Temperature-Programmed\nDesorption of Single Zeolite\nNanoparticles

Zeolites\nare essential solid acid catalysts in various chemical\nprocesses. Temperature-programmed desorption (TPD) is one of the most\nestablished techniques used to characterize the acidity of zeolites\nby measuring the desorption kinetics of probes from bulk samples.\nHowever, conventional TPD can hardly deliver the intrinsic acid properties\nof zeolites because the apparent desorption kinetics are inevitably\nmixed with mass transfer and thermal conduction due to the large sample\namount (∼0.1 g). Herein, we developed an optical microscopy\napproach to measure the TPD spectra of single zeolite nanoparticles,\ntermed oTPD, by in situ monitoring of the reduced scattering intensity\nof individuals as a result of the desorption of probe molecules during\nheating. A significantly reduced sample amount contributed to the\noTPD spectrum, revealing an intrinsic desorption temperature of ∼300\n°C lower than the apparent value and also a greatly narrowed\npeak width from ∼150 to ∼15 °C. Correlating oTPD\nand micro-Raman spectra of the very same individuals further uncovered\na linear dependence between the acidity and the content of silicon\nislands. This study provided unprecedented capabilities for measuring\nthe intrinsic acid properties and the desorption kinetics of single\nzeolite nanoparticles, with implications for better understanding\nthe structure–acidity relationship and for designing better\nzeolite catalysts.