Time Resolved Operando X-ray Techniques in Catalysis, a Case Study: CO Oxidation by O2 over Pt Surfaces and Alumina Supported Pt Catalysts

Abstract

Abstract:The catalytic oxidation of CO by O 2 to form CO 2 over Pt surfaces and supported catalysts is one of the most studied catalytic reactions from both fundamental and applied points of view. This review aims to show how the application of a range of time resolved, X-ray based techniques, such as X-ray diffraction (XRD), Surface X-ray diffraction (SXRD), total X-ray scattering/pair distribution function (PDF), X-ray absorption (XAFS), X-ray emission (XES), and X-ray photoelectron spectroscopies (XPS), applied under operando conditions and often coupled to adjunct techniques (for instance mass spectrometry (MS) and infrared spectroscopy (IR)) have shed new light on the structures and mechanisms at work in this most studied of systems. The aim of this review is therefore to demonstrate how a fusion of the operando philosophy with the ever augmenting capacities of modern synchrotron sources can lead to new insight and catalytic possibilities, even in the case of a process that has been intensely studied for almost 100 years.

Investigation of periodically driven systems by x-ray absorption spectroscopy using asynchronous data collection mode

“…Such advanced nanoscale materials as catalysts and electrocatalysts, 1,2 electromechanical actuators, 3,4 battery and filtration materials 5,6 exhibit their new functionalities due to the changes in their local structures and electronic properties that occur within a range of a few interatomic distances. 1,7 There is a paucity of either available experimental methods or a dedicated research infrastructure in the case of materials in which the response to the external stimulation is weak. In the first class of such materials, such as piezoelectrics, ferroelectrics, classical electrostrictors, and magnetostrictors, 3,8,9 the structural or electronic responses to the external excitation are uniform but weak.…”

“…This subject is in the focus of intense research, aimed at understanding the origins of emerging physicochemical properties and novel functionalities in such materials. 1,2,7 In this paper, we report on the development of a dedicated instrument at the National a) Authors to whom correspondence should be addressed: Igor.lubomirsky@ weizmann.ac.il; istavitski@bnl.gov; and anatoly.frenkel@stonybrook.edu Synchrotron Light Source-II (NSLS-II) that enables such enhanced sensitivity by using the asynchronous excitationprobe mode of X-ray absorption fine-structure (XAFS) spectroscopy. XAFS spectroscopy, which comprises X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS), is a premier synchrotron-based technique, which delivers element-specific information on the chemical state and coordination environment around particular atomic species in a compound.…”

“…XAFS spectroscopy, which comprises X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS), is a premier synchrotron-based technique, which delivers element-specific information on the chemical state and coordination environment around particular atomic species in a compound. 11 In EXAFS, the oscillatory structure of the absorption coefficient within 40-1000 eV past the absorption edge is caused by the interference of the outgoing and scattered photoelectron waves and is commonly described by the equation (within the ith shell) 11 (1) where k is the photoelectron wavenumber, f eff i (k) and δ i (k) are the photoelectron scattering-path amplitude and phase, respectively, S 2 0 is the passive electron-reduction factor, n i is the degeneracy of the scattering path, R i is the effective half-path length (which equals the interatomic distance for single-scattering paths), σ 2 i is the mean-square deviation in R i , and λ i (k) is the photoelectron mean free path.…”

“…Thus, the modulated excitation approach, wherein periodic perturbation of an external parameter is employed to stimulate the system under observation, while time-resolved data are collected simultaneously, can be applied for a system that responds reversibly to the external periodic excitation. These methods with periodic perturbation have been adopted by several groups including Ferri et al, 13,[18][19][20][21] Newton et al, 1,22 and Pascarelli et al, 9,12 at European Synchrotron Radiation Facility (ESRF) and Swiss Light Source (SLS), wherein mostly lock-in methods have been applied for measurements under in situ or operando conditions. These studies showed the potential of MES for XAFS as it drastically increased sensitivity to weak response of the systems under external stimulation.…”

High energy resolution off-resonant spectroscopy: A review

“…HEROS is a new approach and is becoming more and more recognized in the field of X-ray spectroscopy (see, e.g., Refs. [42,[52][53][54][55][56][57][58][59][60][61][62][63][64]). …”