Dynamic three-dimensional migration of Pd single atom species of Pd/TiO2 single atom catalysts during CO oxidation

Heterogeneous catalysis has grown rapidly since the beginning of the twentieth century, and currently it plays a central role in modern industrial catalysis. Single-atom catalysts (SACs) have been recognized as one of the most active frontiers in heterogeneous catalysis, taking the advantage of maximum utilization of precious metals and their superior catalytic performance. SACs do not have static local coordination under reaction conditions, driven by their high surface energy. Understanding the dynamism of SACs under reaction conditions is therefore highly important. So far, all the dynamic process of SACs are all focused on the surface of the support. For the reduced metal oxide support, not all the single atoms (SA) are located on the surface, part of them substituted the metal from the bulk metal oxide support. Notably, the precious metal atoms could migrate dynamically between the bulk and surface of the support in response to certain reaction atmospheres. Such a three-dimensional dynamic process of SA could result in the direct change of active site numbers and the intrinsic catalytic performance of SA species, which could influence the catalytic activity significantly. However, such a process has barely been investigated due to the underestimate of their influence on catalytic activity and the limitation of operando and quantitative technologies. Thus, this project will focus on the dynamic three-dimensional migration of SA of Pd1/TiO2 during CO oxidation process. We aim to develop quantitative and operando methodology to analyze three-dimensional distribution of different Pd1 species, reveal how the dynamic process influences the active site numbers and the intrinsic catalytic activity of Pd1 species and establish the dynamic structure-activity relationship of Pd1/TiO2. The final aim is to provide guidelines for the design of high-performance SACs for a given catalytic process.