Temperature-Programmed Desorption of Single Zeolite Nanoparticles.

Abstract

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