Catalytic converters are widely used to reduce the amounts of nitrogen oxides, carbon monoxide and unburned hydrocarbons in automotive emissions. The catalysts are finely divided precious-metal particles dispersed on a solid support. During vehicle use, the converter is exposed to heat, which causes the metal particles to agglomerate and grow, and their overall surface area to decrease. As a result, catalyst activity deteriorates. The problem has been exacerbated in recent years by the trend to install catalytic converters closer to the engine, which ensures immediate activation of the catalyst on engine start-up, but also places demanding requirements on the catalyst's heat resistance. Conventional catalyst systems thus incorporate a sufficient excess of precious metal to guarantee continuous catalytic activity for vehicle use over 50,000 miles (80,000 km). Here we use X-ray diffraction and absorption to show that LaFe(0.57)Co(0.38)Pd(0.05)O(3), one of the perovskite-based catalysts investigated for catalytic converter applications since the early 1970s, retains its high metal dispersion owing to structural responses to the fluctuations in exhaust-gas composition that occur in state-of-the-art petrol engines. We find that as the catalyst is cycled between oxidative and reductive atmospheres typically encountered in exhaust gas, palladium (Pd) reversibly moves into and out of the perovskite lattice. This movement appears to suppress the growth of metallic Pd particles, and hence explains the retention of high catalyst activity during long-term use and ageing.

Automotive catalysts deteriorate as a result of a decrease in the active surface area of the precious metals, this is caused by the growth of grains under the inherent redox environment of exhaust gases at high temperatures of up to 1000 8C. To compensate for this deterioration, conventional catalysts are loaded with an excess amount of precious metals, although this leads to over-consumption and supply problems. Selfregenerating catalysts, which suppress the grain growth of precious metals, have recently been successfully developed and are based on the repeated movement of the precious metals in and out of perovskite oxides between a solid solution and metallic nanoparticles during the natural changes in the redox conditions.[1] Herein, we report for the first time that this self-regenerating function is realizable in Pt and Rh, as well as in Pd.It has been predicted that the demand for precious metals for automotive catalysts will increase, and that these metals will soon be in short supply as a result of the growth in the number of automobiles in China and India and the global

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ABSTRACT:In situ electrochemical X-ray absorption fine structure (XAFS) measurements were performed at the Pt L 3 and Ce L 3 edges of the Pt−CeO x /C catalyst, which was prepared by a combined process of precipitation and coimpregnation methods, as well as at the Pt L 3 edge of the conventional Pt/C catalyst in oxygen-saturated H 2 SO 4 solution to clarify the role of CeO x in the reduction of the overpotential for the oxygen reduction reaction (ORR) at the Pt−CeO x nanocomposite compared with the conventional Pt/C catalyst. XAFS measurements clearly show that the enhancement of ORR activity is attributed to the inhibition of Pt oxide formation by the CeO x layer, of which Ce 3+ was oxidized to Ce 4+ instead of Pt at the Pt oxide formation potential.

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We investigate LiVS2 and LiVSe2 with a triangular lattice as itinerant analogues of LiVO2, known for the formation of valence bond solid (VBS) state out of S = 1 frustrated magnet. LiVS2, which is located at the border between a metal and a correlated insulator, shows a first ordered transition from a paramagnetic metal to a VBS insulator at Tc ∼ 305 K upon cooling. The presence of VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of VBS state. We argue that the high temperature metallic phase of LiVS2 has a pseudo-gap, likely originating from the VBS fluctuation. LiVSe2 was found to be a paramagnetic metal down to 2 K. A question that arises is whether or not similar melting of the VBS state and appearance of exotic metallic phases can occur in inorganic frustrated systems. In the inorganic systems, however, application of an external pressure is expected not to melt but to stabilize VBS due to a predominant volume effect. In CuIr 2 S 4 , the lattice shrinks appreciably in the VBS perhaps due to the formation of strongly bonded singlet molecules and the VBS can be stabilized through -pV (p : pressure, V : volume) term in the corresponding free energy [11][12]. Effects of negative pressure on the VBS states of inorganic systems, on the other hand, have not been investigated so far.The inorganic LiVO 2 in which the magnetic V 3+ ions (3d 2 , S = 1) form a triangular lattice is known to be a paramagnetic insulator with strong antiferromagnetic interactions between the localized S = 1 moments at high temperatures. Upon cooling, at T c ∼ 500 K, LiVO 2 exhibits a first ordered phase transition to a VBS state with a characteristic spin gap of ∼ 1600 K, evidenced by the formation of vanadium trimers. With this system, one can apply "negative" pressure by replacing oxygens with larger anions such as S and Se [13,14,16]. More over, the negative pressure may increase the overlap between V 3d and p-orbital (O 2p, S 3p, and Se 4p), and increase the electronic band width. Thus, this vanadium-based triangular system provides a good opportunity to study effects of negative pressure on VBS states in inorganic materials.In this Letter, we demonstrate that LiVS 2 is indeed an itinerant analogue of LiVO 2 with suppressed VBS. We found that in LiVS 2 a phase transition from a paramagnetic metal to a trimer VBS insulator occurs at T c ∼ 305 K that is lower than that of LiVO 2 . In LiVSe 2 with highest negative pressure, the phase transition is suppressed down to 2 K. In the high temperature metallic phase of LiVS 2 , strong temperature dependence of the bulk susceptibility, χ, was observed, which is similar to the pseudo-gap behavior found in underdoped superconducting cuprates. We argue this is an evidence for a pseudo-gap formation by short-range spin singlet fluctuations in the paramagnetic metallic phase of LiVS 2 .Powder samples of LiVS 2 , LiVSe 2 and their solid solution LiVS 2−x Se x were prepared by a soft-chemical method followed by a solid-state reactio...

Automotive catalysts deteriorate as a result of a decrease in the active surface area of the precious metals, this is caused by the growth of grains under the inherent redox environment of exhaust gases at high temperatures of up to 1000 8C. To compensate for this deterioration, conventional catalysts are loaded with an excess amount of precious metals, although this leads to over-consumption and supply problems. Selfregenerating catalysts, which suppress the grain growth of precious metals, have recently been successfully developed and are based on the repeated movement of the precious metals in and out of perovskite oxides between a solid solution and metallic nanoparticles during the natural changes in the redox conditions.[1] Herein, we report for the first time that this self-regenerating function is realizable in Pt and Rh, as well as in Pd.It has been predicted that the demand for precious metals for automotive catalysts will increase, and that these metals will soon be in short supply as a result of the growth in the number of automobiles in China and India and the global

An x-ray absorption fine-structure (XAFS) spectroscopy beamline, BL01B1, was installed at a bending magnet source at SPring-8 and has been open to users since October 1997. It was designed for XAFS experiments covering a wide energy range. Position tables and automatical control programs were established to adjust the x-ray optics and achieve the designed performance of the beamline under each experimental condition. This has enabled conventional XAFS measurements to be made with a good data quality from 4.5 to 110 keV. Keywords: XAFS; high-energy; beamlines.143 radiation light will be reported elsewhere. The results show that the target specifications for the measured beam have almost been completely achieved except for sagittal focusing: a photon flux of 109-10 ~ phs/s with AE/E of <2x 104, a vertical beam size focused by a mirror of < 0.2 mm, and a ratio of the higher harmonics contaminant of < 10 .5 with mirrors.To achieve the designed performance of the beamline in a wide energy range, the beamline optics should be adjusted to the optimal position for each experiment. Because rearranging the monochromator and/or mirrors involves the realignment of many components, such rearranging can be done a few times per day. To achieve quick and easy adjustment, we prepared tables at the positions of the optical components and developed automatic control programs. This report gives an overview of the beamline status and some representative results highlighting the performance of BL01B 1.