Solid Wacker-type catalysts (Pd-V2O5 or Pd-CeO2 supported on alumina and Pd-doped KH3PV1Mo11O40) show a marked decline in activity in the gas phase selective oxidn. of 1-butene to Me Et ketone, whereas the selectivity passes through a max. After about 5-6 h onstream, nearly steady-state behavior is reached, characterized by a slower deactivation rate and a slight decline in selectivity. The initial change in the catalytic behavior is discussed in terms of the formation of adsorbed species and changes in the valence state of V and Pd during the catalytic reaction. Both these deactivation effects can be reversed by an oxidizing treatment at 300°. The second, slow deactivation is instead related to the crystn. of V-oxide particles and is not reversible. It is also shown that Pd-doped V heteropoly acid has a much higher initial activity and selectivity, but the catalyst rapidly deactivates. [on SciFinder(R)]