Characterizing industrial catalysts using in situ XAFS under identical conditions‡

In situ X-ray absorption spectroscopy (XAS) in catalysis research has traditionally been conducted by making one measurement at a time on a single sample. In an industrial research environment this is especially limiting as sample throughput (productivity) and turnaround time (direct project relevance) are critical issues in the use of XAS in a fast-moving technology delivery project. In order to address these issues we have developed and implemented a four-channel ionization chamber combined with two different in situ cells that allows XAS data to be collected simultaneously from four samples, or four regions, in transmission geometry without any sample or detector movement. In the development of this new capability it was realized that there are other benefits from this simultaneous detection in addition to increased productivity. Namely, (i) the use of EXAFS to determine the structure of a catalyst in situ axially at four different positions down a catalyst bed; (ii) the ability to collect up to four XAFS spectra simultaneously and thereby avoid any scan-to-scan uncertainties, and (iii) the added confidence in the ability to discriminate small differences in similarly prepared catalysts which is typical in the development of a commercial catalyst. Specific illustrations of each of these applications are shown. The methodology is simple to implement and could be used on any XAFS beamline with a horizontal fan of radiation, such as at a typical bending magnet or wiggler source beamline.