GB792645A - Preparation of catalyst particles - Google Patents

Abstract

<PICT:0792645/III/1> Catalysts comprising a platinum group metal deposited on alumina, are made by submerging pre-formed shapes of absorptive alumina in a large quantity of water circulated through a bed of the alumina pieces, slowly adding a solution of the platinum group metal thereafter continuing to circulate the solution, and finally drying and calcining the impregnated alumina. The alumina is preferably obtained by hydrolysing aluminium alcoholate, but gamma, alpha, or eta-alumina may be used, and may also contain up to 5 per cent of silica. The alumina is shaped by spray-drying alumina gel, setting to spherical form in an immiscible fluid, or by pilling or extrusion with or without a lubricant. A suitable apparatus comprises an impregnating vessel 10, connected at the base to a tube 12 and an airlift riser 13. The pre-formed alumina shapes rest on a screen 11, and water is circulated by passing air through a nozzle 16, whereby water is forced up the riser and cross-over line 14 to the vessel 10. In an example, alumina gel made by hydrolysing aluminium amylate and drying the sol at 250 DEG F. is ground and mixed with water. The mixture is extruded and broken into pellets. After heating at 1050 DEG F., the pellets are loaded into the vessel 10 and immersed in water, circulating through the apparatus. Thereafter a 10 per cent solution of chlor-platinic acid is added over 1/2 hour, and the solution circulated for a further 1/2 hour. The pellets are then removed, dried, and calcined at 1000 DEG F. for 4 hours, and subsequently treated with hydrogen at 800 DEG F. to form the metal. The pellets contain from 0.5 to 2 per cent of platinum. The inner core of the pellet is free from platinum which is concentrated on the outer layer. A uniform distribution of metal throughout the body of the pellet is achieved by adding to the circulating solution, absorptive modifiers, e.g. acetic, tri-chloracetic, nitric or hydrochloric acid; aqua regia; aluminium or ammonium salts; phenols, chlorhydrin or sulphonic acids. Examples are given illustrating the use of the catalyst for hydroforming naphtha.