Synthesis and properties of Fe/SBA-15

Composites involving Fe and mesoporous silica SBA-15 were obtained by means of a novel method. Anhydrous FeCl3 was deposited on SBA-15 from gaseous phase at 220-250 degrees C and then the adsorbed chloride was hydrolyzed. Iron oxychloride which occurs in the composites was surprisingly stable against further hydrolysis, and chlorine could only be completely removed after a long and multi-step treatment with gaseous water. We hypothesize that similar problem might have occurred in course of preparation of other metal-modified mesoporous silicas (also obtained by wet route), but it was ignored by most researchers, who have not analyzed their composites for the presence of chlorine. Iron was present in most Fe-SBA-15 materials as akaganeite (beta-FeOOH). The akaganeite phase in SBA-15 was stable against dehydration, and it did not convert into anhydrous oxide on calcination at 250 degrees C for 1 day.