Mechanism of potassium loss by desorption from an iron oxide catalyst for the styrene process

Several types of experiments have been done with molecular beam and mass spectrometric methods to characterize the desorption processes of potassium from a commercial styrene (potassium promoted iron oxide) catalyst. The loss of potassium as desorption of K is found to be mainly thermal, with an activation energy close to 1.0 eV (97 kJ/mole), which probably is associated with release of K from the initially bound positions in the bulk. The directly measured rate of loss as K appears too small to account for the experimentally observed total rate of loss. A new loss mechanism as electronically excited but not easily field ionizable potassium atoms is detected with an activation barrier of 1.7 eV (164 kJ/mole). Excited states may be important for the total loss both through direct emission of excited K atoms, and since excited states may give rise to cluster formation at the surface and more rapid loss as clusters Kn.