Colloidal “surfactant-free” Pt nanoparticles (NPs) within the size range 1–4 nm supported on Fe3O4 were synthesized and applied as model systems to systematically study the role of size effects for strong metal–support interactions (SMSIs) with CO oxidation as a model reaction. Kinetic studies, isotopic labeling experiments with 18O2, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were applied to explore the reaction mechanism and the surface of the catalyst before and after reductive pretreatments. It was found that pure iron oxide was catalytically active in CO oxidation, and experimental evidence for a Mars van Krevelen mechanism between CO and lattice O was found. The turnover frequencies (TOFs) for small Pt NPs (≤3 nm) supported on iron oxide and normalized to the number of Pt atoms located at the periphery of the Pt–support interface were similar under reaction conditions, indicating that the reaction mainly proceeds at the interface. However, with increasing particle size, the contribution of a Langmuir–Hinshelwood mechanism of chemisorbed CO and O2 in addition to the Mars van Krevelen mechanism increases. After reductive pretreatment, the activity of the catalyst decreased significantly, which could be related to partial encapsulation of the monometallic Pt NPs with FeO x . To study whether also on the nanoscale an interaction between Pt and iron oxide similar to the beneficial or detrimental SMSI effect observed for the Pt particles supported on iron oxide can also be achieved, bimetallic Fe–Pt NPs of a mean size of 3–4 nm were deposited on inert Al2O3. It could be shown that surface segregation of Fe and formation of FeO x after reduction and exposure to oxygen took place. As a result, the activity of bimetallic NPs decreased due to loss of active Pt surface, revealing an effect similar to the detrimental SMSI detected for Pt NPs on FeO x support after reductive pretreatment.

Colloidal synthesis and characterization of intermetallic tin-rich platinum–tin nanoparticles with detailed surface characterization.

Uniform, alloyed Cu-In-Zn-S nanoflowers with sizes of11.5±2.1 nm and31±5 nm composed of aggregated 4.1 nm and 5.6 nm primary crystallites, respectively, were obtained in a one-pot, heat-up reaction between copper, indium, and zinc acetate withtert-dodecanethiol in the presence of trioctylphosphine oxide. Larger aggregates were obtained by dilutingtert-dodecanethiol with oleylamine, which lowered the reactivity of the indium and zinc precursors and led to the formation of copper rich particles. The thermal decomposition oftert-dodecanethiol stabilizing the primary crystallites induced their agglomeration, while the presence of trioctylphosphine oxide on the surface of the nanoflowers provided them with colloidal stability and prevented them from further aggregation.

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