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Positron Emission Imaging in catalysis

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PII: S0926-860X(97)00131-2 ELSEVIER Applied Catalysis A: General 160 (1997} 125-138 APPLIED CATALYSIS A: GENERAL Positron emission imaging in catalysis a • B.G. Anderson ' , R.A. van Santen a, L.J. van I Jzendoorn b aDepartment of Chemical Engineering and Chemistry, Schuit Institute of Technology. Eindhoven Universi(v of Tcchnologx; PO Box 513, 5600 MB Eindhoven, Netherlands hDepartment of Technical Physics, Schuit Institute of Catalysis, Eindhoven University of Technology+ PO Box 513. 5600 MB Eindhoven, Netherlands Abstract In situ imaging technology developed for nuclear medicine is now being applied to study the kinetics of heterogeneous catalytic reactions under actual process conditions. Minute quantities of molecules (ca. 10 -~ tool), radio-labeled with positron-emitting isotopes such as ltC;13 N; or t50 are injected as pulses into the feed streams of chemical reactors. Subsequent coincident detection of pairs of gamma photons produced via positron--electron annihilation allows the concentration of reactants, intermediates and products to be mapped as a function of both time and position within the reactor bed. As well as providing qualitative information regarding the mechanism of the reaction under investigation the data obtained can be compared with mathematical models based on the reaction kinetics in order to refine parameters such as activation energies and pre-exponential factors for elementary reaction steps. Since the technique is capable of imaging transient phenomena, information is provided that is not accessible to steady-state techniques. Keywords: Transient kinetics; Positron emission: In situ imaging: Chemical reactor 1. Introduction Although the kinetics of heterogeneous catalytic reactions are still most often measured in the steady state there is a growing interest in transient methods since the latter allows one to distinguish directly between various possible reaction mechanisms and to measure the rates of the indivi

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