Studies of palladium-support interactions and their influence on the reactions of H/sub 2/ and CO

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6917434

Rieck, J S

Dispersion, support composition, and promoter composition profoundly affect the activity and selectivity of Pd for CO hydrogenation. Temperature-programmed desorption, temperature-programmed surface reaction, temperature-programmed reduction, and temperature-programmed oxidation were used to gain a better understanding of how these factors alter the behavior of Pd. A portion of this investigation was devoted to a theoretical analysis of the influence of intra- and interparticle mass transfer on the temperature-programmed techniques. The distribution of adstates for CO chemisorption shifts from linear sites to bridge sites with decreasing Pd dispersion. Since CO dissociation is more favorable on bridge sites, the activity for CO dissociation, and hence for methanation, increases with decreasing dispersion. The activation energy for methanation, however, does not vary with dispersion. Studies of Pd/TiO/sub 2/, Pd/La/sub 2/O/sub 3/, and Pd/SiO/sub 2/ promoted with TiO/sub 2/, La/sub 2/O/sub 3/, CeO/sub 2/, Pr/sub 6/O/sub 11/, Nd/sub 2/O/sub 3/, and Sm/sub 2/O/sub 3/ have revealed that, during catalyst reduction, portions of the support or promoter undergo reduction and migration onto the surface of the Pd particles. Promotion with alkali metal oxides does not alter the chemisorption capacity of Pd/SiO/sub 2/ for CO and H/sub 2/, but does induce a redistribution of the CO adstates. The titania- and rare earth oxide-promoted catalysts exhibit a higher methanation activity relative to Pd/SiO/sub 2/. Alkali promoters decrease the CO dissociation activity of Pd/SiO/sub 2/, and make the nascent carbon less reactive to H/sub 2/. Consequently, alkali-promoted Pd/SiO/sub 2/ is less active for methanation than Pd/SiO/sub 2/.

• Research Organization: California Univ., Berkeley (USA)
• OSTI ID: 6917434
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010408* -- Coal
Lignite
& Peat-- C1 Processes-- (1987-)
ACTIVATION ENERGY
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYST SUPPORTS
CATALYTIC EFFECTS
CERIUM COMPOUNDS
CERIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
DESORPTION
ELEMENTS
ENERGY
HYDROGENATION
KINETICS
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
METALS
METHANATION
NEODYMIUM COMPOUNDS
NEODYMIUM OXIDES
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PLATINUM METALS
PRASEODYMIUM COMPOUNDS
PRASEODYMIUM OXIDES
PROMOTERS
RARE EARTH COMPOUNDS
REACTION KINETICS
REDUCTION
SAMARIUM COMPOUNDS
SAMARIUM OXIDES
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SPECIFICITY
SURFACE PROPERTIES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS