Catalysis of Organic..

Auten, Crump, Singh and Chandler 31536. Dendrimer Templates for Ptand Au CatalystsAbstractBethany J. Auten, Christina J. Crump, Anil R. Singh and Bert D. ChandlerDepartment of Chemistry, Trinity University, 1 Trinity Place, San Antonio, TX,78212-7200bert.chandler@trinity.eduWe are developing a new method for preparing heterogeneous catalysts utilizingpolyamidoamine (PAMAM) dendrimers to template metal nanoparticles.(1) In thisstudy, generation 4 PAMAM dendrimers were used to template Pt or Au DendrimerEncapsulated Nanoparticles (DENs) in solution. For Au nanoparticles prepared bythis route, particle sizes and distributions are particularly small and narrow, withaverage sizes of 1.3 ± 0.3 nm.(2) For Pt DENs, particle sizes were around 2 nm.(3)The DENs were deposited onto silica and Degussa P-25 titania, and conditions fordendrimer removal were examined.The focus of these studies has been on identifying mild activation conditions toprevent nanoparticle agglomeration. Infrared spectroscopy indicated that titaniaplays an active role in dendrimer adsorption and decomposition; in contrast,adsorption of DENs on silica is dominated by metal-support interactions. Relativelymild (150° C) activation conditions were identified and optimized for Pt and Aucatalysts. Comparable conditions yield clean nanoparticles that are active COoxidation catalysts. Supported Pt catalysts are also active in toluene hydrogenationtest reactions.IntroductionIndustrial heterogeneous catalysts and laboratory-scale model catalysts arecommonly prepared by first impregnating a support with simple transition metalcomplexes. Catalytically active metal nanoparticles (NPs) are subsequently preparedthrough a series of high temperature calcination and / or reduction steps. Thesemethods are relatively inexpensive and can be readily applied to numerous metalsand supports; however, the NPs are prepared in-situ on the support via processes thatare not necessarily well understood. These inherent problems with standard catalystpreparation techniques are considerable drawbacks to studying and understandingcomplex organic reaction mechanisms over supported catalysts.(4)