Catalytic vapor-phase hydration of propylene on the metal sulfate-silica gel catalyst

The vapor-phase hydration of propylene was carried out over metal sulfate-silica gel catalysts under various conditions. It was found that the catalytic activity obeys a simple rule. Namely, the catalyst containing a sulfate of trivalent metal was the most active and the catalyst containing a sulfate of bivalent metal followed this, while the catalyst containing a sulfate of univalent metal showed no activity. Further, the catalytic activity was found to decrease in the order of Fe > Al > Cr > Cu > Zn > Co > Cd > Ni > Mn > Mg > K, Na. Thus, it was shown that nearly the same order as that of the decreasing hydrogen ion concentration in the hydrolysis holds for the catalytic activity. From the results described above, it was considered that the catalyst would be acidic and the surface acidity would be related closely to the catalytic activity. Results of the acidity measurement showed that the catalysts are actually acidic and supported the view described above. From the results of acidity measurements and X-ray diffraction studies, it was presumed that the observed acidity would result from an interaction between silica gel and sulfate. To relate the catalytic activity with the surface acidity, a rate equation r = k1pH2OpC3H6 − k2piso-C3H7OH was derived. From the proportionality between the acidity of 1.5 ≥ H0 ≥ −3.0 and the rate constant, it was concluded that acids existing in this region would contribute to the catalytic activity.