Influence of water/alkoxide ratio on the properties of Ru/Al2O3 xerogel catalysts

A series of Ru/Al2O3 catalysts were prepared by the sol-gel method using wa ter/alkoxide ratios, h, of 1, 2, 3, 6 and 9. An increase in h resulted in ( i) total BET surface area (149 to 426 m(2) g(-1)), (ii) particle size (SEM) distribution (1.3/1.7 mm to 0.05/0.14 mm) and (iii) pore characteristic (p ore distribution, volume, size and shape) changes. Indeed the pore volume w as found to increase linearly with h. Low h values (h < 3) produced compact gel precipitates that had comparatively lower surface areas while better h ydrolysis (h > 3) gave rise to more porous gels with larger surface area an d finer texture. Alumina crystallinity as well as ruthenium reducibility of calcined samples (773 K) were largely unaffected by h. XRD spectra reveale d the presence of RuO2 after calcination. There was a significant effect on the percent weight loss (50 to 60%) of the samples on heating for h < 3. T he characterisation results show that the degree of hydrolysis can control the properties of Ru/Al2O3 catalysts in a predictable manner. (C) 1999 Else vier Science B.V. All rights reserved.