Alloy Formation and Stability in Pd−Cu Bimetallic Catalysts

Abstract

The temperature-programmed reduction of three Pd−Cu/KL-zeolite bimetallic catalysts has been studied using X-ray absorption near edge spectroscopy (XANES) and infrared spectroscopy with the probe molecule CO. We show that complete alloying with electronic perturbation of both components (with respect to their metallic state) is reached over the full range of compositions analyzed. It is also shown that the effect of reduction temperature on the nature of the surfaces exposed by the active phases, as well as the sintering processes, is primarily governed by the Pd:Cu ratio.

In-situ XPS Study on the Reducibility of Pd-Promoted Cu/CeO2 Catalysts for the Oxygen-assisted Water-gas-shift Reaction

“…Pd therefore destabilizes surface CuO clusters over ceria, promoting low temperature reduction to copper metal. It is interesting to note that while Pd/Cu alloying is reported in several catalyst systems employing low total metal loadings [19,30], we find no evidence for such alloying in our high loading, Cu-rich sample. The possibility of SMSI effects operating in these systems was also explored by examining the corresponding Ce 3d Xp spectra of the ceria support during in-situ H 2 reduction.…”

Pd–Cu interaction in Pd/Cu-MCM-41 catalysts: Effect of silica source and metal content

“…The spectrum of the 4PdCu-sil sample after CO removal shows a very weak and broad band between 2000 and 1850 cm −1 due to bridged adsorption of CO on a few Pd 0 sites [25]. The CO-Cu + band observed in the monometallic Cu-sil sample is absent in bimetallic catalysts despite the large copper content in their surface revealed by XPS.…”

“…Conversely, in 4PdCu-TEOS material, bands owing to both CO-Pd 0 and CO-Cu + interactions are recorded under CO atmosphere and after Ar and heat treatment. These bands may be assigned to: (i) linear adsorption of CO on Cu + (2119 cm −1 ); (ii) The changes in the spectra after the introduction of Cu may be explained by an ensemble effect: namely, Cu "dilutes" palladium particles [13,25,49,63,64]. Thus, in bimetallic TEOS-derived samples, copper decreases the amount of bridged CO-Pd 0 adsorbed on large particles and, therefore, increases the amount of linear CO-Pd 0 species [8], while in the less dispersed silicate-derived samples, the presence of copper makes it possible to see only the bridged Pd 0 -CO species.…”

“…Bimetallic Pd/Cu catalysts on active carbon are promising catalysts for this process [4]. Nevertheless, the microporous texture of the support can significantly limit possible applications of the catalytic system because the Pd/Cu ratio governs the effect of the reduction temperature on the nature of the surfaces exposed by Pd and Cu and the sintering processes [25].…”

Hydroreforming of the oils from LDPE thermal cracking over Ni–Ru and Ru supported over hierarchical Beta zeolite

“…Usually the aim is to form an alloy of the two metals and hence co-impregnation is used [20,21]. A complete review on the performance of bimetallic catalysts (containing Pd) can be found in the work of Coq and Figueras [22].…”