Spatial resolution of a velocity-selected ion imaging microscope for surface reaction kinetics mapping

Area of Science:

• Heterogeneous catalysis
• Surface science
• Physical chemistry

Background:

• Experimental validation of microkinetic models is essential for bottom-up catalysis.
• Current methods integrate reactivity over large surfaces, potentially confounding spatial effects.
• Velocity-resolved kinetics experiments are advancing but face limitations with spatial phenomena.

Purpose of the Study:

• To develop and validate an ion imaging microscope for spatially resolved kinetic data acquisition.
• To overcome limitations of current methods by analyzing reactions on a microscale.
• To enable precise characterization of catalytic processes with spatial resolution.

Main Methods:

• Design and optimization of a novel ion imaging microscope.
• Utilizing laser ionization of gaseous reaction products above a catalytic surface.
• Employing velocity mapping and electrostatic lensing for spatial deblurring and magnification.
• Analysis of ion trajectories and transmission properties via electrostatic simulations.

Main Results:

• The ion imaging microscope successfully collects spatially resolved kinetic data.
• The system provides deblurred spatial images of reaction product distributions.
• Spatiotemporal flux and speed-distributions of desorbing gas can be determined.
• Simulations confirm transmission is dependent on pinhole radius and surface temperature (∝r²/TSurface).
• Image resolution is largely independent of surface temperature (∝r), offering consistent performance at varying temperatures.

Conclusions:

• Velocity-filtered ion imaging microscopy offers a powerful tool for heterogeneous catalysis research.
• This technique allows for detailed investigation of spatially dependent reaction kinetics.
• The method's temperature independence is advantageous for studying high-temperature catalytic reactions.