Process for coating crystalline silica polymorphs

Claim 2

A process for coating a crystalline silica polymorph with essentially amorphous silica which comprises contacting the silica having the external part of at least a portion of the channels in the crystalline silica polymorph occupied with a blocking compound with an aqueous solution of an alkali metal silicate for a period of about 5 minutes to about 11/2 hours while maintaining the pH of the solution in the range 7.5-11.5.

Claim 3

The process of claim 1 wherein the crystalline silica is a silicalite.

Claim 4

The process of claim 1 wherein the silica is a zeolite.

Claim 5

The process of claim 1 wherein the pH is maintained in the range 7.5-10.5.

Claim 6

The process of claim 1 wherein the blocking compound is the template employed to prepare the silica polymorph.

Claim 7

The process of claims 1, 2, 3, 4 or 5 wherein the temperature of the aqueous solution is maintained in the range 70-90° C.

Claim 8

A process for preparing a crystalline silica polymorph coated with amorphous silica which comprises initiating crystallization of silica in a crystallization medium in the presence of a template compound to produce said polymorph, separating the resulting polymorph from the crystallization medium without removing a significant amount of the template compound from the channels in the polymorph, contacting the thus obtained polymorph with an aqueous solution of an alkali metal silicate for a period up to 11/2 hours while maintaining the pH of the solution in the range 7.5-10.5 and thereafter separating the unreacted silicate from the polymorph and removing the template compound.

Claim 9

A process for preparing a crystalline silica polymorph coated with amorphous silica which comprises initiating crystallization of silica in a crystallization medium in the presence of a template compound to produce said polymorph, separating the resulting polymorph from the crystallization medium without removing a significant amount of the template compound from the channels in the polymorph, contacting the thus obtained polymorph with an aqueous solution of an alkali metal silicate for a period up to 11/2 hours while maintaining the pH of the solution in the range 7.5-10.5 and thereafter separating the unreacted silicate from the polymorph and removing the template compound.