General Rules of Coverage-Affected Activity Trends and a Widened Optimal Adsorption Energy Zone in Locating the Catalyst

The non-Langmuirian nature of a catalyst surface caused by the adsorbate–adsorbate interactions generally results in an activity gap between the theoretical evaluation and experimental measurement. However, a general theory to understand this is still lacking and the optimal activity window has yet to be identified. Here, three typical coverage-dependent adsorption energy variation behaviors, including linear, logarithmic, and Z-type functions (where the adsorption energy initially remains stable and then rapidly decreases to a plateau), are quantitatively investigated in terms of how they influence the activity trend using a two-step catalytic model. Compared to the conventional volcano-shaped curve without coverage effect, the coverage-affected activity curve generally shows a broadened peak area and activity upshift on the left side of the volcano curve, while the right side remains little changed. The broadened peak area indicates that more catalysts than expected can exhibit excellent catalytic activity under the realistic conditions. More importantly, we reveal that the width of the broadened peak area is mainly determined by the adsorption energy difference affected by the coverage from 0 to 1 ML (named as the maximum coverage error) and is almost independent of the types of coverage effects, while its threshold can be directly identified by the half principle we proposed earlier (EI°,opt ≈ (μR + μP)/2). Quantitatively, the activity increase on the left side correlates with the transition-state structure type of product dissociation and the maximum coverage error. Following these rules, a strategy for quickly sketching the coverage-affected activity curve is discussed. These findings have important implications for catalyst design and make it convenient to quantitatively assess the experimental activity.