1995 Volume 21 Issue 6 Pages 1161-1169
In order to evaluate the deactivation of a hydrophobic Pt/SDBC catalyst used for a hydrogen isotopic exchange reaction, changes over time in the reaction rate of H2/HDO (v) isotopic exchange over the catalyst induced by the addition of nitric acid, nitrates and nitrogen oxides were studied experimentally. Deactivation was discussed in terms of the balance of the active sites.
The catalyst was poisoned by HNO3 reversibly and the poisoning was well explained in terms of the competitive adsorption of HNO3 with H2 or HDO onto the catalytic active sites. The poisoning kinetics were explained by the Zeldovich rate equation.
Neutral nitrates of fission products such as Sr (NO3) 2 showed negligible poisoning effects on the catalyst. ZrO (NO3) 2 showed very similar poisoning behavior with HNO3, and this was considered to result from hydrolysis reactions which produced HNO3.
No deactivation was observed by the introduction of NO, NO2 or NH3 into the reactor. Instead of poisoning, the reaction rate was accelerated by NO or NO2 and this was considered to be due to local heating of the catalyst surface by exothermic reactions between nitrogen oxides and hydrogen.