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Our previous study showed that a rhodium (Rh) cocatalyst is indispensable for ring hydrogenation of benzoic acid over a titanium(IV) oxide (TiO2) photocatalyst. In this study, we explored ring hydrogenation under an Rh-free condition by using two kinds of cocatalyst that were inactive for this reaction when used solely. Cyclohexanecarboxylic acid as the ring hydrogenation product was successfully obtained when ruthenium (Ru) and palladium (Pd) were simultaneously loaded on TiO2, indicating that this bimetallic system can be used in place of an Rh cocatalyst in ring hydrogenation. The state and distribution of Ru and Pd in particles loaded on TiO2 were investigated by transmission electron microscopy, X-ray photon spectroscopy, and X-ray absorption near edge structure analysis. The functions of Ru and Pd as cocatalysts are discussed on the basis of results of characterization and activity tests. The effects of different contents of Ru and Pd in Ru–Pd/TiO2 prepared by a two-step photodeposition method on catalytic activity and the features of the reaction system were investigated in detail. [ABSTRACT FROM AUTHOR]

Improvement of the low-temperature activity for NO oxidation catalysts is a crucial issue to improve the NOx storage performance in automotive catalysts. We have recently reported that the lattice oxygen species in SrFeO3−δ (SFO) are reactive in the oxidation of NO to NO2 at low temperatures. The oxidation of NO using lattice oxygen species is a powerful means to oxidize NO in such kinetically restricted temperature regions. This paper shows that Fe-site substitution of SFO with Mn or Co improves the properties of lattice oxygen such as the temperature and amount of oxygen release/storage, resulting in the enhancement of the activity for NO oxidation in a low-temperature range. In particular, NO oxidation on SrFe0.8Mn0.2O3−δ is found to proceed even at extremely low temperatures <423 K. From oxygen release/storage profiles obtained by temperature-programmed reactions, Co doping into SFO increases the amount of released oxygen owing to the reducibility of the Co species and promotes the phase transformation to the brownmillerite phase. On the other hand, Mn doping does not increase the oxygen release amount and suppresses the phase transformation. However, it significantly decreases the oxygen migration barrier of SFO. Substitution with Mn renders the structure of SFO more robust and maintains the perovskite structure after the release of oxygen. Thus, the oxygen release properties are strongly dependent on the crystal structure change before and after oxygen release from the perovskite structure, which has a significant effect on NO oxidation and the NOx storage performance. [ABSTRACT FROM AUTHOR]

Ni–Cu alloy supported on γ-Al2O3 catalysts prepared by high-temperature hydrogen reduction exhibit high catalytic activity and durability for a three-way catalytic reaction under both oxidative and reductive conditions because of their self-regenerating feature. DFT calculations showed that Ni-oxide was reduced to Ni metal by CO in the presence of Cu metal because of the Ni–Cu alloy effect but was not in the absence of Cu metal. [ABSTRACT FROM AUTHOR]

The efficiency of catalytic systems for the removal of nitrogen oxides (NOx) from automotive exhaust gases is strongly affected by the oxygen concentration in the exhaust gas. To overcome this problem, an oxygen storage material has been used in the purification systems. This study demonstrates the NO reduction under various oxygen concentrations over Pd/Sr3Fe2O7−δ catalysts in which Fe is partially replaced by other transition metals (Mn, Co, Ni, and Cu). Pd/Sr3(Fe0.8Ni0.2)2O7−δ with a layered perovskite structure showed the highest NO reduction activity among the examined catalysts under a wide range of oxygen concentrations. Ni3+ was found to replace Fe3+ rather than Fe4+ in Sr3Fe2O7−δ. Pd/Sr3(Fe0.8Ni0.2)2O7−δ showed significantly improved oxygen storage capacity as compared to Pd/Sr3Fe2O7−δ, which was attributed to the redox between Ni3+ and Ni2+ accompanying the Fe4+/Fe3+ redox reaction during oxygen release/storage processes. This study provides useful information for the design of novel catalysts with a perovskite-type structure. [ABSTRACT FROM AUTHOR]

A core–shell structure of Ag–Cr dual cocatalyst loaded-Ga2O3 was found to significantly enhance the formation rate of CO and selectivity toward CO evolution for the photocatalytic conversion of CO2 where H2O is used as an electron donor. [ABSTRACT FROM AUTHOR]

A feasibility study of a “range-extended” EXAFS measurement was conducted on the Pt L3-edge of Pt/Al2O3 in the presence of Au2O3. The Pt L3-edge EXAFS spectrum of the Pt/Al2O3 sample was successfully obtained without any interference at the Au L3-edge by means of high energy resolution fluorescence detection (HERFD) of the Pt Lα1 line with a Bragg type X-ray emission analyser crystal. A newly observed significant enhancement of the EXAFS oscillation amplitude was discussed on the points of the core-hole lifetime width and X-ray energy width. We also successfully obtained reasonable physical parameters by a conventional EXAFS curve fitting on the HERFD-EXAFS data. The HERFD-EXAFS technique can broaden the scope of application of EXAFS spectroscopy for complicated samples with many different elements. [ABSTRACT FROM AUTHOR]

A feasibility study of a “range-extended” EXAFS measurement was conducted on the Pt L3-edge of Pt/Al2O3 in the presence of Au2O3. The Pt L3-edge EXAFS spectrum of the Pt/Al2O3 sample was successfully obtained without any interference at the Au L3-edge by means of high energy resolution fluorescence detection (HERFD) of the Pt Lα1 line with a Bragg type X-ray emission analyser crystal. A newly observed significant enhancement of the EXAFS oscillation amplitude was discussed on the points of the core-hole lifetime width and X-ray energy width. We also successfully obtained reasonable physical parameters by a conventional EXAFS curve fitting on the HERFD-EXAFS data. The HERFD-EXAFS technique can broaden the scope of application of EXAFS spectroscopy for complicated samples with many different elements. [ABSTRACT FROM AUTHOR]

Praseodymium-modified gallium oxide (Pr/Ga2O3) was found to show enhanced activity and selectivity toward CO evolution in the photocatalytic conversion of CO2 using H2O as an electron donor in an aqueous solution of NaHCO3 as compared to those of bare Ga2O3. The as-prepared Pr species, including Pr(OH)3 and Pr2O2CO3, on the surface of Ga2O3 were transformed into Pr hydroxycarbonates (Pr2(OH)2(3−x)(CO3)x) and Pr carbonate hydrates (Pr2(CO3)3·8H2O) in an aqueous solution of NaHCO3, and then the Pr2(OH)2(3−x)(CO3)x was further transformed into Pr2(CO3)3·8H2O by CO2 bubbling under photoirradiation. This indicates that CO2 molecules dissolved in water can be captured and stored using Pr species in an aqueous solution of NaHCO3 under CO2 bubbling. More importantly, Pr2(OH)2(3−x)(CO3)x and Pr2(CO3)3·8H2O accumulated on the surface were decomposed to CO over the Ga2O3 photocatalyst with a Ag cocatalyst. Consequently, Ag/Pr/Ga2O3 exhibits much higher activity (249 μmol h−1 of CO) than the pristine Ag-loaded Ga2O3 (136 μmol h−1 of CO). [ABSTRACT FROM AUTHOR]

This study proves that a small amount of Pd loading (1 wt%) on Sr3Fe2O7−δ can dramatically enhance the oxygen-storage properties of Sr3Fe2O7−δ. The topotactic oxygen intake and release between Sr3Fe2O6.75 and Sr3Fe2O6 takes place in response to gas switching between an O2 flow and H2 flow, regardless of the presence or absence of Pd loading. The effect of Pd loading is significant for the oxygen-release process under H2 atmosphere; that is, highly dispersed Pd metal nanoparticles sized less than 1 nm formed on Pd/Sr3Fe2O7−δ to promote H2 dissociation, resulting in the improvement of the oxygen-release temperature and rate. Pd/Sr3Fe2O7−δ with a layered perovskite structure has a higher oxygen-release property at lower temperature than Pd/SrFeO3−δ with a perovskite phase without the layered structure. These facts indicate that the surface reaction as well as the crystal structure are responsible for the oxide ion mobility in perovskite structure, and also provide guidelines for designing novel oxygen-storage materials. [ABSTRACT FROM AUTHOR]

Our previous study showed that a rhodium (Rh) cocatalyst is indispensable for ring hydrogenation of benzoic acid over a titanium(IV) oxide (TiO 2 ) photocatalyst. In this study, we explored ring hydrogenation under an Rh-free condition by using two kinds of cocatalyst that were inactive for this reaction when used solely. Cyclohexanecarboxylic acid as the ring hydrogenation product was successfully obtained when ruthenium (Ru) and palladium (Pd) were simultaneously loaded on TiO 2 , indicating that this bimetallic system can be used in place of an Rh cocatalyst in ring hydrogenation. The state and distribution of Ru and Pd in particles loaded on TiO 2 were investigated by transmission electron microscopy, X-ray photon spectroscopy, and X-ray absorption near edge structure analysis. The functions of Ru and Pd as cocatalysts are discussed on the basis of results of characterization and activity tests. The effects of different contents of Ru and Pd in Ru-Pd/TiO 2 prepared by a two-step photodeposition method on catalytic activity and the features of the reaction system were investigated in detail.

Loading Ag and Co dual cocatalysts on Al-doped SrTiO 3 (AgCo/Al-SrTiO 3 ) led to a significantly improved CO-formation rate and extremely high selectivity toward CO evolution (99.8%) using H 2 O as an electron donor when irradiated with light at wavelengths above 300 nm. Furthermore, the CO-formation rate over AgCo/Al-SrTiO 3 (52.7 μmol h -1 ) was a dozen times higher than that over Ag/Al-SrTiO 3 (4.7 μmol h -1 ). The apparent quantum efficiency for CO evolution over AgCo/Al-SrTiO 3 was about 0.03% when photoirradiated at a wavelength at 365 nm, with a CO-evolution selectivity of 98.6% (7.4 μmol h -1 ). The Ag and Co cocatalysts were found to function as reduction and oxidation sites for promoting the generation of CO and O 2 , respectively, on the Al-SrTiO 3 surface., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Improvement of the low-temperature activity for NO oxidation catalysts is a crucial issue to improve the NO x storage performance in automotive catalysts. We have recently reported that the lattice oxygen species in SrFeO 3-δ (SFO) are reactive in the oxidation of NO to NO 2 at low temperatures. The oxidation of NO using lattice oxygen species is a powerful means to oxidize NO in such kinetically restricted temperature regions. This paper shows that Fe-site substitution of SFO with Mn or Co improves the properties of lattice oxygen such as the temperature and amount of oxygen release/storage, resulting in the enhancement of the activity for NO oxidation in a low-temperature range. In particular, NO oxidation on SrFe 0.8 Mn 0.2 O 3-δ is found to proceed even at extremely low temperatures <423 K. From oxygen release/storage profiles obtained by temperature-programmed reactions, Co doping into SFO increases the amount of released oxygen owing to the reducibility of the Co species and promotes the phase transformation to the brownmillerite phase. On the other hand, Mn doping does not increase the oxygen release amount and suppresses the phase transformation. However, it significantly decreases the oxygen migration barrier of SFO. Substitution with Mn renders the structure of SFO more robust and maintains the perovskite structure after the release of oxygen. Thus, the oxygen release properties are strongly dependent on the crystal structure change before and after oxygen release from the perovskite structure, which has a significant effect on NO oxidation and the NO x storage performance.

A core-shell structure of Ag-Cr dual cocatalyst loaded-Ga 2 O 3 was found to significantly enhance the formation rate of CO and selectivity toward CO evolution for the photocatalytic conversion of CO 2 where H 2 O is used as an electron donor.

This study proves that a small amount of Pd loading (1 wt%) on Sr 3 Fe 2 O 7-δ can dramatically enhance the oxygen-storage properties of Sr 3 Fe 2 O 7-δ . The topotactic oxygen intake and release between Sr 3 Fe 2 O 6.75 and Sr 3 Fe 2 O 6 takes place in response to gas switching between an O 2 flow and H 2 flow, regardless of the presence or absence of Pd loading. The effect of Pd loading is significant for the oxygen-release process under H 2 atmosphere; that is, highly dispersed Pd metal nanoparticles sized less than 1 nm formed on Pd/Sr 3 Fe 2 O 7-δ to promote H 2 dissociation, resulting in the improvement of the oxygen-release temperature and rate. Pd/Sr 3 Fe 2 O 7-δ with a layered perovskite structure has a higher oxygen-release property at lower temperature than Pd/SrFeO 3-δ with a perovskite phase without the layered structure. These facts indicate that the surface reaction as well as the crystal structure are responsible for the oxide ion mobility in perovskite structure, and also provide guidelines for designing novel oxygen-storage materials.

A combination of in situ time-resolved DXAFS and ICP-MS techniques reveals that the formation process of Rh nanoparticles (NPs) from rhodium trichloride trihydrate (RhCl(3)·3H(2)O) in ethylene glycol with polyvinylpyrrolidone (PVP) at elevated temperature is a first-order reaction, which indicates that uniform size Rh NPs appear consecutively and these Rh NPs do not aggregate with each other.