Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Investigation of Surface Structures of Supported Vanadium Oxide Catalysts by UV−vis−NIR Diffuse Reflectance Spectroscopy

Abstract: UV−vis−NIR diffuse reflectance spectroscopy (DRS) was applied to study the local structures of V(V) cations on various oxide supports (Al2O3, ZrO2 TiO2, Nb2O5, CeO2, and SiO2) under hydrated and dehydrated conditions. The edge energy (Eg) of the LMCT transitions of V(V) cations was used to elucidate the local structures of V(V) cations, and a correlation between the edge energy and the number of the covalent V−O−V bonds (CVB) around the central V(V) cations was established based on some V(V) reference compounds/oxides. For TiO2, Nb2O5, and CeO2 supported vanadia catalysts, the strong support absorption in the same region as the V(V) cations prevents a reliable determination of the local structure of the surface vanadium oxide species by either the LMCT band position or the edge energy. For Al2O3, ZrO2, and SiO2 supported vanadia catalysts, the average CVB number derived from the edge energy allows the assignment of the possible structure of the surface vanadium oxide species, which is a strong function of...

Direct synthesis of hydrogen peroxide from H2 and O2 using Pd and Au catalysts

Abstract: The direct synthesis of hydrogen peroxide from H2 and O2 using a range of supported metal catalysts is described and discussed. A detailed study of the factors influencing the formation and decomposition of hydrogen peroxide is presented for a Pd/sulfonated carbon catalyst in a methanol/water solvent. The use of low temperatures (1–2 °C) and short reaction (residence) time are identified as the key factors that favour high selectivity to hydrogen peroxide. Decomposition of hydrogen peroxide, mainly via further hydrogenation, prevents the formation of high concentrations of hydrogen peroxide. Combustion of hydrogen to water is a competing reaction that becomes significant at higher temperatures, but this can be partially inhibited by the addition of HBr. A second set of supported Pd and Au catalysts are evaluated for the direct synthesis of hydrogen peroxide using supercritical CO2 as a solvent. The use of supercritical CO2 is shown to be beneficial when compared with hydrogen peroxide formation at a temperature just below the critical temperature for CO2. However, at the critical temperature of CO2 (31.1 °C), the decomposition of hydrogen peroxide is rapid and only low rates of hydrogen peroxide formation are observed. At low temperature (2 °C) supported Au catalysts are shown to be very selective for the synthesis of hydrogen peroxide. The rate of hydrogen peroxide synthesis is enhanced markedly when Pd is present with Au and a detailed scanning transmission electron microscopy study shows that the 2–9 nm metal nanoparticles present in this supported catalyst are a Au∶Pd alloy.

LogP: a practical model of parallel computation

Abstract: enough to be generally useful and to keep the algorithm analysis tractable. Ideally, producing a better algorithm under the model should yield a better program in practice. The Parallel Random Access Machine (PRAM) [8] is the most popular model for representing and analyzing the complexity of parallel algorithms. A LogP A Practic

NOrec: streamlining STM by abolishing ownership records

Abstract: Drawing inspiration from several previous projects, we present an ownership-record-free software transactional memory (STM) system that combines extremely low overhead with unusually clean semantics. While unlikely to scale to hundreds of active threads, this "NOrec" system offers many appealing features: very low fast-path latency--as low as any system we know of that admits concurrent updates; publication and privatization safety; livelock freedom; a small, constant amount of global metadata, and full compatibility with existing data structure layouts; no false conflicts due to hash collisions; compatibility with both managed and unmanaged languages, and both static and dynamic compilation; and easy acccommodation of closed nesting, inevitable (irrevocable) transactions, and starvation avoidance mechanisms. To the best of our knowledge, no extant STM system combines this set of features.While transactional memory for processors with hundreds of cores is likely to require hardware support, software implementations will be required for backward compatibility with current and near-future processors with 2--64 cores, as well as for fall-back in future machines when hardware resources are exhausted. Our experience suggests that NOrec may be an ideal candidate for such a software system. We also observe that it has considerable appeal for use within the operating system, and in systems that require both closed nesting and publication safety.

Molecular structures of supported metal oxide catalysts under different environments

Abstract: The use of in situ Raman spectroscopy to study the molecular structures of supported metal oxide catalysts under different environments is reviewed. The molecular structures under ambient (hydrated) and dehydrated conditions are presented. The effect of moisture at elevated temperatures is also presented and discussed with regard to its implications for catalytic phenomena. The molecular structural transformations during C2–C4 lower alkane (LPG) oxidation, methane oxidation, methanol oxidation and selective catalytic reduction of NO with NH3 reaction conditions are presented. In situ spectroscopy during catalytic reaction with simultaneous activity/selectivity measurement (‘operando’ spectroscopy) is emphasized owing to its contribution to the fundamental understanding of catalytic performance. The reducibility of the different surface metal oxide species, the relevance of surface coverage (surface monomeric vs polymeric species) and the specific oxide support are discussed when LPG, methane, methanol or hydrogen is the reducing agent. In situ Raman spectroscopy provides molecular-level information about the surface metal oxide species: structures, stability and transformations under different environments. In many cases, the use of complementary spectroscopic techniques results in a more complete understanding of the molecular structure–activity/selectivity relationships for supported metal oxide catalysts. Copyright © 2002 John Wiley & Sons, Ltd.