Abstract
Hydrocarbon trapping is a technique of great relevance, since a substantial part of hydrocarbon emissions from engines are released from engines before the catalyst has reached the temperature for efficient conversion of the hydrocarbons. In this work, the influence of doping zeolite beta (BEA) with Fe, Pd, and La on the storage and release of propene and toluene is studied. Five monolith samples were prepared; Fe/BEA, La/BEA, Pd/BEA, Pd/Fe/BEA, and Pd/La/BEA using incipient wetness impregnation, and the corresponding powder samples were used for catalyst characterization by Inductively coupled plasma sector field mass spectrometry (ICP-SFMS), Temperature-programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and Scanning transmission electron microscopy with Energy dispersive X-ray analysis (STEM-EDX). The hydrocarbon trapping ability of the samples was quantified using Temperature-programmed desorption (TPD) of propene and toluene, and in situ Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results from the TPD experiments show that the addition of Pd and La to the zeolite affected the release patterns of the stored hydrocarbons on the trapping material in a positive way. The in situ DRIFTS results indicate that these elements provide H-BEA with additional sites for the storage of hydrocarbons. Furthermore, EDX-mapping showed that the La and Pd are located in close connection.
Highlights
Exhaust aftertreatment is crucial to reduce emissions from large fleets of vehicles all over the world
The results show that the desorption maximum of propene is primarily located explained by the low SiO2/Al2O3 ratio of the zeolite used in the present study, which is consistent around 250 ◦ C for all samples, including the BEA reference sample
The La/BEA sample has a desorption peak at 240 ◦ C, which increases in the presence of Pd, despite that the Pd/BEA sample exhibits no desorption peak in this region. These results show that there is clear interaction between the La and Pd, which was concluded from the Temperature-programmed oxidation (TPO) experiments in which a clear shift of the oxidation temperature of Pd was found when La was added to Pd/BEA
Summary
Exhaust aftertreatment is crucial to reduce emissions from large fleets of vehicles all over the world. The addition of Pd together with other redox active metals to HC trap systems has been proven to be beneficial for emissions from gasoline-based fuels This was observed by Lupescu et al as they studied direct-injected gasoline into the exhaust aftertreatment system of a Ford Focus passenger car. They found that the Brønsted acid sites, Pd, and redox-active metals allow the polymerisation of stored HC compounds and that the base redox metal helps stabilize the Pd from sintering [30]. To our knowledge, no studies are available in the open literature that compare and evaluate the effect of promoting zeolite beta with Pd, La, and Fe used as a hydrocarbon trap, which is the objective of the present study
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