In this paper an XRD, FTIR and TPD investigation of NO2 surface adsorption sites of δ, γ Al2O3 and barium supported δ, γ Al2O3 is reported. Aim of this study is to bring additional light on the surface structures involved in NOx adsorption. Two samples of barium supported aluminas have been prepared and aged at 800 °C. These samples were characterised in comparison with the relative alumina support. The XRD characterisation of these samples shows the presence of barium carbonate and barium aluminate supported on alumina. The comparison of the FTIR spectra, before and after NO2 adsorption, has revealed the formation, upon NO2 contact, of a complex variety of nitrate and nitrite groups. The thermal desorption of nitrate and nitrite species has been simultaneously studied by means of FTIR spectroscopy and by TPD technique.

Publisher Summary This chapter presents acetylene and alkene oligomerization on ETS-10 having induced BrOnsted acidity. H-ETS-10, prepared by a careful thermolysis of ammonium-exchanged ETS-10, is found to have significant BrOnsted acidity as revealed by its ability to protonate adsorbed pyridine. Interaction of methyl-acetylene with the BrOnsted acid sites of H-ETS-10 results in protonation, followed by a formation of oligomeric species with carbocationic character. The π-delocalization of the positive charge of oligomers results in a characteristic spectroscopic response both in the infrared (IR) and ultraviolet-visible (UV-Vis). Propylene is also found to undergo oligomerization on H-ETS-10.

After a brief overview of the reasons why, in spite of the high fraction of framework Ti(IV) atoms, Engelhard titanosilicate (ETS-10) cannot be used as competitive catalyst in partial oxidation reactions, we draw the attention on the fact that the high cation density of ETS-10 can be the key property for potential new catalytic applications of this recent material. Among all, cation exchange with Cu2+ can yield to Cu-ETS-10, a promising material for environmental catalysis. We so present a detailed characterization of this material using N2, CO and NO as probe molecules. In spite of the rather high complexity of the obtained spectra, a comparison with similar experiments (described in the literature or ad hoc performed for this work) on other Cu-exchanged zeolites and on Cu2O dispersed on silica and on MCM-41, allows a full interpretation of the spectroscopic properties. It is shown that copper is present both as counterion and in the form of Cu2O nanoclusters dispersed in the ETS-10 channels and in the external surface. Finally, IR spectroscopy has been used to demonstrate that Cu-ETS-10 is active in the decomposition of NO.

The reaction of 1-butene over ferrierite has been studied by 13C MAS NMR. It is shown that extensive double bond isomerisation and the formation of dimers, mainly dimethyl-hexenes and trimethyl-pentenes, dominate the early catalytic events. Strong interactions between the butene double bond and the Brönsted acid sites shift and broaden the butene olefinic signal extensively. The olefinic carbon signals of isobutene and butene dimers are not observed in these experiments because of the interactions mentioned above and the effect of carbon scrambling. At higher reaction temperatures, the formation of isobutene dominates the spectra and this catalytic event parallels the consumption of 3,4,4-trimethyl-2-pentene. It is suggested that that 3,4,4-trimethyl-1-pentene isomerises to 2,4,4-trimethyl-1-pentene which in turn, rapidly cracks to form isobutene. At higher reaction temperatures, isobutene undergoes extensive secondary reaction leading to C1–C5 paraffins and aromatic coke.

The interaction of CD3CN with dehydrated H3PW12O40 in solid form has been studied by IR spectroscopy, and results are compared with those obtained for other CD3CN/acidic or CD3CN/superacidic solid systems (like zeolites in the acidic form and the perfluorosulfonic membrane H-NAFION). The formation of CD3CN···H+···NCCD3 adducts is demonstrated. These species are characterised by a characteristic band at 2330 cm−1 and by a very broad absorption below 2000 cm−1. On the basis of theoretical DFT ab initio calculations and by comparison with experimental results obtained on the analogous H5O2+ adducts, the above bands are assigned respectively to the ν(CN) and to the ν(N···H+···N) modes of the protonated (CD3CN)2H+ dimers.

An IR and UV-VIS study of the interaction of methyl and ethyl acetylene with the acidic form of zeolite ETS-10 is here presented. It is shown that, in the first adsorption step (at room temperature) pi hydrogen-bonded adducts are formed between the alkyl acetylene and the zeolite hydroxy groups. These hydrogen bonded species act as precursors in the second step, where oligomerization takes place, leading to formation of carbocationic double bond conjugated systems of increasing length.

A zeolitic material containing Ti chains activated by light allows a shape-selective transformation of organic compounds; the molecules that can enter into the zeolitic cavities are protected from the light-induced processes, while the other are degraded.

Carbon monoxide and dinitrogen adsorbed, at nominally liquid‐nitrogen temperature, on Mg 2+ ‐exchanged ETS‐10 were found to form Mg 2+ ...CO and Mg 2+ ...N 2 adducts involving cations located in the main channels (12‐membered rings) of the titanosilicate molecular sieve. These adducts gave main IR absorption bands at 2190 and 2203 cm -1 for CO, and at 2336 and 2339 cm -1 for N 2 , which were assigned to the fundamental stretching mode of the diatomic molecules polarized by the electric field created by Mg 2+ ions. Corresponding adducts with Na + and K + ions, not exchanged with Mg 2+ , were also present. The results, which are relevant to the potential use of ETS‐10 as a catalyst, lend support to previous structural studies suggesting the existence of two different cation sites along the main channel of ETS‐10.

The vibrational spectroscopy of H2, N2, CO and NO adsorbed on the zeolite ferrierite is described. The spectral modifications induced by the adsorption process on the protonic form are compared with those observed on the alkaline-exchanged forms. Different environments of Brønsted sites and of alkaline counterions in ferrierite are evidenced, which differ in the local electric field associated with the cationic species. These different environments are associated with the cation locations in the channels and cavities. In particular, ions located in the 10-membered ring channels are more available for the interaction with CO, N2 and H2, while ions in the cages form weaker adducts. On passing from lithium-, to sodium- and to potassium-exchanged samples, the local fields probed by H2, N2 and CO are increasingly dependent upon the distribution of the ions in the framework. In K-ferrierite the interaction cannot be solely described in terms of 1:1 K+/B (B=N2, CO) adducts. As far as H-ferrierite is concerned, it is inferred from the observed shift of the ν(OH) mode upon interaction with H2, N2 and CO that the bridged strong acid groups show an acid strength very similar to that observed for H-ZSM-5, H-mordenite and H-Beta.

The interactions of H2O with solid H3PW12O40 have been studied by TR spectroscopy, and the results are compared with those obtained for H2O interacting with other acidic or superacidic solid systems (acidic zeolites and the perfluorosulfonic membrane H-Nafion). In fully dehydrated HPW a heterogeneous family of hydroxyls is evidenced which, by interaction with water, leads to the formation of neutral 1:1 H-bond adducts. At higher water pressures, the formation of symmetric diaquahydrogen ions, and of clusters of protonated water is also observed. The H2O...H+...OH2 symmetrical adducts are characterized by a very broad absorption in the 1400-700 cm(-1) range, which, by comparison with theoretical studies on gas-phase dusters and with experimental results obtained on H5O2+ salts, is assigned to the vO...H+...O mode. On the contrary, the IR spectra of fully dehydrated HPW do not show any absorption in this range.

In order to investigate the potentialities of an integrated IR and H-1 NMR study of the acidity of Bronsted sites, a spectroscopic study of the interaction of CD3CN (at different coverages) with zeolites H-ferrierite and H-beta is reported. The formation of H-bonded CD3CN adducts of different strength with silanols and with strong Bronsted sites is described. It is shown that an integrated spectroscopic study gives complementary information on the observed H-bond adducts. While the presence of isosbestic points in IR spectra allows a clear demonstration of the existence of equilibria between species, H-1 NMR spectra give information about dynamic adsorbate exchange phenomena.

The vibrational properties of triflic acid and of triflic acid–acetonitrile adducts adsorbed in silicalite channels are described. The spectroscopic modifications induced on triflic acid by the acid–base interaction are compared with those of the HCl/acetonitrile adducts formed in situ in the silicalite channels, and with those of the H‐ZSM‐5/acetonitrile and of the H‐Nafion/ acetonitrile systems. It is concluded that triflic acid in silicalite shows an acidity almost comparable to that of H‐ZSM‐5 and of H‐Nafion.

The vibrational properties of triflic acid and of triflic acid–acetonitrile adducts adsorbed in silicalite channels are described. The spectroscopic modifications induced on triflic acid by the acid–base interaction are compared with those of the HCl/acetonitrile adducts formed in situ in the silicalite channels, and with those of the H‐ZSM‐5/acetonitrile and of the H‐Nafion/ acetonitrile systems. It is concluded that triflic acid in silicalite shows an acidity almost comparable to that of H‐ZSM‐5 and of H‐Nafion.

The IR and H-1-MAS NMR spectroscopy of zeolite H-beta in interaction with CD3CN is described, Two families of strong Si(OH)AI Bronsted sites have been clearly distinguished: a first family, characterized by an NMR signal at 4.4 ppm and an IR peak at 3614 cm(-1) (isolated bridged hydroxys) and a second family, characterized by a broad band in the 3-7 ppm NMR range and in the 3600-3200 cm(-1) IR range, due to bridged hydroxys which are perturbed by H-bond interactions with the zeolitic framework. This last family of hydroxys form weaker adducts with acetonitrile.

The interaction of 1-butene with zeolite H-ferrierite has been studied at increasing temperatures (between 300 and 670 K) by using IR and UV-vis spectroscopies, with the aim to isolate in situ the species precursors to isobutene and high-temperature coke. The bimolecular mechanism of conversion of butene to isobutene on the fresh catalyst has been confirmed, since low branched C8 chains are observed. At 300 It, the main products of the interaction are the butene isomers 2-cis- and 2-trans-butene. At temperatures between 300 and 393 K, the presence of monoenic allylic carbocations is observed, and at temperatures between 473 and 573 K, neutral and carbocationic polyenes are present. At temperatures greater than or equal to 623 KI the polyenyl unsaturated chains cyclize to form mono- and polycyclic aromatics. These experimental features are explained on the basis of mechanisms in which the protonated intermediates (formed by protonation of butene) can produce, by further reaction with butene molecules, mainly two kinds of products: (i) polyenyl allyl carbocations (by a butene hydride abstraction) and (ii) octane carbocations (by dimerization), which then evolve (by cracking) to isobutene.

The IR spectroscopy of HCl adsorbed on silica and on silicalite and of HCl-B (B = (CH3)(2)O, (CH3CH2)(2)O, THF) adducts formed in silicalite channels at similar to 210 K is described in detail. The whole subject is divided in three parts. The first part concerns the IR study of the HCl interaction with silica and silicalite. The formation of weak H-bonded adducts between silanols and HCl molecules has been observed; the number of HCl molecules in the adducts increases with the HCl dosage. The HCl molecules adsorbed on silicalite behave as partially hindered rotators. The experimental results are supported by ab initio and molecular dynamics calculations. In the second part, the TR study of HCl-B complexes (B = (CH3)(2)O, (CH3CH2)(2)O, THF, and benzene) either adsorbed on silica or entrapped in silicalite channels is described. In the third part, the results obtained for HCl-B adducts in silicalite are compared with those obtained in cryogenic matrixes and in solution. It is inferred that the acid strength of HCl is appreciably influenced by the presence of the siliceous framework. This result allows discussion of the effect of long-distance interactions (framework effect) on the acid strength of structural Bronsted sites of zeolites.

The CH3CN···HCl hydrogen-bonded complex has been synthesized in the channels of silicalite, a purely siliceous microporous material with the MFI structure. The IR spectra of this complex show that the effect of the solid environment on the vibrational properties of CH3CN···HCl adducts is significant and that the framework enhances the strength of the hydrogen bond.

We report a study of the local copper environment in Cu-I-Y prepared by gas phase reaction of H-Y with CuCl and in Cu-II-Y prepared by conventional ion exchange with aqueous cupric salt. For the Cu-I-Y sample, the effect of the interaction with CO and NO will also been reported. XANES, W-Vis and IR (NO dosed at 77 K) techniques prove that the copper species in the prepared samples have the desired oxidation state. Reduction of Cu-I-Y with CO leads to the formation of small copper clusters well identified by EXAFS, XANES and UV-Vis spectroscopies, while interaction with NO partially oxydate Cu-I to Cu-II. For both as prepared Cu-I-Y and Cu-II-Y samples EXAFS does not observe first shell Cu-Cu bond lengths, so excluding the presence of ''so called'' Cu-dimers in zeolites prepared following our methods.

The interaction of Bronsted sites of H−β (AH) with bases B with proton affinity (PA) ranging in the 118 (N2) to 204 (NH3) kcal mol-1 interval leads to the formation of 1:1 adducts. The vibrational manifestations of these adducts change considerably as a function of the proton potential. In 1:1 neutral adducts characterized by weak-medium hydrogen bonds, the shift of the ν(AH) mode (Δν) is proportional to the shift caused by the same bases on the Si−OH (weak) Bronsted acid used as a standard. As far as the 1:1 adducts formed with ethers and tetrahydrofuran (THF; PA = 196 kcal mol-1), the situation is more complex owing to high ionicity acquired by the hydrogen bond. When stronger bases are used (pyridine, Py), the true proton transfer is observed. The ν(AH···B) modes of the medium-strong 1:1 adducts are modulated by Fermi resonances with 2δ and 2γ overtones and with internal modes of A and B moieties. A general review of the phenomenon is given. Also the spectra of the ionic 1:1 adducts formed with Py and...

It is now well accepted that the interaction of NH3 with the Bronsted acid sites of zeolites leads to the formation of NH4+ ions that are strongly H-bonded to the basic oxygens of the lattice; nevertheless, unambiguous evidence of their local siting is still lacking, In this contribution we report a detailed assignment of the IR vibrational features of NH4+ ions which reveals that mainly bidentate and tridentate species with various local symmetry are stabilized inside the cages and channels of ZSM-5, MORD, beta, SAPO-34, and Y zeolites. Tetrademate species, mainly in MORD, are also found. In addition, it is shown that Fermi-type resonance interactions lead to the appearance of several bands in the mu(NH) stretching region of the vibrational spectrum that do not, correspond to different NH oscillators. Finally, the solvation of NH4+ in the presence of excess ammonia is also investigated, and the IR manifestations, observed when reversibly adsorbed NH3 is present in the channels and cavities, are explained in terms of N2H7+ and nNH(7)(+). nNH(3) structures.