Microstructure and kinetics on supported metal catalysts

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

OSTI ID:7043445

Lee, C P

The effects of thermal and gas treatments on the microstructure, surface composition, hydrogen uptake, and kinetics of CO hydrogenation and ethane hydrogenolysis over silica supported Pt, Rh, and Ni particles have been studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), hydrogen chemisorption, and kinetics in a differential flow reactor. TEM shows that Pt particles on SiO/sub 2/ and ..gamma..-Al/sub 2/O/sub 3/ form predominantly (100) crystal planes with either the (100) plane or the (110) plane in contact with the support if particles are grown in pure H/sub 2/. Heating cubic particles in air and in gases other than H/sub 2/ causes a transformation to spherical shapes above 500C, which can be transformed back to cubes by heating in H/sub 2/. Rh particles form primarily hexagonal structures in either H/sub 2/ or N/sub 2/. When 15% Ni/SiO/sub 2/ catalysts are oxidized at 460C and then reduced in H/sub 2/ at 300C, hydrogen chemisorption areas increase while methanation activities decrease. Heating progressively up to 650C produces a decrease in surface area and an increase in methanation activity. XPS confirms total oxidation and reduction of Ni by 350C. TEM shows that particles spread on the SiO/sub 2/ surface upon oxidation and form clusters of smaller Ni particles upon low temperature reduction. These results show that solid state redispersion occurs upon oxidation-reduction cycling but that the methanation activity is low on freshly reduced Ni. When 5% Rh/SiO/sub 2/ catalysts are oxidized at 500C and then reduced in H/sub 2/ at 250C, the activity increases by up to three orders of magnitude. Heating progressively up to 650C produces a decrease in activity to nearly its original value.

• Research Organization: Minnesota Univ., Minneapolis (USA)
• OSTI ID: 7043445
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010408* -- Coal
Lignite
& Peat-- C1 Processes-- (1987-)
ACTIVATION ENERGY
AIR
ALKANES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
ELECTRON MICROSCOPY
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ELEMENTS
ENERGY
ETHANE
FLUIDS
GASES
HEAT TREATMENTS
HYDROCARBONS
HYDROGEN
HYDROGENATION
KINETICS
METALS
METHANATION
MICROSCOPY
MICROSTRUCTURE
NICKEL
NITROGEN
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ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PARTICLE SIZE
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PLATINUM
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SURFACE AREA
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TRANSITION ELEMENTS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY SPECTROSCOPY