Wie-Hin Pan

Bio: Wie-Hin Pan is an academic researcher from ExxonMobil. The author has contributed to research in topics: Alkyl & Sulfide. The author has an hindex of 11, co-authored 15 publications receiving 440 citations.

X-ray absorption spectroscopic evidence for a unique nickel site in Clostridium thermoaceticum carbon monoxide dehydrogenase

Abstract: Carbon monoxide dehydrogenase (COdH) in Clostridium thermoaceticum is an ..cap alpha../sub 3/..beta../sub 3/ protein containing six nickels per molecule, in addition to a number of Fe-S clusters. Previous electron paramagnetic resonance (EPR) spectroscopic work has suggested that nickel is involved in binding CO forming an EPR-detectable species, which is probably a key intermediate in the oxidation of CO to CO/sub 2/ and in the synthesis of acetate. In order to better define the nature of this nickel site, Ni X-ray absorption spectra have been recorded and interpreted by comparison with model compounds. The extended X-ray absorption fine structure (EXAFS) spectrum for oxidized COdH is different from that of other Ni enzymes. Both the EXAFS and the X-ray absorption edge spectra suggest a Ni site containing substantial sulfur ligation. The Ni X-ray absorption edge spectrum of rubredoxin-oxidized COdH exhibits a characteristic shoulder with an inflection point at 8336 eV. Such a feature is absent in octahedral model compounds, whereas a well-resolved peak is observed in square-planar Ni complexes. A distinct 1s ..-->.. 3d transition at 8333 eV is observed in a tetrahedral model. The lack of correspondence suggests that square-pyramidal and distorted-square-planar geometries are plausible candidates for the COdH Ni site.more » Treatment of rubredoxin-oxidized COdH with hydrogenase and H/sub 2/ shifts the Ni edge to lower energies, indicating Ni-based reduction. 34 references, 3 figures.« less

Reactions of MoS3, WS3, WSe3, and NbSe3 with lithium. Metal cluster rearrangement revealed by EXAFS

Abstract: be ascribed to the stabilization experienced by an highly charged cation (Ni(II1)) in an environment of increasing negative charge (due to the increase of C104ions). On increasing the NaC10, concentration, because of the opposite effects described above, the difference in stability of the Ni(II1) complexes with [9]aneN3 and cyclam, expressed by MI/,, which is quite small a t low NaC104 concentrations (0.1 M NaC104, = 25 mV), becomes larger and larger (7 M, 160 mV). Moreover for NaC104 concentrations greater than 3 M (see Figure 6), the El~2(Ni(III) /Ni(II)) value for the [ 16]aneNs complex becomes less positive than that of the cyclam analogue, thus inverting the previously established, apparently well-defined order.

Lubricating oil compositions.

Abstract: A lubricating oil composition formulated with a viscosity index (VI) improver composition including a combination of an ethylene α-olefin copolymer having no greater than 66 mass % of units derived from ethylene, and a linear diblock copolymer including at least one block derived primarily from a vinyl aromatic hydrocarbon monomer, and at least one block derived primarily from diene monomer.

Structure and Function of the Catalyst and the Promoter in Co—Mo Hydrodesulfurization Catalysts

Abstract: Etude de la structure d'un catalyseur utilise pour une hydrodesulfuration et plus particulierement etude de la localisation et de la structure des ions molybdene et cobalt a la surface de l'alumine. Discussion sur le role d'un promoteur modifiant un catalyseur, notamment determination du nombre de sites actifs

Importance of Co-Mo-S Type Structures in Hydrodesulfurization

Abstract: The great current interest in hydrodesulfurization (HDS) and other hydrotreating reactions is related to the need for efficient upgrading of crude oil fractions or coal-derived liquids. The catalysts used for such reactions generally consist of molybdenum (or tungsten) supported on high surface area aluminas with cobalt or nickel added as promoters. Great efforts have been devoted to the understanding of the structural and chemical form in which the different elements are present in the active catalyst and to the establishment of correlations between such information and the various catalytic functions. This massive research effort has given valuable information on many aspects of such catalyst systems (for recent reviews of the extensive literature, see, e.g., Refs. 1–11). However, it has not been possible to reach general agreement on the types of structures present in the active catalysts and the origin of promotion

Inorganic Clusters as Single-Source Precursors for Preparation of CdSe, ZnSe, and CdSe/ZnS Nanomaterials

Abstract: Molecular inorganic clusters, which are stable under ambient conditions, can be used as convenient single-source precursors for controlled preparation of 2−9-nm CdSe and CdSe/ZnS nanocrystals and 2−5-nm nanocrystals of ZnSe. The use of a cluster-based single-source precursor allows nanomaterial growth to be initiated at low temperature without the pyrolytic step for nucleus formation traditionally required for lyothermal growth processes. The elimination of the pyrolytic step allows greater synthetic control, slow thermodynamic growth at lower temperatures, high crystallinity, and reaction scalability (>50 g/L) while maintaining size dispersity at ∼5%.