High-pressure STM study of NO reduction by CO on Pt(100)

High-Pressure Scanning Tunneling Microscopy

This is a Review of recent studies on surface structures of crystalline materials in the presence of gases in the mTorr to atmospheric pressure range, which brings surface science into a brand new direction. Surface structure is not only a property of the material but also depends on the environment surrounding it. This Review emphasizes that high/ambient pressure goes hand-in-hand with ambient temperature, because weakly interacting species can be densely covering surfaces at room temperature only when in equilibrium with a sufficiently high gas pressure. At the same time, ambient temperatures help overcome activation barriers that impede diffusion and reactions. Even species with weak binding energy can have residence lifetimes on the surface that allow them to trigger reconstructions of the atomic structure. The consequences of this are far from trivial because under ambient conditions the structure of the surface dynamically adapts to its environment and as a result completely new structures are often formed. This new era of surface science emerged and spread rapidly after the retooling of characterization techniques that happened in the last two decades. This Review is focused on the new surface structures enabled particularly by one of the new tools: high-pressure scanning tunneling microscopy. We will cover several important surfaces that have been intensely scrutinized, including transition metals, oxides, and alloys.

Behavior of a Metal Organic Framework Thin-Film at Elevated Temperature and Pressure as Studied with an Autoclave-Inserted Atomic Force Microscope

Bridging the gap in studying surface reactions, processes, and morphology and measuring at (catalytic) relevant conditions is crucial for our understanding of the working principles of porous crystalline materials. Scanning tunneling microscopy is limited because of the required conductivity of the sample, whereas atomic force microscopy (AFM) is often challenging in use owing to the physical mechanism underlying the technique. Herein, we report a tailor‐made autoclave‐inserted AFM, able to measure at ∼20 bar and ∼110 °C. First, we show the ability to obtain nanometer resolution on well‐defined test samples at before‐mentioned conditions. Second, to demonstrate the possibilities of analyzing morphological evolutions at elevated temperatures and pressures, we use this setup to measure the stability of a surface‐anchored metal‐organic framework (SURMOF) in‐situ at pressures of 1–20 bar in the temperature range between 20 and 60 °C. It was found that the showcase HKUST‐1 material has a good physical stability, as it is hardly damaged from exposure to pressures up to 20 bar. However, its thermal stability is weaker, as exposure to elevated T damaged the material by influencing the interaction between organic linker and metal cluster. In‐situ measurements at elevated T also showed an increased mobility of the material when working at such conditions. Combining the strength of AFM at elevated T and p with ex‐situ AFM and spectroscopic measurements on this MOF showcases an example of how porous materials can be studied at (industrially) relevant conditions using the autoclave‐inserted AFM.

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

Application of surface-science techniques, such as XPS, SXRD, STM, and IR spectroscopy under catalytic reactions conditions yield new structural and chemical information. Recent experiments focusing on CO oxidation over Pt and Pd model catalysts were reviewed.