Effect of temperature Ramp on hydrocarbon desorption profiles from zeolite ZSM‐12

Abstract

AbstractZeolite ZSM‐12 with different Si:Al molar ratios and one‐dimensional channels with 12 oxygen ring apertures (12R) was synthesized and characterized by different techniques such as: X‐ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer‐Emmett‐Teller surface area (BET), elemental analysis by atomic absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR) of adsorbed pyridine, and NH3 temperature‐programmed desorption (TPD). The synthesized samples were tested as hydrocarbon (HC) trap adsorbents using toluene and ethylene as heavy and light probe molecules for HCs in the exhaust stream at engine cold‐start. High heating rate desorption experiments were performed using the Phytronix Laser Diode Thermal Desorption system (S‐960 LDTD) coupled with an Atmospheric Pressure Chemical Ionization (APCI) chamber (Phytronix Technologies, Canada) after adsorption of toluene‐ethylene mixtures. Three heating rates, which reflect the actual heating rates of the catalytic muffler, were used for the desorption process: 3 °C/s, 5 °C/s, and 9 °C/s. For all solids considered in this study, the two HCs desorbed above 240 °C, which is the light‐off temperature of the three‐way catalyst. Ag‐ZSM‐12 with different Si:Al ratios was found the most appropriate HC trapping adsorbent in spite of its slightly lower adsorption capacity. A high desorption temperature for ethylene and toluene was associated with the large density of strong Lewis acid sites in this solid.