THE EFFECT OF ALUMINA STRUCTURE ON SURFACE SITES FOR ALCOHOL DEHYDRATION

We have studied the effect of alumina form(-/, 5, and a), and impurities, on 2-propanol dehydration activity. In a steady-state flow reactor experiment, α-alumina was approximately 1000 times less reactive (in terms of moles propene formed/s/m2) than reforming grade γ-alumina. The structure of the transitional alumina (γ vs δ) played a smaller role than Na contamination in determining alcohol dehydration activity. For instance, δ-alumina was ≈3-6 times less reactive than reforming grade γ-alumina in its activity for alcohol conversion, while Na-poisoned γ-alumina was ≈180 times less reactive. The number of surface sites on these aluminas were determined using temperature-programmed reaction (TPR) of 2-propanol. It was found that ≈1-2 × 1018 alcohol molecules/m2 reacted to form propene on all of the aluminas independent of alumina form or impurity concentration. The temperature at which the alcohol reacted to form propene in the TPR experiment correlated inversely with steady-state alcohol dehydration activity. The peak desorption temperature (TP) during TPR ranged from 440 K for reforming grade γ-alumina to 600 K for α-alumina. These results are discussed in terms of a model for the nature of reactive sites on the surface of alumina. © 1992.