Nature of the metal-support interface in supported metal catalysts: Results from X-ray absorption spectroscopy

Abstract

X-ray absorption spectra characterizing the metal-support interface in supported metal complexes and supported metal catalysts are summarized and evaluated. Single-metal-atom transition metal complexes on non-reducible metal oxide supports are bonded with metaloxygen bonds with metal-oxygen distances of approximately 2.15 A; the bonding distance is only weakly sensitive to the oxidation state of the metal. Nearly this same metal-oxygen distance is characteristic of the metal-support interface in metal-oxide-supported metal clusters following high temperature reduction in H a (HTR: T > 450~ The metals at the interface may be polarized sufficiently that they bond with the oxygen of the support much as the cations in mononuclear complexes bond with it. When the supported metals are treated in H a at low temperatures (LTR: T < 350~ or are prepared under He with partially hydroxylated supports, a longer metal-support oxygen distance is observed, typically 2.5-2.7 A. This distance is suggested to characterize interactions between zero-valent metals and support oxygen. Changes in the performance of supported metal catalysts resulting from differences in the temperature of pretreatment in H 2 are attributed to changes in the electronic properties and/or morphology of the metal clusters, which are suggested to be related to the concomitant changes in the structure of the metal-support interface.

Characterization of Iridium Catalyst for Decomposition of Hydrazine Hydrate for Hydrogen Generation

“…The size of the Ir nanoparticle, which was estimated from the Scherrer equation assuming an instrumental line broadening factor of 0.115°, ranged from 1.5 to 1.8 nm [9], as shown in Table 1. Such a small particle generally displays lattice contraction [10]. The lattice expansion indicated from the XRD peak position is in contrast to the general phenomena observed for small metal particles.…”

Hydrogen as a Modifier of the Structure and Electronic Properties of Platinum in Acidic Zeolite LTL: A Combined Infrared and X-ray Absorption Spectroscopy Study

“…The structure of the metal-support interface, Le., a Pt-0 distance in the range 2.5-2.7 8, in R-300 and a P t -0 distance below 2.3 A for TPD-500 and TPD-690, agrees with more extensive studies?, 17 The model that accounts for the shortening of the P t -0 distance proposes that after reduction at 300 "C hydrogen is present between the platinum particle and the support. This hydrogen desorbs at temperatures above 450 "C, bringing about a shortening of the Pt-0 distance to ca.…”

Ion-dipole interactions between adsorbed CO and support cations in Pt/K-LTL

“…9 J.C. Baltzer AG, Science Publishers [16][17][18][19][20]. Previous infrared studies indicate that zeolite acid sites withdraw electrons from small metal particles making them electron-deficient, whereas metal clusters supported in basic zeolites are electron-rich [21][22][23][24][25].…”