An Fe/ZSM-5 catalyst with a very high Si/Al ratio was prepared, and using it, the effect of NO upon the kinetics of N2O decomposition was studied. The addition of small, nonstoichiometric amounts of NO was observed to cause the rate to increase by more than an order of magnitude. The kinetics were well-fit by a rate expression that was first order in the partial pressure of N2O for the situation without added NO and separately for the situation where NO was added. The Arrhenius parameters of the rate coefficient differed for the two situations. The results are consistent with a mechanistic scheme wherein the reaction proceeds via an oxide-oxo redox cycle in the absence of NO. The results suggest that the NO-assisted decomposition of N2O does not require a second iron site adjacent to the active site and that NOx species adsorbed on the same cation site could serve as locations for oxygen storage if, in fact, the promotional effect of NO is related to such storage.
Methylamine synthesis from ammonia and methanol was studied using an amorphous silica−alumina catalyst. A combined thermodynamic and kinetic analysis shows that the selectivity
ratio initially observed at high methanol conversion is a kinetic ratio, not a thermodynamic
ratio. In some cases in the past this kinetic ratio has been taken to represent thermodynamic
equilibrium. However, if the reaction is allowed to continue beyond the point where conversion
of methanol and dimethyl ether is essentially complete, the product composition continues to
change, albeit at a much lower rate. Eventually the thermodynamic selectivity ratio is obtained.
A simple kinetic model was developed that captures this behavior, and this model was used to
assess whether a membrane reactor might be used to alter the overall selectivity of methylamine
synthesis. Four different membrane reactor configurations were considered. There were
operational regimes where each configuration showed advantages, but these either occurred at
low conversions or required extremely large reactors. These configurations are limited by
currently available catalysts and membrane materials. The impact of membrane reactors could
be increased with catalysts that retain high activity during methylamine disproportionation,
i.e., after all methanol has been consumed. The development of membrane materials with better
permselectivities would also increase the attractiveness of membrane reactor processes.
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