A catalyst including a modified silica support having a titanium modifier metal, and a catalytic metal on the modified silica support. A proportion of the modifier metal is present in the form of mononuclear titanium moieties or is derived from a mononuclear titanium cation source at the commencement of modification. The invention also discloses a corresponding modified silica support, a method of producing the catalyst or the modified silica support, and a process for preparing an ethylenically unsaturated acid or ester in the presence of the catalyst.