Tuning the Pt/CeO₂ Interface by in Situ Variation of the Pt Particle Size

Abstract

Pt-CeO2-Al2O3 catalysts play an important role in diesel oxidation and three-way catalysis. In this study, the fast structural dynamics of both platinum and ceria in a 1 wt %Pt/5 wt %CeO2-Al2O3 catalyst prepared by flame spray pyrolysis have been systematically investigated under reducing and oxidizing conditions to elucidate the role of the Pt–CeO2 interface for CO oxidation and fast oxygen storage/release of ceria. The catalyst showed enhanced catalytic activity, particularly after application of a reducing/oxidizing conditioning step at 250 °C, with a pronounced dependence on the reducing agent (C3H6 < H2 < CO). In situ time-resolved X-ray absorption spectroscopy (XAS) at the Ce L3-edge unraveled a dependence of the reduction extent of ceria during temperature-programmed reduction on the noble metal constituent and the applied reducing agent. Dynamic reducing/oxidizing cycling (2% H2 ↔ 10% O2 or 2% CO ↔ 10% O2) at various temperatures (150, 250, and 350 °C) showed that the reducibility of ceria increased at higher temperature and by using a more strongly reducing reaction mixture. This coincides with the trend in catalytic activity. Time-resolved XAS data recorded at the Pt L3-edge and Ce L3-edge during redox cycling revealed a close relationship between the Pt oxidation state and the ceria redox response. The formation of reduced Pt particles was found to induce variations in ceria reducibility under transient conditions and was identified as a decisive prerequisite for ceria reduction at low temperatures. Variations in the extent of ceria reduction during the reducing/oxidizing cycles indicate an evolution of the Pt–ceria interface from an inactive state toward an optimal activated state due to reduction and slight sintering of the noble metal particles. Further growth of Pt particles leads to a decrease in ceria reduction rate due to the smaller Pt–CeO2 interface perimeter. A schematic model illustrating the role of Pt for ceria reducibility is developed and the optimal Pt particle size derived. The results are relevant for various applications, particularly for catalysts operated at low temperature under highly dynamic reaction conditions such as exhaust gas catalysts.

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X‐ray Probes

“…Chemie size and spacing can also be tuned after synthesis by redox cycling, using ap re-selected temperature and reduction gas, for example,H 2 or CO. [60] This is in line with an early Tu rbo-XAS study of Nagai et al [61] showing temperature-dependent in situ redispersion in Pt/CeZrYO x automotive catalysts upon redox cycling.…”

“…[59] By combining O 2 and N 2 plasma (N 2 *) Pt ALD,Dendooven et al [56] independently tuned the Pt NP size and center-to-center distance on ap lanar support (Figure 5a). GISAXS showed that after depositing as elected number of Pt NPs by MeCpPtMe 3 -O 2 ALD,subsequent MeCpPtMe 3 -N 2 *ALD only increased their size,w hile keeping the center-to-center distance constant: i) the constant q y -values of the lobe maxima evidence the constant NP spacing, while ii)the shift of the lobe minima in q y and q z to lower values and the appearance of as econdary lobe is characteristic for an increasing NP width and height, respectively.N otably,aQXAS study showed that the Pt NP size and spacing can also be tuned after synthesis by redox cycling, using ap re-selected temperature and reduction gas, for example,H 2 or CO. [60] This is in line with an early Tu rbo-XAS study of Nagai et al [61] showing temperature-dependent in situ redispersion in Pt/CeZrYO x automotive catalysts upon redox cycling.…”

Origin of the High CO Oxidation Activity on CeO2 Supported Pt Nanoparticles: Weaker Binding of CO or Facile Oxygen Transfer from the Support?

“…Ganzler et al. reported that small Pt clusters supported on CeO 2 are much more active than atomically dispersed Pt and a size of ∼1.4 nm was reported to be optimal . The origin of the high CO oxidation activity on ceria supported Pt nanoparticles was proposed to be due to highly active sites at the Pt−CeO 2 interface.…”

Cerium(III) Nitrate Derived CeO2 Support Stabilising PtOx Active Species for Room Temperature CO Oxidation

“…The construction of such tandem catalytic systems requires advanced synthetic methodologies for both the ceria preparation and the active component deposition. The scalable methods of preparation of CeO 2 supports vary from the cerium salts solution hydrolysis to the flame spray pyrolysis . Among these methods the simplest and most straightforward one is the thermal decomposition of cerium salts, such as Ce(NO 3 ) 3 ⋅ 6H 2 O, Ce 2 (C 2 O 4 ) 3 , (NH 4 ) 2 [Ce(NO 3 ) 6 ], and Ce 2 (CO 3 ) 2 O ⋅ H 2 O .…”