The Properties of Silica-Metal Catalysts Prepared by Homogeneous Method and Their Activities for the Dehydration of 2-Propanol

Abstract

The properties of the silica-coppera(II), -cobalt(II), -nickel(II), -aluminium(III), -iron(III), -chromium(III), -zirconium(IV) and -cerium(IV), prepared by precipitation from h omogeneous solution, and their catalytic activities for the dehydration of 2-propanol were compared with those of the catalysts prepared by usual coprecipitation method. The differencial thermal analysis showed an exothermic peak at 690°C for the coprecipitated silica-copper, and a small exothermic peak at 720°C for the homogeneous silica-copper. Similar thermal behavior was found for the other silica-metals. Infrared absorption at 580 cm^-1 and X-ray diffraction peaks at 2θ=35.5° and 38.5°, which indicate the formation of CuO, appeared at 750°C for the silica-copper, but did not at 600°C. From these results it was found that all the metals were combined with silica gel below about 600°C, but thermal stabilities were higher for the homogeneous catalysts.
Kinetic studies using a flow rea ctor indicated that the dehydration was of first-order reaction and the order of the activities of the homogeneous catalysts was as follows: silica Al>-Ni>-Fe>-Cu>-Zr>-Co>-Cr>-Ce. From the changes in relative activities caused by the addition of KOH and the behavior of pH titration curves for the catalysts, it was concluded that the active site for the dehydration was Lewis acid site and the number of the acid site was larger for the homogeneous catalysts than the coprecipitated catalysts.