Disentangling Catalytic Activity at Terrace and Step Sites on Selectively Ru-Modified Well-Ordered Pt Surfaces Probed by CO Electro-oxidation

Abstract

In heterogeneous (electro)catalysis, the overall catalytic output results from responses of surface sites with different catalytic activities, and their discrimination in terms of what specific site is responsible for a given activity is not an easy task. Here, we use the electrooxidation of CO as a probe reaction to access the catalytic activity of different sites on high Miller index stepped Pt surfaces with their {110} steps selectively modified by Ru at different coverage. Data from in situ FTIR spectroscopy and cyclic voltammetry evidence that Ru deposited on {110} steps modifies the surface in a non-trivial way, only favoring the electrocatalytic oxidation of CO over {111} terraces. Moreover, these {111} terraces become catalytically active throughout a large potential window. On the other hand, after the deposition of Ru on {110} steps, the partial oxidation of a CO adlayer (by stripping voltammetry and in situ FTIR potential steps) show that those {110} steps that remain free of Ru seem to be not influenced by the presence of this metal. As a result, the remaining CO adlayer is oxidized on these Ru-free {110} steps at potentials identical to those observed in steps of pure stepped Pt surfaces (in absence of Ru). Firstly, these This is a previous version of the article published in ACS Catalysis. 2016, 6(5): 2997-3007. doi:10.1021/acscatal.6b00439 2 findings suggest that COads behaves as a motionless species during its oxidation. Secondly, they evidence that the impact caused by the presence of Ru in the catalytic activity of Pt(s)-[(n-1)(111)×(110)] stepped surfaces depends on the crystallographic orientation of Pt sites. These results help us to shed new light about the role of Ru in the mechanism of oxidation of CO and allow a deeper understanding regarding the CO tolerance in Pt-Ru catalysts.

Understanding CO oxidation reaction on platinum nanoparticles

“…For these decorated stepped surfaces, the kinetics still follows the mean field L-H mechanism. On the other hand, on Ru decorated stepped surfaces a significant catalytic effect is observed [48]. Moreover, one voltammetric peak at ca.…”

“…As the coverage increases, steps become completely Adatom decoration of the step sites has also been used to get further insights into the oxidation process of CO on these surfaces. Two different behaviors have been described according to the oxophilic character of the deposited adatom [47,48]. It…”

Promotion of Glycerol Oxidation by Selective Ru Decoration of (100) Domains at Nanostructured Pt Electrodes

“…To the best of our knowledge, there has been no detailed study of CO oxidation at Ru‐decorated Pt (100) or (100) stepped surfaces. Therefore, our discussion of Figure will instead refer to the numerous reports on Ru‐decorated (111) stepped surfaces ,,,. The most interesting feature appearing in the CO stripping profile after Ru decoration is a small shoulder located at 0.5 V vs RHE.…”

“…Most importantly, this identification is supported by the detailed study by Farias et al . on CO ads oxidation at Ru‐decorated [(111)×(110)] Pt single‐crystals in perchloric acid ,. It was demonstrated that CO oxidation at (111) terraces close to Ru‐covered steps gave rise to a signal very similar to the shoulder at 0.5 V vs RHE in Figure ; the signal became sharper and more intense with growing Ru coverage at the steps ,.…”

“…Using bimetallic catalysts may lead to improvements over pure Pt catalysts by enhancing the glycerol electrooxidation reaction or by steering its product selectivity. Broadly speaking, there are two distinct types of bimetallic Pt electrodes: the first features a homogeneous bulk mixing of the two metals (usually in the form of nanoparticles), while in the second case the co‐catalyst is introduced as an adatom on the Pt surface ,. Ruthenium is a well‐known promoter of oxidation reactions at Pt electrodes;, several studies have addressed the bimetallic combination of Pt and Ru as a catalyst towards the oxidation of methanol, CO,, hydrogen and glycerol .…”