Preparation of a composite γ-zirconium phosphate silica with large specific surface and its first characterisation as acid catalyst

A composite of gamma -zirconium phosphate (gamma -ZrP) and silica (40% in weight of gamma -ZrP) was prepared by hydrolysis of tetraethylsilicate in the presence of exfoliated gamma -ZrP. The exfoliation of gamma -ZrP was obtained in 1:1 (v/v) acetone/water solution at 80 degreesC. The presence of silica prevented the re-aggregation of the exfoliated gamma -ZrP lamellae. After heating at 650 degreesC, the greater part of gamma -ZrP was present in the composite as bilamellar packets of zirconium phosphate acid pyrophosphate while about 20% was transformed into alpha -Zr(O3POH)(2). The surface acid P-OH groups of these lamellar species (about 1. 1 meq. g(-1)) were not destroyed by thermal treatment up to 750 degreesC. The composite exhibited a specific surface area of 421 m(2) g(-1) of which about 191 m(2) g(-1) was attributable to exfoliated lamellae of zirconium phosphate. The catalytic properties of the composite were preliminarily investigated for the conversion of ethylbenzene to styrene at different temperatures and different EB/O(air) ratios as a function of the contact time. The results are compared with pure gamma -ZrP calcined at 650 degreesC. Catalytic activity was strongly influenced by the total amount of the surface acidic groups of the samples. The gamma -ZrP/SiO2 composite showed a higher conversion rate (about five times) than calcined gamma -ZrP. (C) 2001 Elsevier Science B.V. All rights reserved.