Abstract: Desulfurization catalyst comprising an iron group metal and a Group VIB metal is modified by refluxing with an aqueous solution of an alkali or alkaline earth metal, or a transition metal. The pore size distribution of the catalyst is improved.

Abstract: Desulphurization catalysts particularly CoMo are improved by treating with water free from added salts.The water washing improves the pore size distribution of the catalyst.

Abstract: The regeneration of a Pt group metal-acid-resistant, alkali-metal deficient zeolite catalyst comprises (a) a burn off at 500.degree. C max (b) a treatment with inert gas, 0.5-20% vol 0.sub.2 and 5-500 ppm vol Cl at 400.degree.-550.degree. C (c) a purge and (d) a reduction in a stream of H.sub.2 at 200.degree.-600.degree. C.The treatment with inert gas, 0.sub.2 Cl is believed to redistribute the Pt group metal and restore catalyst activity in a way that burn-off alone cannot do.The Cl may be added as Cl, Cl,HCl or an organic chlorine-containing material. The catalysts may have a SiO.sub.2 - Al.sub.2 O.sub.3 molar ratio of at least 5:1 to ensure acid resistance and the preferred catalyst is Pt-H-mordenite which has been used for the selective cracking of n-paraffins in petroleum fractions.