Catalyst having a core and surface layer and use of same in olefin oligomerization

A process for the oligomerization of an olefin, which comprises contacting under oligomerization conditions a feed comprising at least one olefin with an olefin oligomerization catalyst comprising a particulate molecular sieve comprising a core having deposited thereon a surface layer, the core comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, and the surface layer comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:selected element ratio than that of the core.

A process for the manufacture of a particulate molecular sieve, which comprises heating an aqueous synthesis mixture comprising a source of silicon, a source of aluminium, a source of monovalent inorganic cations, the synthesis mixture having dispersed therein crystals of a molecular sieve containing silicon and aluminium, the molar ratio of silicon to aluminium in the crystals being lower than the molar ratio of silicon to aluminium in their respective sources in the synthesis mixture, to cause crystallization of a molecular sieve layer from the synthesis mixture onto the surfaces of the crystals.