Dendrimer-mediated synthesis of subnanometer-sized Rh particles supported on ZrO2

• Published in: Journal of catalysis Vol. 266; no. 2; pp. 331 - 342
• Main Authors: SIANI, Attilio, ALEXEEV, Oleg S, DEUTSCH, D. Samuel, MONNIER, John R, FANSON, Paul T, HIRATA, Hirohito, MATSUMOTO, Shinichi, WILLIAMS, Christopher T, AMIRIDIS, Michael D
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 10.09.2009; Elsevier BV
• Subjects: Catalysis; Catalysts; Chemical reactions; Chemical synthesis; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Ethane hydrogenolysis; Binary compound; Particle size; Support; Nanoparticle; EXAFS; Template; Particle; Chemical reduction; Nanoparticles; Dendrimers; Amine; Zirconium oxide; Synthesis; Platinoid; Diameter; Branched polymer; Hydrogenolysis; Transition element compounds; Transition metal; Metal particle; Complexes; Ethane; EXAFS spectrometry; Heterogeneous catalysis; Particle size distribution; Transmission electron microscopy; Rhodium; Frequency; Aqueous solution; Dendritic structure; Room temperature
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2009.06.025

Nearly uniform Rh particles with sizes below 1nm were prepared on a ZrO2 support via a dendrimer-mediated synthetic route. The coordination environment of Rh was monitored by EXAFS during all preparation steps and HRTEM was used to image the resulting supported Rh nanoparticles. The structure-sensitive ethane hydrogenolysis reaction was used to probe the catalytic properties of the Rh/ZrO2 materials produced. We have achieved the synthesis of ZrO2 -supported Rh particles with sub-nanometer dimensions and very narrow particle size distributions using G4OH-PAMAM dendrimers as templates. The different steps of this process were characterized by EXAFS and HRTEM measurements. The results indicate that partially hydrolyzed Rh3+ species in an aqueous solution can interact with amide/amine groups in the interior of G4OH dendrimers to form (Rh3+ ) x -G4OH complexes. Rh3 clusters were subsequently formed in the same solution following room temperature reduction of the (Rh3+ ) x -G4OH complexes with NaBH4 . These Rh3 clusters can be delivered intact on the surface of the ZrO2 support. The formation of highly dispersed and nearly uniform Rh particles with sizes below 1nm was observed following thermal removal of the dendrimer component. The structure-sensitive reaction of ethane hydrogenolysis was used for the evaluation of Rh/ZrO2 samples with different metal particle sizes. A substantial decrease in turnover frequency was observed when the particle diameter decreased below 1.5nm, consistent with mechanistic explanations advanced previously in the literature for this reaction. [PUBLICATION ABSTRACT]