The changes of structure and electronic state of copper ion species during the heat treatment of copper ionexchanged ZSM-5 zeolite (CuZSM-5) as well as the interaction with CO molecules have been investigated by using various spectroscopic techniques such as infrared (IR) and emission spectroscopy (ES), electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) consisting of a XANES (X-ray absorption near edge structure) and an EXAFS (extended X-ray absorption fine structure) and through the measurements of heat of adsorption and adsorption isotherm. About 70% of the divalent copper ions (Cu 2+ ) exchanged in CuZSM-5 were found to be reduced to the monovalent copper ions (Cu + ) during the heat treatment at 873 K in vacuo, the latter species having a linear or a planar coordination structure with a coordination number of 2 or 3 with respect to the nearest-neighboring oxygen atoms at a distance of 1.98 Å. It was found from the ES data that the Cu + species strongly interact with CO molecules at room temperature. The ratios of the number of CO species interacting with Cu + species, the former being obtained from the adsorption isotherm data and the latter being obtained from the XANES data, are estimated to be 0.97 for the irreversible CO adsorption and 1.14 for the reversible CO adsorption, respectively. Furthermore, it was revealed that there exist at least two types of Cu + species differing in the strength of the interaction with CO; one gives a heat of adsorption of about 120 kJ mol -1 and an IR absorption band at 2159 cm -1 due to the irreversibly adsorbed CO species, and the other exhibits 100 kJ mol -1 and a band at 2151 cm -1 , which is also ascribed to a similar species. When CO is adsorbed on the Cu + species, the coordination structure around the Cu + species changes and the distance between the Cu + ion and the nearest-neighboring oxygen atom changes from 1.98 to 2.05 Å, as is evidenced from the EXAFS data. The coordination number of the carbon atom in the adsorbed CO is estimated to be 1.4, and a value of 1.89 Å is obtained as a distance of Cu-C. The coordination structure recovers by the heat treatment at 573 K. This implies that the irreversible adsorption of CO molecules is responsible for the change of coordination structure around the Cu + species. Combination of IR and XAFS data leads to the interpretation that in the irreversible CO adsorption the Cu + species on which a CO molecule is strongly adsorbed to give an IR band at 2159 cm -1 is coordinated to two lattice oxygen atoms and that the Cu + species on which a CO molecule is weakly adsorbed to give a 2151 cm -1 -band is coordinated to three lattice oxygen atoms.

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Adsorption properties of copper ion-exchanged mordenite (CUM) for dinitrogen molecules ( N 2 ) were examined at 298 K. The intensive IR absorption band observed at 2299 cm-' was attributed to the NZ species strongly adsorbed on CUM. The interaction of NZ with CUM is explored using adsorption calorimetry, X-ray absorption fine structure (XAFS), electron spin resonance (ESR), and photoemission spectroscopy. The differential heat and entropy of adsorption for N2 on CUM were 60 kJ mol-' and 60 J K-' mol-' at the initial stage of adsorption, respectively, and those for NZ on NaM (sodium-type mordenite) gave the values of 32 kJ mol-' and 130 J K-' mol-', revealing that the N2 molecules are in the localized state resulting from the strong interaction with CUM. The monolayer capacity is estimated to be 4.12 cm3 g-' for NZ on CUM-150, which gives a value of 0.22 for the Nz/Cu ratio. XAFS and emission data for CUM degassed at 873 K exhibit pair bands at 8.983 and 8.994 keV and 18 700 and 20 800 cm-I, respectively. The former pair band is assigned to the 1s-4p transition, and the latter pair band is assigned to the 3d94s1-3dl0 transition. It is also found that the ESR band intensity for Cu(I1) decreases with increasing pretreatment temperature. These spectral data are reasonably explained by assuming the presence of Cu(1) species in mordenite. It is proved from the emission data that the adsorption site including Cu(1) species easily formed by heat treatment at 873 K in vacuo is effective for N2 adsorption. Such easy conversion of Cu(II) to Cu(1) may be due to the spatial distribution of ion-exchanged sites on mordenite. The appearance of a strong IR band at 2299 cm-' is due to the adsorption of N2 on the Cu(1) species and to the induction of a transition moment by the strong field of this site. Although a rather high value of heat of adsorption might suggest chemisorption, it is made plausible that this type of N2 adsorption is physisorption.

The adsorption isotherms of benzene, toluene, and chlorobenzene were measured for titanium dioxide (rutile) samples having a controlled number of surface hydroxyl groups, from which the amount of irreversible adsorption (V|") was obtained for each sample. The Virr values for benzene and toluene were the largest on the dehydroxylated surface, and they decreased linearly with increasing degree of surface hydroxylation of the sample. The value for toluene was larger than that for benzene, probably because of an enhanced electron density of the aromatic ring due to the presence of a methyl group carrying an electron-donating nature. The Vte value for chlorobenzene agreed with that for benzene on the dehydroxylated surface but was greater than those for the other two adsorbates on the surface with a higher concentration of hydroxyl groups. The IR absorption band due to the C-C stretching vibration of the aromatic ring shifted to the lower wavenumber with reference to the case of gaseous state, showing that these molecules are adsorbed through the formation of a Ti4+-ir-electron type complex on the dehydroxylated surface and by the formation of a --electron type complex on the hydroxylated surface. Furthermore, by applying the Mulliken-Puranik charge-transfer theory to the relationship between the shift and intensity of the OH absorption band, we found that toluene can be adsorbed only by the --electron interaction as in the case of benzene adsorption while chlorobenzene can be adsorbed by a different mechanism from the cases of the other two adsorbates. Chlorobenzene is adsorbed on the hydroxylated surface through the interaction between surface OH grovjps and the chlorine atoms of chlorobenzene, in addition to the --electron interaction, with so-called dual-site adsorption.

The state of copper ion exchanged in ZSM-5-type zeolite has been investigated through the IR and adsorption-heat measurements at 301 K by using CO as a probe molecule. As a result, it was proved that there are at least three kinds of adsorption sites for a CO molecule on the copper ion-exchanged ZSM-5, which are responsible for the IR bands at 2159, 2149, and 2136 cm-1, as well as the differential adsorption-heats of 91, 82, and ∼70 kJ mol-1. Corresponding to these data, TPD also gives three desorption peaks at 363, 442, and 542 K. An excellent linear relationship has been established between the stretching vibrational frequencies due to the adsorbed CO species and the differential adsorption-heat values. When CO gas is introduced to the 723 K-treated sodium ion-exchanged ZSM-5, this sample provides the adsorption-heat of about 35 kJ mol-1 in the whole adsorption region studied and the weak IR bands at 2175 and 2112 cm-1. For the sodium ion-exchanged ZSM-5 and CO system, the above correlation does not hold in the same plot containing Cu−CO species. This fact is interpreted in terms of the difference in the nature of bonding between the electrostatic force for the sodium ion-exchanged ZSM-5 and CO system and the covalent nature for the copper ion-exchanged ZSM-5 and CO system. More detailed discussions are also made on the nature of the Cu−CO bond.