Reduction of nitric oxide by carbon monoxide and hdyrogen over a silica-supported rhodium catalyst

Thesis/Dissertation · Thu Dec 31 23:00:00 EST 1981

OSTI ID:6917249

Hecker, W C

The mechanism and kinetics of NO reduction by CO, by H/sub 2/, and by mixtures of CO and H/sub 2/ over a Rh/silica catalyst were studied in detail. Experiments were carried out in a specially designed microreactor which doubled as an infrared cell. Gas phase compositions were measured by a unique GC system which permited accurate determination of NH/sub 3/, NO, N/sub 2/O, N/sub 2/, CO, and CO/sub 2/. Power law parameters and apparent activation energies characteristic of the rate of NO depletion and the rates of N/sub 2/O, N/sub 2/, and NH/sub 3/ formation were determined for each of the three reaction systems. Langmuir-Hinshelwood models were proposed to describe NO reduction by CO and NO reduction by H/sub 2/ and were shown to be consistent with both the infrared and the rate measurements. During NO reduction by CO, the rates of NO, N/sub 2/O, and N/sub 2/ exhibited slight positive-order dependencies on P/sub CO/, negative-order dependencies on P/sub NO/, and activation energies of 34 Kcal/mole. During NO reduction by H/sub 2/, the rates of NO, N/sub 2/O, N/sub 2/, and NH/sub 3/ exhibited strong positive-order dependencies on P/sub H/sub 2//, moderate negative-order dependencies on P/sub NO/, and activation energies of 22-27 Kcal/mole. The catalyst surface was again dominated by Rh-NO/sup delta/-under low and moderate NO conversion conditions. Strong effects of catalyst pretreatment on reaction rates, product selectivity, and infrared spectra were seen. Preoxidation (with 1-2% NO) gave greater activity, greater selectivity to N/sub 2/, and higher frequency IR bands for adsorbed NO than prereduction. A proposal that preoxidized Rh is more electropositive than the prereduced Rh is shown to be consistent with all of these observations.

• OSTI ID: 6917249
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
ELEMENTS
HYDROGEN
KINETICS
METALS
MINERALS
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
NONMETALS
OXIDATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
REACTION KINETICS
REDUCING AGENTS
REDUCTION
RHODIUM
SILICA
SILICON COMPOUNDS
SILICON OXIDES
TRANSITION ELEMENTS