Reaction pathway design and optimization in heterogeneous catalysis: I. Optimal proportion of multi-pathways designed by the transient response method

An optimal proportion of multi-pathways in heterogeneous catalysis has been designed by the transient response method, as a possible model reaction, using carbon monoxide oxidation on differently prepared zinc oxides, on which two different reaction pathways occur in parallel. Two polycrystalline ZnO samples have been studied: one prepared by the New Jersey Zinc Co. (K25-ZnO) and the other by Kanto Chemical Co. (Kan-ZnO). The turnover frequency (TOF) calculated from the apparent steady state rate (SSR) on K25-ZnO (dual reaction path mechanism with L-H and E-R) is 20-370 times larger than one on Kan-ZnO (dual E-R path mechanism) at 150°C. The instantaneous TOF (transient state rate = TSR) evaluated from the transient response curves on K25-ZnO is 1.0-1.5 times higher than the steady state TOF at 150°C. The yield of CO₂ produced due to the cyclic operation of the proposed P_CO-jump is 31% higher than ones due to steady state operation. The computer simulation analysis concludes that the optimal reaction path proportion is 95.3% for the L-H path and 4.7% for the E-R path at SSR, and 61% for the L-H path and 39% for the E-R path at TSR, which can be designed by choosing gas compositions and operating procedures.