Solid Acidity of Ground Mixture of Gibbsite-Hydrous Silica

Abstract

In an attempt to apply surface activity of mechanochemicai dehydrate to catalytic property, the behavior of gibbsite-hydrous silica mixture during mechanical grinding were investigated.
Gibbsite, Al(OH), , and hydrous silica, SiO2.n H20, were mixed in the ratio 10/90 (SiO2/AlxO3) and ground. r-A1203 of imperfect spinel structure and amorphous silica were formed by mechanochemical dehydration, and a considerable amount of solid acidity appeared on th surface through substitutiort (AIS eSi) between both particles. However, the acidity was not developed strongly (the highest value was O.2mrnol/g) because of the growth of secondary particles by aggregation and the adsorption of water from atmosphereoccurred during further grinding, Whereas, when the adsorped surface was cleanedup by heating, the amount of acidity in the range of high temperature from 800 to 1000 C was increased rapidly (the highest yalue was O.9mmol/g) and became almost equal to that ef commercial silica-alumina catalyst having same composition.On the other hand, when the mixture was ground in vacuum- to prevent the adsorption of water, ev-A120s was formed rapidly by accerelation of mechaRochemical dehydration.
It was suggested that the rapid increase in acidity was caused by elevatihg thermal stability of r-A1203 in high temperature ranges.