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NH3 temperature-programmed desorption (NH3 -TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx . Herein, we propose an interpretation of NH3 -TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+ , Cu+ , [CuOH]+ centers, dimeric [Cu-O-Cu]2+ , [Cu-O22- -Cu]2 species, segregated CuO nanocrystals and Bronsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3 -TPD experiment. Thus, a rigorous interpretation of the NH3 -TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers.

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Ferrierite based catalyst is expected to be used for high-temperature decomposition of N2O. The stability of the ferrierite structure and divalent cations in ferrierite in this process were analysed using XRD, SEM, FTIR, 27Al and 29 Si MAS NMR. This study provides detailed information regarding to Al removal from zeolite that is either involved in the Bronsted acid sites or formation of local cationic sites responsible for bonding divalent cations. The Al atoms, which stabilize divalent cations in cationic positions, have the potential to be resistant to prolonged exposure to the conditions of high-temperature decomposition of N2O. The presence of water led to the destruction of the iron active sites for N2O decomposition in iron ferrierite. Moreover, the negative role of residual sodium ions eventually remaining in the commercial ferrierite was proven to induce the irreversible collapse of the zeolite framework.

(27) Al 3Q MAS NMR and UV/Vis spectroscopy with bare Co(II) ions as probes of Al pairs in the zeolite framework were employed to analyze the location of framework Al atoms in the channel system of zeolite ZSM-5. Furthermore, the effect of Na(+) ions together with tetrapropylammonium cation (TPA(+)) in the ZSM-5 synthesis gel on the location of Al in the channel system was investigated. Zeolites prepared using exclusively TPA(+) as a structure-directing agent (i.e., in the absence of Na(+) ions) led to 55-90% of Al atoms located at the channel intersection, regardless the presence or absence of Al pairs [Al-O-(Si-O)2 -Al sequences in one ring] in the zeolite framework. The presence of Na(+) ions in the synthesis gel did not modify the Al location at the channel intersection (55-95% of Al atoms) and led only to changes in i) the distribution of framework Al atoms between Al pairs (decrease) and single isolated Al atoms (increase), and ii) the siting of Al in distinguishable framework tetrahedral sites.

Al-rich template-free BEA* zeolite (Si/Al 4.6) was synthesized and its structure was analyzed in comparison with the conventional H-BEA* zeolite of Si/Al 11.3 using XRD, N2 sorption, SEM, FTIR, 27Al 3Q and 29Si MAS NMR spectroscopy, and DFT calculation of the deprotonation energies. The Al-rich H-BEA* exhibited a high concentration of Bronsted and Lewis sites, both of high acid strength, although AlSiAl sequences were present in the framework. In Al-rich Fe-BEA* the exchanged Fe ions, Fe–oxo species, and Fe–oxo oligomers were identified by UV–vis spectroscopy. Cracking of n-decane, alkylation of benzene with benzyl alcohol and hydroamination of styrene with aniline to (anti)Markovnikov phenyl-[2-phenylethyl]amine over H-BEA*, and decomposition of N2O and NH3-SCR-NOx over Fe-BEA* were investigated in relation to the concentration and nature of acid and Fe-redox sites. The high concentration of Al-related active sites and the highly regular structure of Al-rich beta zeolite are directly manifested in enhanced activity compared with conventional Si-rich beta zeolite.

The heterogeneity and redox behavior of Fe-cationic species in Fe-ZSM-5 catalysts for N 2 O decomposition and NH 3 -SCR-NO x were analyzed by Mossbauer and UV–Vis spectroscopy, TPR-H 2 , and reaction kinetic measurements. Iron was introduced into ZSM-5 zeolites of similar Si/Al but with different populations of close (Al–Si–Si–Al sequences in one ring – Al pairs) and far distant (single Al in different rings) Al atoms in the zeolite framework. It has been found that Al pairs in 6MRs of the framework greatly stabilize divalence of bare Fe(II) ions and [Fe(II)–O–Fe(II)] 2+ complexes even in oxidizing atmosphere. These species were completely oxidized only with N 2 O and recognized as the most active sites in N 2 O decomposition. On the contrary, the prevailing concentration of single Al atoms resulted at comparable conditions in high population of Fe(III)-oxo species. Fe(III)-oxo species of low nuclearity with partially compensated positive charge by the zeolite framework facilitate the formation of highly active oxygen species in an O 2 -containing atmosphere and are the most active sites in NH 3 -SCR-NO x . These findings show that manipulation of the structure of Fe-cationic species can be achieved by the synthesis of zeolites with different distributions of Al atoms between Al pairs and single Al atoms in the framework. This represents a potential for tailoring of catalytic properties of Fe-zeolite based catalysts for abatement of nitrogen oxides.

Nanostructured materials typically offer enhanced physicochemical properties because of their large interfacial area. In this contribution, we present a comprehensive structural characterization of aluminosilicate hybrids with polymer-conjugated nanosized zeolites specifically grown at the organic-inorganic interface. The inorganic amorphous Al-O-Si framework is formed by alkali-activated low-temperature transformation of metakaoline, whereas simultaneous copolymerization of organic comonomers creates a secondary epoxide network covalently bound to the aluminosilicate matrix. This secondary epoxide phase not only enhances the mechanical integrity of the resulting hybrids but also introduces additional binding sites accessible for compensating negative charge on the aluminosilicate framework. This way, the polymer network initiates growth and subsequent transformation of protocrystalline short-range ordered zeolite domains that are located at the organic-inorganic interface. By applying an experimental approach based on 2D (23)Na-(23)Na double-quantum (DQ) MAS NMR spectroscopy, we discovered multiple sodium binding sites in these protocrystalline domains, in which immobilized Na(+) ions form pairs or small clusters. It is further demonstrated that these sites, the local geometry of which allows for the pairing of sodium ions, are preferentially occupied by Pb(2+) ions during the ion exchange. The proposed synthesis protocol thus allows for the preparation of a novel type of geopolymer hybrids with polymer-conjugated zeolite phases suitable for capturing and storage of metal cations. The demonstrated (23)Na-(23)Na DQ MAS NMR combined with DFT calculations represents a suitable approach for understanding the role of Na(+) ions in aluminositicate solids and related inorganic-organic hybrids, particularly their specific arrangement and clustering at interfacial areas.

Siting of Al atoms in the framework T sites, in zeolite rings and channel/cavity system, and the distribution of Al atoms between single Al atoms and close Al atoms in various Al-O-(Si-O)n-Al sequences in Si-rich zeolites represent key parameters controlling properties of counter ion species. Framework Al siting and distribution is not random or controlled by simple rules and depends on the conditions of the zeolite synthesis. Al in Al-O-(Si-O)2-Al in one 6-MR and single Al atoms predominate in Si-rich zeolites and their population can be varied to a large extent. The siting and distribution of framework Al atoms dramatically affect catalytic activity/selectivity both of protonic and transition metal ion-containing zeolite catalysts.

New type of redox heterogeneous catalysts based on geopolymer aluminosilicate materials was developed and their catalytic properties have been demonstrated on industrially important reactions. Geopolymers can be regarded as amorphous analogues of zeolitic materials (three dimensional network of SiO 4 and AlO 4 tetrahedra with negative charge of the network balanced by extra-framework cations, variability in chemical composition, ion exchange properties, presence of rings forming cationic sites for bare cations), but possessing some advantages as network formation at ambient or low temperatures, mesoporosity and low cost preparation. It is shown that the geopolymer network enables incorporation of transition metal ions as active centres for catalytic reactions. The catalytic activity of geopolymer-based catalysts with Fe, Co and Cu metal ions in extra-network sites and Pt species is demonstrated on the selective catalytic reduction of nitrogen oxides by ammonia and the total oxidation of volatile hydrocarbons. These findings open a potential for synthesis of new types of robust catalysts for heterogeneously catalysed reactions.

The structure, properties and activity of the counter Co, Cu and Fe ion species depending on the distribution of aluminium atoms in the framework between Al pairs of Al–O–(Si–O)2–Al sequences in one ring and isolated Al atoms (Al–O–(Si–O)n>2–Al sequences) in two rings are analyzed. The effect of the Al distribution on the activity of metal ion species is investigated for reactions of technology importance, i.e. SCR-NOx by propane, and decomposition of NO and N2O under real conditions of NOx streams. Zeolite samples of BEA, MFI and FER structures, of similar composition for each topology, but with basically different distribution of Al atoms in the framework, were either selected from commercial samples or prepared by the developed synthesis. The concentration of Al pairs and isolated Al atoms in the framework was determined by the combination of 29Si MAS NMR and quantitative analysis of the Vis spectra of dehydrated Co-zeolites with Co(II) ions exchanged to a maximum degree. The structure and reactivity of the metal sites was described by UV–Vis, FTIR of skeletal vibrations and adsorbed NO, TPR-H2 and reactions of C3H8-SCR-NOx/H2O, and NO and N2O decomposition. It is concluded that the local negative framework charge, originated from Al pairs and isolated Al atoms, constitutes a decisive parameter controlling the structure and reactivity of the counter metal ion species. The bare Co(II), Cu(II) and Fe(II) ions are balanced by Al pairs, while Co-oxo and Cu-oxo or Cu(I) species are adjacent to isolated Al atoms. The Cu(I) ions in vicinity of isolated Al atoms in Cu-MFI zeolites are the most active sites in NO decomposition. Co-oxo species attached to isolated Al atoms in Co-BEA zeolites, in contrast to bare Co(II) ions, exhibit high activity in C3H8-SCR-NOx/H2O in the presence of water vapor. N2O decomposition to elements over Fe-FER requires two Fe ions at a defined distance of β cationic sites, with each Fe(II) cation charge-balanced by an Al pair.

New heterogeneous catalysts for ring opening metathesis polymerization (ROMP) have been prepared by immobilization of RuCl2(p-cymene)(PCy3) (Cy = cyclohexyl) on silica and siliceous mesoporous molecular sieves SBA-15 and MCM-41. Activity of these catalysts was investigated in ROMP of norbornene (NBE) and its derivatives (dicyclopentadiene, 5-norbornene-2-yl acetate). High molecular weight polymers (Mw up to 400 000) were prepared in yields up to 80% using catalysts based on mesoporous sieves. In contrast, with catalyst based on conventional silica the yield did not exceed 28% (ROMP of NBE). Filtration test proved that the catalytic activity was bound to the solid phase. Catalysts could be easily separated from the reaction mixture in contrast to the corresponding homogeneous system. Therefore, polymers with reduced amounts of catalyst residues were obtained.

The N 2 O decomposition over Fe-ferrierite, Fe-beta, and Fe-ZSM-5 has been recently studied [K. Jisa, J. Novakova, M. Schwarze, A. Vondrova, S. Sklenak, Z. Sobalik, J. Catal. 262 (2009) 27] and a superior activity of Fe-ferrierite with respect to Fe-beta and Fe-ZSM-5 has been shown. In this study, we investigated (1) plausible active sites for the N 2 O decomposition over Fe-ferrierite and (2) the origin of the distinct reactivity of Fe-ferrierite, Fe-ZSM-5 and Fe-beta employing a combined theoretical (periodic DFT) and experimental (UV–vis–NIR spectroscopy, IR spectroscopy, 29 Si MAS NMR spectroscopy and catalytic batch experiments) approach. We evidenced that two Fe(II) cations accommodated in two adjacent six-membered rings in the eight-membered ring channel ( β sites) of Fe-ferrierite (the calculated Fe–Fe distance is 7.4 A) form the active site responsible for the superior activity of this catalyst in the N 2 O decomposition in the absence of NO. Similar structures can be formed in Fe-beta. However, the probability of their formation is very low. For Fe-ZSM-5, the geometrical arrangement of the cationic positions is far from that in Fe-ferrierite and it is not suitable for the N 2 O decomposition. Therefore, the predicted order of the activity of the Fe(II) exchanged zeolites agrees with our experimental findings and it is: Fe-ferrierite ≫ Fe-beta > Fe-ZSM-5. We further showed that the accommodation of divalent cations in rings forming cationic sites can lead to significant rearrangements of the local structures of the zeolite framework, and therefore, the precise structure of sites binding a divalent cation cannot be derived from results of X-ray diffraction experiments, but can be inferred from theoretical calculations.

The role of the distribution of aluminium in the framework of beta zeolites in the formation of various types of counter Co species of different activity in C3H8–SCR–NO in the absence/presence of 10% water vapour was investigated. Different concentrations of Al atoms in the Al–O–(Si–O)2–Al sequences in one ring (Al pairs) and isolated Al atoms in Al–O–(Si–O)n>2–Al sequences located in two framework rings of parent BEA* zeolites were obtained by variation of the zeolite synthesis and by post-synthesis dealumination. Al atoms in the framework and their distribution were characterized by the combination of 29Si MAS NMR of the parent BEA* zeolites and UV–Vis spectroscopy of the maximum-Co(II)-loaded BEA*. The concentration of Al pairs corresponded to the concentration of bare Co(II) ions in dehydrated maximum exchanged-Co(II)-BEA* calculated from the Vis spectra. Co-BEA* zeolites prepared by ion exchange from Co nitrate solution contained bare Co(II) ions balanced by Al pairs, which were formed preferentially, and “monovalent” Co-oxo species balanced by the isolated Al atoms. The relative concentration of bare Co(II) ions and Co-oxo species depends on the degree of Co(II) ion exchange and the concentration of Al pairs and isolated Al atoms in the zeolite framework. Superior activity was found with the counter Co-oxo species balancing isolated Al atoms, surviving even in wet (10% H2O) NOx streams. The bare Co(II) ions were active in dry NOx streams, but their activity was negligible in wet NOx streams. A highly active catalyst (more than twice than the other Co-BEA*) can be prepared by using a BEA zeolite containing a predominant concentration of isolated Al atoms in the framework.

New hybrid catalysts for olefin metathesis were prepared by immobilization of Hoveyda–Grubbs type Ru alkylidenes on a siliceous SBA-15 support via exchange of chloro ligands for substituted carboxylates. Catalysts proved a high activity in ring closing metathesis of 1,7-octadiene and diethyl diallylmalonate, reusability and low Ru leaching. In Ring Opening Metathesis Polymerization of norbornene and cyclooctene, SBA-15 supported catalyst gave higher yields of high-molecular-weight polymers than corresponding catalyst with conventional silica support.

We employed 29Si and 27Al (3Q) magic-angle spinning (MAS) NMR spectroscopy and density functional theory/molecular mechanics (DFT/MM) calculations to investigate the effect of Al/Si substitutions and the presence of silanol nests on the 29Si and 27Al NMR parameters as well as the local geometry of SiO4 and AlO4− tetrahedra of the nearest and next-nearest neighboring Si and Al atoms. The silicon-rich zeolite of the chabazite structure (Si/Al 38) was chosen for this study as a representative model of silicon-rich zeolites since it exhibits a low number of distinguishable T sites. Our computational results show the following: (I) Al atoms can occupy three different crystallographic T sites in the framework of chabazite (Si/Al 38). This result is in agreement with two observed 27Al NMR resonances. (II) An Al/Si substitution causes a downshift of the 29Si chemical shift of the nearest neighboring Si atoms (Al−O−Si) by 4−11 ppm. (III) The effect of a more distant Al/Si substitution (Al−O−Si−O−Si) is significant...

The effect of the presence of Al−O−Si−O−Al and Al−O−Si−O−Si−O−Al sequences in the ZSM-5 zeolite framework on the local geometry of AlO4− tetrahedra and the 27Al NMR parameters was investigated employing 27Al 3Q MAS NMR spectroscopy and DFT/MM calculations. The presence of an Al atom as a next-nearest (Al−O−Si−O−Al) and next-next-nearest (Al−O−Si−O−Si−O−Al) neighbor can significantly affect both the local geometry of AlO4− tetrahedra as well as 27Al NMR isotropic chemical shift (up to 4 ppm). There is no systematic contribution of Al in Al−O−Si−O−Al or Al−O−(Si−O)2−Al chains to the 27Al isotropic chemical shift, and not even the direction can be predicted without explicit DFT calculations. Our combined experimental and computational approach employing 27Al (3Q) MAS NMR spectroscopy supported by DFT/MM calculations (Sklenak, S.; Dědecek, J.; Li, C.; Wichterlova, B.; Gabova, V.; Sierka, M.; Sauer, J. Angew. Chem., Int. Ed. 2007, 46, 7286.) can be employed only for ZSM-5 samples having a low or negligible con...

The Al siting in the ZSM-5 zeolite was investigated by (27)Al 3Q MAS NMR spectroscopy and QM/MM calculations. It was found that the occupation of the framework T-sites by Al and the concentration of Al in these T-sites are neither random nor controlled by a simple rule. They both depend on the conditions of the zeolite synthesis. At least 12 out of the 24 distinguishable framework T-sites of ZSM-5 are occupied by Al in the set of the investigated zeolite samples. A partial identification of the Al sites is possible. The calculated (27)Al NMR shielding values were converted to (27)Al isotropic chemical shifts using the experimental isotropic chemical shift of 60.0 ppm referenced to the aqueous solution of Al(NO(3))(3) and the corresponding calculated NMR shielding of 490.0 ppm of a silicon rich (Si/Al 38) chabazite structure zeolite as a secondary internal standard. The observed (27)Al isotropic chemical shifts of 50.0 and 54.7 ppm correspond to Al atoms in the T20 and T6 sites, respectively. The pair of measured isotropic chemical shifts of 52.9 and 53.7 ppm can be assigned to the T4, T8 pair. At the low-shielding end, two assignments are plausible. The smallest deviations between the calculated and observed isotropic chemical shifts are reached for the assignment as follows: T24 (64.8 ppm) is not occupied in the samples and that the observed isotropic chemical shifts 63.6, 62.8, and 60.0 ppm belong to T1, T17, and T7, respectively. It follows then that T-sites T12 (60.8 ppm), T3 (61.7 ppm), and T18 (62.0 ppm) are most likely not occupied by Al in our ZSM-5 samples. If we assume that the calculated isotropic chemical shifts are systematically larger than the observed ones then we can assign the largest observed isotropic chemical shifts of 63.6 and 62.8 ppm to the least shielded T24 and T1 sites, respectively, and 60.0 ppm to T12. Then the sites T3 (61.7 ppm), T18 (62.0 ppm), and T17 (62.5 ppm) would be unoccupied by Al in our ZSM-5 samples. It was further shown that there is no simple linear relationship between the observed (27)Al isotropic chemical shifts and the average Al-O-Si angles.

The Al siting in the silicon rich ZSM-22 and Theta-1 zeolites of the TON structure was investigated analyzing already published 27Al 3Q MAS NMR experimental data using QM/MM calculations. The results of our computations show that Al atoms can be located in 6 framework T positions because the two eightfold sites (T1 and T2) split into four fourfold T sites after an Al/Si substitution. The observed resonance at 55.5 ppm corresponds to the T4 site which is predominantly occupied by Al. This site is not located on the surface of the TON ten-membered ring channel and thus the protonic sites related with the majority of Al atoms in the TON structure exhibit a significantly limited reaction space. The 27Al NMR signals centered at 57.6 and 58.7 ppm correspond to either the T2 and T3 sites, respectively, or only to T2. The T2 and T3 sites accommodate some 40% and up to 10%, respectively, of Al while the T1 site is unoccupied by Al. Isotropic shifts of 61.1 and 61.6 ppm were calculated for Al atoms located in the T1-1 and T1-2 sites, respectively. The effect of a silanol "nest" as a next-next-nearest neighbor on the 27Al isotropic chemical shift of Al located in the T4 site is calculated to be less than 1 ppm.

The effect of the inner particle structure on Li insertion activity and electronic structure of the nano-crystalline Li–Ti–O spinels was studied on materials prepared by solid state and solvothermal synthesis. The high temperature prepared materials of composition corresponding to Li 4 Ti 5 O 12 feature particles with characteristic size of ca. 200 nm with randomly distributed defects. The products of solvothermal synthesis with composition Li 1.1 Ti 1.9 O 4+ δ , feature cubic particles of characteristic dimension of ca. 50 nm; the characteristic particle size differs from that of the coherent domain determined by X-ray diffraction. The reduction of the solvothermal and high temperature synthesized nano-crystalline spinels in Li containing solutions leads according to 6 Li MAS NMR spectra to Li insertion into tetrahedral 8b and octahedral 16c position, respectively. Additional broad NMR signal attributable to a Knight shift was observed in spectra of partially reduced high temperature spinels. In the case of solvothermal spinels is the Knight shift signal less pronounced and appears only in spectra of samples in which the phase transition occurs on the local level. The UV–vis–NIR spectra of the partially reduced Li–Ti–O spinel samples correspond to expected semiconductor character of Li–Ti–O spinels. Both types of materials are characterized by band gap of 3.8 eV (high temperature spinel) and 3.5 eV (solvothermal material). Partial reduction accompanied with Li insertion causes additional optical transition in the visible to near infrared region, which can be attributed to formation of trivalent Ti, character of which changes with degree of reduction. The behavior observed for partially reduced high temperature spinels is similar to that reported for TiO 2 (anatase). The spectral behavior of the partially reduced solvothermal spinels is more complex and reflects suppressed phase transition.

Decane-SCR-NOx in the presence of water vapor and NO decomposition were investigated over Cu ions exchanged in ZSM-5 zeolites with various Si/Al and Al distribution. The local environment of the Cu ions in cationic sites was characterized by the combination of 29Si MAS NMR, Vis–NIR spectroscopy of Cu(II) ions, Cu(I) Vis emission spectroscopy and UV–Vis spectroscopy of Co(II) ions as probes for the presence of Al pairs in the framework. The Cu(II) ions coordinated to four framework oxygens of the α- or β-type cationic sites containing Al-O-(Si-O)2-Al sequences represent the most active sites in decane-SCR-NOx. On contrary, the Cu(I) ions coordinated to two or three framework oxygens and located at the channel intersection adjacent to the single Al atoms in the α- or β-site control predominantly reaction of NO decomposition.

The effect of framework aluminum content and local density on the NOx reduction with decane under lean burn conditions, i.e. in high excess of oxygen and water vapor (12%) over Cu-ZSM-5 zeolites with various Cu/Al and Si/Al ratios was investigated. The concentration of “Al pairs” located in one ring and balanced by divalent cations was estimated using divalent cobalt ions as probes. The portion of Cu ions located in vicinity of “Al pairs” or adjacent to a single framework AlO2− entity was monitored by vis–NIR spectra of Cu2+ ions. The most active and stable Cu ions in C10H22-SCR-NOx under lean burn conditions appeared to be those located in vicinity of two Al atoms in one ring coordinated the cation.

Three procedures were employed for the preparation of Fe-zeolites with ZSM-5 (MFI), ferrierite (FER) and beta (BEA) structures: ion exchange from FeCl3 solution in acetyl acetonate and solid-state ion exchange from FeCl2 using an oxygen or nitrogen stream. A combination of UV–VIS–NIR spectra, IR spectra of skeletal vibrations and of adsorbed NO, as well as voltammetry provided information on the type of Fe species introduced. Single Fe(III) ion complexes (Fe(H2O)6−xOHx) in hydrated zeolites were reflected in the charge-transfer bands at 33 100, 37 300 and 45 600 cm−1. The single Fe(II) ions at cationic sites in evacuated zeolites yielded (through perturbation of framework T–O bonds) characteristic bands (910–950 cm−1) in the region of the skeletal window. These Fe(II) ions with adsorbed NO were also reflected in vibrations at 1880 cm−1. Dinuclear Fe–oxo complexes yielded the Vis band at 28 200 cm−1. Voltammetry indicated the presence of Fe oxides (hematite) through the reduction peak at −0.7 V. Such oxide-like species were also reflected in the absorption edge at 19 800 cm−1, and a doublet at 11 000 and 11 800 cm−1 in the Vis spectra. Fe(II)–NO vibrations at 1840, 1810 and 1760 cm−1 belonged to the undefined exposed Fe cations, probably originating from supported oxides. Using an ion exchange procedure, employing FeCl3 in acetyl acetonate, exclusively Fe ions at cationic sites could be introduced at low concentrations (Fe/Al 0.2; all three types of Fe species, single Fe ions, dinuclear Fe–oxo complexes and Fe oxides were formed.

CoNH4-beta and CoH-beta zeolites, with various Co loadings, were prepared by Co ion exchange into NH4- and H-beta parent zeolites, from which the template was removed by calcination of the as-synthesized beta zeolite in a stream of ammonia and oxygen, respectively. It has been found that the CoNH4-beta zeolites in contrast to CoH-beta zeolites exhibit high and stable activity in selective catalytic reduction of NOx with propane in the presence of water vapor (10%). To analyze the reasons for the exception activity of CoNH4-beta zeolites, both zeolite preparations were studied with respect to the state and location of aluminum, character of Al-related acid sites, and Co ion-exchange capacity by means of FTIR spectra of OH groups of dehydrated zeolites and those after adsorption of d3-acetonitrile, and by 29Si, 27Al, and 27Al 3Q MAS NMR spectra. The procedure of template removal using ammonia provides a charge balance of the framework by NH4+ ions and thus preserves framework TO bonds from perturbation and dealumination. The Co-beta zeolite with high concentrations of regularly Td coordinated Al atoms in the framework (CoNH4-BEA) contains besides the “bare” Co ions the Co ion species adjacent to a single framework Al atom, which moreover, do not adsorb base molecules. These Co species are expected to bear extraframework oxygen(s), and they are suggested to be responsible for the high and stable SCR-NOx activity at a high content of water vapor in the reactant stream, as their concentration correlates with the C3H8SCR-NOx activity under water vapor presence.

Zeolites having MFI, FER and *BEA topology were loaded with iron using solid state cation exchange method. The Fe:Al atomic ratio was 1:4. The zeolites were characterized using nitrogen adsorption, FTIR and DR UV–Vis–NIR spectroscopy. The catalytic activity in NO oxidation and the occurrence of NO x adsorption was determined in a fixed-bed mini reactor using gas mixtures containing oxygen and water in addition to NO and NO2 and temperatures of 200–350 °C. Under these reaction conditions, the NO x adsorption capacity of these iron zeolites was negligible. The kinetic data could be fitted with a LHHW rate expression assuming a surface reaction between adsorbed NO and adsorbed O2. The kinetic analysis revealed the occurrence of strong reaction inhibition by adsorbed NO2. FER and MFI zeolites were more active than *BEA type zeolite. MFI zeolite is most active but suffers most from NO2 inhibition of the reaction rate. FTIR and UV–Vis spectra suggest that isolated Fe3+ cations and binuclear Fe3+ complexes are active NO oxidation sites. Compared to the isolated Fe3+ species, the binuclear complexes abundantly present in the MFI zeolite seem to be most sensitive to poisoning by NO2.

A highly active silver/alumina catalyst for continuous reduction of NO to nitrogen with octane under lean conditions was prepared. The effect of impregnation time and precursor concentration on the catalyst activity was investigated. The catalyst was characterized by means of XRF, H2-TPR, and UV-Vis to correlate recorded results with different preparation methods. UV-Vis measurements indicated that the highest and most stable activity is obtained with Ag/alumina exhibiting predominantly monoatomically dispersed silver.

Free ferric oxides of a red bed series were analyzed by rock-magnetic techniques (IRM component analysis) and by two less traditional methods: visible spectroscopy and voltammetry. All three methods have low limits of detection, making them suited for this type of analysis. The red bed samples studied contained clay minerals, quartz, and calcium carbonate as major constituents. Free Fe oxides occurred at a concentration of 0.3–2.1%, i.e. in the majority of the samples below the detection limit of X-ray powder diffraction. The combination of the employed analytical techniques enabled to characterize the mineralogy of free ferric oxides and to estimate the ratio of goethite and to hematite. This ratio changes substantially within the section that probably indicates paleoclimatic changes.

The effect of the framework Al content and synthesis procedure on the number of framework Al atoms located on the surface of (Al)MCM-41 channels and the distribution of the Al atoms between single Al atoms and various Al-O-(SiO)1,2-Al species was investigated. The total number of accessible framework Al atoms on the channel surface was obtained from the ion exchange capacity for Na+ ions and pyridine adsorption. The number of Al pairs on the surface and their distribution between different local arrangements of the channel surface was estimated using VIS spectroscopy of Co2+ ions. At low framework Al contents, Al atoms occupy only accessible T sites on the surface of the channel walls. In aluminium-rich (Al)MCM-41, a significant part of Al atoms is incorporated inside the channel walls and these Al atoms do not form cationic sites. Al atoms on the wall surface preferentially form Al-O-(SiO)1,2-Al sequences, enabling siting of divalent cations. Different synthesis procedures resulted in differences in Al distribution. The channel surface of the (Al)MCM-41 is formed by two regular local structures containing two types of deformed six-membered rings with Al-O-(SiO)1,2-Al sequences forming cationic sites.

Coordination and bonding of Co ions at cationic sites in zeolites of ZSM-5, FER, and MOR structures were investigated by X-ray absorption and by UV−Vis and FTIR spectroscopy. Co(II) ions, exchanged under conditions in which no hydrolysis took place, were coordinated exclusively to framework oxygen atoms; no Co−O−Co bridging structures were found. Three types of Co ion coordination and three types of perturbation of the framework T−O bonds at the corresponding cationic sites were distinguished by Vis spectra of the Co(II) ions and IR spectra of skeletal vibrations. EXAFS and FTIR showed that Co ion bonding at exchangeable sites of pentasil ring zeolites requires substantial deformation of the adjacent framework T−O bonds to attain coordination to four or three framework oxygens with Co−O bond distances of 1.99 to 2.06 A. Such coordination is possible only with certain cationic site structures α, β, and γ, which are very similar for ZSM-5, ferrierite, and mordenite. Slight differences in these local framewo...

The occurrence of “Al pairs” in the framework of ZSM-5 and their spatial distribution in zeolites was estimated by using exchanged Co2+ ions as probes for “Al pairs”. The visible spectra of Co2+ ions were employed to monitor the distribution of Co2+ ions, and thus “Al pairs”, among the individual cationic sites, i.e. local framework arrangements at defined positions in the zeolite channels. The effects of concentration of aluminum in the framework and conditions of zeolite synthesis on the presence of “Al pairs” and their spatial distribution in the ZSM-5 framework were investigated. It has been shown that the distribution of Al atoms in the framework is not controlled by statistic rules, but depends on the conditions of zeolite synthesis and aluminum concentration in the framework.

Selective catalytic reduction of NO with methane (CH4-SCR) in an excess of oxygen over Co ions located in ZSM-5 of various Si/Al composition and in ferrierite, mordenite, chabazite and beta zeolite was investigated. From the comparison of the dependence of the TOF values per Co ion for NO conversion to N2 and Co ions distribution among the cationic sites on total Co ion concentration, the catalytic activity of the individual Co ions was estimated. The α-type Co2+ ions, located in the main channel of mordenite and ferrierite and coordinated above the rectangle of four framework oxygens of the channel wall exhibit the highest activity in these zeolites. On the other hand, the β-type Co2+ ions coordinated in the plane of four oxygens of the deformed six-member ring located in the channel intersection of ZSM-5 and in channels of beta zeolite control the activity of these Co zeolites. The sequence of activity of Co2+ ions in CH4-SCR of NO was FER Coα>ZSM-5 Coβ>BEA Coβ≈ZSM-5 Coα≫FER Coβ≈MOR Coα≫CHA Co≈MOR Coβ. A correlation between the activity of the individual Co ions in CH4-SCR of NO and a distance between the cationic sites was observed.

Zeolites are highly important heterogeneous catalysts. Besides Bronsted SiOHAl acid sites, also framework AlFR Lewis acid sites are often found in their H-forms. The formation of AlFR Lewis sites in zeolites is a key issue regarding their selectivity in acid-catalyzed reactions. The local structures of AlFR Lewis sites in dehydrated zeolites and their precursors--"perturbed" AlFR atoms in hydrated zeolites--were studied by high-resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)3AlOH groups and are characterized by a broad (27)Al NMR resonance (δi = 59-62 ppm, CQ = 5 MHz, and η = 0.3-0.4) with a shoulder at 40 ppm in the (27)Al MAS NMR spectrum. Dehydroxylation of (SiO)3AlOH occurs at mild temperatures and leads to the formation of AlFR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)3Al Lewis sites exhibit an extremely broad (27)Al NMR resonance (δi ≈ 67 ppm, CQ ≈ 20 MHz, and η ≈ 0.1).

Catalytic activity in NO decomposition of Cu-Beta zeolites with different Cu/Al/Si composition, diffuse reflectance UV–vis–NIR spectra of Cu ions of hydrated Cu-Beta zeolites, and concentration of Bronsted and Lewis sites in parent Beta zeolites, determined by quantitative analysis of FTIR spectra of adsorbed d 3 -acetonitrile, were investigated. Cu-Beta zeolites exhibit high and stable activity in NO decomposition in the temperature range 580–750 K and Si/Al ratio 12.7–42. Strong dependence of activity in NO decomposition per Cu ion (TOF) on Cu/Al loading indicates the presence of three Cu species in Cu-Beta zeolites. Cu ions incorporated at low Cu loading are balanced by two framework Al atoms and are inactive in NO decomposition. Species responsible for NO decomposition are formed at medium Cu loading and represent Cu ions balanced by single-framework Al atoms. At high Cu loading, a new type of inactive, noncationic Cu species (small clusters of Cu 2 O) is formed. Bronsted and Lewis sites themselves do not contribute to the catalytic activity of Cu-Beta zeolites in NO decomposition. However, the presence of Lewis sites in the parent zeolites is connected with the occurrence of the framework sites containing two close Al atoms and bonding the Cu ions which are not active in NO decomposition. A comparison of Cu ion activity in Beta and ZSM-5 is discussed.

The effect of framework Al content on the number of framework Al atoms on the surface of (Al)MCM-41 channels and the distribution of these Al atoms among single Al atoms and various Al–Si–Al and Al–Si–Si–Al pairs was investigated. The number of framework Al atoms on the wall surface was characterized by the ion exchange capacity for Na+ ions, number of Al pairs on the surface by exchange capacity for Co2+ ions. Two different geometrical arrangements of Al pairs were characterized by VIS spectroscopy of bare Co2+ ions. At low framework Al content, Al atoms occupy only T sites on the surface of the channels. In aluminum rich (Al)MCM-41, Al atoms are incorporated also into the inner volume of the channel walls and at Si/Al∼11 only about 50% of Al atoms are on the channels surface. Al atoms on the wall surface preferentially form Al–Si1,2–Al pairs, enabling siting of divalent cations. Number of single Al atoms increases with framework Al content and overcome 50% of surface Al atoms for Si/Al∼11. The Al–Si1,2–Al pairs are present in two cationic sites and also the distribution of Al pairs into these sites depends on the framework Al content.

The uniformity and ordering of the surface of (Al)MCM-41 channel walls was investigated employing bare Co(II) ions as probes. VIS spectra of Co(II) ions evidenced the presence of two types of uniform cationic sites in dehydrated Co-(Al)MCM-41 in a wide range of Si/Al/Co chemical composition (Si/Al = 11-76, Co/Al = 0.08-0.44). These cationic sites represent centers of two types of uniform domains, containing in minimum 18 surface T atoms, present on the surface of the channel walls of (Al)MCM-41. These domains represent majority of the inner surface of the (Al)MCM-41 molecular sieve.

Ion-exchanged Co ions and nitrosyl complexes in CoH– and CoNaK–ferrierites with a Co loading up to Co/Al=0.4 were investigated by diffuse reflectance UV–Vis–NIR, FTIR in the region of the skeletal and NO vibrations, and EXAFS measurements. Co(II) ion coordination, cation-induced perturbations of the framework T–O bonds of the hosted cationic sites, and Co–O distances of three typical ion-exchanged α-, β-, and γ-type Co ions in ferrierite are described. The α-type Co ions, coordinated to the rectangle of framework oxygens in the wall of the main ten-member ring channel, exhibit an open coordination sphere, weak bonding to the framework oxygens, and a high tendency to form dinitrosyl complexes upon NO adsorption. The β-type Co ions, the most populated ones in the whole concentration range, are coordinated to four framework oxygens of the deformed six-member ring of the ferrierite cavity at a distance of 1.99 A. They exhibit medium-strength bonding to framework oxygens and, compared to the α-type Co ions, a substantially suppressed ability to bind dinitrosyls. The γ-type Co ions provide the highest perturbation of the hosted framework T–O bonds and thus the strongest bonding to framework oxygens attributed to the “boat-shaped” site of ferrierite. The tendency of the Co ions to relocalize under severe thermal/hydrothermal calcination of Co–ferrierite increased in the sequence γ

Selective catalytic reduction of NO with methane (CH 4 -SCR) in an excess of oxygen was investigated over CoH–, CoNa–, CoNaK–, CoBa–, and Co x O y –Co-zeolites of ZSM-5, ferrierite, and mordenite structures. The exchanged Co ions have been shown to exhibit activity in CH 4 -SCR of NO, while protons or oxide-like Co species in Co–zeolites contribute to the CH 4 -SCR activity mostly by enhancement of the oxidation of NO to NO 2 . The sequence of Co–zeolites activity in CH 4 -SCR of NO (per zeolite weight) was Co–ZSM-5≅Co–ferrierite⪢Co–mordenite for the highest Co loadings at Si/Al of 12, 8.4, and 9.2, but for the average Co ion site in the zeolite (in terms of turnover frequency, TOF, values) it was Co–ZSM-5>Co–ferrierite⪢Co–mordenite. From a comparison of the dependence of TOF values for NO conversion to N 2 per Co ion and of the relative concentrations of the exchanged α-, β-, and γ-type Co ions (determined from quantitative analysis of the characteristic Co(II) Vis spectra) on the total Co concentration, the most active Co sites were estimated. The α-type Co ions, bound to framework oxygens of the wall of the main channel of mordenite and ferrierite, are the most active among the Co ions in these zeolites. On the other hand, in ZSM-5 the β-type Co ions, coordinated to the deformed six-membered ring at the intersection of straight and sinusoidal channels possess the highest activity. The main factors contributing to the individual Co ions' activity are suggested to be cation location in the inner zeolite volume, coordination to the framework, and distances between the Co ions.

Diffuse reflectance electronic spectra have been utilized to investigate the local geometry of cobalt centers substituted in the three-dimensional framework of CoAPO-5 and -11 molecular sieves. Structural changes induced by calcination in an oxidative atmosphere, evacuation and hydrogen treatment, as well as by adsorption of amines and water are discussed in terms of the steric conditions of cobalt incorporation in the aluminophosphate matrix. We suggest a template–framework interaction between the framework cobalt centers and neutral amine-type templates as an alternative stabilizing effect in the as-synthesized samples. Spectral changes observed after calcination in oxygen are interpreted as distortion-induced charge transfer effects without oxidation of the divalent cobalt ions. Formation of oxygen vacancies in the close vicinity of the cobalt sites is proposed to explain the adsorption properties of the framework cobalt centers.

Siting of the Co 2+ ions in dehydrated Co–ZSM-5 is suggested based on a VIS optical study, the MFI topology and parallelism between the spectra of the Co 2+ ions and local framework structures in ZSM-5, mordenite and ferrierite. The proposed Co 2+ ion sites represent a first attempt to describe the cationic sites for transition metal ions in the MFI structure. Co ions exchanged in CoMeH–ZSM-5 zeolites (Me=Na + , K + , Ca 2+ , Ba 2+ ) with compositions of Co 2+ /Al molar ratios up to 0.5 and Si/Al molar ratios between 12 and 22 have been studied by diffuse reflectance VIS spectroscopy. Three characteristic spectral components, α, β and γ, i.e. a single band at 15 100 cm −1 (α), four bands at 16 000, 17 150, 18 600 and 21 200 cm −1 (β), and a doublet at 20 100 and 22 000 cm −1 (γ), have been ascribed to three Co ion types located at different cationic sites. The α-type Co ions are suggested to be coordinated to four oxygen atoms of the straight channel wall. The β-site is located at the deformed six-member ring at the intersection of straight and sinusoidal channels. The β-type Co ions predominate at all the Co loadings in Co–ZSM-5. The Co ions at ‘boat-shaped’ γ-site are located in the sinusoidal channel, and they represent a minor concentration of the Co ions in ZSM-5. A distribution of Co ions among those cationic sites was established.

NO decomposition over Cu-loaded molecular sieves of chabazite structure with different framework negative charge density was investigated. Cu-ZnAlPO-34 with framework charge density (Al + P)/Zn = 15 exhibited high and stable catalytic activity in NO decomposition while Cu-chabazite with Si/Al = 2.7 was inactive. This evidences that the number of aluminum atoms balancing Cu ions in cationic sites controls the catalytic activity of Cu ion. Ions balanced by single framework aluminum atoms exhibit high activity in NO decomposition while ions balanced by two framework aluminum atoms are inactive. Topology of cationic sites is not the limiting parameter for NO decomposition over Cu ions located in molecular sieves.

Cu+ emission spectra of Cu2+ ion exchanged and reduced natural and synthetic CuNa-, CuCa-, CuCs- and CuBa-chabasites were used to identify cationic sites of the Cu+ luminescence centres in this zeolite. Two different Cu+ emission bands with maxima at 500 and 540 nm were observed; the emission at 540 nm prevailed at higher Cu loadings. The concentration dependence of the intensity of 500 and 540 nm emission bands indicated that both bands correspond to the single Cu+ ions. The effect of the presence of co-cations in Cu-chabasites on the luminescence spectra was employed for the identification of the cationic sites corresponding to the individual emission bands. Cu+ emission at 500 nm reflects the Cu+ ion located at the cationic site in the eight-membered ring. Cu+ emission at 540 nm is attributed to the Cu+ ion coordinated to three oxygen atoms of the regular six-membered ring. The Cu+ ion in this site is suggested to be located above the six-ring plane, similar to the siting of Cu+ ions in Y zeolite.

VIS−NIR diffuse reflectance spectra of Co2+H−mordenites and co-cation (K, Cs, Ca, Ba)-containing Co−mordenites with Co/Al varying from 0.0015 to 0.35 were studied. Three different sites-coordinations of the Co2+ ions in dehydrated mordenite were found from interpretation of optical spectra, and the populations of these sites depending on Co-ion concentration were established. The assignment of characteristic absorption bands in the VIS spectrum to the Co2+ ions located at individual cationic sites was based on knowledge of siting of K, Cs, Ca, and Ba ions in mordenite structure. Co2+ ions are located in sites A and C of the mordenite pocket and in site E of the main channel. In site A, occupied preferentially in CoH−mordenite, the Co2+ ion is coordinated to six framework oxygens of the twisted eight-ring. The number of coordinated framework oxygens and detail geometry of the “boat-shape” site C is not known. This site is occupied only at high Co loading. Site E, consisted of four oxygens forming a rectang...

Cu+ ions, with characteristic emission at 540 nm, have been considered to be responsible for the high activity of Cu-ZSM-5 in NO decomposition. However, two types of Cu+ ions located in different structures, i.e. in ZSM-5 and Y, exhibit the 540 nm emission, but the Cu ions in Y zeolite do not exhibit such a unique activity in NO decomposition. Therefore, Cu+ emission spectra and luminescence decay of the Cu2+ ion exchanged and reduced in CuH-ZSM-5, CuH-, CuRb-, CuCs- and CuBa-mordenites and Cu-Y zeolites were used to identify cationic sites corresponding to the Cu+ luminescence centres in these zeolites emitting at 540 nm. The Cu+ ions with a single luminescence decay correspond to those with C3v symmetry in Y zeolite, while the Cu+ ions possessing a double-exponential decay represent Cu+ cationic sites in ZSM-5 and mordenite, different from that described for Cu-Y, but the local arrangement of these Cu+ sites is similar in Cu-ZSM-5 and Cu-mordenite. The effect of the presence of Rb, Cs and Ba co-cations and pyridine adsorption in CuH-mordenites on the luminescence spectra was used to identify the cationic site represented by the 540 nm emission in mordenite. These Cu+ ions are located in site E of the mordenite main channel. The elongated six-ring of this site is composed of two five-rings sharing two oxygens, and the Cu+ ions are suggested to be coordinated close to the rectangle of the main channel wall. The 540 nm Cu+ emission of the Cu-ZSM-5 was attributed to the Cu+ ion in a site with a local arrangement similar to that of mordenite. The Cu+ ions are located in the main (straight) channels of the ZSM-5 matrix and are coordinated to the oxygen oblong of the channel wall. The cationic site is formed, as in mordenite, by an elongated six-ring composed of two five-rings. Thus, the structure of the Cu active site in Cu-ZSM-5 was suggested.

The effect of the presence of water vapor in the gas stream on the absorption spectra of AgH-ZSM-5 zeolites at high temperatures was investigated using UV–Vis DR spectroscopy. Ag m n + silver species exhibiting an absorption band at 37 700 cm − 1 are formed in highly loaded AgH-ZSM-5 treated in an oxygen stream. The presence of water in the gas stream results in the fast erosion of the band at 37 700 cm − 1 and the intensity of the band is fully recovered under water-free conditions. Ag m n + silver species in the AgH-ZSM-5 zeolite and their optical properties are stable under high-temperature treatment of zeolite under various conditions. Thus, the preparation of chemically/thermally stable sensing material based on silicon-rich zeolites containing metal ion species suitable for sensor applications under sever conditions was demonstrated.

Cu and Co ions in Na- and H-forms of ZSM-5 and ferrierite were used to elucidate siting-coordination-bonding of bare divalent cations and cation-extra-framework ligand complexes (with NO, CO, NO2, H2O and NH3) in high silica zeolite matrices. By using a multi-spectroscopic approach involving VIS-NIR diffuse reflectance spectra of the Cu2+ and Co2+ ions, Cu+ luminescence, FTIR spectra of skeletal T-O-T vibrations and vibrations of adsorbed molecules (ligands), information on the bonding of the bare cations and cation-guest-ligand complexes to the framework oxygen ligands was obtained. Based on our previous results on characteristic spectral features of the Cu siting in dehydrated ZSM-5, a correlation between coordination of the Cu ions in hydrated and dehydrated ZSM-5 zeolites at various Cu/Al/Si ratios was established, and the importance of Al distribution in the framework (so called ‘Al pairs’ and single Al atoms) for the Cu ion exchange and siting in zeolites was evidenced. Owing to the stable divalency of Co2+ in zeolites, this cation was used to monitor coordination-bonding of bare divalent cations and cation-ligand complexes in ferrierite. It has been found that the Co2+ ions induce local perturbations of the T-O-T bonds adjacent to the cation reflected in three characteristic (‘deformation’) shifts of the T-O-T framework vibrations. Simultaneously measured d-d transition spectra of the Co2+ ions, providing information on the symmetry of the framework oxygen atoms bonding a bare cation, indicated that the changes in T-O-T vibrations are accompanied by changes of VIS spectra. Depending on the strength and number of the extra-framework ligands, this local framework deformation induced by the Co2+ ion is partly. or eventually completely, removed (T-O-T vibration ‘relaxation’ shift) upon adsorption of molecules with formation of cation-guest-ligand complexes (also detected via ligand vibration itself).

Catalytic activity of Co ions in CoNaK- and CoH-ferrierites in selective catalytic reduction of NO with methane depending on Co loading was investigated. The previously determined distribution of the exchanged Co ions in Co-ferrierites at three different cationic sites, differring in coordination of the Co ions to framework oxygens, has been utilized to analyze catalytic activity of the Co ions. The type of coordination of the Co ions dramatically affects their reactivity in the selective catalytic reduction of NO with methane. The Co ions coordinated to four framework oxygens of the wall of the main channel exhibit the highest activity, while the Co ions placed in a "boat shape", the most packed site of ferrierite show the lowest activity.

A series of CuNa−ZSM-5 zeolites with different Cu/Al and Si/Al ratios and CuCaNa− and CuCeNa−ZSM-5 zeolites were prepared by Cu2+ ion exchange from Cu acetate and Cu chloride solutions in order to investigate the complexation of the Cu ions in hydrated and dehydrated zeolites. VIS−NIR d−d spectra of the Cu2+ ions in hydrated and Cu+ luminescence spectra of the dehydrated zeolites were used to indicate the coordination of the Cu ions in the zeolites. It has been found that the “monovalent” [Cu2+−ligand]+ complexes are present and predominate in ZSM-5 with low content of aluminum and high Cu loading and in those zeolites where Ca2+ or Ce3+ ions were preexchanged. Similarly, the Cu ions detected by Cu+ emission at 540 nm in dehydrated zeolites exhibit the same trend in population in dependence on the Cu(Ca,Ce)/Al/Si compositions of the ZSM-5 zeolite. These Cu ions were in our previous work indicated as those balanced by a single Al framework atom, exhibiting a rather open, close to planar ligand field enviro...

It has been shown that two main Cu sites present in ion exchanged Cu-ZSM-5 which differ in positive charges on the Cu 2+ ion, exhibit substantially different redox properties and reactivity towards NO molecules investigated by IR spectra of adsorbed NO and CO, and Cu + emission spectra. The Cu ion with low positive charge (tested by electron density transfer from NO molecule to the cation) is assumed to be balanced by a low negative charge, i.e., a single framework AI atom. This Cu site preferably forms Cu + dinitrosyl complexes and exhibits high stability of Cu + even in oxygen at high temperature (720 K) compared to the other Cu ions with higher positive charges, which are suggested to be balanced by two framework AI atoms. A decisive role of local negative framework charge adjacent to the cation as well as total negative framework charge given by Si/Al ratio for the redox properties and reactivity of the Cu ions has been indicated.