GB396712A - Improvements in or relating to catalytic and like contact masses containing platinum - Google Patents

Abstract

Catalysts for the oxidation of sulphur dioxide to sulphur trioxide comprise a carrier consisting of a dried hydrous oxide gel, such as silica gel, or a base-exchange compound, platinum introduced by impregnation and a promoter consisting of a compound of one or more of the metals iron, nickel, aluminium, copper, bismuth, molybdenum, beryllium, vanadium, tin, chromium or preferably manganese, in an amount up to 5 per cent by weight of the mass. The carrier may consist of one or more hydrous oxide gels, which includes both hydrogels and gelatinous precipitates or mixtures thereof. Suitable oxides are those of silicon, germanium, chromium, tungsten, titanium, aluminium or tin. The catalyst may be prepared in a variety of ways, for example, a carrier may be treated simultaneously or successively with a solution of a promoter substance and of a platinum compound and then treated to convert the platinum into metal; a carrier may be charged with a reacting gas such as hydrogen, hydrogen sulphide, carbon monoxide, arsine, phosphine, stibine, water gas, formaldehyde, or sulphur dioxide, then treated simultaneously or successively with a solution of a platinum compound and of a promoter substance and finally treated to obtain metallic platinum. The carrier may be first treated with the solutions and then with the reacting gas. The promoter substance may be incorporated in the carrier gel at any stage of its manufacture and the mass then treated with a platinum solution, either before or after drying, and then treated to form metallic platinum in the mass. This method is applicable when the promoter is a metal oxide such as alumina or stannia and can be incorporated in the form of a non-dehydrated hydrous oxide gel. A carrier including a non-dehydrated gel may be charged with a solution of a promoter substance, dried, and then treated with a platinum solution. The non-dehydrated gel may be one which when dried has a low apparent density and may be obtained by immersing any non-dehydrated gel in water at a temperature of 175-200 DEG F. for several hours. The carrier may also be treated with a platinum solution which is converted to metallic platinum and the mass is then treated with a solution of a promoter substance. If the platinum compound used is ammonium chloroplatinate, the mass is heated to about 360 DEG C., and if the platinum is present in the carrier as the sulphide after impregnation, the mass is heated in a stream of air at 500 DEG C. for about 4 hours. To obtain a rigid catalyst which will withstand rough usage, a reinforcing material may be incorporated at any stage in the preparation of the catalyst. The reinforcing substance may be any material which becomes plastic under suitable treatment and which when baked is changed into a non-plastic rigid solid. Suitable substances are clays containing a large percentage of aluminium silicate or aluminium and silica, e.g. Japanese clay, ball or fire clay, or mixtures thereof. The mass is preferably baked at temperatures from 800 DEG C. but not exceeding 900 DEG C. According to examples, the following catalytic masses are obtained by the methods described above. (1) A carrier of silica gel is mixed with a small amount of alumina gel, acting as a promoter, and the mass impregnated with platinum. (2) A carrier of silica gel impregnated with chromium oxide is treated with ammonium chloroplatinate. (3) and (4) In a similar catalyst, the promoter is manganese sulphate. (5) Silica gel is impregnated with aluminium sulphate and ammonium chloroplatinate and mixed with Japanese clay. The mass is ground, extruded, dried and baked. (6) Silica gel is impregnated with manganese sulphate and dried. The hard porous mass is then treated with ammonium chloroplatinate, which is converted to platinum sulphide and the mass heated to convert the sulphide to metallic platinum. (7) A gel of tungsten oxide is treated as in example (3). (8) A mixed gel of tungsten and tin oxides is dried and the hard porous mass treated with ammonium chloroplatinate and heated to obtain metallic platinum. The mass is treated with a solution of vanadyl sulphate and heated to obtain vanadium oxide. (9) A carrier consisting of dried titanium oxide gel of low apparent density is treated with a solution of aluminium chloride and ammonium chloroplatinate and heated. (10) Silica gel is charged with hydrogen sulphide and treated with a solution of platinic chloride and copper sulphate. The mass is dried and heated in air at 500 DEG C. to convert the sulphide into platinum and copper oxide. (11) A carrier including silica gel fines is treated with beryllium sulphate and ammonium chloroplatinate solutions and then heated. (12) A carrier containing a newly dehydrated base-exchange compound such as glauconite is treated as in example (11). Specifications 280,939, 286,708, and 314,858, [all in Class 1 (i), Chemical processes &c.], are referred to. The Specification as open to inspection under Sect. 91 comprises the use of a porous carrier generally and is not limited to the oxidation of sulphur dioxide to sulphur trioxide. This subject-matter does not appear in the Specification as accepted.