Isomer-Selective Detection of Aromatic Molecules in Temperature-Programmed Desorption for Model Catalysis

Area of Science:

• Surface Science
• Analytical Chemistry
• Heterogeneous Catalysis

Background:

• Temperature-programmed desorption (TPD) is crucial for studying surface reactions.
• Distinguishing between structural isomers on surfaces can be challenging with conventional methods.
• Resonance-enhanced multiphoton ionization (REMPI) offers potential for selective molecule detection.

Purpose of the Study:

• To evaluate the selectivity and sensitivity of REMPI-TPD for analyzing molecules on a Pt(111) surface.
• To assess REMPI-TPD's applicability in heterogeneous catalysis.
• To compare REMPI-TPD with electron ionization mass spectrometry (EI-Q-MS).

Main Methods:

• Utilized a Pt(111) single crystal surface.
• Dosed three different molecules onto the crystal.
• Performed temperature-programmed desorption (TPD) experiments.
• Employed resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOF-MS).

Main Results:

• Successfully discriminated between structural isomers ethylbenzene and p-xylene using REMPI-TPD.
• Demonstrated that electron ionization (EI) in a quadrupole mass spectrometer (Q-MS) cannot achieve this discrimination.
• Showcased REMPI-TOF-MS sensitivity comparable to commercial EI-Q-MS.
• Achieved detection of less than 0.6% of a monolayer.

Conclusions:

• REMPI-TPD is a selective and sensitive technique for surface analysis.
• This method holds promise for applications in heterogeneous catalysis.
• REMPI-TPD offers advantages over conventional EI-Q-MS for isomer discrimination.