Atomic layer deposition of iridium(III) acetylacetonate on alumina, silica-alumina, and silica supports

The deposition of noble metal particles and films by atomic layer deposition (ALD) has recently gained interest in the fields of catalysis and microelectronics. However, there is little information on the mechanisms governing the reactions of noble metals with high surface area supports. In this work, iridium(III) acetylacetonate was deposited from gas phase onto alumina, silica-alumina, and silica supports to gain insight into the reaction mechanisms. According to elemental analysis and infrared spectroscopy, ligand exchange reaction between iridium acetylacetonate and surface OH groups took place on all substrate surfaces, but the iridium deposition on alumina and silica-alumina appeared to be hindered by sterical effects of the acetylacetonate ligands. Part of the iridium on silica was in metallic form. To reduce the content of iridium, reactive sites of the support surfaces were blocked with H-acetylacetonate (2,4-pentanedione). The blocking reduced the iridium content by more than 90% on alumina but by only 30-50% on silica-alumina. The attempted blocking had almost no effect on silica as expected. According to the results of this work, ALD can provide a feasible method for preparing iridium catalyst with reasonable iridium loadings.