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Addition of H2S to methyl acrylate was performed in a batch reactor at 413 K, 400 rpm and at different concentrations in methyl acrylate and H2S in the presence of a commercially available mixed magnesium–aluminum basic oxide, namely the KW 2200 catalyst. Under chemical regime, the rate law was shown to follow a “poisoned” Eley–Rideal mechanism in which H2S reacts in the adsorbed state, whereas methyl acrylate, also capable of being adsorbed on the catalyst, would react in a physisorbed state. FT-IR study of methyl acrylate and H2S adsorption performed on MgO are in agreement with these kinetic results. Co-adsorption experiments showed that both methyl acrylate and H2S were strongly adsorbed on MgO. By varying the order of introduction of the two reactants, i.e. adsorption of H2S followed by methyl acrylate addition or methyl acrylate adsorption followed by H2S addition, it was shown that chemisorbed H2S species like HS− species which result from H2S dissociative adsorption were the active species and that strongly adsorbed methyl acrylate was not involved in the reaction.

Low-temperature CO adsorption on TiO2 (anatase) has been investigated by FTIR spectroscopy on (i) a pure sample, (ii) a sample on which the sites for CO adsorption at room temperature are blocked b...

Ozone adsorption has been studied by IR spectroscopy at low temperature. Although alumina is more acidic than TiO2, as shown by pyridine adsorption, IR spectroscopy did not detect O3 species adsorbed on strong Lewis Al3+ sites. However, O3 decomposition occurred and pyridine specific poisoning evidenced that such sites were involved in the decomposition. Quantum chemistry calculations confirmed such a result and specified that the remaining O(1D) resulting from the decomposition, in addition to physisorbed O2, was attached to the aluminum ion constituting the Lewis sites. The oxygen molecules would then gradually be desorbed.

FT-IR spectroscopy has been applied in a study of methanol adsorption on MINaY zeolites (M=Li, K, Rb, Cs). Coordinatively and/or hydrogen bonded methanol was registered in the temperature range 300–473 K. Dehydration of methanol to dimethyl ether occurred at 573 and 623 K. It was found that the activity of the catalyst for methanol dehydration strongly depends on the kind of alkali metal cation, and well correlates the IR data relative to methanol adsorption.

The amount of platinum introduced by ion exchange on TiO2 anatase (63 m2 g–1) can be increased by repeating the exchange procedure after reduction of the catalyst under hydrogen. From IR spectroscopy studies, two kinds of Lewis acid sites on the TiO2 support (α and β sites) have been found to participate in the ion-exchange mechanism. Only the strongest Lewis acid sites (α sites) are involved in anion exchange, whereas both kinds of sites participate in cation exchange. These adsorption sites are partly liberated by reduction under hydrogen allowing further ion-exchange procedures and thus increasing the amount of platinum. By modelling the quantity of platinum introduced by each exchange, a limit for the amount of platinum is expected to be reached after several exchange–reduction cycles: 1.3 wt.% for anion exchange and 3.1 wt.% for cation exchange.

The reduction of CeO2 by hydrogen has been studied from 300–1200 K by several complementary techniques: temperature-programmed reduction (TPR) and magnetic susceptibility measurements, Fourier-transform infrared (FTIR), UV–VIS diffuse reflectance and X-ray photoelectron (XP) spectroscopy. Two CeO2 samples were used with B.E.T. surface areas of 115 and 5 m2 g–1, respectively. The concentration of Ce3+ was determined in situ by measuring the magnetic susceptibility and the CeIII photoemission line. The reduction began at 473 K, irrespective of the initial surface area of the ceria. In the case of the low-surface-area sample, an intermediate reduction step was observed between 573 and 623 K, corresponding to the reduction of the surface. This intermediate step was less easily observed in the case of the high-surface-area ceria. In both cases, the reduction led to a stabilised state with the formal composition CeO1.83. Temperatures higher than 923 K were required to reduce the ceria further. The surface CeIII content determined by XPS was close to that determined by magnetic susceptibility measurements. The intensity of the 17 000 cm–1 band in the UV–VIS reflectance spectrum also varied with the degree of reduction. Finally, the evolution of the surface species observed by IR spectroscopy was in good agreement with the results from the other techniques. The IR results indicated large changes in the concentration and nature of both the hydroxyl and the polydentate carbonate species during the reduction process. The adsorption of oxygen on samples previously reduced to the composition CeO1.83 led to almost complete reoxidation at room temperature. The state of the initial B.E.T. surface did not influence the oxidation process. A slight excess adsorption of oxygen was evident on the surface. This was thermodesorbed at 380 K under vacuum.

Comparison of IR spectra of species formed from adsorption of different bases on the acidic OH groups of zeolites (HY, MFI) indicates that O3 basicity is close to that of CO. Calculations confirm such a result ; in particular they involve that the terminal oxygen atoms of ozone are the basic centers.

Pyrrole has been adsorbed on various metal oxides: reduced or unreduced ceria, alumina dehydroxylated to varying extents and an NaX zeolite. Pyrrole adsorption was found to be either non-dissociative or dissociative (on the more basic adsorption sites), the pyrrolate anion being formed in the latter case. When bound to surface hydroxy groups through an easily polarizable H bond, the pyrrolate anion was thought possibly to be non-planar; complex progressions of IR bands were then observed involving the combination of CH-stretching modes with a ring-deformation vibration. When pyrrole was non-dissociatively adsorbed through an NH⋯O bridge with O2– moderately basic surface centres, the shift of the NH-stretching frequency reflected the O2– basicity. Interaction with surface hydroxy groups led to NH⋯(OH) hydrogen-bridged species, which have been found to be either cyclic or linear according to whether the hydroxy groups are monodentate or bidentate, respectively.

An FTIR study shows that methanethiol is adsorbed dissociatively on ZrO2 leading to thiolate species and associatively, giving rise to H-bonded and coordinated species, less stable than the CH3S— species. Only coordinated and H-bonded species are formed by dimethyl sulfide adsorption. Heating in the presence of a gas phase shows that, besides the dismutation of CH3SH into (CH3)2S and H2S, side reactions occur on the surface leading to methoxy and formate species.

Reactivity of surface methoxides, ethoxides, 2-propoxides and tert-butoxides on thoria with water, an alcohol, and on heating has been studied by FT-IR spectroscopy. It was shown that at least two surface alkoxides are formed; simple (I) and the bridged (II) ones. Structure II can be hydrolyzed or alcoholyzed to structure I, and vice versa, structure I can form structure II upon heating. Alkoxides with β-hydrogens decompose to the corresponding alkenes. As indicated by kinetic data, the reaction scheme can be assumed as consecutive: I→II→alkene.

Les spectres infrarouges des especes irreversiblement adsorbees donnees par CCI3 CH2 OH, CCI3 CD2 OH, CF3 CH2 OH, HC [math] CCH2 OH et HC [math] CCD2 OH sur alumine (activee a 880 K) et par CCI3 CH2 OD, CF3 CH2 OD et DC [math] CCH2 OD sur AI2 O3 —OD sont analyses dans la region 4 000 — 1 000 cm— 1 . La similitude des spectres obtenus par adsorption d'un alcool ROH et du compose ROD correspondant dans la region 1 500 — 1 000 cm— 1 montre sans ambiguite la formation d'especes de type alcoolate. Ces especes sont heterogenes. L'utilisation d'echantillons d'alumine actives a 1 150 K permet de determiner le nombre d'ondes ν (OH) des groupements hydroxyle resultant de l'adsorption dissociative. Dans les conditions operatoires utilisees (temperature d’adsorption : 310 K), la formation des especes carboxylates peut etre consideree comme negligeable. L'etude des vibrations ν (CH) ne permet pas de mettre en evidence la presence d'especes coordinees. Dans le cas de l'adsorption de l'alcool propargylique, l'etude de la region des vibrations du groupement acetylenique montre que l'adsorption ne se fait pas par coupure de la liaison [math] C — H mais uniquement par dissociation de la liaison OH.

Les glissements, par effets de solvant, de la bande d’absorption a 245 nm du spectre ultraviolet du penladiyne-1,3, de l’hexadiyne-2,4 et de l’hexadiyne-2,4 (D6 ) sont etudies. Les interactions dispersives sont differentes quand le solvant est un alcane lineaire ou un alcane non lineaire; ceci est du a des interactions dispersives localement orientees entre ces solvants et la molecule solute en forme de bâtonnet; la variation de la polarisabilite de la molecule solute dans la transition electronique est evaluee. Aucun effet general de la polarite des solvants n’est observe. Les interactions avec les solvants fluores sont differentes.

The i.r. and Raman spectra of eight 1-butynes: CH3CH2CCH, CH3CH2CCD, CH3CD2CCH, CH3CD2CCD, CD3CH2CCD, CD3CH2CCD, and CD3CD2CCD have been measured. From a comparative analysis of the spectra, together with those of other related molecules, all the fundamental vibrations, with the exception of the torsional vibration of the methyl group, have been assigned for each of the eight molecules. The splitting of the degeneracy of the CCH bend into two frequencies is discussed. The fundamental δ(CCD) is found to exhibit coupling with an A′ skeletal deformation mode while γ(CCD) is assigned to a Q branch at a constant wavenumber (494 cm−1) in the i.r. spectrum of the studied RCCD compounds.

Comparative adsorption of CH3 16OH and CH3 18OH on thoria shows the formation of four types of methoxy species resulting from methanol O−H dissociation. Species I, characterized by the highest ν(C−O) wave-number, reacts with CO2 at room temperature, leading to the formation of methyl carbonate species while the others are almost unreactive. Species I is considered as monodentate, the others as bi or tridentate. Their structure is related to the local arrangement of the exposed faces.

The Raman spectra of three 2-butynes: CH 3 CCCH 3 , CH 3 CCCD 3 and CD 3 CCCD 3 , and four 2-pentynes: C 2 H 5 CCCH 3 , C 2 H 5 CCCD 3 , C 2 D 5 CCCH 3 and C 2 D 5 CCCD 3 in the liquid state have been measured. From a comparative analysis of the spectra, together with previous work on 1-butynes, a vibrational assignment is derived. The analysis of the 2000–2400 cm −1 range allowed us to precise the Fermi resonance interaction between ν(CC) and 2ν a (CC CC). An assignment of the several bands shown by the Raman spectrum of 3-hexyne in this range has been proposed.

Bands due to the in-plane bending mode of hydrogen-bonded surface hydroxy groups are observed on alumina, zirconia, magnesia and thoria samples. Their assignment is based on the effect of dehydration by heating under evacuation, and isotopic exchange using D2O and H2O18. The observed frequencies are apparently related to the position of the cut-off limit of the samples, suggesting a coupling of the δOH mode with the ν(MOH) mode.

The i.r. spectrum of a ZrO 2 sample activated at 723 K mainly presents two bands at 3775 and 3670 cm -1 characterizing two types of OH groups (type I and type II respectively). The latter is not affected by CO 2 introduction while the former is involved in the formation of hydrogenocarbonate species. CH 3 OH adsorption on activated ZrO 2 leads to the appearance of two strong bands at t160 and 1054 cm -1 . Use of CH 1 3 8 OH shifts both towards lower wavenumbers (1122 and 1023 cm -1 respectively). This clearly shows that they correspond to the v (C-O) mode o f two types of methoxy species (I and II respectively) resulting from the dissociation of the methanol O-H bond. Their reactivity towards CO 2 is quite different: type I species react and lead to the formation of a methyl carbonate like species while type II are almost unreaetive. Extension of the study to ethanol provides also evidence of two types of ethoxy species. The assignment of species I to monodentate groups and species II to bridged ones allows us to explain their different reactivity towards CO 2 considering that the first step of the reaction is an electron donor-acceptor interaction.

Les spectres infrarouges et Raman de pentadiynes-1,3 (CH3 — C ≡ C — C ≡ CH, CH3 — C ≡ C — C ≡ CD, CD3 — C ≡ C — C ≡ CH et CD3 — C ≡ C — C ≡ CD) ont ete analyses. Les 14 vibrations fondamentales ont ete identifiees pour chacune des quatre especes isotopiques. L’etude comparee des spectres entre eux et a ceux de composes voisins a permis de proposer une attribution des differentes bandes.

Infrared results provide spectroscopic evidence that H2S and CO2 interact on γ-alumina giving rise to thiocarbonate surface species leading to the formation of carbonyl sulphide.

The adsorption of SO, on alumina leads to the formation of several species such as SO3=, HSO3- and coordinated SO2. In addition sulfates are produced under oxidizing conditions. However, definitive vibra- tional assignments are hampered by the paucity of data below 1000 cm-1 where alumina is strongly absorbing. On the other hand, silica is partially transparent at low frequencies and subtractive IR spectroscopy has permitted us to observe bands which are tentatively assigned to the SO bending modes of bisulfite (HSO3-, 635 cm-I) and disulfite (S2O5-, 660 cm-I) surface species on sodium promoted silica catalysts when SO and H2O are coadsorbed. H2S addition to a surface pretreated with SO2 gives rise to a new band at 680 cm-1 which is pos- sibly due to S2O3 orS2O on the surface. The results are discussed in terms of intermediates in the Claus process (2 H2S + SO2 + 3/n Sn + 2 H2O).

The adsorption of formaldehyde on different oxides (silica, pure and fluorided alumina, magnesia, titania, thoria, zirconia, and iron oxide) has been studied by FT-IR spectroscopy in the temperature range 170-570 K. The following adsorbed species have been identified and characterized spectroscopically: (i) physisorbed HCHO, (ii) coordinated HCHO, (iii) dioxymethylene, (iv) polyoxymethylene, (v) formate ions, and (vi) methoxy groups. On silica at 170 K formaldehyde physisorbs on surface OH groups and, by warming, polymerizes producing linear polyoxymethylene. On ionic oxides at about 250 K dioxymethylene is always observed, generally together with variable amounts of the linear polymer that has been isolated on magnesia at 170 K. Heating up to or above room temperature results in the disproportionation of dioxymethylene into formate and methoxide groups, probably via a Cannizzaro-type mechanism. Such a route probably parallels an oxidative route, involving direct oxidation of dioxymethylene into formates, as observed on iron oxide.

The adsorption of formaldehyde on different oxides (silica, pure and fluorided alumina, magnesia, titania, thoria, zirconia, and iron oxide) has been studied by FT-IR spectroscopy in the temperature range 170-570 K. The following adsorbed species have been identified and characterized spectroscopically: (i) physisorbed HCHO, (ii) coordinated HCHO, (iii) dioxymethylene, (iv) polyoxymethylene, (v) formate ions, and (vi) methoxy groups. On silica at 170 K formaldehyde physisorbs on surface OH groups and, by warming, polymerizes producing linear polyoxymethylene. On ionic oxides at about 250 K dioxymethylene is always observed, generally together with variable amounts of the linear polymer that has been isolated on magnesia at 170 K. Heating up to or above room temperature results in the disproportionation of dioxymethylene into formate and methoxide groups, probably via a Cannizzaro-type mechanism. Such a route probably parallels an oxidative route, involving direct oxidation of dioxymethylene into formates, as observed on iron oxide.

Among the spectroscopic methods used for the characterization of the chemical nature of chemisorbed species, infrared transmission spectroscopy has certainly found the most frequent application. Adsorption of alcohols on alumina has been studied for many years1,2. Despite this fact, even most fundamental questions concerning the system have not been yet answered. A most striking example is the process of adsorption (dissociation or coordination) and the nature of the adsorption sites on γ-Al2O3surface. To solve this problem, we have undertaken a series of infrared experiments using non-deuterated and deuterated alcohols, the vibrational spectra of which had been previously reported in the gaseouos and liquid state3 . Some experiments have been also carried out with methanethiol for comparison. A very detailed analysis of the spectra allows us to determine the nature of irreversible and reversible species. Poisoning experiments precise the mechanism of the adsorption process.

HCHO adsorption on activated thoria produces, at 240K, a species characterized as dioxymethylene; by heating at room temperature, it leads to formate and methoxy groups: the three species are observed by adsorption of HCHO on anatase at room temperature.

But-1-yne has been adsorbed at room temperature on a series of LiNa, Na and CsNaX and Y zeolites and also on CsNaX,9Cs and CsNaY,9Cs samples containing nine Cs atoms occluded by a unit cell. An IR study of the 3000–2800 cm−1 frequency range clearly showed that but-1-yne isomerized into but-2-yne on CsNaX,9Cs whereas the observation of a band near 1950 cm−1 in the case of CsNaY,9Cs characterized the formation of buta-1,2-diene. Such partial transformation of but-1-yne to isomers did not occur on LiNa and Na samples, allowing one to study the basicity of such zeolites from the ν(CH) shift which decreases in the following order: NaX > LiNaX > NaY > LiNaY. The main feature is the observation of at least two perturbed ν(CH) bands for the NaX and NaY samples, revealing the heterogeneity of the basic sites. This result is discussed taking into account the presence of cations in different positions.

The i.r. spectrum of a mixture of CO and H2 adsorbed on ZnO or Cu-ZnO Shows a pair of weak bands at 2770 and 2661 cm–1 while a mixture of CO and D2 gives rise to a corresponding single band at 2020 cm–1; these bands are assigned to vibrations of surface formyl species.

Les spectres infrarouge (region 1 600-3 400 cm-1 ) des especes fortement adsorbees donnees par le butyne-1, le butadiene-1,2 et le butyne-2 sur A12 O3 sont semblables. Il correspond a ces trois composes une meme espece bien definie : CH3 CH2 C [math] C — Al (surface). Ce resultat est explique par l’isomerisation, au contact de Al2 O3 , de l’alcyne ou du diene introduit. Apres des temps de contact plus longs, a cette espece s'ajoutent des especes, mal definies, formees peut-etre par polymerisation sur la surface.

Hydrogen adsorption on thoria activated at 973 K (ThO2-973) leads to weak bands at 1115 and 860 cm–1 and a shoulder at 910 cm–1 due to partially reversibly adsorbed bridged species Th—H—Th. The uptake is very small. The adsorption of CO on ThO2-973 turns the disc orange-yellow and gives rise to a large number of species, some of which are reversibly adsorbed. These species are characterized by a band at 2171 cm–1 and are coordinated to Lewis-acid sites. In addition to the carbonate and formate species, at least four types of irreversibly adsorbed species are formed. Three of them are characterized by bands in the 1200–1000 cm–1 frequency range and can be assigned to v(CO) vibrations of –O—CC—O– species; another possibility is the formation of CO2–2 species because of the strong basicity of thoria. The irreversibly adsorbed species are very sensitive to O2 and H2O but are not reduced by H2. Irreversibly adsorbed hydrogen species react with reversibly adsorbed CO species or CO gas, leading to species similar to those formed on adsorption of HCHO.

Adsorption of CO2, C5H5N, CH3OCH3 and CD3OCD2H on ThO2 has been studied by Fourier-transform infrared spectroscopy. CO2 adsorption gives rise to several types of species: polydentate carbonates, bidentate carboxylates, bidentate carbonates, hydrogenocarbonates, monodentate carbonates and linear CO2 species. The carbonate species have been identified on the basis of the splitting of the v3 vibration and of thermal-stability considerations. These results show that thorium dioxide is a basic oxide. Considering the va(CO2) mode of linear CO2 species, the v8a mode of pyridine, the v(CH) band of CD3OCD2H and the v(COC) modes of CH3OCH3, it is concluded that some Th4+ ions are very weak Lewis-acid sites. The OH groups giving rise to the 3740 cm–1 band are basic (some are involved in the formation of hydrogenocarbonate species), while some of the OH groups corresponding to the 3655 cm–1 band are very weak proton donors.

The adsorption of H2S, CH3SH and (CH3)2S has been studied by gravimetry and infrared spectroscopy. Some experiments have been carried out with preadsorbed pyridine as a poison. The results show that (CH3)2S is bonded to Lewis acid sites and that 60 µmol g–1 are irreversibly coordinated to stronger sites of this type. Dissociative chemisorption has been observed for H2S and CH3SH. Poisoning experiments lead us to conclude that the first adsorption steps involve either a coordinative adsorption (ca. 30 µmol g–1) or a hydrogen bond between a surface basic oxygen atom and the H atom of the SH bond (ca. 50 µmol g–1). The reversible adsorption of CH3SH is thought to occur by these two processes besides another one in which the S atom is H bonded to a hydroxyl surface group. These results clarify the nature of the adsorption sites of alumina.

A Fourier-transform infrared study, together with microcalorimetric measurements, have identified two types of surface interactions during the coadsorption of methanol and CO2 on alumina. Methanol displaces CO2 from hydrogen carbonates, while gaseous CO2 reacts with adsorbed methoxy groups, leading to adsorbed methyl carbonate-like species characterized by very strong bands at 1623, 1476 and 1370 cm–1.

A study of the adsorption sites of thoria has been made using scanning transmission electronic microscopy (STEM) and Fourier-transform infrared spectroscopy (FTIR). The STEM study showed that the thoria surface was composed mainly of (110)(211) and (111) faces in about equal proportions. The infrared study of activated ThO2 at 873 K indicated the existence of two remaining hydroxyl groups at 3660 and 3510 cm–1. With water adsorption, a third one appeared at 3745 cm–1 which was thermally less stable. Methanol adsorption gave rise to three kinds of species: (i) one reversibly adsorbed at room temperature and linked by hydrogen bonds in which thoria acts as a proton receiver; (ii) two methoxy species characterized by ν(CO) bands at 1127 cm–1(species I) and 1060 cm–1(species II). Species I desorption bands led to methanol whilst species II, much more thermally stable, gave methanol, dimethyl ether and carbon monoxide. Species I, which corresponds to the hydroxyl species at 3745 cm–1, are of the Th—OMe (Th—OH) type, and are formed on the (110) faces. Species II, which correspond to hydroxyl species at 3660 cm–1, are of the [graphic omitted] type, and are formed on the (211) faces. The third hydroxyl species, characterized by the ν(OH) band at 3510 cm–1, is probably due to species of the [graphic omitted] type appearing on (111) faces. The stability and reactivity of the methoxy species are shown to depend on their structure, and therefore on the local arrangement of the surface.