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| - Direct Observation of Surface Ethyl to Ethane Interconversion upon C2H4 Hydrogenationover Pt/Al2O3 Catalyst by Time-Resolved FT-IR Spectroscopy
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| - Time-resolved FT-IR spectra of ethylene hydrogenation over alumina-supported Pt catalyst were recorded at25 ms resolution in the temperature range of 323−473 K using various H2 concentrations (1 atm total gaspressure). Surface ethyl species (2870 and 1200 cm-1) were detected at all temperatures along with the gas-phase ethane product (2954 and 2893 cm-1). The CH3CH2Pt growth was instantaneous on the time scale of25 ms under all experimental conditions. At 323 K, the decay time of surface ethyl (122 ± 10 ms) coincideswith the rise time of ethane (144 ± 14 ms). This establishes direct kinetic evidence for surface ethyl as therelevant reaction intermediate. Such a direct link between the temporal behavior of an unstable surfaceintermediate and the final product in a heterogeneous catalytic system has not been demonstrated before. Afraction (25%) of the asymptotic ethane growth at 323 K is prompt, indicating that there are surface ethylspecies that react much faster than the majority of the CH3CH2Pt intermediates. The dispersive kinetics isattributed to the varying strength of interaction of the ethyl species with the Pt surface caused by heterogeneityof the surface environment. At 473 K, the majority of ethyl intermediates are hydrogenated prior to therecording of the first time slice (24 ms), and a correspondingly large prompt growth of ethane is observed.The yield and kinetics of the surface ethylidyne are in agreement with the known spectator nature of thisspecies.
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