Metal oxide support effects on the hydrogenation of cyclohexene and crotonaldehyde using microwave synthesized rhodium and iridium nanoparticles
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Nanoparticles (NPs) are an exciting new class of materials with unique physical and chemical properties, which have been studied for applications in semiconductors, drug delivery, heavy metal sequestration, and heterogeneous catalysis. The last decade has seen an exponential growth in noble metal NP catalysis research. The scarcity and price of these metals has created a need for more highly efficient catalysts and the surface-area-to-volume ratio of NPs can alleviate that demand. Highly selective catalysis is still dominated by homogeneous catalysts, but their lack of recyclability makes them unusable for industrial settings where durability is the top priority. The Humphrey group has pioneered the synthesis of monometallic, core-shell, and alloyed noble metal NPs of different sizes and morphologies, facilitated by microwave heating. However, support media effects have not been studied in the group, as strong metal-support interactions (SMSI) and hydrogen spillover have been shown to alter the observed catalytic activities. v Herein, mono metallic Rh NPs (~5nm) have been immobilized on amorphous metal oxides (SiO₂, Al₂O₃, TiO₂, Nb₂O₅, and Ta₂O₅) to study the effects these supports play in the hydrogenation of alkenes and the chemoselectivity hydrogenation of α,β-unsaturated aldehydes. Cyclohexene was utilized as a model alkene to assess the reactivities of said catalysts. In addition, controlled growth of Ir NPs in aqueous media is in development. Computational and experimental data has shown higher selectivity towards unsaturated alcohol products from the hydrogenation of α,β-unsaturated aldehydes and ketones. Unfortunately, not much research has been done Ir NPs due to their small particles sizes. Viscous solvents are typically used in NP synthesis to avoid particle agglomeration, but Ir since NPs don’t typically grow past 2 nm, other solvents can be used during synthesis. This allows the use of less viscous, greener solvents, such as water. Herein, the synthesis of Ir NPs in water is explored and the largest free-standing Ir NPs (2.98 nm) are presented. Also, 2.71 nm Ir NPs can be achieved after 1 minute, making them desirable for large sacel synthesis of these materials.