LEEM and PEEM as Probing Tools to Address Questions in Catalysis

Abstract

Catalysis is a hot topic in research with the focus on finding catalysts that show better activity or selectivity on processes on technological or industrial interest. The use of model systems of applicable materials has proven to be a successful approach in the last decades to obtain information on the fundamental properties of these materials, leading eventually to a better understanding how real catalysts work. This knowledge is extremely important in the sense that it allows an optimization of the catalyst composition, thus leading to a rational design of new materials. For these fundamental studies, a variety of probing techniques such as X-ray photo-electron spectroscopy, scanning tunnel microscopy, and temperature programmed desorption have been applied. In this article, we discuss how low energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) can contribute to the fundamental understanding of relevant surface processes taking place on model catalysts. Also, the capability of these techniques on addressing open questions in catalysis is discussed

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

“…For reviews, single crystal studies and a recent NAP‐PEEM variant, which enables high resolution (<100 nm) imaging around 1 mbar from 150–1200 K, refer to. [ 95,187,193–198 ]…”

“…For reviews, single crystal studies and a recent NAP-PEEM variant, which enables high resolution (<100 nm) imaging around 1 mbar from 150-1200 K, refer to. [95,187,[193][194][195][196][197][198] Figure 6. a) Illustration of operando photoemission electron microscopy (PEEM) and kinetics by imaging: [97,[185][186][187] a) an ongoing catalytic reaction on a structurally-heterogeneous sample, for example, a polycrystalline Pd foil, is monitored simultaneously by PEEM and MS. Local data obtained from the intensity analysis of PEEM video-sequences for each individual (hkl)-domain (µm-scale) are compared with global (averaged) MS data.…”

“…Variations may be due to different surface structures (e.g., ( 100), ( 110), (111) thus having different intensities), but also adsorbates/reactants change the work function (Figure 6b-d). [185][186][187][188][189][190][191][192][193][194][195][196] The local evolution of surface coverage is hence directly reflected by the local PEEM image intensity. For example, during catalytic CO oxidation on polycrystalline Pd, the catalytically active (oxygen covered; low work function; Figure 6b) surface regions appear bright on the PEEM screen and can be easily differentiated from the inactive (CO covered; high work function; Figure 6d) surface, which looks dark.…”

Major Advances and Challenges in Heterogeneous Catalysis for Environmental Applications: A Review

“…Tests performed on two samples both in a vacuum and under in high pressure demonstrated the ability of in situ examinations of heterogeneous catalysis and surface chemistry at an atomic resolution and at a wide pressure range, from UHV to a pressure higher than 1 atm. Other researchers [67] focused on the main advantages of both low energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) for understanding structural and chemical alterations on the surface of model catalysts in real time and under well-defined environments when chemical reactions take place. The LEEM/PEEM method to model approaches in catalysis is possibly important due to many aspects, e.g.…”

Heterogeneous Surfaces as Structure and Particle Size Libraries of Model Catalysts

“…Once a surface process can be visualized in situ by an imaging technique (e.g. by low-energy electron microscopy (LEEM [ 49 , 50 ]), ellipso-microscopy for surface imaging [ 51 ], reflection anisotropy microscopy [ 51 ], infrared and Raman imaging [ 52 ], metastable impact electron emission microscopy ([ 53 ]) etc. ), the concept of kinetics by imaging can be applied, provided a relation between the local image intensity and kinetic parameters can be identified.…”