First steps in combining modulation excitation spectroscopy with synchronous dispersive EXAFS/DRIFTS/mass spectrometry for in situ time resolved study of heterogeneous catalysts

The synchronous combination of time resolved (energy dispersive) EXAFS, diffuse reflectance infrared spectroscopy (DRIFTS), and mass spectrometry (MS), applied within the general framework of concentration modulation spectroscopy, is demonstrated for in situ and time-resolved study of the behaviour of Rh/Al2O3 and Pd/Al2O3 catalysts during CO/NO redox cycling at 573 K. We show that by applying a phase sensitive detection technique the quality of information arising from the experiment is significantly improved. Moreover, in the case of the dispersive EXAFS the acuity of this technique is greatly enhanced and a surface sensitivity in the normally bulk sensitive EXAFS measurement can be induced. Lastly we apply this approach to a system (0.3 wt% Rh/Al2O3) that cannot normally be studied in any meaningful way with transmission based and highly time resolved EXAFS, and show that this method may provide a novel experimental window through which it is possible to restore highly time resolved structural-kinetic information from previously intractable systems.