Activated chemisorption of hydrogen on supported ruthenium. I. Influence of adsorbed chlorine on accurate surface area measurements

Journal Article · Wed Jul 01 04:00:00 EDT 1987 · J. Catal.; (United States)

DOI:https://doi.org/10.1016/0021-9517(87)90221-1· OSTI ID:5306343

Lu, K; Tatarchuk, B J

Irreversible hydrogen adsorption onto Ru/Al/sub 2/O/sub 3/ catalysts prepared from RuCl/sub 3/ occurs with apparent activation energies as high as 16 kcal/mole at half-saturation coverage, whereas little or no apparent activation energy barriers are encountered over catalysts prepared in the absence of chlorine from Ru/sub 3/(CO)/sub 12/. Adsorption uptakes measured at 298 K on chlorine-containing specimens can be as little as one-half the value measured at 373 K even though 24-h equilibration times are used. Addition of low chlorine levels to chlorine-free precursors of 2.8-nm diameter indicates that the first chlorine adatoms to adsorb produce about six activated adsorption sites per chlorine adatom. Further chlorine addition to 2.8-nm crystallites poisons a maximum of 20% of the available hydrogen adsorption sites while ca. 38% of the remaining sites become so activated that they can be populated only after adsorption at ca. 373 K. Additional studies demonstrate that the above-noted effects cannot be attributed to (i) titration of surface oxygen, (ii) incomplete reduction of the catalyst, or (iii) hydrogen spillover. Rather, it appears that the presence of electronegative adatoms decreases electron density at nearby ruthenium atoms thereby inhibiting electron donation to, and dissociative chemisorption of, incoming hydrogen molecules. Observations from these studies suggest that hydrogen adsorption measurements may severely underestimate the number of surface ruthenium atoms. The magnitude of such errors increase at lower adsorption temperatures and at higher chlorine coverages. 29 references.

• Research Organization: Auburn Univ., AL (USA)
• DOE Contract Number: AC22-83PC60044
• OSTI ID: 5306343
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 106:1; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
ADSORPTION
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYSTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
CHEMISORPTION
CHLORIDES
CHLORINE
CHLORINE COMPOUNDS
COMPARATIVE EVALUATIONS
COMPLEXES
CONTAMINATION
ELEMENTS
ENERGY
HALIDES
HALOGEN COMPOUNDS
HALOGENS
HYDROGEN
MEASURING METHODS
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
REFRACTORY METAL COMPOUNDS
RUTHENIUM
RUTHENIUM CHLORIDES
RUTHENIUM COMPLEXES
RUTHENIUM COMPOUNDS
SEPARATION PROCESSES
SORPTION
SURFACE AREA
SURFACE PROPERTIES
SYNTHESIS
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS