Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

Journal Article · Fri May 01 00:00:00 EDT 1987 · J. Catal.; (United States)

DOI:https://doi.org/10.1016/0021-9517(87)90005-4· OSTI ID:5450134

Kip, B J; Duivenvoorden, F B.M.; Koningsberger, D C; Prins, R

Hydrogen-to-metal (H/M) ratio exceeding unity for Pt and Rh and exceeding 2 for Ir were measured for highly dispersed Pt, Rh, and Ir catalysts supported on Al/sub 2/O/sub 3/ and SiO/sub 2/. Since the coordination of hydrogen to metal atoms is unknown for such highly dispersed catalysts, the metal surface area of these catalysts cannot be calculated from the hydrogen chemisorption values. Therefore EXAFS (extended X-ray absorption fine structure) measurements were performed to determine the metal particle size and thereby to calibrate hydrogen chemisorption results. The H/M ratio determined by hydrogen chemisorption is a linear function of the average metal coordination number determined by EXAFS. This linear relationship is independent of support but varies with the metal with the H/M ratio increasing in the order Pt < Rh < Ir. Several hypothesis for the high H/M values are discussed. Spillover and subsurface hydrogen are excluded as explanations and only multiple adsorption of hydrogen on metal surface atoms is shown to be capable of explaining all experimental observations. The H/M/sub surface/ stoichiometry differs among Pt, Rh, and Ir in the order H/Pt < H/Rh < H/Ir, analogous to the order of stability of corresponding metal polyhydride complexes and of theoretical expectation. 73 references.

• Research Organization: Eindhoven Univ. of Technology, Netherlands
• OSTI ID: 5450134
• Journal Information: J. Catal.; (United States), Vol. 105:1
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CATALYSTS
PHYSICAL PROPERTIES
IRIDIUM
PARTICLE SIZE
PLATINUM
RHODIUM
ALUMINIUM OXIDES
CATALYST SUPPORTS
CHEMISORPTION
DISTRIBUTION
HYDROGEN
SILICA
SURFACE AREA
X-RAY SPECTROSCOPY
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
METALS
MINERALS
NONMETALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SIZE
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
TRANSITION ELEMENTS
400201* - Chemical &amp; Physicochemical Properties