DETERMINING STEP: THE MECHANISM OF WATER-GAS SHIFT REACTION CATALYZED BY PLATINUM By

The mechanism of water-gas shift reaction, CO+ H 20 = CO2+ H 2, catalyzed by evapo-rated platinum films was investigated by means of tracers of l3C and 180 over the tem-perature from 410 to 450°C on the basis of the theory of stoichiometric number determi-nation of the rate-determining step. The stoichiometric number ~r of the rate-determining step was determined to be unity by tracing the transfer of carbon atoms between CO and COz by 13C, i. e. the rate-determining step consists in any constituent step of transfer of carbon atoms. The transfer of oxygen atoms among CO, H 20 and CO2 traced by 180, which was observed simultaneously with the former, showed that the ratio of the total forward rate of transfer of oxygen atoms from CO to CO2 and HzO to its reverse total rate is close to unity, which enables us to exclude several steps of the constituent steps of transfer of carbon atoms from being rate-determining. Assuming that the reaction 123 follows the sequence of steps, CO~CO(a), HzO~H(a)+OH(a), CO (a)+ OH (a).<- " X (a)