Decay of metastable phases in a model for the catalytic oxidation of CO

Abstract

We study by kinetic Monte Carlo simulations the dynamic behavior of a Ziff-Gulari-Barshad model with CO desorption for the reaction CO + O-->CO(2) on a catalytic surface. Finite-size scaling analysis of the fluctuations and the fourth-order order-parameter cumulant show that below a critical CO desorption rate, the model exhibits a nonequilibrium first-order phase transition between low and high CO coverage phases. We calculate several points on the coexistence curve. We also measure the metastable lifetimes associated with the transition from the low CO coverage phase to the high CO coverage phase, and vice versa. Our results indicate that the transition process follows a mechanism very similar to the decay of metastable phases associated with equilibrium first-order phase transitions and can be described by the classic Kolmogorov-Johnson-Mehl-Avrami theory of phase transformation by nucleation and growth. In the present case, the desorption parameter plays the role of temperature, and the distance to the coexistence curve plays the role of an external field or supersaturation. We identify two distinct regimes, depending on whether the system is far from or close to the coexistence curve, in which the statistical properties and the system-size dependence of the lifetimes are different, corresponding to multidroplet or single-droplet decay, respectively. The crossover between the two regimes approaches the coexistence curve logarithmically with system size, analogous to the behavior of the crossover between multidroplet and single-droplet metastable decay near an equilibrium first-order phase transition.

Discontinuous non-equilibrium phase transition in a threshold Schloegl model for autocatalysis: Generic two-phase coexistence and metastability

“…Below, we let C m denotes the concentration of the metastable state, J nuc denotes the nucleation rate for supercritical droplets, and V grow denotes the charac- teristic radial growth velocity of such nuclei. Then, consistent with the general Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory for nucleation kinetics, [52][53][54] as in previous studies of nucleation-mediated kinetics for non-equilibrium systems, 11,27,40 we anticipate that…”

“…For a more detailed analysis, by analogy with thermodynamic systems, we anticipate a nucleation rate with the specific form J nuc ∼ exp[−c nuc /δp], where δp = p − p e measures the driving force for nucleation. 11,27,40 It is natural to write c nuc ∝ (σ eff ) 2 , where σ eff denotes the effective line tension at interface between coexisting states. 27,41 If one also accounts for the feature that the asymptotic growth velocity for large droplets (with near-planar interfaces) should scale like V grow ∝ δp, 11,27,30,55 then it follows that FIG.…”

“…We do emphasize the difficulty in developing a rigorous treatment of metastability even in thermodynamic systems 38,39 let alone non-equilibrium systems. 11,27,40,41 For example, it is expected that metastable states cannot be defined as unique analytic extensions of stable states.…”

Response of a catalytic reaction to periodic variation of the CO pressure: IncreasedCO2production and dynamic phase transition

“…Other work by the present authors [17] indicates that near the coexistence line between the active and the CO poisoned regime, the decay times of the metastable states are different if the ZGB-k model is driven into the CO poisoned state from the active phase, or if it is driven into the active phase from the CO poisoned state. Based on this result, we expect that the catalytic activity of the system will increase when the system is subjected to periodic variation of the external CO pressure, only when one takes into account that the time it takes the system to decontaminate is different from the time it takes it to contaminate.…”

Reversal of Magnetisation in Ising Ferromagnet by the Field Having Gradient

“…The effect of finite size on linear reversal mechanism was studied in a nano scale Fe-Pt [11]. A decay of metastable phase for catalytic oxidation of CO was modelled and studied [12]. Reversal modes were simulated for Iron nano-pillar in an obliquely oriented field [13].…”