Effects of Particle Size on Strong Metal–Support Interactions Using Colloidal “Surfactant-Free” Pt Nanoparticles Supported on Fe₃O₄

Abstract

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.

Identification of Active Sites in Pt–Co Bimetallic Catalysts for CO Oxidation

“…The synthesis of the Pt–Co/Al 2 O 3 catalyst could be summarized into three steps, as schematically illustrated in Figure a. First, Pt nanoparticles were synthesized following the established method, which uses ethylene glycol (EG) as the solvent and reductant. Briefly, 1 g of H 2 PtCl 6 · n H 2 O was dissolved in 50 mL of EG in a round-bottom flask equipped with a water-cooled condenser, to which 50 mL of 0.5 M NaOH solution in EG was added.…”

“…On Pt/Al 2 O 3 , the reaction orders in CO and O 2 are −0.86 and 1.08 (Figure 2e,f), respectively, in agreement with the competitive Langmuir−Hinshelwood mechanism that the activation of O 2 is the rate-determining step. 6,35,40 In the case of Pt−Co/Al 2 O 3 , however, the reaction orders are −0.43 in CO and 0.16 in O 2 , indicating that the presence of the PtCo alloy greatly inhibits the CO poisoning. Also, the nearly zero order in O 2 suggests that the activation of O 2 is no longer the In Situ XAFS Characterizations of the Real Structures of Pt−Co/Al 2 O 3 .…”

Selective 5-Hydroxymethylfurfural Hydrogenolysis to 2,5-Dimethylfuran over Bimetallic Pt-FeOx/AC Catalysts

“…As shown in Figure 4a, the Fe 2p 3/2 peaks at 710.1 and 711.5 eV could be attributed to the Fe 2+ and Fe 3+ species, respectively. In addition, there were two peaks in the Fe XPS spectra at binding energies of 715.2 and 719.0 eV, which corresponded to the satellite peaks of the Fe 2+ and Fe 3+ , respectively [41]. Compared with 2% FeO x /AC, the introduction of Pt caused partial Fe 3+ to be reduced to Fe 2+ and the binding energies for Fe 2p to be transferred to lower values with an increase of Pt loading.…”

Ultralong-lifetime Ti/RuO2–IrO2@Pt anodes with a strong metal–support interaction for efficient electrochemical mineralization of perfluorooctanoic acid

“…The strong metal–support interaction (SMSI) achieved by calcination provides a novel approach to further optimize the electrocatalytic activity and stability of metal catalysts by constructing their geometric and electronic structure. 21–23 Based on the SMSI hypothesis, many studies have focused on improving the activity of Pt-based catalysts by selecting different metal oxide supports, such as CeO 2 , TiO 2 , Fe 3 O 4 , etc ., and lots of achievements are made on this issue. 22,24–27 However, constructing electrocatalytic materials with a SMSI structure has not been reported before.…”

“…21–23 Based on the SMSI hypothesis, many studies have focused on improving the activity of Pt-based catalysts by selecting different metal oxide supports, such as CeO 2 , TiO 2 , Fe 3 O 4 , etc ., and lots of achievements are made on this issue. 22,24–27 However, constructing electrocatalytic materials with a SMSI structure has not been reported before. We hypothesized that encapsulating metallic Pt within each RuO 2 –IrO 2 particle with tailored dimensions would maintain their intrinsic characteristics and substantially improve the overall electrocatalytic performance, which would undoubtedly be significant progress for electrochemical oxidation technology.…”