Ultradispersed sulfide catalysts: how many atoms for an active site?

While sulfide nanoparticles have been extensively studied for hydrotreatment catalysis, the role of few-atom sulfide clusters or single atoms in catalysts has received far less attention. Although these small entities are often present in conventional catalysts, their contribution has largely been overlooked. To date, their structure remains unclear, and it is unknown whether they can compete with sulfide nanoparticles in terms of catalytic performance. In this work, we aim to shed light onto these questions and determine the minimum number of atoms required to define the active site for three industrially relevant catalytic reactions.