Design of catalytic active species and their identification via operando methodology

Identification of active site structure is the very first step to understand catalytic reaction mechanism. In heterogeneous catalysis, the identification is very difficult due to the species heterogeneity at the surface. This always leads to a range of different surface species that behave differently under reaction conditions. Such heterogeneity poses a huge challenge in establishing the structure-activity relationship of real active sites. Here I will introduce two synthetic routes that can lead to well defined catalytic actives species.

First, a colloidal route is developed by decoupling single site Cu2+ species from CuO dimers and clusters. On one hand, Cu2+ single site is the most active species among the three for CO oxidation. On the other hand, CuO cluster requires higher activation energy than that of single site, but is the only active species for water-gas-shift. Operando EPR, EXAFS and XRD suggest that the active species for single site and clusters are CuO46-/CuO23- and Cu/Cu2O clusters, respectively.
Second, a molecular route enables the formation of “synthetic enzyme” that has uniform coordination sphere. The activation upon CO and H2 of such “Ru enzyme” is carefully studied, showing a precatalyst structure of RuCl4- and the active species Ru(CO)2Cl2+ for CO oxidation.

I will further present our contribution towards the life and death of colloidal Pd@Pt catalysts under oxygen reduction reaction. An identical location TEM technique is introduced to correlate the loss of activity with the change of catalysts composition and morphology.