Radio-labelled ammonia

Figure 23 further shows that after changing the flow to NHs/He, [ N]-NH3 desorbs and travels as a pulse through the reactor. This indicates that [13N]-NH3 exchanges rapidly with [ Nj-NHs. At first sight, this exchange process is very similar to the experiment shown in Figure 22. However, in this case, radio-labelled ammonia is not in full equilibrium on 7-almnina. After switching to imlabelled ammonia, first of all, the available Lewis sites are saturated. The time to satmate the 7-alumina bed with ammonia, measured with the mass spectrometer at the outlet of the reactor, is equal to the retention time of radiolabelled ammonia in the catalyst bed. Thus, the radiolabelled ammonia moves with the saturation front, where aimnonia adsorption/desorption is in quasi equilibrium. We conclude that gas phase anunonia clearly facilitates desorption of [ Nj-NHs it remains adsorbed at the same bed position without ammonia in the gas phase. This proves that Adsorption Assisted Desorption takes place for aimnonia desorption from 7-alumina.

The radio-labelled PEP experiments have shown that the pre-adsorbed oxygen favours the dissociation of ammonia, which leads to production of N2, N2O and NO. The product selectivity strongly depends on the temperature. Below 423 K, mainly nitrogen and nitrous oxide were formed and above this temperature, NO was formed. The PEP experiments indicate that all ammonia reacts at the beginning of the catalyst bed, and that [13n]-NH3 is partly converted into gaseous products and partly remains... 

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