(561b) Measuring and Relating the Electronic Structure of Alloys to Their Chemical and Catalytic Performance
- Conference: AIChE Annual Meeting
- Year: 2009
- Proceeding: 2009 Annual Meeting
- Group: Catalysis and Reaction Engineering Division
- Time: Thursday, November 12, 2009 - 12:51pm-1:12pm
Alloy catalysts often exhibit significantly different chemical and catalytic behavior than the constitutive elements that form the alloy. We will discuss experimental and theoretical studies that allowed us to identify underlying physical factors which govern the observed different behavior of alloys.
In this context, we will discuss the d-band theory, which relates the electronic structure of transition and noble metals to their chemical activity and catalytic performance. We will show that even small changes in the near Fermi level electronic structure of nonmodel supported catalysts, induced by a formation of an alloy, can be experimentally measured and related in accordance with the d-band model to the chemical activity and catalytic performance of these materials. Our results also show that the critical shifts in the d-band center in alloys are the result of the formation of new electronic states in response to alloying rather than charge redistribution among constitutive alloy elements. Our analysis led us to a formulation of a simple and physically transparent model that allows us to a priori predict the general effect of alloying on the electronic structure of a material and therefore on its chemical performance. To accomplish the objectives we have used multiple experimental tools including Extended and Near Edge X-ray Absorption Spectroscopy (EXAFS and XANES), Electron Energy Loss Spectroscopy (EELS) and Density Functional Theory (DFT) calculations.
Our findings are illustrated in multiple examples where various Pt and Ni alloy were studied.