Zeolite beta doped with La, Fe, and Pd as a hydrocarbon trap

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.