Using a combination of surface X-ray diffraction and mass spectrometry at realistic pressures, the CO oxidation reactivity of a Rh(111) model catalyst has been studied in conjunction with the surface structure. The measurements show that a specific thin surface oxide is always present in the high activity regime of Rh-based CO oxidation.

A new scanning tunneling microscope reactor used for high-pressure and high-temperature catalysis studies Review of Scientific Instruments 79, 084101 (2008) To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy.

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.