Structure analysis of phosphated zirconia catalysts using XRD and nitrogen adsorption methods

Phosphated zirconia catalysts were prepared by impregnating two different precursors (zirconium hydroxide and crystalline ZrO2) with an aqueous solution of diammonium hydrogen phosphate. X-ray powder diffractograms and nitrogen adsorption isotherms at −196°C on pure and phosphated zirconia catalysts were investigated. The pore volume was calculated from the adsorption 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, as compared to pure zirconia. The influence of phosphation on the structure of zirconium hydroxide and zirconia during the calcination course was studied.