Intermetallic Pt-Cr clusters in zeolites as models of bimetallic aromatisation and reforming catalysts

Journal Article · Sat May 01 04:00:00 EDT 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1133· OSTI ID:6251907

Joyner, R W; Johnston, P ^[1]; Shpiro, E S; Tuleuova, G J ^[2]

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1. Univ. of Liverpool (United Kingdom)
2. N.D. Zelinsky Institute of Organic Chemistry, Moscow (Russian Federation)

A variety of both structural (EXAFS, XANES, XRD, TEM) and surface-sensitive (XPS, LEISS) techniques have been applied to study the formation, dispersion, composition, and local structure of zeolite-hosted platinum-chromium metal alloys. Both XPS and XANES indicated a two-step reduction of Cr(VI) to Cr(III) and Cr(O) states, while the analysis of EXAFS data demonstrates the formation of platinum-chromium alloy particles after reduction at 823 K. Chromium stabilises small (9-10 [angstrom]) platinum particles at lower temperatures (623 K) and when alloyed the particle size increased to 12-20 [angstrom]. The Cr/Pt ratio in the alloy is low (<20% chromium), and is independent of the overall Cr/Pt ratio in the ZSM-5, possibly due to space limitations inside the zeolite voids. TEM suggests the formation of some flattened, raft-like metal particles at the external surface of the zeolite. Based on LEISS measurements of surface segregation in a Pt[sub 70]Cr[sub 30] alloy film and thermodynamic considerations, a model of the catalyst particles is proposed in which the outermost monolayer consists entirely of platinum and the second shell is enriched in the additive metal, chromium. 32 refs., 9 figs., 6 tabs.

• OSTI ID: 6251907
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 141:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
ALLOYS
AROMATIZATION
ATOMIC CLUSTERS
CATALYSTS
CATALYTIC REFORMING
CHEMICAL ANALYSIS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
ELECTRON MICROSCOPY
ELECTRON SPECTROSCOPY
FILMS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ION SCATTERING ANALYSIS
MATERIALS
MICROSCOPY
MINERALS
NONDESTRUCTIVE ANALYSIS
PARTICLE SIZE
PARTICLES
PHOTOELECTRON SPECTROSCOPY
PLATINUM ALLOYS
PLATINUM METAL ALLOYS
REDUCTION
REFORMER PROCESSES
SILICATE MINERALS
SIZE
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
TRANSMISSION ELECTRON MICROSCOPY
VALENCE
X-RAY SPECTROSCOPY
ZEOLITES