Effects of Reduction Temperature and Metal−Support Interactions on the Catalytic Activity of Pt/γ-Al₂O₃ and Pt/TiO₂ for the Oxidation of CO in the Presence and Absence of H₂

Abstract

TiO2- and gamma-Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in situ FTIR spectroscopy after activation at various conditions, and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When gamma-Al2O3 was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density on Pt, altering its chemisorptive properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive toward H2 than CO. Consequently, Pt/TiO2 shows substantially lower selectivities toward CO oxidation under PROX conditions than Pt/gamma-Al2O3.

Ligand Capping of Colloidally Synthesized Nanoparticles—A Way to Tune Metal–Support Interactions in Heterogeneous Gas‐Phase Catalysis

“…toluene hydrogenation on Pt/TiO 2 [11] ) the SMSI effect was found to decrease the overall catalytic activity (by diminishing the number of active sites through encapsulation of the metal particles by the oxide), in other cases it can considerably improve activity (e.g. CO oxidation on Pt/TiO 2 [12] ). Such synergism can for instance result from the fact that the oxide provides special adsorption sites at the perimeter of the particles, [11] induces a different particle morphology, [7] or delivers active species.…”

“…Such synergism can for instance result from the fact that the oxide provides special adsorption sites at the perimeter of the particles, [11] induces a different particle morphology, [7] or delivers active species. [12] Since CO oxidation on Pt, for instance, suffers from the fact that CO is strongly bound to Pt and thus poisons the surface so that O 2 cannot adsorb at low temperatures, a supply of oxygen by the support should improve the performance drastically. Indeed, this type of SMSI effect was recently observed: [13] The interaction of Pt with FeO, which delivers oxygen at the border between the two constituents, was exploited in the development of a very efficient catalyst for PROX (preferential oxidation of CO in the presence of hydrogen) which already works at room temperature.…”

CO oxidation over Pt/SnO2 catalysts

“…Tin dioxide is an n-type semiconductor with a wide band gap (3.6 eV) and rutile bulk structure [13]. In the past decades, SnO 2 has attracted much attention for its various applications in catalysis, gas sensing, rechargeable Li battery and optical electronic devices [13][14][15][16]. It should be marked that SnO 2 is one of the most widely used semiconductor oxides for the manufacturing of sensors applied in the environment monitoring [17].…”

Kolloidchemisch hergestellte ligandenstabilisierte Nanopartikel – ein Weg zur Beeinflussung starker Metall‐Träger‐Wechselwirkungen in der heterogenen Gasphasenkatalyse

“…B. Hydrierung von Toluol an Pt/TiO 2 [11] ) setzt der SMSIEffekt die katalytische Aktivität des Systems herab (durch Verminderung der Zahl aktiver Oberflächenplätze aufgrund des Überwachsens der Metallpartikel durch das Oxid), in anderen Fällen jedoch führt er zu einer beträchtlichen Aktivitätszunahme (z. B. Oxidation von CO an Pt/TiO 2 [12] ). Ein derartiger Synergismus kann beispielsweise aus der Tatsache resultieren, dass das Oxid spezielle Adsorptionsplätze an der Grenzfläche zu den Partikeln bereitstellt, [11] eine veränderte Partikelmorphologie induziert [7] oder aktive Spezies zu den Nanopartikeln transportiert.…”

“…Ein derartiger Synergismus kann beispielsweise aus der Tatsache resultieren, dass das Oxid spezielle Adsorptionsplätze an der Grenzfläche zu den Partikeln bereitstellt, [11] eine veränderte Partikelmorphologie induziert [7] oder aktive Spezies zu den Nanopartikeln transportiert. [12] [13] Pt auf FeO, das Sauerstoff an der Grenzfläche zwischen den beiden Komponenten bereitstellt, ergab einen sehr effizienten Katalysator für die bevorzugte Oxidation von CO in Gegenwart von H 2 (PROX), der bereits bei Raumtemperatur arbeitet. Trotz der möglichen Beteiligung von FeAtomen in tieferen Schichten [14] wurde diskutiert, dass die katalytisch aktive Spezies eine das Pt teilweise bedeckende, dünne und stark reduzierte Schicht aus FeO ist, die durch Wasserstoff regeneriert wird.…”