Novel catalysts for environmental and energy-related conversions are increasingly emerging from rational design based on the understanding of relationships between structure at the molecular level and catalyst performance. Gold that is highly dispersed on metal oxides has surprisingly been found to be an active and selective catalyst for numerous reactions, [1,2] including CO oxidation.[3] Contradictory hypotheses have been advanced to account for the CO oxidation activity, [4][5][6][7][8][9][10][11][12][13] and the nature of the active sites and reactive oxygen intermediates remains elusive. [14,15] Herein we show by timeresolved spectroscopy of working catalysts consisting of gold nanoclusters on nanocrystalline CeO 2Àx that h 1 -superoxide and peroxide intermediates are formed at one-electron defect sites at the metal-support interface and oxidize adsorbed CO to CO 2 . The reactive oxygen species are not formed on conventionally prepared CeO 2 , and their formation on nanocrystalline CeO 2Àx is enhanced by the presence of the gold. This report is the first that unambiguously identifies and quantifies reactive oxygen species in low-temperature CO oxidation catalysis. The new concept advanced here is the representation of the catalytically active species as a composite that uniquely facilitates the formation of reactive oxygen species at the metal-support interface. The generality of the concept is exemplified by results showing that the nanocrystalline oxide can be either CeO 2Àx or Y 2 O 3 .[16] This concept opens new avenues to the design of novel materials with improved activities and selectivities for catalytic oxidation.We prepared high-surface-area (S BET = 180 m 2 g À1 ; BET refers to Brunauer, Emmett, and Teller) and thermally stable nanocrystalline CeO 2Àx with the fluorite structure by selfassembly in a liquid-crystal phase of individual CeO 2 nanoparticles with an average diameter of 5 nm.[17] Calcination of the nanocrystalline CeO 2Àx at 873 K either in the absence or in the presence of 20 wt % H 2 O produced minor changes in the BET surface area (S BET = 160 m 2 g À1 ). CeO 2 was also prepared by a conventional precipitation-calcination method to facilitate a comparison with the nanocrystalline material and to allow investigation of the influence of the surface structure.[12] Deposition-precipitation of gold on the two supports yielded samples with gold loadings in the range of 0.9-4.6 wt %. These samples were characterized by the following spectroscopic methods as they functioned as catalysts for CO oxidation at steady state in flow reactors: X-ray absorption near edge structure (XANES); extended Xray absorption fine structure (EXAFS); Raman; IR. Each of the samples catalyzed CO oxidation but gold supported on conventional CeO 2 was much less active than that on the nanocrystalline support. The spectra provide information that characterizes the oxidation state(s) and structure of the gold atoms as well as reactive oxygen species derived from the support and reactants.Highly active gold supported o...

China’s methadone maintenance treatment program was initiated in 2004 as a small pilot project in just eight sites. It has since expanded into a nationwide program encompassing more than 680 clinics covering 27 provinces and serving some 242 000 heroin users by the end of 2009. The agencies that were tasked with the program’s expansion have been confronted with many challenges, including high drop-out rates, poor cooperation between local governing authorities and poor service quality at the counter. In spite of these difficulties, ongoing evaluation has suggested reductions in heroin use, risky injection practices and, importantly, criminal behaviours among clients, which has thus provided the impetus for further expansion. Clinic services have been extended to offer clients a range of ancillary services, including HIV, syphilis and hepatitis C testing, information, education and communication, psychosocial support services and referrals for treatment of HIV, tuberculosis and sexually transmitted diseases. Cooperation between health and public security officials has improved through regular meetings and dialogue. However, institutional capacity building is still needed to deliver sustainable and standardized services that will ultimately improve retention rates. This article documents the steps China made in overcoming the many barriers to success of its methadone program. These lessons might be useful for other countries in the region that are scaling-up their methadone programs.

The addition of iron to high-area TiO2 (Degussa P25, a mixture of anatase and rutile) increases the number of oxygen defect sites that react with O2 to form peroxide and superoxide species. In the presence of gold nanoclusters on the TiO2 surface, the superoxide species become highly reactive, and the activity of the supported gold catalyst for CO oxidation is approximately twice that of the most active comparable catalysts described in the literature. Images of the catalyst obtained by scanning transmission electron microscopy combined with spectra of the catalyst measured in the working state (Raman, extended X-ray absorption fine structure, and X-ray absorption near-edge structure) indicate strong interactions of gold with the support and the presence of iron near the interfaces between the gold clusters and the TiO2 support. The high activity of the catalysts is attributed to the presence of defects in these sites that activate oxygen.

This article is a review of the physical characterization of well-defined site-isolated molecular metal complexes and metal clusters supported on metal oxides and zeolites. These surface species are of interest primarily as catalysts; as a consequence of their relatively uniform structures, they can be characterized much more precisely than traditional supported catalysts. The properties discussed in this review include metal nuclearity, oxidation state, and ligand environment, as well as metal-support interactions. These properties are determined by complementary techniques, including transmission electron microscopy; X-ray absorption, infrared, Raman, and NMR spectroscopies; and density functional theory. The strengths and limitations of these techniques are assessed in the context of results characterizing samples that have been investigated thoroughly and with multiple techniques. The depth of understanding of well-defined metal complexes and metal clusters on supports is approaching that attainable for molecular analogues in solution. The results provide a foundation for understanding the more complex materials that are typical of industrial catalysts.

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The selective hydrogenation of nitrobenzene (NB) over Ni/γ-Al 2 O 3 catalysts was investigated using different media of dense phase CO 2 , ethanol, and n-hexane. In dense phase CO 2 , the total rate of NB hydrogenation was larger than that in organic solvents under similar reaction conditions; the selectivity to the desired product, aniline, was almost 100% over the whole conversion range of 0-100%. The phase behavior of the reactant mixture in/under dense phase CO 2 was examined at reaction conditions. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions of CO 2 with the following reactant and reaction intermediates: NB, nitrosobenzene (NSB), and N-phenylhydroxylamine (PHA). Dense phase CO 2 strongly interacts with NB, NSB, and PHA, modifying the reactivity of each species and contributing to positive effects on the reaction rate and the selectivity to aniline. A possible reaction pathway for the hydrogenation of NB in/under dense phase CO 2 over Ni/γ-Al 2 O 3 is also proposed.

The gas phase (1 atm, 453 K) hydrogenation of p-chloronitrobenzene (p-CNB) over a series of laboratory-synthesized and commercial Pd (1–10% wt) supported on activated carbon (AC) and non-reducible (SiO2 and Al2O3) and reducible (ZnO) oxides has been examined. Reaction over these catalysts generated the target p-chloroaniline (p-CAN) (via selective hydrogenation) and nitrobenzene (NB)/aniline (AN) as a result of a combined hydrodechlorination/hydrogenation. A range of Pd nanoparticles with mean sizes 2.4–12.6 nm (from HRTEM and H2/CO chemisorption) were generated. Both the p-CNB transformation rate and H2 chemisorption increased with decreasing Pd size. Residual Mo (from the stabilizer used in the synthesis of Pd colloids) suppressed activity, but this was circumvented by the use of poly(N-vinyl-2-pyrrolidone) (PVP). Pd/AC generated p-CAN and AN as principal products, Pd on SiO2 and Al2O3 exhibited hydrodechlorination character generating AN and NB, and Pd/ZnO promoted the sole formation of p-CAN at all levels of conversion. Reaction selectivity is linked to Pd electron density with the formation of Pdδ+ on AC and the occurrence of Pdδ− on SiO2 and Al2O3. Reaction exclusivity to p-CAN over Pd/ZnO is attributed to the formation of PdZn alloy (demonstrated by XPS), which selectively activates the −NO2 group. This is the first report that demonstrates 100% selectivity for p-CNB → p-CAN over supported Pd.

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