Kinetics and selectivity of methyl-ethyl-ketone combustion in air over alumina-supported PdOx–MnOx catalysts

A study is presented of the kinetics and oxidation selectivity of methyl-ethyl-ketone (MEK) in air over bimetallic PdOx(0–1 wt% Pd)–MnOx(18 wt% Mn)/Al2O3 and monometallic PdOx(1 wt% Pd)/Al2O3 and MnOx(18 wt% Mn)/Al2O3 catalysts. Reaction rate data were obtained at temperatures in the 443–523 K range and for MEK partial pressures in the reactor feed of between 6.5 and 126.6 Pa. Products of both MEK combustion and partial oxidation reactions were found. Monometallic Pd/Al2O3 was the most selective catalyst for complete oxidation whereas the partial oxidation of MEK in the presence of manganese oxides was significant. The maximum yield for the partial oxidation products (acetaldehyde, methyl-vinyl-ketone, and diacetyl) was always below 10%. Kinetic studies showed that the rates of CO2 formation over PdOx/Al2O3 were well-fitted by the surface redox Mars–van Krevelen (MvK) kinetic expression and also by a Langmuir–Hinshelwood (LH) model derived after considering the surface reaction between adsorbed MEK and oxygen as the rate-determining step. In the case of the Mn-containing catalysts the MvK model provides the best fit. Irrespective of the model, the kinetic parameters for the bimetallic Pd–Mn catalysts were between the values obtained for the monometallic samples, suggesting an additive rather than a cooperative effect between palladium and manganese species for MEK combustion.