Catalytic Dehydration of Acetic Acid on a Graphitized Platinum Surface

Article abstract of DOI:10.1021/j100289a027

Absolute reaction rates have been measured in a continuous flow microreactor for the steady-state, catalytic dehydration of acetic acid to ketene at pressures between 8 x 10^-7 and 7 x 10^-4 Torr and temperature between 500 and 800 K.The catalyst was a polycrystalline platinum wire containing a approximately a monolayer of graphitic carbon.At 675 K or above, for the entire range of pressures studied, the order of the dehydration reaction is unity with respect to acetic acid pressure.In this regime, the apparent activation energy is 1 +/= 1 kcal/mol, and the extrapolated probability at 1/T = 0 (2.5-10) x 10^-4.Under these conditions,the rate of dehydration is determined by a competition between the rates of desorption and surface reaction of molecularly adsorbed acetic acid.For temperatures below 540 K and pressures of 3.5 x 10^-4 Torr and above, the reaction rate is independent of acetic acid pressure, and the apparent activation energy is 27 +/= 2 kcal/mol.Under these conditions, the rate of decomposition of a surface intermediate controls the rate of reaction.A mechanistic model is developed and discussed which described accurately both the temperature and the pressure dependence of the rate of dehydration.