Kinetic measurements have been made for the oxidation of CO, C2H4, H2 and natural gas by nitric oxide on SnO2/Cr2O3 and on Al2O3/Cr2O3 catalysts. The interaction of NO with catalysts was examined by adsorption, infrared spectra and electric conductivity measurements. The adsorption isotherms of NO on SnO2/Cr2O3 catalysts are of the Freundlich type in the pressure range from 3 to 50 Torr. Evaluation of the NO chemisorption rate by the Elovich equation yielded two linear segments with a distinct break between them. The instantaneous adsorption of NO on the partially reduced SnO2 was larger than that of the unreduced sample. The rate of adsorption was ten times higher. A very large increase in the amount of adsorbed NO was obtained by adding Cr2O3 to SnO2. Electric conductivity measurements during NO adsorption revealed that both negatively and positively charged No are present on pure and doped SnO2. The catalytic reactions on pure SnO2 occurred only above 360°C. Small amounts of Cr2O3 in the SnO2 lowered the reaction temperatures by 100-200°C. The efficiency of SnO2/Cr2O3 exceeded that of Al2O3/Cr2O3. It is suggested that on the partially reduced SnO2 the Sn3+ ions are the active catalytic sites for NO and that nitric oxide dissociates upon chemisorption. The slowest step of the reduction of NO is assumed to be the oxidation of reduced centers on the catalyst, which involves the formation of nitrogen molecules. The high activity of catalysts containing chromium oxide is attributed to the chromium ions incorporated into the surface layer of the carrier which can easily be reduced by fuels and rapidly reoxidized by NO.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Mechanical Engineering
- Physical and Theoretical Chemistry
- Fluid Flow and Transfer Processes