A hydrogel comprising water, and a plurality of titanium-silica-chromium nanoparticle agglomerates, wherein each titanium-silica-chromium nanoparticle agglomerate is an agglomeration of titanium-silica-chromium nanoparticles, the agglomerates having an average titanium penetration depth designated x with a coefficient of variation for the average titanium penetration depth of less than about 1.0 wherein a silica content of the hydrogel is of from about 10 wt. % to about 35 wt. % based on a total weight of the hydrogel.