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Oxidation of organic substrates on metal oxide catalysts can be viewed as entailing a transfer of electrons from the organic moeity to the catalytic center, and is expected to involve the electron-accepting levels in the metal center. This investigation deals with the study of the electron-transfer processes associated with the C−H bond breaking reaction in adsorbed methoxide species in the course of methanol oxidation on supported MoO3. It is shown that the activity of a series of catalysts duly correlates with the unoccupied density of electronic states of the parent metal oxides. The unoccupied levels are probed with near-edge X-ray absorption spectroscopy (NEXAFS). The particular system chosen for study is that of methanol oxidation on supported molybdenum oxide, a reaction in which C−H bond breaking is rate-determining. The findings of this study are in good agreement with the known facts about the reaction and allow a deeper understanding of various reported effects. For example, the positive relationships between the catalytic activity and the decreasing electronegativity of the support ion, the increasing reducibility of the dispersed molybdenum centers, and the increasing size of the molybdenum ensembles can all be explained by the increasing ease of accommodation of charge by the metal centers. The findings in this study should be of importance in understanding other C−H bond breaking reactions and multicomponent catalyst systems.

The conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5, TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses. Reasonable agreement between the results of the two methods is obtained at the pH at which the ζ potentials of the particles are zero. The tops of the valence bands are found to be shifted to higher potential energies on the order Ta2O5 < TaON < Ta3N5, whereas the bottoms of the conduction bands are very similar in the range −0.3 to −0.5 V (vs NHE at pH = 0). From the results, it is concluded that TaON and Ta3N5 are promixing catalysts for the reduction and oxidation of water using visible light in the ranges λ < 520 nm and λ < 600 nm, respectively. It is also demonstrated that the proposed UPS technique is a reliable alternative to electrochemical analyses for determining the absolute band gap positions for materials in aqueous solutions that would otherwise be difficult to measure using electrochemical methods.

LaTiO2N, a Ti-based oxynitride, was studied as a visible-light (420−600 nm)-driven photocatalyst. DFT calculation for LaTiO2N indicated that the top of the valence band consists predominantly of N 2p orbitals with a small contribution by O 2p orbitals, while the bottom of the conduction band is made up entirely of empty Ti 3d orbitals. LaTiO2N was synthesized from a La2Ti2O7 precursor at 1123 K under NH3 flow. The relationship between the preparation condition and the photocatalytic activities of H⁺ reduction to H2 and H2O oxidation to O2 was examined. It was found that the photocatalytic activity for O2 evolution increased with nitridation time, reaching a maximum at 72 h. Further treatment beyond 72 h lowered the rate of O2 evolution. The rate of H2 evolution was almost independent of nitridation time. The relationship between nitridation time and the rate of O2 evolution is discussed on the basis of X-ray photoelectron spectroscopy (XPS) analyses.

The mechanism of methanol oxidation over highly dispersed 1% MoO3/SiO2 was studied using a combination of steady state and transient kinetic measurements together with in situ Fourier transform infrared (FTIR) observations of surface-adsorbed species. The main reactive intermediates were methoxide species formed on surface Mo centers. Deuterium substitution experiments showed that these species decomposed through a rate-determining C−H bond-breaking step to form the primary product of reaction, formaldehyde. The steady state data gave an apparent activation energy of 89 kJ/mol, while the oxidation rate of the surface intermediate gave an activation energy for the rate-determining step of 108 kJ/mol. The difference in these gives a heat of adsorption of −19 kJ/mol. Although the oxidation reaction occurred on the Mo centers, the methoxide species were found to migrate to the silica support by reversibly displacing mobile silica OH groups. Two kinds of methoxide species were distinguished, spectators and active intermediates. Only the active intermediates could be oxidized at temperatures lower than 300 °C, and these were the actual participants in the reaction. Quantitative FTIR measurements indicated that the number of methoxide species on the silica support was about six times larger than the number of Mo centers. Thus, the silica surface, which was otherwise inert, participated in a noninnocent manner, holding a substantial population of the reactive intermediates.

Transient absorption spectra of the layered compound K4Nb6O17, which is known as a photocatalyst for splitting water into H2 and O2, were measured by the femtosecond UV pump and visible probe technique. Under band-gap excitation of a K4Nb6O17 single crystal and a spin-coated K4Nb6O17 film, a broad transient absorption extending over the whole visible region, which could be ascribed to photogenerated carriers in K4Nb6O17, was observed, and its decay behavior was analyzed on the basis of second-order kinetics. Dynamics of photoexcited Ru(bpy)3²⁺ intercalated at K4Nb6O17 interlayers was also investigated. Intercalation of Ru(bpy)3²⁺ in K4Nb6O17 is known to give visible light response for photocatalytic chemical reaction. Observed transient bleaching of Ru(bpy)3²⁺ band showed fast and nonexponential decay differing from that of Ru(bpy)3²⁺ in water. The decay mechanism is discussed in terms of electron transfer between Ru(bpy)3²⁺ and K4Nb6O17.

The mechanism of formate decomposition on a NiO(111) surface is investigated using the density functional method and (NiO)x cluster models. The reaction consists of three steps:  (1) configuration change from bidentate to monodentate, (2) HCOO rotation around the CO axis, and (3) H atom transfer from the formate to the surface O atom. The bidentate form is more stable by 21 kJ/mol than the monodentate one, and the energy barrier measured from the former is 25 kJ/mol, which is consistent with the recent experimental finding that the mutual conversion is an equilibrium reaction. There is no essential reaction barrier during the HCOO rotation about the CO axis. The migration of H atoms from formate to the surface O atom is the rate-limiting step, and the activation energy is estimated to be 73 kJ/mol. The product is the surface OH groups and adsorbed CO2 molecule, which is consistent with the recent experimental stidies.

Molybdenum oxide catalysts (1 wt %) supported on SiO2 (L-90, 95 m²/g), SiO2 (EH-5, 350 m²/g), Al2O3 (96 m²/g), and TiO2 (52 m²/g) were characterized using Raman spectroscopy and near-edge and extended X-ray absorption fine structure (NEXAFS and EXAFS, respectively) spectroscopies. The structural possibilities (tetrahedral and distorted octahedral) for the Mo active center were explored using ab initio calculations through the Hartree−Fock method using a 3-21G(d) basis set. The Raman vibrational frequencies and bond lengths obtained from EXAFS were compared to ab initio calculations to arrive at the likely structures for the isolated Mo centers on each support. The studies revealed a mixture of tetrahedral Mo sites along with crystalline MoO3 for the MoO3/SiO2 (L-90) catalyst. The Mo sites for the MoO3/SiO2 (EH-5) catalyst were found to be a mixture of isolated, tetrahedral, and distorted octahedral sites. The MoO3/Al2O3 catalyst was found to have isolated, tetrahedral sites. Finally, the MoO3/TiO2 catalyst was found to have distorted octahedral Mo active centers. Complementary information from Raman, NEXAFS, and EXAFS spectra and ab initio calculations were required to arrive at the structural assignments for the Mo centers in the present study. Importantly, however, the calculations indicate the possible existence of other stable geometries and help explain the many diverging conclusions in the literature concerning the structure of supported molybdenum oxide catalysts.

The adsorption and reaction of 1-methylcyclopentene (MCPE) and 1-methylcyclopentanol (MCPOH) on HZSM-5 were studied by in-situ FTIR spectroscopy at 150−295 K. For MCPE, weakly adsorbed species, i.e., alkyl group adsorption on the acidic OH group, were predominant below 196 K. At 196 K and above, the π-OH complex was formed followed by stepwise formation of stable alkenyl carbenium ions and alkoxy species, characterized respectively by an IR band at 1520 cm^-1 and by the shift of C−H stretching frequencies. For MCPOH, dehydration occurs at 268 K and MCPE is produced. The latter further forms alkenyl carbenium ions and alkoxy species progressively with the increase in temperature.

Vibrational study by Raman spectroscopy was made of the layered perovskite compounds of the formula M2La2Ti3O10 (M = H, Li, Na, K, Rb), K2La2Ti3O10·2H2O, and H2La2Ti3O10·nH2O. The spectral features above 400 cm^-1 were similar in all of the unhydrated samples suggesting that the bands originated from the vibrational modes of the La2Ti3O10 perovskite layer. Lattice dynamical calculations were performed with the use of a potential field derived from the molecular dynamics on the M2La2Ti3O10 (M = Li, Na, K). The assignment of the Raman bands higher than 400 cm^-1 was made on the basis of the results of lattice dynamical calculations and was confirmed by comparing the spectral feature of K2La2Ti3O10 with that of H2La2Ti3O10, K2La2Ti3O10·2H2O, and H2La2Ti3O10·nH2O.

CO adsorption and oxidation over Au/Al2O3 were studied by infrared (IR) spectroscopy at 150 K. Two types of CO adsorption were found on the support, Al2O3, with the existence of gaseous CO (266 Pa). An additional band of adsorbed CO at 2110 cm^-1 was found on Au/Al2O3 at 150 K in the presence of gaseous CO and was assigned to CO adsorbed on ultrafine gold particles dispersed on Al2O3 support. After evacuation at the same temperature, the band of CO adsorbed on the ultrafine gold particles decreased in intensity and shifted to 2118 cm^-1, whereas the CO adsorbed on Al2O3 disappeared. The band at 2118 cm^-1 was assigned to CO irreversibly adsorbed on the ultrafine gold particles at 150 K. CO oxidation by O2 took place on Au/Al2O3 in the presence of CO and O2 gas mixture even at 150 K, whereas CO irreversibly adsorbed on Au/Al2O3 and could not be oxidized by the exposure to O2 at the same temperature. Therefore, the reversibly adsorbed CO on the ultrafine gold particles was found to be the active CO species for CO oxidation at 150 K. By spectral analysis, the reversibly adsorbed CO was found to show a band at 2108 cm^-1. The ultrafine gold particles were oxidized by O2 treatment at 573 K, becoming inert for CO oxidation at 150 K, but were easily rereduced at 573 K by evacuation treatment. The recovered Au/Al2O3 also catalyzed CO oxidation at 150 K.

The catalytic deep oxidation of methanol by oxygen on the Pt(111) surface under ambient pressure conditions has been studied by in situ infrared reflection absorption spectroscopy (IRAS). It was found that the Pt(111) surface was covered with formate in a flow of 0.16 kPa of methanol and >1.3 kPa of oxygen mixture at 350 K while it was covered with CO at the oxygen pressure below 1.3 kPa. CO2 was detected in the product gas and the reaction kinetics was examined. The relation between the production rate of CO2 and the coverage of adsorbates as a function of oxygen pressure indicated that the CO2 mainly originated from the formate which was produced from oxidation of methanol. Although CO produced by methanol decomposition seems to be one of precursors of CO2 formation, this reaction was found to be a minor pathway. The detailed mechanism of oxidation of methanol on Pt(111) was discussed.

The hydrogenation of acetylene and ethylene was studied on Au/Al2O3 catalyst. Acetylene and hydrogen reacted readily to produce ethylene, but not to ethane on the catalyst in the temperature range between 313 and 523 K. The hydrogenation of ethylene on the catalyst occurred only at much higher temperatures over 573 K. The activity of the selective hydrogenation of acetylene over Au/Al2O3 catalyst depends on the size of ultrafine gold particles of Au/Al2O3 catalyst, which showed a maximum at about 3.0 nm in diameter.

The mechanism of ethylene hydrogenation on Pt surfaces has been investigated using the density functional method and the Ptn cluster models (n = 7, 10) modeling the Pt(111) surface. The energetics were investigated along the overall hydrogenation reactions:  adsorption of ethylene onto the hydrogen preadsorbed Pt cluster, successive H atom migrations to adsorbed ethylene, and formation of ethane. Among the configurations considered here, the di-σ and π configurations gave the local minima. The di-σ configuration was found to be more stable than the π configuration for both the hydrogen free and preadsorbed surfaces. The calculated activation energy was larger for the second hydrogenation. Both the di-σ and π configurations lead to a common product, surface ethyl, from which the second hydrogenation occurs. The surface ethyl produced ethane in the eclipsed conformation, which was desorbed from the surface. Although the hydrogenation from the di-σ configuration is energetically favorable for clean surfaces, the energetics considerably depends on the coadsorbed surface species such as hydrogen atom and carbon deposit, and on the real catalysts, both reactions will proceed comparably.

The reaction of methanol with oxygen on Pt(111) under ultrahigh vacuum condition has been investigated by infrared reflection absorption spectroscopy (IRAS). Molecular and atomic states of adsorbed oxygen existed on the Pt(111) surface, and the adsorption of oxygen at 100 K gave molecularly adsorbed oxygen that dissociated to adatoms at ~160 K. Formate species, which gave the symmetric C−O stretching band at 1327 cm^-1, was observed when methanol-adsorbed Pt(111) surface, which was precovered by molecular oxygen, was heated to 160 K. The IRAS band of formate was verified by comparison with the band of the formate derived from formic acid on the Pt(111) surface and by the isotope shift of the band observed by using deuterated methanol. The amount of produced formate was proportional to the amount of the molecularly adsorbed oxygen. The formate band disappeared at 270 K, at which temperature desorption of CO2 and H2 was observed on temperature-programmed desorption spectra. Molecular oxygen on the Pt(111) surface dissociated at 300 K and the produced adatoms did not oxidize methanol, but the methanol was decomposed to CO and H2. Molecularly adsorbed oxygen is thus considered to be responsible for the oxidation of methanol to formate.

Mechano-catalytic overall water splitting on Cu2O, NiO, and Co3O4 was investigated in order to reveal the reaction mechanism. The experimental results indicated that metallic elements of these oxides were generated during the reaction. Also, elemental metals Cu, Ni, and Co were oxidized into Cu2O, NiO, and Co3O4, respectively, when water was reduced into H2 by the metal powders under the same reaction condition. The metallic particles covered with the metal oxides evolved both O2 and H2. These results suggest that a redox reaction between the metal and metal oxide may be responsible for H2 and O2 formation of the mechano-catalytic overall water splitting.

Adsorption and reaction of 2-methylpropene (isobutene) on zeolites (ZSM-5 and faujasite (Y zeolite)), a silica−alumina, and a silica were investigated below room temperature by infrared (IR) spectroscopy. On silica, isobutene molecules that adsorbed on silanol groups simply desorbed below 230 K in vacuum, while isobutene π-bonded to the acidic OH groups (π-complex) on acid catalysts reacted to dimer alkoxy (2,4,4-trimethylpentoxy) groups. The structure of the reaction product, dimer alkoxy groups, was found to be restricted by the pore size of zeolites; 2,4,4-trimethyl-2-pentoxy species were identified on silica−alumina and Y zeolite similarly to those on mordenite, while the reaction of isobutene resulted in 2,4,4-trimethyl-1-pentoxy species on the acidic OH groups in the pores of ZSM-5. Therefore, the space restriction of the pore size of zeolites on the reaction product was directly observed by the low-temperature IR study.

Adsorption and reactions of 2-methylpropene (isobutene) on mordenite were investigated between 150 and 300 K by infrared (IR) spectroscopy. The methyl groups of isobutene interacted with the acidic OH groups of mordenite below 160 K, which was converted to the strongly interacted π-bonded isobutene to the acidic OH groups (π-complex). Above 200 K, the π-bonded isobutene dimerized even under evacuation condition. The stable 2,4,4-trimethyl-2-pentoxy species was identified by FT-IR by comparison with the spectra of the adsorbed C8 olefins. The expected monomeric reaction intermediate, the 2-methyl-2-propoxy (tert-butoxy) species, was not observed. This is probably due to the rapid migration and reaction of the adsorbed isobutene molecules.

Hydrogenation of ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen in the 10³ Pa range was investigated by infrared reflection absorption spectroscopy (IRAS). The IRA peaks assigned to di-σ-bonded ethylene and ethylidyne were observed on Pt(111) under the flow of 1.3 × 10² Pa of ethylene and 6.5 × 10³ Pa of hydrogen at 200−300 K, and the apparent activation energy of ethylene hydrogenation was estimated to be 37 ± 5 kJ mol^-1 from the rate of temperature-dependent ethane production. The ethylene hydrogenation on ethylidyne-covered Pt(111) was also examined under the same condition. The peak due to the di-σ-bonded ethylene was not observed on ethylidyne-covered Pt(111), although the similar rate of hydrogenation and the similar activation energy (39 ± 5 kJ mol^-1) were obtained as those on clean Pt(111). The π-bonded ethylene, which has been previously proposed as an intermediate by the sum−frequency generation (SFG) experiment under the catalytic hydrogenation condition and by IRAS under the low-temperature condition, was not detected in the present study. The similarity of the rate and activation energy for clean and ethylidyne-covered Pt(111) surfaces suggests that the rate of hydrogenation does not depend on either coverage of di-σ-bonded ethylene or ethylidyne. The role of the observed species in the hydrogenation of ethylene is discussed.

Hydrogen adsorbed on Ru/ZrO2 was studied by FT-IR (Fourier transform infrared) spectroscopy. While the Ru−H (Ru−D) species was not observed, the H2O (D2O)-like species was formed by H2 (D2) introduction on ZrO2. The H2O (D2O)-like species was characterized by a band at around 1600 (1190) cm^-1 due to the bending mode and by a broad band at 2500−3800 (2000−2700) cm^-1 attributed to the stretching mode. The H2O (D2O)-like species was stable under evacuation at 300 K, but desorbed as H2 (D2) at 370 K. The H2O (D2O)-like species was considered to be produced by spillover of hydrogen (deuterium) atoms dissociatively adsorbed on Ru particles to react with the surface lattice oxygen atoms of ZrO2. The heat of formation and the activation energy of the H2O (D2O)-like species formation from H2 (D2) were 134 ± 11 (172 ± 11) kJ mol^-1 and 28.6 ± 3.2 (36.6 ± 5.6) kJ mol^-1, respectively. The difference between the H2O-like species and adsorbed H2O molecules on Ru/ZrO2 was also examined.

The decomposition of formic acid on (2 × 2) NiO(111)/Ni(111) was studied by infrared reflection absorption spectroscopy (IRAS). Formic acid molecules adsorbed dissociatively on the surface to form formate which decomposed to H2, CO2, H2O, and CO at 340−415 and 520 K. The vacant sites after the decomposition of formate were probed by the adsorption of CO at 100 K. On clean NiO(111) at 100 K, IRAS peaks of two types of adsorbed CO were observed at 2146 and 2079 cm^-1, which were assigned to the CO on fully-oxidized Ni cation sites and less-oxidized Ni cation sites, respectively. The CO peaks were not observed on the formate precovered surface. The IRAS peak of adsorbed CO at 100 K on the fully-oxidized Ni cation sites appeared when the surface was heated to decompose formate around 340−415 K. After decomposition at 520 K, the intensities of both peaks of CO were recovered to the initial intensities. It was thus concluded that the sites of decompositions at 340−415 and 520 K are the fully-oxidized Ni cation sites and less-oxidized Ni cation sites, respectively. The behavior of hydroxyl species produced by dissociative adsorption of formic acid was next investigated using deuterated formic acid (DCOOD). The hydroxyl species (−OD) formed by the dissociative adsorption of formic acid (DCOOD) was observed at 2536 cm^-1 below 343 K, while the isolated OD groups appeared at 2713 cm^-1 and around 500 K. The mechanism of decomposition of formate at each temperature is discussed.

Adsorption dynamics of linear olefins (C2−C4) on D-ZSM-5 with no Lewis acid sites was examined below 180 K by IR spectroscopy. Below 170 K, olefins except ethene adsorbed on Brønsted acid sites (BAS) by very weak hydrogen-bonding with their alkyl groups, which were then released and migrated on the wall of the zeolite cage without any specific adsorption sites by increasing the temperature. Further heating caused the conversion to strong hydrogen bonding of C&dbd;C to BAS (π-complex), indicating that the formation of π-complexes is an activated process.

Product gas analysis using quadrupole mass spectrometer (QMS) and infrared reflection absorption spectroscopy (IRAS) have been performed to investigate the catalytic decomposition of formic acid on NiO(111) film grown on Ni(111) surface under steady-state conditions and the results have been compared with the previous results obtained in vacuum condition. The rates of the catalytic reactions as measured by product gas analysis at various pressures of formic acid and also at different substrate temperatures revealed two reaction paths for the decomposition of surface formate under equilibrium with gas-phase formic acid. The dehydrogenation producing H2 and CO2 with the activation energy of 22 ± 2 kJ/mol was preferred even at the low temperature of 373 K over the dehydration producing CO and H2O which occurred at a higher temperature of above 423 K with the activation energy of 16 ± 2 kJ/mol, where the activation energy refers to the reaction of formic acid in gas phase to the product substances. The apparent reaction order was 0.5 with respect to the pressure of formic acid for both reactions. IRA spectroscopy using both normal and deuterated formic acid revealed the presence of two kinds of formate species:  bidentate formate aligned normal to the surface and monodentate formate. The result is in contrast with our previous finding of only the tilted-bidentate formate species on the surface under vacuum. Pressure-dependent features of the IRA spectra suggested that the monodentate formate is the intermediate for the catalytic decomposition reactions. The combined use of gas analysis and IRAS results enabled us to derive the values of 58 ± 3 and 49 ± 3 kJ/mol as the activation energy for the dehydrogenation and dehydration reactions, respectively, of the monodentate formate on the surface.

A novel reaction path was found for the double-bond migration (DBM) of 1-butene on very strong Brønsted acid sites (BAS) of zeolites, ZSM-5 and mordenite (MOR), in the absence of protonation below 230 K with the activation energies of 49 ± 4 kJ·mol^-1 on D-ZSM-5 and 38 ± 8 kJ·mol^-1 on D-MOR (DM20). By using deuterated zeolites, it was proved that the protonated intermediate is not essential to the conversion of the 1-butene to the hydrogen-bonded cis- and trans-2-butenes on the BAS of ZSM-5 and MOR. If the widely accepted protonated intermediate is assumed, the acidic OD groups should be converted to OH groups upon the DBM of 1-butene to 2-butenes. Nevertheless, the OD groups of zeolites forming 1:1 complex with 1-butene remained unchanged even after the double-bond migration. The isotope exchange reaction of OD groups due to the proton transfer occurred at higher temperature than the DBM. However, the DBM on a deuterated faujasite (FAU) zeolite (DY5.6 and DY4.8) proceeded accompanied by the H/D exchange reaction of the acidic OD groups, suggesting that the protonated intermediate is essential for the reaction on rather weak BAS. Thus, the existence of a new type of reaction catalyzed by very strong BAS is demonstrated, which takes place more facilely than the proton transfer.

The dehydration of formate adsorbed on Ni(110) has been studied by the direct observation of the CO(a) produced on the surface by means of time-resolved infrared reflection absorption spectroscopy (TR-IRAS). By the quantitative analysis of the temperature-programmed desorption and TR-IRAS results, it was found that the dehydration proceeds simultaneously with the dehydrogenation. The primary kinetic isotope effect (kH/kD) using HCOO(a) and DCOO(a) was observed not only in the dehydrogenation but also in the dehydration (kH/kD = 3.3 at 300 K). This result suggests that the rate-determining step (RDS) is the C−H bond dissociation in both processes. These suggestions let us propose a possible mechanism of the dehydration of formate on Ni(110); the RDS of the dehydration is the C−H bond dissociation which is the same as that of the dehydrogenation, and the produced CO2(a) is the precursor of the production of CO(a) and O(a).

Unstable intermediates are indispensable ingredients of chemical reactions, but their identification at solid surfaces has been hampered by the lack of techniques to detect short-lived and fractionally generated species. We succeeded in identifying the intermediate in a thermal decomposition reaction by utilizing the picosecond temperature jump induced by the irradiation of laser pulses and the observation by sum-frequency generation spectroscopy. We verified that the decomposition of formate on the NiO(111) surface is preceded by the transformation of stable bidentate formate to unstable monodentate formate, which is the reactive intermediate, and two species are found to be in equilibrium before decomposition.

The dynamic behavior of adsorbed formate on Ni(110) in the presence of gaseous formic acid was studied by time-resolved infrared reflection absorption spectroscopy. The preadsorbed formate (DCOO(a)) was replaced by the postexposed formic acid (HCOOD) to form HCOO(a) on Ni(110) in the temperature region between 230 and 300 K, where the formate was stable under vacuum and no decomposition of formate was observed. It was confirmed that the preadsorbed DCOO(a) desorbed as DCOOD accompanied by formation of HCOO(a) via the deuterium atom transfer from HCOOD.

A novel reaction of the double-bond migration (DBM) of 1-butene on Brønsted acid sites (BAS) of zeolites in the absence of proton transfer from BAS to the adsorbed olefin was found. The widely accepted protonated intermediate should result in the conversion of the acidic OD groups to OH upon the DBM. Nevertheless, the OD groups forming a 1:1 complex with the adsorbed 1-butene were unchanged even after the reaction. The isotope exchange of OD groups occurred at a higher temperature than that of the DBM. Thus, the existence of a new type of reaction on BAS is demonstrated, which takes place more easily than the proton transfer.

The site conversion of some bridged (b-) methoxy species to the terminal ones on ZrO2 was directly observed by infrared spectroscopy between 523 and 623 K, accompanied by thermal decomposition of coadsorbed formate species. The observed site conversion was interpreted in terms of methoxy migration on the ZrO2 surface, which was previously supposed to occur in the H/D isotope exchange reaction of both methoxy groups with b-OD groups.