Amorphous silica or silica-alumina spherical particles and process for preparation thereof

Amorphous silica-alumina spherical particles composed of X-ray diffractometrically substantially amorphous silica-alumina containing less than 25% by weight of Al.sub.2 O.sub.3, and less than 12% by weight of Na.sub.2 O,

• wherein individual particles have
• (a) a spherical shape having a circularity (A) represented by the following formula:
• ##EQU7## in which r1 denotes the radius of a circumcircle of said particle and
• r2 denotes the radius of an inscribed circle of said particle, the circularity (A) being in the range of from 0.90 to 1,
• (b) a notched surface having a notching degree (B) represented by the following formula:
• ##EQU8## in which .DELTA.t denotes the depth between a peak and a trough in the radial direction of a notch on a cross-section of said particle and
• r1 is as defined above,
• the notching degree (B) being in the range of from 1 to 10%, and
• (c) a primary particle size represented by the formula 2r1, in which r1 is as defined above, in the range of from 0.1 to 20 .mu.m,
• and wherein said particles having a moisture absorption smaller than 13% by weight when said particles are held in an atmosphere maintained at a temperature of 25.degree. C. and a relatively humidity of 90% for 24 hours,
• said particles being obtained by acid-treating zeolite particles having an X-ray diffraction pattern inherent to the structure of P zeolite and having a spherical shape and a notched surface to remove the sodium component contained therein.