A pre-catalyst composition comprising a) a silica support comprising silica wherein an amount of silica ranges from about 70 wt. % to about 95 wt. % based upon a total weight of the silica support, b) a chromium-containing compound wherein an amount of chromium ranges from about 0.1 wt. % to about 5 wt. % based upon the amount of silica, c) a titanium-containing compound wherein an amount of titanium ranges from about 0.1 wt. % to about 20 wt. % based upon the amount of silica, d) a carboxylic acid wherein an equivalent molar ratio of titanium-containing compound to carboxylic acid ranges from about 1:1 to about 1:10, and e) a nitrogen-containing compound with a molecular formula containing at least one nitrogen atom wherein an equivalent molar ratio of titanium-containing compound to nitrogen-containing compound ranges from about 1:0.5 to about 1:10.