Heterogeneous Catalysis DOI: 10.1002/anie.201105790 Observing Oxygen Storage and Release at Work during Cycling Redox Conditions: Synergies between Noble Metal and Oxide Promoter** Mark A. Newton,* Marco Di Michiel, Anna Kubacka, Ana Iglesias-Juez, and Marcos Fernµndez-García* The ability of many materials to store and release gases lies at the core of a range of economically and environmentally important technologies. [1–6] To this end much research is directed towards developing materials that have an optimal storage capacity for the gases. However, in many cases, the implicitly “static” notion of “capacity” is only half the story. For practical operation gas uptake and release functions also need to be kinetically adapted to the process situation. [1, 2] The preeminent application that utilizes gas storage and release properties in a highly dynamic situation is three-way catalyst (TWC) operation for pollution abatement. Within this application TWCs have to respond to a rapidly alternat- ing (1–2 Hz) redox environment. [3–7] The principal role CeZrO 4 has within the TWC paradigm relates to the oxygen storage capacity (OSC). The OSC [7] ensures efficient conversion of CO and hydrocarbons into CO 2 in reducing conditions and of NO into N 2 at oxidizing conditions, even when the feedstock has become, respectively, diminished or enriched in oxygen with respect to a stoichio- metric mixture. [4, 6] CeZrO 4 has come to be seen as an optimal material for application in TWCs on the basis of its OSC properties and the increased thermal stability it bestows upon the catalyst system. [5] In spite of these considerations, only a few studies [8] have attempted to deal with the dynamic structural reactive aspects of its behavior. These studies have used extended X-ray absorption fine structure (EXAFS) spectroscopy at the cerium L III and zirconium K edges to study a 1 wt % Pt/CeZrO 4 catalyst [8a] or environmental TEM to analyze the redox state of CeZrO 4 particles during reducing/oxidizing conditions. [8b] Herein, we go further by coupling time-resolved hard (86.8 keV) X-ray diffraction (HXRD) or palladium K edge energy-dispersive EXAFS to diffuse reflectance infrared spectroscopy (DRIFTS) and mass spectrometry (MS). [9] This approach permits us to directly investigate the struc- ture–activity relationship of the supported Pd nanoparticles, the nanoscale CeZrO 4 phases, and the adsorbates that are formed or converted over them, at the same time, and with subsecond time resolution. We therefore directly detect and kinetically quantify oxygen storage and release. Moreover, we elucidate several distinct facets to the synergetic interaction of the CeZrO 4 and Pd phases. Figure 1 shows firstly (top left panel) on-line mass spectrometry pertaining to CO 2 production during alternate NO–CO–NO exposure at 673 K over two systems having similar Pd particle size (see the Supporting Information): 2 wt % Pd/Al 2 O 3 (2PdA) and 4 wt % Pd/33 wt% CeZrO 4 / Al 2 O 3 (4Pd33ZCA) samples. This CO–NO single cycle is taken from within a larger experiment comprising 10 cycles as described previously. [9, 10] The color maps show HXRD data derived from 33ZCA and 4Pd33ZCA samples during CO/NO cycling at 673 K at Figure 1. Temporal variation in m/z 44 (CO 2 ) observed for alternate NO–CO–NO exposure (13.86 s each gas) at 673 K over 2PdA (*) and 4Pd33ZCA (*) and variations in HXRD (color maps) observed during CO/NO cycling at 673 K over 33ZCA and 4Pd33ZCA samples and for cycling time between each gas of 13.86 s. The bottom right panel shows the result obtained for the 4Pd33ZCA at 673 K but with a gas exposure time of 21.41 s. The white arrows in the inset (A) highlight changes of d spacing in the Pd [111] reflection toward the end of the CO phase of the cycling. [*] Dr. M. A. Newton, Dr. M. Di Michiel European Synchrotron Radiation Facility 6, Rue Jules Horowitz, BP220, Grenoble, F-38043 (France) E-mail: newton@esrf.fr Dr. A. Kubacka, Dr. A. Iglesias-Juez, Prof. M. Fernµndez-García Instituto de Catµlisis y Petroleoquímica, CSIC, C/Marie Curie 2 28049, Madrid (Spain) E-mail: mfg@icp.csic.es [**] We thank the ESRF for access to facilities. Trevor Mairs, Pierre Van Vaerenbergh, Pascale Dideron, Dominique Rohlion, and Marchial Lambert are all gratefully thanked for their technical contributions to this work. Andy Fitch (ESRF) is also thanked for his advice regarding processing of the HXRD data. Supporting information for this article, including experimental details, is available on the WWW under http://dx.doi.org/10.1002/ anie.201105790. A ngewandte Chemi e 2363 Angew. Chem. Int. Ed. 2012, 51, 2363 –2367  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim