GB735390A - Reforming catalysts - Google Patents

Abstract

A catalyst suitable for reforming hydrocarbons comprises alumina and a platinum metal, the alumina having been derived from a material in which alumina trihydrate predominates. In preparing the catalyst, an alumina hydrogel is precipitated by adding ammonium hydroxide to a solution of aluminium chloride, aluminium sulphate, or sodium aluminate, the gel is washed and is then converted to a form in which alumina trihydrate predominates, by ageing at a pH of 8-10 for several days, or by seeding with crystallites of gibbsite; the progress of the transition may be followed by X-ray diffraction analysis of a dried sample. The trihydrate, as gibbsite, bayerite, or an intermediate crystalline form, preferably constitutes about 65-90 per cent of the total alumina hydrate; from 5-35 per cent of alumina monohydrate may be present. The preferred platinum metals are platinum, palladium, rhodium and iridium; ruthenium and osmium are less suitable. An acidic promoter, e.g. a fluoride, chloride, sulphate, or phosphate, or silica, zirconia, boria, molybdena, or chromia may be added either before or after the incorporation of the platinum metal. An aqueous solution of chloroplatinic acid may be added to a slurry of the alumina hydrate, followed by aqueous hydrogen sulphide solution; alternatively a platinum sulphide solution may be used. The resulting slurry is dried rapidly at a pH of 6-9, formed into tablets or pills, with the addition of a die lubricant, and then calcined in an oxygen-containing gas at 750-1200 DEG F. Before use the catalyst is reduced by heating in a stream of hydrogen. Preferably the catalysts contain 0.1-1 per cent by weight of platinum metal and 0.2-1.5 per cent by weight of fluoride, added as ammonium fluoride or hydrogen fluoride. The catalysts prepared according to the invention have pores of a larger volume than catalysts prepared from alumina monohydrate, and have a longer life before regeneration is necessary. Tests are described for determining the crystal form of alumina hydrates by X-ray diffraction, and the surface area and pore volume distribution for various catalysts are given. Processes are described in which the catalysts are used in reforming naphthas and naphtha fractions for the production of high octane gasoline, benzene, toluene, and xylene. Reforming is carried out in the presence of hydrogen under the usual conditions, with the catalyst as a fixed bed or in the fluidized state.