The adsorption of CO2, CH4, and N-2 at 303 K by MIL-91(Al), one of the few porous phosphonate-based-MOFs, has been investigated by combining advanced experimental and computational tools. Whereas CH4 and N-2 adsorption isotherms exhibit type I behavior, the reversible CO2 isotherm displays an unusual inflection point at low pressure. In situ X-ray powder diffraction and infrared spectroscopy showed structural changes of this small-pore MOF upon CO2 adsorption. Grand canonical Monte Carlo simulations delivered a detailed picture of the adsorption mechanisms at the microscopic level. The so-predicted arrangements of the confined CO2 molecules were supported by analysis of the in situ diffraction and infrared experiments. It was shown that while adsorbed CH4 and N-2 are located mainly in the center of the pores, CO2 molecules interact with the hydrogen-bonded POHN acidbase pairs. This results in a relatively high adsorption enthalpy for CO2 of ca. -40 kJ mol(-1), which suggests that this material might be of interest for CO2 capture at low pressure (postcombustion).

Adsorption and release of the biologically active nitric oxide (NO) was evaluated over a series of highly flexible iron(III) dicarboxylate MOFs of the MIL-88 structure type, bearing fumaric or terephthalic spacer functionalized or not by polar groups (NO2. 2OH). As evidenced by ex situ X-ray powder diffraction and in situ IR spectroscopy, it appears that if the contracted dried forms of MIL-88 do not expand their structures in the presence of NO, the combination of very narrow pores and trimers of iron polyhedra leads to the adsorption of significant amounts of NO either physisorbed (very narrow pores) and/or chemisorbed [iron(II) or iron(III) coordinatively unsaturated metal sites (CUS)]. The delivery of NO under vapor of water or in simulated body fluid does not exceed 20% range of the total adsorbed amount probably due to a partial release that occurs between the adsorption/desorption setup and the chemiluminescence release tests. Some of these solids nevertheless exhibit a significant release at the biological levels over a long period of time (>16 h) that make these biocompatible and biodegradable MOFs of interest for the controlled release of NO.

The reducibility of sulfate species by CO was studied over ceria and Ce0.63Zr0.37O2 mixed oxide with or without platinum, using infrared spectroscopy and thermogravimetry. The mechanism for sulfate reduction appeared to be based on three main points. Firstly, the exchange between surface and bulk-like sulfate species is required. The sulfate reduction indeed occurs at the oxide surface and bulk-like species need to migrate toward the surface to be further reduced. Secondly, it was observed that surface sulfate species are more easily reduced by CO on the reduced oxide. Therefore, platinum loading which favors the oxide reduction, also favors the sulfate reduction by CO. Finally, the reduction of sulfated Pt-free samples occurs in only one step, which is linked to the own reducibility of the surface sulfate species, probably through a direct interaction with CO. The amount of sulfur stored from sulfate reduction with CO is markedly more important than the one detected from reduction with H2. Furthermore, the oxygen storage capacity (OSC) for sulfated samples is higher than the one for sulfate-free samples. This is tentatively explained by the partial replacement of oxygen by sulfur atoms in the compound lattice.

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The nature, concentration and reducibility by H2 of sulfate species formed from SO2 oxidation were studied over a range of Pt/CexZr1−xO2 catalysts using infrared spectroscopy and thermogravimetry. Ionic sulfates were formed over ceria and Ce-containing catalysts, even at high Zr content. The sample-specific surface area, the presence of platinum and the zirconium proportion affected the rate and extent of formation of sulfate in the bulk of the materials. Sulfate reduction by H2 first occurred at the CexZr1−xO2 surface. Bulk-like S-containing species subsequently migrated towards the surface to continuously replace surface sulfates removed by the reduction. The temperature required for sulfate migration as well as that necessary for sulfate reduction increased with the Zr content. The amount of stored sulfur is closely linked to the specific surface area of the sample. Finally, we have clearly shown that thermogravimetry was an appropriate technique for evaluating the oxygen storage capacity (OSC) of sulfated ceria–zirconia mixed oxides, despite the additional complexity due to the presence of sulfate compounds and various reduced S-species that can be formed during sample reduction.

High surface area aluminium hydroxyfluoride exhibiting the pyrochlore-type structure has been synthesized using microwave hydrothermal process. The optimization of the crystallite size and surface area of the material has been performed by varying some synthesis parameters, i.e. the nature of the aluminium precursor, the choice of solvents and the addition of a small amount of ether. The as-prepared solid contains nanosized particles as calculated by XRD (average particle size: 12 nm) leading to a surface area around 140 m(2) g(-1). These results have been confirmed by TEM observations. The framework is built of AlF(6-x)(OH)(x) species which have been characterized and quantified by high field (27)Al NMR. A random distribution of F atoms and OH groups is evidenced to occur on the 48f sites. Inside the channels, water molecules interact with the framework by hydrogen bonding either with fluoride ions or OH groups present in their vicinity. The use of probe molecules has shown that the pyrochlore exhibits a Lewis acidity lying between that of gamma-Al(2)O(3) and that of the strong Lewis acid beta-AlF(3) adopting the hexagonal tungsten bronze form. Surface OH groups have been characterized by IR spectroscopy and exhibit weak Bronsted acidity.

A study of the zeotypic giant pores chromium(III) tricarboxylate Cr(III)3OF(x)(OH)(1-x)(H2O)2 x {C6H3-(CO2)3}2 x nH2O (MIL-100) has been performed. First, its thermal behavior, studied by X-ray thermodiffractometry and infrared spectroscopy, indicates that the departure of water occurs without any pore contraction and no loss in crystallinity, which confirms the robustness of the framework. In a second step, IR spectroscopy has shown the presence of three distinct types of hydroxy groups depending on the outgassing conditions; first, at high temperatures (573 K), only Cr-OH groups with a medium Brønsted acidity are present; at lower temperatures, two types of Cr-H2O terminal groups are observed; and at room temperature, their relatively high Brønsted acidity allows them to combine with H-bonded water molecules. Finally, a CO sorption study has revealed that at least three Lewis acid sites are present in MIL-100 and that fluorine atoms are located on a terminal position on the trimers of octahedra. A first result of grafting of methanol molecules acting as basic organic molecules on the chromium sites has also been shown, opening the way for a postsynthesis functionalization of MIL-100.

The positions of nu8a and nu*(NH) bands in the spectrum of protonated 2,6-dimethylpyridine vary with the strength of Brønsted acidity: the higher the nu*(NH) wavenumber and the lower the nu8a wavenumber, the stronger the acidity. The results obtained with 2,6-dimethylpyridine adsorption correlate with those obtained by CO adsorption experiments on a series of faujasite zeolites (LiHNaY, KHNaY, HY, HY(SA), HNaX). These relations were extended to gamma-Al2O3 having weak Brønsted acidity, not detected by pyridine and hardly detected by CO. The number (0.1 per nm2) and the strength (corresponding to delta nu (OH) by CO = 155 cm(-1)) of the most acidic OH groups of Al2O3, as well as the position of the corresponding nu (OH) band (<3700 cm(-1)) are deduced from 2,6-dimethylpyridine adsorption experiments.

By hydrolysis of an ethanolic gallium nitrate solution, gamma-Ga2O3 was prepared as a single-phase polymorph having a specific surface area of 160 m2 g(-1). Surface acidity and basicity of this material was studied by IR spectroscopy, using pyridine, 2,6-dimethylpyridine, acetonitrile, and carbon dioxide as spectroscopic probe molecules. For comparison, a gamma-Al2O3 sample having a surface area of 290 m2 g(-1) was also studied. On partially hydroxylated gamma-Ga2O3, the main O-H stretching bands were found at 3693 (sharp) and at 3660-3630 cm(-1) (broad), and the material proved (by adsorbed dimethylpyridine) to have a weak Brønsted acidity. Surface Lewis acidity of gamma-Ga2O3 was revealed (mainly) by adsorbed pyridine, which gave the characteristic IR absorption bands of Lewis-type adducts at 1612, 1579, 1488, and 1449 cm(-1) (values noted under an equilibrium pressure of 1 Torr at room temperature); the corresponding Lewis acid centers (coordinatively unsaturated Ga3+ ions) were found to be weaker, although more abundant, than those present on the surface of gamma-Al2O3 (unsaturated Al3+ ions). Another significant difference between gamma-Ga2O3 and gamma-Al2O3 is the smaller thermal stability of pyridine and 2,6-dimethylpyridine Lewis adducts formed on the gallium oxide. The surface basicity of gamma-Ga2O3 was studied by using carbon dioxide and deuterated acetonitrile as IR probe molecules. Adsorbed CO2 gave carbonate and hydrogen-carbonate surface species similar to those formed by gamma-Al2O3. Adsorbed acetonitrile gave rise to acetamide species, which revealed the basic character of surface O2- ions. These acetamide species were found to be more abundant on gamma-Ga2O3 than on gamma-Al2O3.

CO adsorption has been followed by IR spectroscopy on a Pt/CeO2 sample (Pt loading = 0.5%) treated under oxygen and vacuum or reduced by H-2 and then evacuated at various temperatures. The sample contains highly dispersed Pt. Attention is paid to the presence of an unusual nu((CO)) band at 1937 cm(-1) on the reduced sample. Such a band is in particular not observed when the support is fully covered by CO ( CO adsorption at liquid nitrogen temperature) or by methanol, allowing one to assign it to CO bridged species bound to both Pt very lowly coordinated and to the support, e. g. to sites at the periphery of very small Pt particules. Experiments performed after sample reduction at 423 K followed by increasing evacuation temperature between 423 and 673 K showed that the increase of the latter provokes a sintering of the Pt particles, due to ceria surface O2- mobility.

High-surface-area amorphous gallia–silica samples (Si:Ga=3, 10, 20, 40) were prepared by a sol–gel route involving hydrolysis of an ethanolic solution of silicon tetramethoxide and gallium nitrate. Nitrogen adsorption (77 K) showed the materials obtained to be basically mesoporous. The most frequent pore radius resulted to be 0.8 nm in all cases, while surface area ranged from 476 to 586 m2g−1. Both, NMR spectroscopy and IR spectroscopy of adsorbed probe molecules (CO and pyridine) showed the gallia–silica samples to have distinctive Brønsted and Lewis acidity. According to NMR spectra of both 29Si and 1H, Brønsted acidity should be assigned to Si(OH)Ga groups formed by partial substitution of gallium for silicon in the silica matrix. Lewis acidity is assigned to coordinatively unsaturated Ga3+ ions.

Iron has been introduced into MCM-41 samples in two ways: i) during the synthesis together with either Si or Si+Al, or Si+Nb and ii) via impregnation or CVD (post-synthesis methods) on MCM-41, AIMCM-41, and NbMCM-41. All the materials exhibit well hexagonal ordered mesoporous MCM-41 structure. Iron species formed were identified by FTIR spectra of adsorbed NO and estimated as follows: i) iron isolated cations in extra framework sites, ii) iron in the skeleton, iii) Fe2+-O-Fe3+ Clusters. The relationship between their content depends on the chemical composition of MCM-41 samples and the Fe-doping procedure.

The acidity of amorphous B2O3−SiO2 has been investigated by infrared spectroscopy using the following three probe molecules presenting a wide range of basic strength:  pyridine, acetonitrile, and carbon monoxide. The results are compared to those obtained on γ-Al2O3. No coordination of carbon monoxide is observed on B2O3−SiO2 even at low temperatures, whereas strongly coordinated CO species are formed on γ-Al2O3 under such conditions. Coordinated pyridine and acetonitrile show important infrared frequency shifts on both metal oxides, indicating strong charge transfer from the probe molecules to the surface Lewis acid centers. However, the thermal stability of coordinated species is much lower on B2O3−SiO2 than on γ-Al2O3, which suggests that there is no direct correlation between charge transfer and adsorption energy. Density functional theory (DFT) calculations on the interaction of these probe molecules with simple models representing Al3+ and B3+ Lewis acid sites adequately reproduce experimental obser...

Adsorption of NO and coadsorption of NO and O2 on H-ZSM-5 have been studied at low and room temperature by means of FTIR spectroscopy. For better interpretation of the spectra, experiments involving isotopic labeled molecules have been performed. Low temperature adsorption of NO on H-ZSM-5 results initially in formation of NO which is H-bonded to the zeolite acidic hydroxyls. A second NO molecule is inserted into the OH-NO species at higher coverages, thus forming OH(NO)2 complexes. Different kinds of NO dimers are also formed. Negligible amounts of oxygenated compounds have been detected. In the presence of oxygen, the (di)nitrosyl species are oxidized very fast even at 100 K to N2O3, NO+, NO2, and N2O4. Different kinds of adsorbed N2O3 species have been evidenced. With increasing temperature, NO+ migrates and occupies cationic positions. The latter species interacts with NO at low temperature to give an [ONNO]+ complex. This reaction is used to prove that the different bands in the 2206-2180 cm(-1) region are also due to NO+ species.

The surface properties of iron, chromium, and aluminum fluorides in their hexagonal tungsten bronze (HTB) form have been investigated by infrared spectroscopy. The presence of hydroxyls is clearly observed. H/D exchange experiments with different deuterated probe molecules having various molecular sizes show that they are localized inside of the channels of the structure. The nu(OH) bands in the infrared spectra of these materials are downward shifted compared to those of corresponding metal oxides, whereas the delta(OH) in-plane bending mode presents an unusual high wavenumber. These spectral features are compared to those observed on zeolites, for which hydroxyl environment and bridged conformation are similar. HTB compounds exhibit both strong Lewis and Bronsted acid sites. The use of two basic probes with a different size (pyridine and ammonia) allows one to localize and to quantify these two kinds of acidity. Bronsted acidity is related to the presence of hydroxy groups into the microporous channels and to chemisorbed HF, whereas Lewis acidity is due to defect sites both on the outer surface of crystallites and in the channels. The strength of acid sites is unambiguously found stronger than that reported for Al, Cr, and Fe oxides. This result is discussed taking into account the electronegativity of fluorine but also the bridged conformation of OH groups, as in the case of zeolites.

CuAlMCM-41 and CuNbMCM-41 mesoporous molecular sieves with various Si/Cu ratios were synthesised at room temperature (RT) by the method of direct insertion of metal ions during the synthesis. The physicochemical properties of the materials have been investigated by means of XRD, N2 adsorption/desorption, 27Al MAS NMR and 29Si MAS NMR, ESR, H2-TPR and FTIR combined with NO or NO+NO2 adsorption. It has been documented that H2-TPR measurements and FTIR spectroscopic study combined with the adsorption of NO and NO+NO2 are useful methods for the estimation of the localisation of transition metal cations (framework or extra-framework positions). The comparison of results obtained for CuMCM-41 catalysts prepared by the direct synthesis with those for copper-exchanged MCM-41 allows the statement that copper in CuMCM-41 exhibits a different state and behaviour than that in Cu-MCM-41. It could suggest that copper in CuMCM-41 materials is partially located in the skeleton. The catalytic activity was tested in the liquid phase hydroxylation of phenol. CuNbMCM-41 material presents the highest yield of hydroquinone, that is why this catalyst can be attractive material for hydroxylation with selectivity to p-product. The role of copper leaching during the liquid phase reaction in water medium is pointed out.

The platinum dispersion has been determined by chemisorption of H2 and CO on a series of ceria–zirconia supported catalysts covering the full range of composition between ceria and zirconia. The quantities were measured by volumetric techniques and by FTIR spectroscopy. Reduction and measurement temperatures were studied in order to fix a specific H2 chemisorption protocol. The latter is based on the use of double isotherm of hydrogen adsorption at 195K, this low temperature being required to suppress the hydrogen spillover on the support. The irreversible adsorption measured either at saturation or by extrapolation to zero pressure leads to the most reliable dispersion values, in agreement with those deduced from CO chemisorption at room temperature followed by FTIR spectroscopy, technique which allows to discriminate the adsorption on the platinum surface from that on the ceria–zirconia support. By applying these two methods, it was found that, after reduction at 473K, platinum dispersion is always higher on the mixed oxides than on the pure ceria or zirconia supports. It was nearly constant at 60–65% for a wide range of composition of the mixed oxide between Ce0.15Zr0.85 and Ce0.68Zr0.32.

The texture and surface properties of copper-containing aluminosilica and niobiosilica mesoporous molecular sieves of MCM-41 type, in which all elements were introduced during the synthesis, have been studied by means of XRD, N-2 adsorption, H-2-TPR, FTIR combined with pyridine and NO adsorption as well as in the skeletal region, and the test reaction. The results were compared with those obtained earlier for Cu post synthesis exchanged AlMCM-41 and NbMCM-41. All the results and this comparison allow the suggestion that copper is partially located in the skeleton of both MCM-41 materials, which exhibit redox and acidic properties.

gamma-Ga2O3 and alpha-Ga2O3 samples were prepared as single-phase materials having a high surface area. Ga-71 NMR showed the simultaneous presence of tetracoordinated (Ga-IV) and hexacoordinated (Ga-VI) in gamma-Ga2O3, whereas in alpha-Ga2O3 most of the gallium present was found to be as GaVI. However, the apparent rate of methanol conversion into dimethyl ether (at 473 K) was nearly the same for both samples, when due account was taken of their respective surface area. The unexpected high activity of alpha-Ga2O3 was explained from IR spectroscopic results obtained by using acidity probes like CO and pyridine. These spectroscopic probe molecules showed, for both samples, the presence of strong Lewis acid sites related to coordinatively unsaturated (cus) Ga-IV ions which, for the case of alpha-Ga2O3, strongly suggests surface reconstruction. By contrast, CO2 adsorption revealed a higher basicity for the alpha-polymorph, as compared to alpha-Ga2O3. This basicity can be directly correlated to a larger amount of surface Ga-VI ions which results in a higher degree of ionicity.

Adsorption of NO on Co–ZSM-5 results in formation of three kinds of Co3+–NO species (1970, 1957 and 1940 cm−1) and Co2+(NO)2 dinitrosyls (1894 and 1811 cm−1). All these species disappear after evacuation at elevated temperatures. However, a very short evacuation of the sample with preadsorbed NO at 673 K, followed by quenching to room temperature, results in appearance of a band at 1857 cm−1. This band is assigned to Co2+–NO linear species produced after partial destruction of the dinitrosyls. The reasons for the different pathways of the dinitrosyl decomposition are discussed.