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For stringent regulations of exhaust gases from gasoline-powered vehicles, small amount of platinum-group metals (PGMs) in automotive catalysts is highly required. To satisfy this requirement, applications of base-metal catalysts such as Fe and Mn have been vigorously discussed and investigated. Previously, we reported that rare earth metals containing hexagonal Fe and Mn oxides work as effective support materials and active species in CO oxidation, C3H6 oxidation, and NO reduction. However, most of the base-metal oxides could be readily decomposed by gasoline engine aging at approximately 1000 °C. In this study, we show that hexagonal YbMnO3 (h-YbMnO3) can be obtained as single-phase using the simple coprecipitation method with H2O2. Moreover, h-YbMnO3 can function as a oxygen storage material, which maintains its hexagonal structure after hydrothermal aging at 1000 °C for 25 h owing to the small ionic radius of Yb. On the other hand, isostructural YMnO3 (h-YMnO3) can be easily decomposed under the same aging condition. The catalytic performances of Pd loaded materials (Pd/h-YbMnO3, Pd/Al2O3, and Pd/CeO2-ZrO2 (CZ)) on cordierite honeycomb substrates were evaluated. Among them, Pd/h-YbMnO3 exhibited the highest oxidation activities even though it had significantly lower specific surface area (SSA). In particular, Pd/h-YbMnO3 exhibits a strong effect on paraffin oxidation such as C3H8, which is less reactive than other olefinic and aromatic hydrocarbons for automotive catalysts. [ABSTRACT FROM AUTHOR]

Adsorbed hydrogen (H) species on catalyst surfaces are important active intermediates in many catalytic reactions and detailed analyses of them are necessary to understand the catalyses. Inelastic neutron scattering (INS) enables direct and selective observation of H species due to the extremely large incoherent neutron scattering cross section of a hydrogen atom. In the present study, the adsorbed H species on some heterogeneous precious metal catalysts supported by alumina and carbon black were investigated by in situ INS spectroscopy with a newly designed sample cell. The newly designed double-walled long cell gave clear INS spectra with less elastic scattering. Three alumina-supported metal catalysts having Pt, Pd, and Rh metal nanoparticles with different particle sizes exhibited different INS spectra in intensities and band distribution. Observation of the H species on the metal nanoparticles and the alumina surface revealed their properties. In addition, the H atoms stored in Pd nanoparticles were observed as palladium hydride. In contrast, the H species on a Pt catalyst supported by carbon black were found to be strongly adsorbed on the carbon support. The properties of these H species were dependent on both the properties of the precious metals and those of the support materials. [ABSTRACT FROM AUTHOR]

Cu-modified TiO photocatalysts (Cu/TiO) were fabricated by electroless plating and wet impregnation methods. Photocatalytic activity for H production over Cu/TiO by electroless plating method was higher than that over Cu/TiO by impregnation method. Characterization of Cu nanoparticles by HRTEM, STEM-EDX, XRD and XAFS was studied. As compared to the wet impregnation method, the electroless plating method resulted in the formation of Cu nanoparticles with small size and uniform distribution on the TiO surface, which caused the enhancement of H production. XAFS measurement provided the evidences for the chemical state change of Cu species during the photocatalytic reaction. The process that Cu species varied from Cu into Cu via Cu as the intermediate under photoirradiation is very important for the H production, which indicates that the metallic Cu nanoparticles acted as the active sites and restrained the photogenerated charges recombination. [ABSTRACT FROM AUTHOR]

The possibility of the direct electron transition between the donor/acceptor level generated by adsorbed molecules and the conduction/valence band for photo-illuminated semiconductor-type metal oxide is discussed. The effective wavelength is shifted to a longer wavelength by the formation of donor/acceptor level derived from adsorbed molecule (called here 'in situ doping'). This photo-activation mechanism by 'in situ doping' gives us attractive ways for the removing the limit of band-gap energy, and the utilization of visible light. [ABSTRACT FROM AUTHOR]

Basic nanospace was synthesized by the homogeneous modification of FSM-16 with 3-(triethoxysilyl)pyridine, which is a rigid substrate without an alkyl chain as linker. Aldol condensation of butanal gave the corresponding dimer in high yields over 3-(triethoxysilyl)pyridine-modified FSM-16. A copper-pyridine complex was immobilized within the interior of FSM-16 using the modified pyridyl group as a ligand and the oxidative coupling polymerization of 2,5-dimethylphenol proceeded with high regio-selectivity. Graphical Abstract: Basic nanospace was synthesized by the homogeneous modification of FSM-16 with 3-(triethoxysilyl)pyridine, which is a rigid substrate without an alkyl chain as linker. Aldol condensation of n-butyraldehyde gave the corresponding dimer in high yields over 3-(triethoxysilyl)pyridine-modified FSM-16. A copper-pyridine complex was immobilized within the interior of FSM-16 using a modified pyridyl group as the ligand and the oxidative polymerization of 2,5-dimethylphenol proceeded with high regio-selectivity.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Nb2O5/Al2O3 catalysts calcined at high temperatures exhibited the Brønsted acid property. A monolayer of niobic acid-like compound, which has distorted octahedral symmetry, was stabilized over 16 wt% Nb2O5/Al2O3 catalyst calcined at 1,173 K. The two-dimensional Nb–O–Nb network of stabilized niobic acid-like compound probably accounts for the generation of Brønsted acid. [ABSTRACT FROM AUTHOR]

The dynamic reduction behavior of a highly dispersed Pt4+ to Pt0 particles on TiO2 and Al2O3 surfaces under the reductive atmosphere with an in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis. A highly dispersed Pt4+ on TiO2 was reduced to Pt0 even at room temperature. In contrast, a highly dispersed Pt4+ on Al2O3 was gradually reduced to Pt0 even at 473 K. This result may suggest that the semiconductive behavior of TiO2 promotes the low temperature adsorption of hydrogen and supply of hydrogen atom to Pt4+ to be reduced and the activation of hydrogen on Al2O3 requires high temperature. [ABSTRACT FROM AUTHOR]

Alumina-supported niobium oxide promotes Friedel–Crafts reaction of benzyl alcohol and anisole effectively. The optimized condition of the catalyst was 16 wt% as Nb2O5 and calcination temperature of 1173 K. The catalyst exhibits the Brønsted acidity despite calcination at such high temperatures. [ABSTRACT FROM AUTHOR]

The vibronic interactions in a photocatalyst, isolated vanadium oxide on silica, is investigated theoretically employing a vibronic model. The T1 state gives rise to a Jahn-Teller distortion after the excitation. The HOMO is destabilized against the JT distortion, while the system is stabilized because of the JT effect. [ABSTRACT FROM AUTHOR]

Tetradentate thioacetyl porphyrin ligand ( 1) was synthesized to protect gold nanoparticles. 1-protected gold nanoparticles were characterized by UV-vis spectroscopy and XPS. Analysis by XPS showed that all of four thioacetyl groups of 1 were dissociated and bound to the surface of gold nanoparticles in thiolate form. The size of 1-protected gold nanoparticles ( GN:1) was controlled by thioacetyl group/HAuCl4 molar ratio and approached to 2 nm. Compared with a protecting ligand without porphyrin plane ( 2) or dodecanethiol, 1 can control the size of gold nanoparticles efficiently probably due to the tetradentate ligation effect. [ABSTRACT FROM AUTHOR]

The pore-size dependence of the acidic properties of mesoporous silica FSM-16 in the range from 1.8 to 3.8 nm was investigated with the catalysis of 2-butanol dehydration and using FTIR spectra of adsorbed pyridine. The activity was the highest for FSM-16 with a minimum pore diameter, and decreased with increasing pore size. Differences in the acid amounts of siliceous FSM-16 and the strength dependent on the pore diameter were not confirmed by FTIR characterization using pyridine as a probe molecule. [ABSTRACT FROM AUTHOR]

The photo-assisted selective catalytic reduction (SCR) of NO with NH3 (Photo-SCR) was performed over TiO2 modified by supporting 1 wt% of various transition metal (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ta or W) oxides aiming at the improvement of the photo-SCR activity. The addition of Nb, Mo or W oxide to TiO2 was found to enhance the photo-SCR activity. We have reported that the amount of acid sites on TiO2 is one of the key factors to the photo-SCR activity. The increase in the activity depends on the enhancement of acidity of catalyst by the addition of Nb, Mo or W oxide. In contrast, the addition of V, Cr, Mn, Fe, Co, Ni or Cu oxide to TiO2 lowered the photo-SCR activity, although addition of metal cations also changed the acidity of TiO2. We guess that the reduction of the activity was caused by two reasons; the first is that the sites newly formed on these transition metal oxides is not photoactive and the second is that TiO2 supporting V, Cr, Mn, Fe, Co, Ni or Cu oxides had low stabilities under the reaction conditions, i.e., the chemical state of the cations changed during the reaction. Therefore, we concluded that the increase in the acid sites that are active sites for photo-SCR and the stability of the catalysts are important for the photo-SCR. [ABSTRACT FROM AUTHOR]

Three types of CeO2–ZrO2 (Ce:Zr = 1:1 molar ratio) compounds with different oxygen storage/release capacity (OSC) were characterized by means of the Ce K-edge and Zr K-edge XAFS. In order to investigate the relationship between the OSC and local structure, the quantitative EXAFS curve-fitting analysis was applied. By enhancing the homogeneity of the Ce and Zr atoms in the CeO2–ZrO2 solid solution, the OSC performance increased. Additionally, from the XRD analysis, the homogeneous CeO2–ZrO2 solid solution has an ordered cation arrangement, and exhibits the highest OSC. The crystal structure of this CeO2–ZrO2 solid solution is usually termed as “κ-CeZrO4 phase”. However, the OSC performance of κ-CeZrO4 degrades upon a high-temperature treatment under an oxidative atmosphere. The fresh κ-CeZrO4 was aged at 973, 1,273 and 1,473 K under an oxidative atmosphere, respectively. The OSC performance deteriorated as: the fresh sample ≈973 > 1,273 > 1,473 K-aged samples. We also found that, if the temperature was beyond 1,273 K, the Ce/Zr ordered arrangement would collapse and the local structure around Ce and Zr ions would also changed remarkably. These results indicated that OSC was strongly dependent on its atomic structure. [ABSTRACT FROM AUTHOR]

The transparent Ti-containing or Cr-containing mesoporous silica thin films can be prepared on quartz plate using a spin-coating sol–gel method. The spectroscopic characterization has revealed that these thin films contain isolated and tetrahedrally coordinated titanium oxide moieties and chromium oxide moieties in their frameworks, respectively. These mesoporous silica thin films containing metal oxide moieties have demonstrated a strong hydrophilic surface property even before UV-light irradiation and the appearance of the super-hydrophilic property after UV-light irradiation. Especially, the Cr-containing mesoporous silica (CMS) thin film showed the super-hydrophilic property even under visible light irradiation. In the presence of ethylene gas, the polyethylene was successfully formed on the surface of the CMS thin film under UV-light irradiation. After the formation of polyethylene the surface property of the CMS was converted into hydrophobic while keeping its transparency. The isolated and tetrahedrally coordinated titanium oxide moieties and chromium oxide moieties are responsible for these photo-induced surface reactions. [ABSTRACT FROM AUTHOR]

The local structure around Cu supported on Al2O3 was determined by UV/VIS/NIR and XAFS spectroscopic techniques. The relationship between catalytic performance for NO–CO–O2 reaction and the state of supported Cu species is discussed. A new method for estimating the fraction of aggregated to isolated Cu species is proposed. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis is a desirable critical technology for the conversion of CO2 and H2O, which are abundant raw materials, into fuels and chemical feedstocks. Similar to plant photosynthesis, artificial photosynthesis can produce CO, CH3OH, CH4, and preferably higher hydrocarbons from CO2 using H2O as an electron donor and solar light. At present, only insufficient amounts of CO2-reduction products such as CO, CH3OH, and CH4 have been obtained using such a photocatalytic and photoelectrochemical conversion process. Here, we demonstrate that photocatalytic CO2 conversion with a Ag@Cr-decorated mixture of CaGa4O7-loaded Ga2O3 and the CaO photocatalyst leads to a satisfactory CO formation rate (>835 µmol h−1) and excellent selectivity toward CO evolution (95%), with O2 as the stoichiometric oxidation product of H2O. Our photocatalytic system can convert CO2 gas into CO at >1% CO2 conversion (>11531 ppm CO) at ambient temperatures and pressures. Photocatalytic CO2 reduction requires catalysts that are both active and selective. Here, a mixture of CaGa4O7-loaded Ga2O3 and CaO, decorated with Ag@Cr core-shell particles, delivers over 835 µmol h−1 of CO at >95 % selectivity. [ABSTRACT FROM AUTHOR]

Single-atom catalysts have recently been applied in many applications such as CO oxidation. Experimental in situ investigations into this reaction, however, are limited. Hereby, we present a suite of operando/in situ spectroscopic experiments for structurally well-defined atomically dispersed Rh on phosphotungstic acid during CO oxidation. The identification of several key intermediates and the steady-state catalyst structure indicate that the reactions follow an unconventional Mars-van Krevelen mechanism and that the activation of O2 is rate-limiting. In situ XPS confirms the contribution of the heteropoly acid support while in situ DRIFT spectroscopy consolidates the oxidation state and CO adsorption of Rh. As such, direct observation of three key components, i.e., metal center, support and substrate, is achieved, providing a clearer picture on CO oxidation on atomically dispersed Rh sites. The obtained information are used to engineer structurally similar catalysts that exhibit T20 values up to 130 °C below the previously reported Rh1/NPTA. Single-atom catalysts have been studied for CO oxidation, but experimental in situ investigations are limited. Here, the authors use a suite of in situ/operando spectroscopy to identify key intermediates and define design principles to enhance the CO oxidation activity of atomically dispersed Rh on heteropoly acids. [ABSTRACT FROM AUTHOR]

Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period. [ABSTRACT FROM AUTHOR]

A preface to the June 1, 2009 issue of the journal "Topics in Catalysis," is presented.

The dynamic reduction behavior of a highly dispersed Pt4+ to Pt0 particles on TiO2 and Al2O3 surfaces under the reductive atmosphere with an in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis. A highly dispersed Pt4+ on TiO2 was reduced to Pt0 even at room temperature. In contrast, a highly dispersed Pt4+ on Al2O3 was gradually reduced to Pt0 even at 473 K. This result may suggest that the semiconductive behavior of TiO2 promotes the low temperature adsorption of hydrogen and supply of hydrogen atom to Pt4+ to be reduced and the activation of hydrogen on Al2O3 requires high temperature. [ABSTRACT FROM AUTHOR]

The vibronic interactions in a photocatalyst, isolated vanadium oxide on silica, is investigated theoretically employing a vibronic model. The T1 state gives rise to a Jahn-Teller distortion after the excitation. The HOMO is destabilized against the JT distortion, while the system is stabilized because of the JT effect. [ABSTRACT FROM AUTHOR]

The photo-assisted selective catalytic reduction (SCR) of NO with NH3 (Photo-SCR) was performed over TiO2 modified by supporting 1 wt% of various transition metal (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ta or W) oxides aiming at the improvement of the photo-SCR activity. The addition of Nb, Mo or W oxide to TiO2 was found to enhance the photo-SCR activity. We have reported that the amount of acid sites on TiO2 is one of the key factors to the photo-SCR activity. The increase in the activity depends on the enhancement of acidity of catalyst by the addition of Nb, Mo or W oxide. In contrast, the addition of V, Cr, Mn, Fe, Co, Ni or Cu oxide to TiO2 lowered the photo-SCR activity, although addition of metal cations also changed the acidity of TiO2. We guess that the reduction of the activity was caused by two reasons; the first is that the sites newly formed on these transition metal oxides is not photoactive and the second is that TiO2 supporting V, Cr, Mn, Fe, Co, Ni or Cu oxides had low stabilities under the reaction conditions, i.e., the chemical state of the cations changed during the reaction. Therefore, we concluded that the increase in the acid sites that are active sites for photo-SCR and the stability of the catalysts are important for the photo-SCR. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis is a desirable critical technology for the conversion of CO2 and H2O, which are abundant raw materials, into fuels and chemical feedstocks. Similar to plant photosynthesis, artificial photosynthesis can produce CO, CH3OH, CH4, and preferably higher hydrocarbons from CO2 using H2O as an electron donor and solar light. At present, only insufficient amounts of CO2-reduction products such as CO, CH3OH, and CH4 have been obtained using such a photocatalytic and photoelectrochemical conversion process. Here, we demonstrate that photocatalytic CO2 conversion with a Ag@Cr-decorated mixture of CaGa4O7-loaded Ga2O3 and the CaO photocatalyst leads to a satisfactory CO formation rate (>835 µmol h−1) and excellent selectivity toward CO evolution (95%), with O2 as the stoichiometric oxidation product of H2O. Our photocatalytic system can convert CO2 gas into CO at >1% CO2 conversion (>11531 ppm CO) at ambient temperatures and pressures. Photocatalytic CO2 reduction requires catalysts that are both active and selective. Here, a mixture of CaGa4O7-loaded Ga2O3 and CaO, decorated with Ag@Cr core-shell particles, delivers over 835 µmol h−1 of CO at >95 % selectivity. [ABSTRACT FROM AUTHOR]