We consider the factors that govern the activity of bifunctional catalysts comprised of active particles supported on active surfaces. Such catalysts are interesting because the adsorption and diffusion steps, which are often discounted in “conventional” catalytic scenarios, play a key role here. We present an intuitive model, the so‐called “active doughnut” concept, defining an active catalytic region around the supported particles. This simple model explains the role of adsorption and diffusion steps in cascade catalytic cycles for active particles supported on active surfaces. The concept has two important practical implications. First, the reaction rate is no longer proportional to the number of active sites, but rather to the number of “communicative” active sites—those available to the reaction intermediates during their respective lifetimes. Second, it generates an important testable prediction concerning the dependence of the total reaction rate on the particle size. With these tools at hand, we examine six experimental examples of catalytic oxidation from the literature, and show that the active doughnut concept gives valuable insight even when detailed mechanistic information is hard to come by.

中文翻译：

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协同表面颗粒催化：“活性甜甜圈”在催化氧化中的作用

我们考虑控制由负载在活性表面上的活性颗粒组成的双功能催化剂活性的因素。这样的催化剂很有趣，因为吸附和扩散步骤（在“常规”催化方案中通常会打折）在这里起着关键作用。我们提出了一个直观的模型，即所谓的“活性甜甜圈”概念，它定义了负载颗粒周围的活性催化区域。这个简单的模型解释了吸附和扩散步骤在级联催化循环中对负载在活性表面上的活性颗粒的作用。这个概念有两个重要的实际含义。首先，反应速率不再与活动位点的数量成正比，而是与“交流”的数量成正比活性位点-反应中间体在其各自的寿命中可利用的位点。其次，它产生了关于总反应速率对粒度的依赖性的重要可检验的预测。使用这些工具，我们从文献中考察了六个催化氧化的实验示例，并表明，即使难以获得详细的机械信息，主动式甜甜圈概念也能提供有价值的见解。