Kinetic and Spectroscopic Characterization of Cluster-Derived Supported Pt–Au Catalysts

Abstract

Silica-supported bimetallic Pt-Au catalysts prepared via different synthetic routes have been investigated in terms of their structural properties, adsorption of CO, and catalytic activity for the selective catalytic reduction of NO by propylene, the oxidation of propylene in the absence of NO, and the 16 O/ 18 O homoexchange reaction. Catalysts prepared by incipient wetness impregnation from individual Pt and Au precursors exhibited characteristics very similar to those of monometallic Pt catalysts, indicating that in these cases the presence of Au did not affect the catalytic performance of Pt in any significant way. This behavior is consistent with a model in which the two metals remain segregated due to their miscibility gap, and only Pt participates in the adsorption of CO and the reactions under consideration. In contrast, catalysts prepared from aPt 2 Au 4 (C≡C t Bu) 8 organo-bimetallic cluster precursor exhibited different behavior both in terms of CO adsorption and their catalytic activity for the three reactions examined. The combination of the kinetic, spectroscopic, and structural characterization data suggests that in this case Pt and Au remain intimately mixed in the form of Pt-Au bimetallic particles and that the presence of Au in these particles modifies the behavior of Pt.

Structure control of silica-supported mono and bimetallic Au–Pt catalysts via mercapto capping synthesis

“…The presence of this band, which was not detected during the CO adsorption on the monometallic Au0 catalyst, according to literature, is due to formation of bimetallic AuPt particles [45,[48][49][50][51][52]. The band with maximum at 2090 cm À1 is rather complex with shoulders at 2060, 2034, and 2000 cm À1 .…”

“…Upon evacuation, the unresolved signals at 2034 and 2000 cm À1 disappear. The shoulder at 2060 cm À1 persists and can be assigned to CO adsorbed on Pt sites, which are incorporated into gold particles [48][49][50]52]. The absorption at 2090 cm -CO band relative to that on the pure Pt0_400 catalyst [48].…”

“…The absorption at 2090 cm -CO band relative to that on the pure Pt0_400 catalyst [48]. Mihut et al [49], based on the adsorption of 12 CO/ 13 CO mixture on cluster-derived AuPt bimetallic catalysts, concluded that the red-shift is caused by electronic effect due to enhanced -back donation to the adsorbed CO molecule. Mott et al [51] proposed that the electronic effect causing the red-shift is associated with the d-band shift of Pt in the bimetallic particles.…”

Bimetallic Au-Pt nanoparticles synthesized by radiolysis: Application in electro-catalysis

“…In particular, bimetallic platinumbased catalysts have been proposed as promising alternatives to the exceedingly expensive pure Pt electrocatalysts and are already widely used in industry and for proton exchange membrane (PEM) fuel cells. 1,2 Among numerous possible metal combinations, Au-Pt NPs have been studied intensively because of their optical properties, 3 their potential as selective oxidation 4,5 and dehydrogenation catalysts, 6 electrocatalysts, 7,8,9 and selective sensors. Cationic Au-Pt clusters have shown unique reactivity for C-N coupling of methane and ammonia.…”

“…13 Organometallic or coordination complex precursors could also be used with the drawback of pre-imposed Pt-to-Au atomic stoichiometry. 4,17 In this context, it is assumed that radiolytic reduction might provide a convenient route to synthesize alloyed Au-Pt NPs exhibiting desired physicochemical properties. Radiolytic reduction of metal ions in solution is an efficient process to synthesize bimetallic nanoparticles of controlled size and structure.…”