In situ studies of NO reduction by H2 over Pt using surface X-ray diffraction and transmission electron microscopy.

In situ surface X-ray diffraction and transmission electron microscopy at 1 bar show massive material transport of platinum during high-temperature NO reduction with H2. A Pt(110) single-crystal surface shows a wide variety of surface reconstructions and extensive faceting of the surface. Pt nanoparticles change their morphology depending on the gas composition: They are faceted in hydrogen-rich environments, but are more spherical in NO-rich environments, indicating the formation of vicinal surfaces. We conclude that high coverage of NO combined with sufficient mobility of platinum surface atoms is the driving force for the formation of steps on both flat surfaces and nanoparticles. Since the steps that are introduced provide strongly coordinating adsorption sites with potential catalytic benefits, this may be of direct practical relevance for the performance of catalytic nanoparticles under high-pressure conditions.

The ReactorAFM: non-contact atomic force microscope operating under high-pressure and high-temperature catalytic conditions.

An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image model catalysts such as those consisting of metal nanoparticles on flat oxide supports in a gas atmosphere up to 6 bar and at a temperature up to 600 K, while the catalytic activity can be measured using mass spectrometry. The high-pressure reactor is placed inside an Ultrahigh Vacuum (UHV) system to supplement it with standard UHV sample preparation and characterization techniques. To demonstrate that this instrument successfully bridges both the pressure gap and the materials gap, images have been recorded of supported palladium nanoparticles catalyzing the oxidation of carbon monoxide under high-pressure, high-temperature conditions.

The ReactorSTM: atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions.

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. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.