NMR of platinum catalysts: Double NMR of chemisorbed carbon monoxide and a model for the platinum NMR line shape

Journal Article · Wed May 01 04:00:00 EDT 1985 · Physical Review (Section) B: Solid State; (USA)

DOI:https://doi.org/10.1103/PhysRevB.31.5663· OSTI ID:5097825

Makowka, C D; Slichter, C P ^[1]; Sinfelt, J H ^[2]

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1. Univ. of Illinois, Urbana-Champaign (USA)
2. Exxon Research and Engineering Co., Annandale, NJ (USA)

The authors report observation of the NMR line of {sup 195}Pt atoms in the surface layer of small platinum-metal particles on which {sup 13}CO has been chemisorbed. The surface {sup 195}Pt atoms are resolved from those of {sup 195}Pt atoms deeper in the particle by spin-echo double resonance between {sup 195}Pt and {sup 13}C. The particles, supported on {eta}-alumina, had dispersions (fraction of the atoms that are on the surface) of 26% and 76%. Comparison with {sup 195}Pt resonance in Pt carbonyls suggests that the magnitude of the Knight shift of the surface Pt is less than 0.2%. Analysis of the {sup 195}Pt spin-lattice relaxation indicates that the small surface Knight shift results from cancellation of 6s and 5d core-polarization contributions as was found theoretically by Weinert and Freeman for clean Pt surfaces. The {sup 13}C-{sup 195}Pt indirect spin coupling is found to be very similar to those in diamagnetic platinum carbonyl molecules. The results show that CO bonds via the C atom and verify that concepts from studies of large single crystals are valid for the small particles. The key features of the {sup 195}Pt line shapes in these small platinum particles are described by a simple phenomenological model of the spatial Knight-shift variation inside these particles. The model successfully describes the major structure seen in the NMR line shapes of samples with dispersions ranging from 5% to 76%.

• DOE Contract Number: AC02-76ER01198
• OSTI ID: 5097825
• Journal Information: Physical Review (Section) B: Solid State; (USA), Journal Name: Physical Review (Section) B: Solid State; (USA) Vol. 31:9; ISSN 0556-2805; ISSN PLRBA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
656002 -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CARBONYLS
CHALCOGENIDES
CHEMICAL BONDS
CHEMICAL REACTIONS
CHEMISORPTION
DATA
DAYS LIVING RADIOISOTOPES
ELECTRONIC STRUCTURE
ELEMENTS
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HEAVY NUCLEI
INFORMATION
INTERNAL CONVERSION RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
KNIGHT SHIFT
MAGNETIC RESONANCE
MATHEMATICAL MODELS
METALS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PLATINUM
PLATINUM 195
PLATINUM ISOTOPES
PLATINUM METALS
RADIOISOTOPES
RELAXATION
RESONANCE
SEPARATION PROCESSES
SORPTION
SPIN-LATTICE RELAXATION
STABLE ISOTOPES
SURFACE PROPERTIES
TRANSITION ELEMENTS