Oligomerization process and catalysts therefor

A catalyst preparation method which comprises heating a metal oxide having surface hydroxyl groups at a temperature in the range from about 400.degree. to about 600.degree. C., thereafter contacting the metal oxide with titanium tetrachloride vapor in a series of steps at progressively higher temperatures within the range of from about 50.degree. to about 600.degree. C. to deposit titanium tetrachloride on the metal oxide, and then heating the impregnated metal oxide in contact wth hydrogen gas at a temperature in excess of 300.degree. C. up to about 700.degree. C. to reduce the titanium to a valence state of less than +4.