Nonequilibrium Phase Transitions with Hysteresis in Solid Catalysts. The System Copper‐Oxygen‐Propene

Abstract

Catalysis / Non-equilibrium Phenomena / Phase Transitions / SurfacesThe rates of formation of acrolein, CO, and CO from propene and oxygen on oxides of copper as catalysts have been investigated at P C ? H~ = 50 mbar, 4 mbar s po, 5 200 mbar in a differential reactor at 645 and 735 K. Oxygen contents of the catalysts have been determined in sltu by titration with H, at 713 K. Selectivity and rate of oxygen consumption at steady state of the catalyst are not single valued functions of gas phase composition. Mainly the selectivity of acrolein formation follows a closed hysteresis-loop over a finite interval of po2. This phenomenon can be

Influence of various metal oxides in the bistability observed in the oxidative dehydrogenation of 2 — Propanol over copper catalysts

“…During this study, a very particular phenomenon had been observed. Similar bistability and/or oscillatory phenomena have also been observed in other reaction systems using copper as catalyst (Greger et al, 1984;Amariglio et al, 1989). We had found that part of the activity was recovered when the oxygen pressure was lowered below a critical value ("lower critical oxygen pressure, p,"), indicating that the loss of activity was not irreversible as had been indicated by Thomas et al (1980).…”

“…There was thus a bistability in the regions between the higher and lower critical pressures, p h and p,. Similar bistability and/or oscillatory phenomena have also been observed in other reaction systems using copper as catalyst (Greger et al, 1984;Amariglio et al, 1989). In these studies, the interpretations were based on an assumption of a change of composition or structure of the catalyst surface.…”

“…scillation phenomena have first been observed on cop-0 per, in the decomposition of N,O (Hugo and Jakubith, 1972), in the oxidation of CO (Eckert et al, 1973), as well as in the oxidation of propene (Greger et al, 1984;Amariglio et al, 1989). It is now known that oscillations and bistability in heterogeneous catalysis are due to similar causes, with sometimes the same catalytic system being able to exhibit even both behaviours depending on the experimental conditions.…”