High-pressure operando STM studies giving insight in CO oxidation and NO reduction over Pt(110)

Abstract

a b s t r a c tTwo catalytic systems have been studied at high pressures on the Pt(1 1 0) surface on an atomic level. The first system was the oxidation of CO by O 2 towards CO 2 . In the framework of the second reaction, namely NO reduction, the effect of room temperature exposure of the surface to NO and H 2 was investigated.To study these reaction systems at relevant pressures, the ReactorSTM has been used. This is a unique system which consists of a compact STM in which a flow reactor is integrated. The combined reactor with STM is housed inside a conventional vacuum system to allow for traditional surface science preparation and analysis techniques. The STM images obtained with the ReactorSTM under reaction conditions show the lifting of the (1x2) missing row reconstruction by high-pressure CO exposure. The lifting is followed by the formation of the (1x1) metallic Pt(1 1 0) structure for high CO/O 2 ratios and a (1x2) lifted-row type surface oxide structure for more O 2 -rich conditions. The room temperature exposure of Pt(1 1 0) to H 2 results in the formation of a (1x4) missing-row structure and deeper, nested missing rows. The exposure to high-pressure NO removes these missing-row structures.

Trends and advances in Operando methodology

“…When O 2 concentration became low, the Pt surface reconstructed back to flat Pt surface, showing the dynamic nature of the catalytic surface. [12,15] Similar insights were also gained for Pd surface and the widely observed oscillatory behavior of CO oxidation activity could be elegantly explained by formation and disappearance of the highly active nano-oxide phase of Pd. [16] These studies show that well-defined materials under operando conditions can yield precise and important physical and chemical insights on the atomic scale.…”

Surface science under reaction conditions: CO oxidation on Pt and Pd model catalysts

“…9). 74,75 Only after consuming nearly all CO, the diffraction spots of the incommensurate oxide developed (Fig. 8a).…”

“…However, the results of this titration experiment at low CO flux cannot directly be extrapolated to high temperature/pressure conditions, due to orders of magnitude difference in the number of CO molecules impinging on the surface. It was argued that the reaction mechanism changes from LH to MvK on the oxide, 27,[73][74][75] which is expected to have a different dependence on the CO flux. It does, however, provide another suggestion that Pt oxides are active for CO oxidation.…”

Combined scanning probe microscopy and x-ray scattering instrument for in situ catalysis investigations

“…Examples are Xray photoelectron spectroscopy (XPS), 1 X-ray scattering techniques, 2,3 transmission electron microscopy (TEM), 4,5 scanning tunneling microscopy (STM), [6][7][8] and atomic force microscopy (AFM), 9 which have been developed to investigate a wide array of relevant catalytic systems, ranging from single-crystal model catalysts to supported nanoparticles. Each of these techniques contributes only a specific component to our understanding of heterogeneous catalysis.…”