma, A.; Llopis, F.; Monton, J. B.; Weller, S. W. Comparison of Models in Heterogeneous Catalysis for Ideal and Non-ideal Surfaces. Chem. Eng. Sci. 1988, 43, 785−792.



44 (22) Broadbelt, L. J.; Rekoske, J. E. Necessary Levels of Detail in Microkinetic Models of Catalytic Reaction on Nonuniform Surfaces. Chem. Eng. Sci. 1996, 51, 3337−3347. (23) Corma, A.; Xamena, F. L.; Prestipino, C.; Renz, M.; Valencia, S. Water Resistant Catalytically Active Nb and Ta Isolated Lewis Acid Sites, Homogeneously Distributed by Direct Synthesis in a Beta Zeolite. J. Phys. Chem. C 2009, 113, 11306−11315. (24) Nakajima, K.; Baba, Y.; Noma, R.; Kitano, M.; Kondo, J. N.; Hayashi, S.; Hara, M. Nb2O5 3n H2O as a Heterogeneous Catalyst with Water-Tolerant Lewis Acid Sites. J. Am. Chem. Soc. 2011, 133, 4224–4227. (25) Nakajima, K.; Noma, R.; Kitano, M.; Hara, M. Titania as an Early Transition Metal Oxide with a High Density of Lewis Acid Sites Workable in Water. J. Phys. Chem. C 2013, 117, 16028−16033. (26) Chafik, T.; Dulaurent, O.; Gass, J. L.; Bianchi, D. Heat of Adsorption of Carbon Monoxide on a Pt/Rh/CeO2/Al2O3 Three-Way Catalyst Using in-Situ Infrared Spectroscopy at High Temperatures. J. Catal. 1998, 179, 503−514. (27) Guo, X.; Bartholomew, C.; Hecker, W.; Baxter L. L. Effects of Sulfate Species on V2O5/TiO2 SCR Catalysts in Coal and Biomass-fired Systems. Appl. Catal. B 2009, 92, 30−40. (28) Desmartin-Chomel, A.; Flores, J. L.; Bourane, A.; Clacens, J. M.; Figueras, F.; Delahay, G.; Giroir Fendler, A.; Lehaut-Burnouf, C. Calorimetric and FTIR Study of the Acid Properties of Sulfated Titanias. J. Phys. Chem. B, 2006, 110, 858−863. (29) Saur, O.; Bensitel, M.; Mohmmed-Saad, A. B.; Lavalley, J. C.; Tripp, C. P.; Morrow, B. A. The Structure and Stability of Sulfated Alumina and Titania. J. Catal. 1986, 99, 104−110. (30) Jung, S. M.; Grange, P. The Investigation of Mechanism of SCR Reaction on a TiO2-

SO42− Catalyst by DRIFTS. Appl. Catal. B 2000, 27, L11−L16. (31) Zeradine, S.; Bourane, A.; Bianchi, D. Comparison of the Coverage of the Linear CO Species on Cu/Al2O3 Measured under Adsorption Equilibrium Conditions by Using FTIR and Mass Spectroscopy. J. Phys. Chem. B 2001, 105, 7254−7257. (32) Busca, G.; Saussey, H.; Saur, O.; Lavalley, J. C.; Lorenzelli, V. FTIR Characterization of Surface Acidity of Different Titanium Dioxide Anatase Preparation. Appl. Catal. 1985, 14, 245−260. (33) Guglielminotti, E.; Boccuzzi, F. Infrared Spectroscopic Study of Ammonia and Nitric Oxide Adsorption and Reactivity on a Ru/TiO2 Catalyst: Effect of Oxo-Reducing Treatments. J. Chem. Soc., Faraday Trans. 1991, 87, 337−343.


Page 44 of 47

Page 45 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


45 (34) Hadjiivanov, K.; Klissurski, D.; Busca, G.; Lorenzelli, V. Benzene-Ammonia Coadsorption on TiO2 (Anatase). J. Chem. Soc., Faraday Trans. 1991, 87, 175−178. (35) Ramis, G.; Yi, L., Busca, G. Ammonia Activation over Catalysts for the Selective Catalytic Reduction of NOx and the Selective Catalytic Oxidation of NH3. An FT-IR study. Catal. Today 1996, 28, 373−380. (36) Zecchina, A.; Marchese, L.; Bordiga, S.; Paze, C.; Gianotti. E. Vibrational Spectroscopy of NH4+ Ions in Zeolitic Materials: An IR Study. J. Phys. Chem. B 1997, 101, 10128−10135. (37) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds; John Wiley and Sons: New York, 1986. (38) Teunissen, E. H.; van Santen, R. A.; Jansen, A. P. J. ; van Duijneveldt, F. B. NH4+ in Zeolites: Coordination and Solvation Effects. J. Phys. Chem. 1993, 97, 203−210. (39) Lietti, L.; Ramis, G.; Berti, F.; Toledo, G.; Robba, D.; Busca, G.; Forzatti, P. Chemical, Structural and Mechanistic Aspects on NOx SCR over Commercial and Model Oxide Catalysts. Catal.Today 1998, 42, 101−116. (40) Henderson, M. A. The Influence of Oxide Surface Structure on Adsorbate Chemistry: Desorption of Water from the Smooth, the Microfaceted and the Ion Sputtered Surfaces of TiO2(100). Surf. Sci. 1994, 319, 315−328. (41) Henderson, M. A. Structural Sensitivity in the Dissociation of Water on TiO2 SingleCrystal Surfaces. Langmuir 1996, 12, 5093−5098. (42) Henderson, M. A. An HREELS and TPD Study of Water on TiO2(110): The Extent of Molecular Versus Dissociative Adsorption. Surf. Sci. 1996, 355, 151−166. (43) Gong, X. Q.; Selloni, A. Role of Steps in the Reactivity of the Anatase TiO2(101) Surface. J. Catal. 2007, 249, 134–139. (44) Freund, H. J. Oxide Surfaces, Faraday Discuss., 1999, 114, 1−34. (45) Vittadini, A.; Selloni, A ; Rotzinger, F. P.; Grätzel, M. Structure and Energetics of Water Adsorbed at TiO2 Anatase (101) and (001) Surfaces. Phys. Rev. Lett. 1998, 81, 2954−2957. (46) Arrouvel, C.; Digne, M.; Breysse, M.; Toulhoat, H.; Raybaud, P. Effects of Morphology on Surface Hydroxyl Concentration: a DFT Comparison of Anatase–TiO2 and γ-Alumina Catalytic Supports. J. Catal. 2004, 222, 152–166. (47) Buniazet, Z.; Couble, J.; Bianchi, D.; Rivallan, M.; Cabiac, A.; Maury, S.; Loridant, S. Unraveling Water Effects on Solid Acid Catalysts: Case Study of TiO2/SiO2 as a Catalyst for the Dehydration of Isobutanol. J. Catal. 2017, 348, 125–134.



46 (48) Datka, J.; Gil, B.; Kubacka, A. Acid Properties of NaH-mordenites: Infrared Spectroscopic Studies of Ammonia Sorption. Zeolites 1995, 15, 501–506. (49) O. Bortnovsky, O.; Melichar, Z.; Sobalik, Z.; Wichterlova, B. Quantitative Analysis of Aluminium and Iron in the Framework of Zeolites. Macropor. Mesopor. Mater. 2001, 42, 97–102.


Page 46 of 47

Page 47 of 47

47

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


NH3-H2O Coadsorption on 0.7% V2O5/9% WO3/TiO2 FTIR spectra at Ta= 473 K Sulfate - Solid - PH2O= 250 Pa on Solid - PNH3= 100 Pa on Solid - PNH3= 100 Pa on solid - PH20= 250 Pa H2Oads

NH4+

NH3ads

0.2 1800

1600 1400 Wavenumbers (cm-1)

TOC Graphic


1200

Experimental Microkinetic Approach of De-NOx by ... - ACS Publications

Recommend Documents