CO Oxidation and Toluene Hydrogenation by Pt/TiO2 Catalysts Prepared from Dendrimer Encapsulated Nanoparticle Precursors

Abstract

Generation 4 hydroxyl terminated polyamidoamine (PAMAM) dendrimer encapsulated nanoparticles (DENs) were examined as precursors for Pt/TiO 2 catalysts. In this preparation method, the dendrimers were initially used to template and stabilize Pt nanoparticles in solution. DENs were then deposited onto titania, and activation conditions for dendrimer thermolysis were examined. The interactions between PAMAM dendrimers and the titania were found to differ from previous reports of dendrimersupport interactions with silica, alumina, and zirconia. In the case of titania, the amide bonds were found to shift 100 cm -1 , indicating adsorption occurs primarily through amide-titania interactions. Infrared spectroscopy, CO oxidation catalysis, and toluene hydrogenation catalysis were used to evaluate protocols for removing the dendrimer. Thermal decomposition of the DENs in O 2 or CO/O 2 atmospheres led to the formation of surface isocyanates that were preferentially bound to the metal nanoparticles. CO oxidation catalysis was insensitive to the activation protocol used, and infrared spectroscopy of adsorbed CO showed only small differences in the basic surface properties of the resulting Pt catalysts. Toluene hydrogenation catalysis was more sensitive to different activation pretreatments. The most active hydrogenation catalysts resulted from short, low temperature (150°C) hydrogen treatments while longer treatments at higher temperature (300°C) resulted in slightly less active catalysts.

New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions

“…[366][367][368][369][370][371][372][373][374][375] For instance, it has recently been shown by using IR absorption spectroscopy that thermal treatment of the dendrimer-encapsulated nanoparticles (DENs) used in the preparation of a Pt/TiO 2 catalyst in oxidizing atmospheres leads to the formation of surface isocyanates bound to the metal. 376 In Fig. 19, we show another example, from our own laboratory, of how IR absorption spectroscopy can be employed to follow the decomposition of the organic matter during catalyst oxidation, in this case of the poly(amidoamine) (PAMAM) dendrimer used to make the Pt DENs dispersed to ultimately produce a Pt/SiO 2 catalyst.…”

Synthesis of dendrimer-templated Pt nanoparticles immobilized on mesoporous alumina for p-nitrophenol reduction

“…20 Recently, some research studies have revealed that Pt DENs supported on the titania or silica supports could improve the dispersion of Pt NPs and the recoverability of catalysts. [21][22][23] It is well known that mesoporous alumina (MA) is a support with large surface area, uniform pore size and high thermal stability, which is widely employed in catalysis, adsorption, etc. [24][25][26] Pt DENs are deposited on mesoporous alumina, which decreases the sintering of Pt NPs during post-treatment.…”

Screening of Heterogeneous Multimetallic Nanoparticle Catalysts Supported on Metal Oxides for Mono-, Poly-, and Heteroaromatic Hydrogenation Activity

“…The size of the NPs has a direct affect on their catalytic activity, in addition to the known influence of support composition, pretreatment, and other parameters. 19,68,69,117 In the case of titania, TiO 2 supported NPs may be less active because of a strong metal support interaction (SMSI). 68 Because the Rh 1 /Al 2 O 3 (25%)-SiO 2 (75%) catalyst generally underperformed the commercial 0.5% Rh/Al 2 O 3 catalyst for the hydrogenation of naphthalene and quinoline, TEM and XPS were carried out, before hydrogenation, to determine if there was an obvious difference in NP size and oxidation state for this pair of catalysts, and the results are summarized in Table 3.…”