Intraparticle redispersion of Rh and Pt-Rh particles on SiO/sub 2/ and Al/sub 2/O/sub 3/ by oxidation-reduction cycling

Journal Article · Wed Jul 01 04:00:00 EDT 1981 · J. Catal.; (United States)

OSTI ID:6367373

Wang, T; Schmidt, L D

Morphologies produced by oxidation and reduction of 20- to 200-A diameter Rh and Pt-Rh alloy particles on planar amorphous SiO/sub 2/ and ..gamma..-Al/sub 2/O/sub 3/ are examined using high-resolution scanning transmission electron microscopy. Specimens are prepared by vacuum deposition of metals onto thin oxide supports which are then heated in air or H/sub 2/ at pressures of 1 atm. It is found that redispersion of small crystallites of Rh can be achieved by first oxidizing Rh to Rh/sub 2/O/sub 3/ in air at approx. 600/sup 0/C, and then reducing the oxide particles at lower temperatures. Particles after reduction are converted to small clusters of metal 10 to 20 A in diameter or form cracks. Morphologies on Al/sub 2/O/sub 3/ substrates are similar. For Pt-Rh alloys, Rh/sub 2/O/sub 3/ forms at the edge of Pt metal cores. Reduction at 25/sup 0/C then produces small Rh particles at the edges of the original particle. Upon heating to 500/sup 0/C, particles coalesce into roughly their original morphologies, but the cores are primarily Pt and surfaces of particles are enriched in Rh. It is estimated that surface area increases of approx. 100% may occur by these processes. Two mechanisms are suggested for intraparticle redispersion, one caused by the different interfacial energies of metal and metal oxide on the support and the other arising from the mechanism of oxide formation on a metal surface with a small radius.

• Research Organization: Univ. of Minnesota, Minneapolis
• OSTI ID: 6367373
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 70:1; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400* -- Petroleum-- Processing
ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYSTS
CATALYTIC REFORMING
CHALCOGENIDES
CHEMICAL REACTIONS
DISPERSIONS
HIGH TEMPERATURE
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PARTICLES
PLATINUM ALLOYS
PLATINUM METAL ALLOYS
REDUCTION
REFORMER PROCESSES
REGENERATION
RHODIUM ALLOYS
SILICON COMPOUNDS
SILICON OXIDES