In Situ X-ray Absorption Fine Structure (XAFS) Applied to Catalyst Characterization at UOP: Examples and Perspectives

Abstract

A commercial catalyst has to be able to perform multiple functions, including: (i) enable the catalytic chemistry via an active site(s); (ii) allow the feed to reach the active site, and the products to diffuse out; (iii) be able to be manufactured on a cost-effective basis; and (iv) be able to be handled for transportation and loading/unloading into the commercial reactor. Thus, the successful development, manufacture, and deployment of a catalyst involve a range of different attributes that relate back to the physical structure of the formed catalyst. It is clear that the development of an improved catalyst for an existing industrial process, or of a catalyst for a process still being developed, is greatly aided by a complete understanding of the structure of the catalyst. This knowledge of the structure is needed over many different length scales from the atomic-level chemical and geometric information of the active site to the macroscopic properties of the formed catalyst. Moreover, knowledge of the structure under reaction conditions, i.e. in situ, adds additional understanding as it is often the case that the actual catalytic site is only formed, or is only stable, under reaction conditions.While there are many synchrotron-based methods applicable for studying catalyst structure, this article will focus on the application of synchrotron-based X-ray absorption spectroscopy (XAS) in an industrial research program, with a series of specific examples from our work. These examples will highlight some of the particular needs of conducting this type of research in an industrial environment. The article will end with a focus on some of the challenges and barriers of performing industrial research at a synchrotron in the US.Researchers at UOP recognized the potential impact of synchrotron-based methods to characterize catalysts soon after the advent of the modern age of synchrotron radiation science. Indeed, in the early 1980s UOP was one of the first industrial users of CHESS at Cornell University, and the first internal report using extended X-ray absorption fine structure (EXAFS) on the structure of Pt/Rh automotive catalysts was written in 1983. In the mid-to late-1980s, UOP became a charter member of the X18B EXAFS participating research team (PRT) at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (and UOP is still a user of this beamline!). In 1993, UOP signed a memorandum of understanding with UNICAT to become a collaborative access team (CAT) member at the Advanced Photon Source (APS) at Argonne National Laboratory and helped develop the premier spectroscopy beamline on a bending magnet beamline at the APS. In 2005, UOP became a charter member of the Synchrotron Catalysis Consortium at the NSLS, and in 2008 UOP became a CAT member at MR-CAT (replacing its membership of UNICAT, which ceased to be operated as a CAT) at the APS, and actively participates in both of these collaborations. In tandem with these activities, UOP has also participated in, and continues to participate in...

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