Porous silica-alumina particles in which pores with relatively large diameters are present at a high ratio with respect to the total pore volume, and the particles contain crystalline boehmite alumina, are disclosed. The crystalline boehmite alumina-containing porous silica-alumina particles are such that a specific surface area SA measured by the BET method is in a range of 400 to 600 m.sup.2/g, a pore volume PV measured by the BJH method is in a range of 1.0 to 2.2 ml/g, a ratio P10 of a pore volume of pores having pore diameters PD of 10 nm or larger to the total pore volume PV is in a range of 60% or higher, the pore volume of pores having pore diameters of 10 nm or larger being measured by the BJH method, and a mass ratio S/A between silica and alumina is in a range of 2/98 to 70/30.

Porous silica-alumina particles in which pores with relatively large diameters are present at a high ratio with respect to the total pore volume, and the particles contain crystalline boehmite alumina, are disclosed. The crystalline boehmite alumina-containing porous silica-alumina particles are such that a specific surface area SA measured by the BET method is in a range of 400 to 600 m.sup.2/g, a pore volume PV measured by the BJH method is in a range of 1.0 to 2.2 ml/g, a ratio P10 of a pore volume of pores having pore diameters PD of 10 nm or larger to the total pore volume PV is in a range of 60% or higher, the pore volume of pores having pore diameters of 10 nm or larger being measured by the BJH method, and a mass ratio S/A between silica and alumina is in a range of 2/98 to 70/30.

A pseudo-boehmite has a dry basis content of 55-85 wt % and contains a phosphoric acid ester group. The sodium oxide content is not greater than 0.5 wt %, and the phosphorus content (in terms of phosphorus pentoxide) is 1.2-5.7 wt %, relative to 100 wt % of the total weight of the pseudo-boehmite. The pseudo-boehmite has a low sodium content.

The present invention concerns a method of preparing aluminum monohydrate comprising the steps of i) mixing alumina feedstock with ethylenediamine tetraacetic acid, to obtain a feedstock mixture, and ii) subjecting the feedstock mixture to a hydrothermal treatment, wherein the wherein the pH of the feedstock mixture is at least 8. The resulting aluminum monohydrate, although starting from low purity feedstocks, shows an excellent purity and can be calcined to obtain high purity alpha alumina.

The present invention concerns a method of preparing aluminum monohydrate comprising the steps of i) mixing alumina feedstock with ethylenediamine tetraacetic acid, to obtain a feedstock mixture, and ii) subjecting the feedstock mixture to a hydrothermal treatment, wherein the wherein the pH of the feedstock mixture is at least 8. The resulting aluminum monohydrate, although starting from low purity feedstocks, shows an excellent purity and can be calcined to obtain high purity alpha alumina.