Hydrogenation of polycyclic aromatics

A process for the selective hydrogenation of bicyclic aromatic hydrocarbons, e.g. naphthalenes and methylnaphthalenes to produce tetralins comprises contacting the bicyclic aromatic hydrocarbons with a catalyst comprising a platinum group metal on a refractory support at 500 DEG to 900 DEG F. in the presence of hydrogen and at least 0.2% wt. of combined sulphur, calculated as sulphur by weight of feedstock to produce, selectively, partially hydrogenated hydrocarbons, the selectivity being at least 75%. The selectivity is defined as being the fraction Total partially hydrogenation products formed x100 Total bicyclic aromatics converted. The catalyst preferably contains 0.01 to 5.0% by weight of platinum and suitable supports used are the inorganic oxides of Groups II to V, e.g. magnesia, silica, sepiolite, alumina, silica alumina, silica-magnesia, natural and artificial zeolites. The catalyst may be impregnated with chlorine or fluorine. Isomerization of the feedstocks may also take place. The reaction preferably takes place at 100 to 3000 p.s.i.g., an L.H.S.V. of 0.1 to 10 v./v./hr. and a hydrogen hydrocarbon mole ratio of 2:1 to 100:1. Thiophenes are the preferred sulphur compounds and may be introduced into the feedstock, into the hydrogen feed, injected into the reactor or may be used to pretreat the catalyst.