Integration of a Modified Synchrotron Radiation Photoionization Time-of-Flight Mass Spectrometer with a Residual Gas...

In situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) is a powerful tool for detecting gas-phase species including intermediates and products in gas-solid catalytic reactions. However, achieving sensitive and more comprehensive monitoring of gas-phase compounds with different ionization energies in a single measurement remains a significant challenge. In this work, a multiphysics ion trajectory simulation integrating a coupled computational fluid dynamics-direct simulation Monte Carlo (CFD-DSMC) method for continuum-rarefied flow was carried out for tracing the ion motion within the ionization region. The simulation results were applied to the design of the cage lens assembly of a modified SR-PIMS, and a limit of detection (LOD) of 0.67 ppbv (S/N ≥ 3) was achieved under Kr-lamp calibration conditions for toluene. Furthermore, a residual gas analyzer (RGA) was coupled to the SR-PIMS for the complementary detection of organic products with low ionization energies (IEs, generally lower than 11 eV) and H2, CO, CO2 etc. with higher IEs, thereby reducing the need for separate measurements at multiple photon energies. The optimized SR-PIMS setup combined with RGA was successfully applied to probe the intermediates and products generated during the methanol-to-hydrocarbons (MTH) reaction over ZnO/HZSM-5 catalysts, and the time-evolved profiles for major species under different ZnO loadings were obtained and analyzed.