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The materials characterization laboratory is equipped with a custom-made Temperature Programmed Desorption (TPD) system (Figure 1). The system includes Thermcraft split tube furnace with three Yokogawa program controllers, thermal conductivity detector with Gow-Mac power supply control unit, MKS mass flow controllers with a four-channel readout, and a National Instruments communication module with LabVIEW program. The TPD experiment consists of adsorbing a base molecule on the material of interest, while flushing the surface with an inert gas, linearly ramping the temperature, and measuring desorption of the base. The acid properties of the material can be obtained by quantitatively measuring the amount of base desorbed and noting the temperature(s) of desorption.
Figure 1: The custom-made Temperature Programmed Desorption (TPD) system. At CAMMP, the TPD system is used to measure acid properties of zeolites. The strength and concentration of acid sites in zeolites can be obtained based on a single TPD of ammonia experiment. Figure 2 shows an example of the experimental ammonia TPD profile (E) of zeolite Beta and the best-fitted curve (S) generated from the simulated low (L) and high (H) temperature peaks. The H-peak is assigned to desorption of ammonia adsorbed on Brønsted acid sites, whereas the L-peak is assigned to desorption of ammonia adsorbed on structural defects (i.e., potential Lewis acid sites).
Figure 2: Experimental ammonia TPD profile (E) of zeolite Beta and the best-fitted curve (S) generated from the simulated low (L) and high (H) temperature peaks. |
