Labelled oxygen pulse

Ashikawa, I., J.-J. Yin, W. K. Subczynski, T. Kouyama, J. S. Hyde, and A. Kusumi. 1994. Molecular organization and dynamics in bacteriorhodopsin-rich reconstituted membranes Discrimination of lipid environments by the oxygen transport parameter using a pulse ESR spin-labeling technique. Biochemistry 33 4947 1952. 

Contrary evidence, that adsorbed oxygen is involved in the partial oxidation of propene, has been obtained using labelling." When a pulse containing propene and 0-enriched oxygen was passed over a Cu2 0 catalyst at 623 K the ratio of in the acrolein produced was identical to the 0 ... 

Figure 1. Transient response curves for a) n-butane, b) CO2, and c) MA obtained by pulsing a 3.5/1 3.5/1 C4Hio/Ar mixture over an oxygen-treated VPO sample at 653 K. The responses labeled Ox were obtained after the sample was first exposed to 1000 pulses n-butane. The unlabeled responses were obtained after exposure to 8000 pulses.

The ammonia oxidation reaction proceeds in the first part of the catalyst bed [Fig. 16(a)]. This part is subsequently deactivated, mainly by nitrogen species. The high activity of the catalyst is maintained due to the movement of the reaction front to the next positions in the catalyst bed. When [ Nj-NH3 is injected at the moment that the reaction was already 20 seconds on-stream, labelled N species adsorb further on in the catalyst bed. Thus, in time to come, the deactivation front moves to the end of the catalyst bed. When this front reaches the end of the bed, the catalyst is covered with reaction species and the deactivation is observed in the concentration of the products. An experiment with half an amount of the catalyst also supports this reaction front movement. This experiment showed the formation and concentration of the products in the same manner, however, the catalyst remained active for half the time of the normally applied catalyst bed. Thus, below 413 K, the catalyst remains initially active because the reaction zone moves to the next bed positions, after the previous positions became fully covered with the adsorbed reaction species. Injection of a [ N]-NH3 or [ 0]-02 pulse after the initial deactivation, confirmed that the platinum surface is fully covered and that conversion of ammonia and oxygen is low. No significant amount of nitrogen or oxygen species remains adsorbed at the catalyst surface. 

Isotopic labelling of reactants, or a switch to labelled reactant during reaction, can give information on kinetically limiting steps, symmetry patterns in intermediates, the involvement of lattice oxygen, etc. Microreactors and pulse techniques are usually most suitable for such work. 

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