The fluxional interconversion of a catalyst between forms with different structures and properties complicates mechanistic analyses and kinetic modeling efforts. We construct a simple model for a catalyst with two fluxionally interconverting forms, inspired by the interconverting flat (*) and stacked (▲) forms of noble metal sub-nanoclusters. Using a detailed balance, free energy relations, non-dimensionalization, and representative equilibrium constants from ab initio calculations in the literature, ten initial rate parameters are reduced to two. The two remaining parameters control the fluxional interconversion rate and the reactant concentration. For a wide range of these two parameters, we compute the steady-state turnover frequencies, pathway fluxes, intermediate abundances, as well as transient intermediate relaxation rates. The results demonstrate how steady-state abundances and dominant pathways can change with the degree of fluxionality, even when equilibrium constants are unchanged. We conclude that accurate rate expressions must account for non-equilibrium steady-state abundances and fluxes, beyond equilibrium populations. Furthermore, in contrast to the short-lived transients for a non-fluxional catalyst, we show that non-steady transients may persist through many turnovers when fluxional interconversion is slow.

中文翻译：

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通量催化剂的简单模型和光谱分析：中间丰度、通路通量、速率和瞬态

催化剂在具有不同结构和性质的形式之间的流动互变使机械分析和动力学建模工作变得复杂。受贵金属亚纳米团簇的相互转换平面 (*) 和堆叠 (▲) 形式的启发，我们构建了一个具有两种通量相互转换形式的催化剂的简单模型。使用文献中从头算计算的详细平衡、自由能关系、无量纲化和代表性平衡常数，十个初始速率参数减少到两个。其余两个参数控制通量互转化率和反应物浓度。对于这两个参数的广泛范围，我们计算了稳态周转频率、通路通量、中间丰度以及瞬态中间弛豫率。结果表明，即使平衡常数不变，稳态丰度和主要途径如何随着通量的程度而变化。我们得出结论，准确的速率表达式必须考虑超出平衡种群的非平衡稳态丰度和通量。此外，与非通量催化剂的短暂瞬变相比，我们表明当通量相互转化缓慢时，非稳态瞬变可能会持续存在许多周转。