Advances in Catalysis, Vol. 44 by Werner O. Haag, Bruce C. Gates, Helmut Knoezinger

By Werner O. Haag, Bruce C. Gates, Helmut Knoezinger

Because 1948, this sequence has stuffed the distance among the papers that record on and the textbooks that educate within the various components of catalysis study. The editors of and participants to Advances in Catalysis are devoted to recording development during this sector. each one quantity of Advances in Catalysis comprises articles overlaying a topic of vast curiosity. Advances in Catalysis forty four displays the increasing effect of experimental floor characterization at the realizing of catalysis. The catalysts emphasised listed here are consultant of the complexity of cutting-edge expertise; examples comprise catalysts for hydrocarbon re-forming, motor vehicle exhaust conversion, and hydroprocessing to make clean-burning fossil fuels. This quantity includes 3 obituaries spotting the foremost contributions of Dr. Werner O. Hagg, Dr. Charles Kemball, and Dr. John Turkevich.

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1 H NMR A. LINE INTENSITIES: SPILLOVER In oxide-supported catalysts, the 1H NMR signal from the hydrogen on the metal is distinct from that due to hydroxyl groups on the oxide surface, although often the wings of the two signals have a strong overlap (Fig. 11) NMR AS PROBE OF SURFACES OF SUPPORTED METAL CATALYSTS 29 (5). The intensities of these lines (more exactly, their integrals, calibrated in terms of number of nuclei) can be used to investigate spillover. Schematically, the experiment starts with an evacuated catalyst in the spectrometer, and the changes in intensity of 1H/support and of 1H/metal are recorded with increasing hydrogen dosing.

A) Reduced and evacuated (hydroxyl peak Ͱ only). 08 Torr of H2 gas. (c) Difference spectrum b Ϫ a; the Ͱ peak is not visible (no spillover); only the H/Pt or ͱ peak remains. , the integral over the line) of the signal. [Reproduced with permission from Chesters et al. (48). ] high-temperature evacuation. If this is done, however, the 1H dosing experiment must be carried out on a time scale of approximately 1 h since otherwise the slow exchange between the support and on-metal hydrogens will be significant.

For cubic transition metals, it is assumed that the wavefunctions at the Fermi level can be decomposed into s-like and d-like parts and that their exchange interactions are mostly s–s 22 J. J. VAN DER KLINK and d–d like, so that s–d interactions can be neglected. The equations become (37) ␹ ϭ ȐoȐ2B⍀Ϫ1[Ds(Ef)/(1 Ϫ Ͱs) ϩ Dd(Ef)/(1 Ϫ Ͱd)] ϩ ␹orb (15) ϭ ␹s ϩ ␹d ϩ ␹orb K ϭ ␹s(⍀Hhf,s /ȐB) ϩ ␹d(⍀Hhf,d /ȐB) ϩ ␹orb(⍀Hhf,orb /ȐB) ϭ Ks ϩ Kd ϩ Korb (16) S (T1T )Ϫ1 ϭ k(Ͱs)K 2s ϩ k(Ͱd)K 2dRd ϩ (ȐoȐBDd(EF))2H 2hf,orbRorb , (17) where Ds(Ef) and Dd(Ef) are the s-like and d-like densities of state (twice the number of energy levels per unit energy interval and per atom) at the Fermi energy; Ͱs and Ͱd Stoner factors that can be written as Ͱs ϭ IsDs(Ef), Ͱd ϭ IdDd(Ef), (18) where Is and Id are exchange integrals; the three Hhf’s are the hyperfine fields; k(Ͱ) is a function of Ͱ that accounts for the difference in static and dynamic enhancement effects and Rd and Rorb are factors that take into account the relative amount of t2g- and eg- type wavefunctions.

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