Phase distribution in titania–sepiolite catalyst supports prepared by different methods

Abstract

In this study it has been shown that in samples prepared by mechanical mixing of titania and sepiolite, greater titania coverages could be obtained when the mixtures were kneaded in a concentrated acid medium. The distribution of sepiolite and titania at the surface of the mechanical mixtures was studied by the electrophoretic migration technique. The samples were further characterised by nitrogen adsorption, XRD and thermogravimetric techniques. The electrophoretic migration results showed that the addition of sepiolite to titania, kneaded in water, had a dramatic effect on the quantity of titanium oxide present at the support’s surface, both strongly decreasing the molar fraction of titania at the surface, and altering the electrophoretic properties of the mixtures. When kneaded in concentrated acid (HCl, 37%, m/m), the effect of sepiolite addition was greatly reduced. The XRD patterns and BET surface areas of the water-kneaded samples agreed with previously reported results. However, kneading in acid medium induced a slight increase in the BET surface areas of sepiolite and mixtures, but a small decrease for titania. This acid treatment did not alter the XRD patterns of titania and mixtures, compared to the water-kneaded samples. Although the XRD pattern of sepiolite was partially altered, a large part (71%) of sepiolite remained unchanged.