Atsushi Itadani

A more efficient copper-ion-exchanged ZSM-5 zeolitefor N2 adsorption at room temperature: Ion-exchange in anaqueous solution of Cu(CH3COO)2

The copper-ion-exchanged ZSM-5 type zeolite, prepared by ion-exchange in an aqueous solution of Cu(CH3COO)2 and evacuation at 873 K, gives a distinctive IR band at 2151 cm−1 due to the adsorbed CO species. More efficient adsorption of N2 was exhibited by this sample, compared with samples prepared by other methods, implying site-selective ion-exchange in the preparation process. On the basis of X-ray absorption near-edge structure (XANES) spectra the exchanged copper ion was proved to be in a monovalent state; one of the splitting strong bands, due to the 1s–4pz transition of the monovalent copper ion, loses its intensity on N2 adsorption. The extended X-ray absorption fine structure (EXAFS) spectral pattern around the copper ion also changed on N2 adsorption and a shoulder appeared at around 1.5 A (no phase-shift correction), in addition to the strong band at around 1.65 A (no phase-shift correction). It was concluded that the monovalent copper-ion-exchanged site giving the 2151 cm−1 band due to the adsorbed CO species is the active site for specific N2 adsorption. A first principles calculation was carried out with the object of finding the most appropriate model for the CO species adsorbed on the exchanged copper ions in ZSM-5. The data obtained suggest that a three-coordinate copper ion bonded to three lattice oxygen atoms adsorbs CO to give the 2151 cm−1 band. A pseudo-planar structure including the monovalent copper ion bound to three oxygen atoms is assumed to change to a pseudo-tetrahedral arrangement on N2 adsorption. Such a site-selectively ion-exchanged substance has potential for the development of materials for N2 separation or fixation and activation catalysts, as well as for the analysis of NO-decomposition sites.

On the possibility of AgZSM-5 zeolite being a partial oxidation catalyst for methane.

A silver-ion-exchanged HZSM-5 zeolite sample (Ag(H)ZSM-5) evacuated at 573 K exhibited prominent catalytic behavior in the partial oxidation of CH(4) at temperatures above 573 K, exceeding the performance of Ag/SiO(2)Al(2)O(3) and Ag/SiO(2) catalysts. From the infrared (IR) and X-ray absorption fine structure (XAFS) spectra, as well as the dioxygen adsorption measurement, it was concluded that the simultaneous existence of Ag(+) ions and small clusters of Ag particles leads to the partial oxidation of methane. Taking the magnitude of the formation enthalpy (per oxygen atom) of Ag(2)O (DeltaH=26 kJ/mol) into consideration, we propose the interpretation that the dioxygen activated on small Ag metal clusters formed in ZSM-5 elaborates a surface oxide layer on small Ag clusters and the thus-formed species is simultaneously and easily decomposed at 573 K or above, and the oxygen activated in this way on the Ag metal spills over and can react with methane that has been activated by the Ag(+) ions exchanged in ZSM-5, resulting in the high catalytic activity of the Ag(H)ZSM-5 sample in the partial oxidation of methane. This interpretation is also well evidenced by XAFS and IR data. It is anticipated that this material has the potential to be a promising catalyst in the conversion of natural gas into higher value-added chemicals and fuels.

Unprecedented Reversible Redox Process in the ZnMFI—H2 System Involving Formation of Stable Atomic Zn0

In its element: Zn(2+) at the M7 site of MFI-type zeolites activates H(2), via ZnH and OH species, and leads to Zn(0) species. The Zn(0) species returns to its original state, a Zn(2+) ion, upon evacuation of the zeolite at 873 K (see picture). The formation of the Zn(0) species is supported by DFT calculations.

Existence of dual species composed of Cu+ in CuMFI being bridged by C2H2

The interaction of ethyne (C(2)H(2)), as well as of carbon dioxide (CO(2)), with copper-ion-exchanged MFI zeolite (CuMFI) at room temperature was examined. It was found that CuMFI preferentially adsorbs C(2)H(2), while this material does not respond to CO(2). To clarify the specificity of CuMFI, a combination of various experimental techniques and theoretical calculations was adopted. Distinctive interaction energies of 140 and 110 kJ mol(-1) were clearly observed at the initial stage of C(2)H(2) adsorption on CuMFI, suggesting the presence of two types of adsorbed C(2)H(2). Two distinct IR bands at 1620 and 1814 cm(-1) appeared, which were assigned to the C[triple bond]C stretching vibration modes of C(2)H(2) differing in their adsorbed state. Both photoluminescence and X-ray absorption spectra showed that cuprous ions (Cu(+)) in CuMFI act as efficient sites for a marked C(2)H(2) adsorption. From the analysis of the latter spectra and the calculational results based on the density functional theory, the formation of dual Cu(+)...(C(2)H(2))...Cu(+) complexes was indicated for the first time for CuMFI, and such a special configuration of the Cu(+) sites contributed to the extremely strong adsorption of C(2)H(2). In contrast, it was necessary for the linear CO(2) molecule to take a bent structure to be adsorbed on Cu(+) in CuMFI. It was concluded that the difference in the adsorption response of Cu(+) in CuMFI towards C(2)H(2) and CO(2) is due to the chemistry between the nature of electron donation of Cu(+) and the hybrid orbitals of the respective molecules. This work promotes further understanding of the states of active centres in CuMFI for C(2)H(2) activation, as well as for N(2) fixation.

Silicon and phosphorus linkage with iron via oxygen in the amorphous matrix of Gallionella ferruginea stalks.

ABSTRACT Bacterial species belonging to the genus Gallionella are Fe-oxidizing bacteria that produce uniquely twisted extracellular stalks consisting of iron-oxide-encrusted inorganic/organic fibers in aquatic environments. This paper describes the degree of crystallinity of Gallionella stalks and the chemical linkages of constituent elements in the stalk fibers. Transmission electron microscopy revealed that the matrix of the fiber edge consisted of an assembly of primary particles of approximately 3 nm in diameter. Scanning transmission electron microscopy revealed the rough granular surfaces of the fibers, which reflect the disordered assembly of the primary particles, indicating a high porosity and large specific surface area of the fibers. This may provide the surface with broader reactive properties. X-ray diffractometry, selected-area electron diffraction, and high-resolution transmission electron microscopy together showed that the primary particles had an amorphous structure. Furthermore, energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy detected the bands characteristic of the vibrational modes assigned to O-H, Fe-O-H, P-O-H, Si-O-H, Si-O-Fe, and P-O-Fe bonds in the stalks, suggesting that the minor constituent elements P and Si could affect the degree of crystallinity of the fibers by linking with Fe via O. This knowledge about the mutual associations of these elements provides deeper insights into the unique inorganic/organic hybrid structure of the stalks.

Anomalous valence changes and specific dinitrogen adsorption features of copper ion exchanged in ZSM-5 zeolite prepared from an aqueous solution of [Cu(NH3)2]+

Direct ion-exchange of monovalent copper ions into a ZSM-5-type zeolite was carried out using an aqueous solution of diammine–copper(I) ions, [Cu(NH3)2]+, to prepare a copper ion-exchanged ZSM-5 zeolite including only monovalent copper ions, and the effect of monovalent copper ions on the zeolites adsorption properties for dinitrogen (N2) was examined. Strangely enough, the reoxidation of monovalent copper-ion exchanged in ZSM-5 took place in the evacuation process at around 473 K. The changes in valence and structure of the exchanged copper-ions during the evacuation process and the interaction with N2 molecules at room temperature have been investigated by using spectroscopic techniques such as X-ray absorption fine structure (XAFS), IR and photoemission spectroscopy, as well as by measurements of adsorption isotherms and adsorption heats. On the basis of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses, it has become apparent that the Cu+ species exchanged in ZSM-5 zeolite is oxidized by water to form a divalent species having a CuO-like structure through heat-treatment in vacuo at 473 K. Further heat-treatment at temperatures above 673 K caused a reduction of the divalent species to a monovalent one that exhibits a pronounced adsorption feature for N2 even at room temperature. XANES and photoemission data clearly indicated that the Cu+ species in an 873 K-treated CuZSM-5 sample has a three-coordinate structure with lattice oxygen atoms and interacts strongly with an N2 molecule at room temperature. The strong interaction with N2 was also verified through the adsorption heat and IR data: an initial adsorption energy of 85 kJ mol−1 and an absorption band at 2295 cm−1. A prominent feature of this system is that some of the adsorbed species survives after evacuation at 300 K, indicative of a strong interaction between N2 and the three-coordinate copper ion.

Identification of two types of exchangeable sites for monovalent copper ions exchanged in MFI-type zeolite

Three different approaches have been used to characterize the state of exchanged copper ions in copper-ion-exchanged MFI (CuMFI) samples. (1) Two types of an ion-exchangeable site with different adsorption properties for N(2) or CO molecules were identified depending on the pre-treatment temperature (723 or 873 K) of a sample prepared by using an aqueous solution of CuCl(2). (2) The state of the active sites formed by the evacuation of a sample at 873 K that had been prepared using a mixture solution of aqueous NH(4)CH(3)COO and Cu(CH(3)COO)(2) was analysed utilizing both (13)C(18)O and (12)C(16)O to identify the two types of active adsorption sites for CO molecules. (3) CuMFI samples prepared by the ion-exchange method employing anhydrous CuCH(3)COO showed a surprising adsorption feature characterized by a single IR band occurring at 2159 cm(-1) due to the adsorbed CO molecules, but there was no corresponding IR band due to adsorbed N(2) molecules. A successful preparation of CuMFI, in which the monovalent copper ions exclusively occupied another one of the two types of ion-exchangeable sites, was also carried out utilizing the solid-ion exchange method using Cu(CH(3)COO)(2).H(2)O. This site exhibits an IR band occurring at 2151 cm(-1) for CO molecules and also acts as an active site for N(2) molecules. These experimental data correlate, and clearly indicate that there are at least two types of exchangeable sites for copper ions in MFI-type zeolites.

The Variety of Carbon-Metal Bonds inside Cu-ZSM-5 Zeolites: A Density Functional Theory Study

Large-scale density functional theory calculations (DFT) found various types of binding of an unsaturated hydrocarbon (C2H2 and C2H4) to a ZSM-5 zeolite extraframework copper cation. We employed the DFT calculations based on the B3LYP functional to obtain local minima of an unsaturated hydrocarbon adsorbed on one or two copper cations embedded inside ZSM-5, and then compared their stabilization energies. The DFT results show that the stabilization energies are strongly dependent on the copper coordination environment as well as configurations of two copper cations. Consequently, the inner copper-carbon bonds are influenced substantially by a nanometer-scale cavity of ZSM-5.

Success in Making Zn+ from Atomic Zn0 Encapsulated in an MFI-Type Zeolite with UV Light Irradiation

For the first time, the paramagnetic Zn(+) species was prepared successfully by the excitation with ultraviolet light in the region ascribed to the absorption band resulting from the 4s-4p transition of an atomic Zn(0) species encapsulated in an MFI-type zeolite. The formed species gives a specific electron spin resonance band at g = 1.998 and also peculiar absorption bands around 38,000 and 32,500 cm(-1) which originate from 4s-4p transitions due to the Zn(+) species with paramagnetic nature that is formed in MFI. The transformation process (Zn(0) → Zn(+)) was explained by considering the mechanism via the excited triplet state ((3)P) caused by the intersystem crossing from the excited singlet state ((1)P) produced through the excitation of the 4s-4p transition of an atomic Zn(0) species grafted in MFI by UV light. The transformation process was well reproduced with the aid of a density functional theory calculation. The thus-formed Zn(+) species which has the doublet spin state exhibits characteristic reaction nature at room temperature for an O2 molecule having a triplet spin state in the ground state, forming an η(1) type of Zn(2+)-O2(-) species. These features clearly indicate the peculiar reactivity of Zn(+) in MFI, whereas Zn(0)-(H(+))2MFI hardly reacts with O2 at room temperature. The bonding nature of [Zn(2+)-O2(-)] species was also evidenced by ESR measurements and was also discussed on the basis of the results obtained through DFT calculations.

Visible-Light-Derived Photocatalyst Based on TiO2−δNδ with a Tubular Structure

We succeeded in achieving visible-light responsiveness on a tubular TiO(2) sample through the treatment of a tubular TiO(2) that has a large surface area with an aqueous solution of ammonia or triethylamine at room temperature and subsequent calcination at 623 K, which produced a nitrided tubular TiO(2) sample. It was found that the ease of nitridation is dependent on the surface states; washing the tubular TiO(2) sample with an aqueous acidic solution is very effective and indispensable. This treatment causes the appearance of acidic sites on the tubular TiO(2), which was proved by the following experiments: NH(3) temperature-programmed desorption and two types of organic reactions exploiting the acid properties. The prepared samples, TiO(2-δ)N(δ), efficiently absorb light in the visible region, and they exhibit a prominent feature for the decomposition of methylene blue in an aqueous solution at 300 K under irradiation with visible light, indicating the achievement of visible-light responsiveness on the tubular TiO(2) sample. This type of tubular TiO(2-δ)N(δ) sample has merit in the sense that it has a large surface area and a characteristic high transparency for enabling photocatalytic reactions because it has a tubular structure and is composed of thin walls.