There are various reasons why the structure of the catalytically active site is notoriously difficult to capture. One is the complexity of the catalytic process, which occurs at multiple length-scales and which are difficult to capture. The structure of a heterogeneous catalyst is non-uniform and deciding which of the observed structures is relevant to the catalytic action is not obvious. Of course, simplification of the system by using model structures and conditions helps to determine structure – performance relationships. However, such model systems and conditions are not necessarily relevant to the actual catalytic process. Determining the structure of a catalyst while is performs its catalytic function is the domain of operando characterization and is seemingly the best way of capturing structure – performance relations. However, performing an operando characterization does not necessarily yield the catalytically relevant structures.<br/>Catalysis occurs over reactive surfaces, which may change their structure upon interaction with reactants, intermediates and products. During catalytic conversion reactants are converted into intermediates and products, thus changing the gas composition. With such change, the catalyst surface and its catalytic reactivity may change in accord. Thus, multiple structures as function of position within the reactor may exist. Also, the observation of structure in an operando experiment is no guarantee that that structure is relevant to the catalytic reaction. When taking into account relatively simple concepts from reaction kinetics, a distinction between spectator and active species can be made.<br/>Taking recent literature and alumina-supported copper-zinc for methanol synthesis as examples, in situ/operando and time-resolved characterization will be used to identify what are the active components in such catalyst.

About observing active sites with in situ and operando characterization

256th National Meeting (2018)

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