Abstract
This Perspective aims to inform the heterogeneous catalysis and materials science community about the recent advances in Time-of-Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) to characterize catalytic solids by taking large model H-ZSM-5 zeolite crystals as a showcase system. SIMS-based techniques have been explored in the 1980-1990's to study porous catalyst materials but, due to their limited spectral and spatiotemporal resolution, there was no real major breakthrough at that time. The technical advancements in SIMS instruments, namely improved ion gun design and new mass analyser concepts, nowadays allow for a much more detailed analysis of surface species relevant to catalytic action. Imaging with high mass and lateral resolution, determination of fragment ion patterns, novel sputter ion concepts as well as new mass analysers (e.g. ToF, FTICR) are just a few novelties, which will lead to new fundamental insight from SIMS analysis of heterogeneous catalysts. The Perspective article ends with an outlook on instrumental innovations and their potential use for catalytic systems other than zeolite crystals.
Highlights
This Perspective aims to inform the heterogeneous catalysis and materials science community about the recent advances in Time-of-Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) to characterize catalytic solids by taking large model H-ZSM-5 zeolite crystals as a showcase system
Despite the valuable insights SIMS techniques have provided in the 1990’s on both model and powdered catalyst materials, there has been no widespread use in the field of heterogeneous catalysis as compared to e.g. X-ray Photoelectron Spectroscopy (XPS)
Reasons for that might be the more complicated set-up and significantly higher investment costs for ToF-SIMS instruments accompanied by the complex nature of the obtained mass spectra
Summary
Today different mass analysers with more or less high mass resolution exist. One of the main disadvantages of ToF-SIMS is the high rate of fragmentation of the targeted molecules – a serious problem when it comes to the analysis of organic deposit species of e.g. coked zeolite samples This leads mostly to complex mass spectra and the main task is to identify the parent molecules. The advantages over other methods are obvious: high surface sensitivity trace component detection hydrogen detection isotope sensitive; labelling possible molecular information on fragment ions/fragment ion pattern In the following we will discuss three main directions of ToF-SIMS analysis of our selected showcase system of large ZSM-5 zeolite materials: (i) analysis of surface species with high mass resolution, (ii) 3D analysis of inorganic species by sputter depth profiling combined with ToF-SIMS analysis, and (iii) 2D imaging of secondary ions
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