A microstructured reactor based in situ cell for the study of catalysts by X-ray absorption spectroscopy under operating conditions Gopinathan Sankar a,c , Enhong Cao b , Asterios Gavriilidis a,b, * a Materials Chemistry Centre, University College London, 20 Gordon Street, London WC1H 0AJ, UK b Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, UK c Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, UK Available online 9 March 2007 Abstract In situ X-ray absorption spectroscopic studies have been performed at the silver K-edge, of a silver catalyst deposited in a microstructured reactor cell at operating conditions. Oxidative dehydrogenation of methanol to formaldehyde was performed at atmospheric pressure and 773 K with a feed containing 9.7% CH 3 OH, 18.8% O 2 (N 2 as balance) at residence time of 10 ms. The as-prepared catalyst shows that only metallic silver phase is present. Analysis of the EXAFS data recorded during calcination at 773 K in air, indicates that some of the silver metal catalyst is oxidised. Upon introduction of methanol/air mixture, part of the oxygen coordination is removed suggesting that an oxidation/reduction cycle takes place during the reaction. This work demonstrates that such microfabricated reactors can be readily used for in situ X-ray absorption spectroscopy. # 2007 Elsevier B.V. All rights reserved. Keywords: XAS; XANES; EXAFS; Microstructured reactor; Silver; Methanol; Formaldehyde 1. Introduction Metals and supported metal catalysts belong to a family of heterogeneous catalysts, which are routinely used in several reactions. It is well recognised that efficiency of the catalyst, longevity and performance are related to the nature of active sites, intrinsic reactivity and in general the structure of the catalytic system. A variety of techniques are used to determine the structure of the catalysts and among them X-ray based techniques provide direct means of obtaining the atomic- architecture of catalytic materials [1–12]. Other spectroscopic techniques, in particular Raman spectroscopy, is useful in determining catalytic species and reaction intermediates [13– 17]. Although X-ray diffraction is a powerful technique to determine the structure of catalysts, often due to large disorder and amorphous nature of the catalytic material, it is difficult to determine the structure of the catalytic solids by this technique. X-ray absorption spectroscopy (XAS), which consists of X-ray absorption near edge structure (XANES, which provides geometric, electronic and chemical state information) and extended X-ray absorption fine structure (EXAFS, which provides local geometric structure information) is now routinely used to determine the structure of disordered, poorly crystalline and amorphous catalytic materials. This technique does not depend on long-range arrangement of the atoms and it is atom- specific [2–4,7–10,12]. Although, several in situ methods have been developed to study catalytic materials by X-ray absorption spectroscopy, there is still a continued interest in developing new methods, in particular for studies at operating conditions. In recent years, microstructured reactors have been utilized for the study of heterogeneous catalytic reactions [18,19]. With reaction channels down to few microns to hundreds of microns in dimension, microstructured reactors can offer distinct advantages [20,21]. The microscale dimensions result in low transport resistances such that heat and mass transfer are extremely fast and equilibration is nearly instantaneous both thermal and compositional. The small diameters of the reaction channel ensure precise control of residence time. In addition, the small amounts of reactants required minimize danger when using toxic or explosive chemicals. Catalyst materials can be www.elsevier.com/locate/cattod Catalysis Today 125 (2007) 24–28 * Corresponding author at: Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, UK. Tel.: +44 20 76793811. E-mail address: a.gavriilidis@ucl.ac.uk (A. Gavriilidis). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.01.068