Structure analysis of phosphated zirconia catalysts using XRD and nitrogenadsorption methods

Phosphated zirconia catalysts were prepared by impregnating two different p recursors (zirconium hydroxide and crystalline ZrO2) with an aqueous soluti on of diammonium hydrogen phosphate. X-ray powder diffractograms and nitrog en adsorption isotherms at -196 degrees C on pure and phosphated zirconia c atalysts were investigated. The pore volume was calculated from the adsorpt ion branch to explore the modification of porosity for pure and phosphated zirconia. Pore structure analysis shows that phosphated zirconia, resulted from calcination of zirconium hydroxide at low temperature, exhibited high surface area and accessible porosity. Whereas for those calcined at higher temperatures, inaccessible porosity is shown to predominate. Phosphation of crystalline zirconia did not modify either surface area or the porosity, a s compared to pure zirconia. The influence of phosphation on the structure of zirconium hydroxide and zirconia during the calcination course was studi ed. (C) 2000 Elsevier Science B.V. All rights reserved.