The main raw materials of zeolites are silica and alumina, which are among the most abundant mineral components on Earth.fe beta zeolite They can be easily combined with other raw materials like metals to manufacture a wide variety of zeolite structures that do not appear in nature and offer key advantages over natural analogs.fe beta zeolite In particular, the ability to produce zeolite structures in a phase-pure state allows for their use as catalysts in processes such as ammonia oxidation.
Among the most widely used zeolite types are beta and mesoporous structures, which are suitable for high-pressure applications.fe beta zeolite A wide range of catalysts are produced from these zeolites by introducing different kinds of cations into the structure. Recently, bimetallic cation-exchanged zeolite matrices have received considerable attention due to their improved physicochemical properties and catalytic performance in ammonia oxidation.
Fe and La have a strong effect on the HC trapping capacity of beta zeolite, which is an important consideration when designing industrial catalysts for hydrocarbon conversions.fe beta zeolite However, the underlying mechanism has not been clearly elucidated. This study aims to investigate the effect of doping zeolite beta with Pd, Fe, and La on its ability to adsorb and release propene and toluene using an incipient wetness impregnation method. Five monolith samples of zeolite beta containing Fe/BEA, La/BEA, Pd/BEA, and Pd/Fe/La/BEA were prepared by this process. The zeolite powders were characterized by N2-sorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), and scanning transmission electron microscopy energy-dispersive spectroscopy with EDX to characterize the elemental composition and the catalytic performance of the resulting monoliths.
The zeolite characterization revealed that all the samples showed well-resolved XRD patterns typical for BEA zeolite.fe beta zeolite A type I N2-sorption experiment confirmed the presence of large pores in the zeolite structure. The XPS results showed that the addition of La and Fe to BEA does not significantly affect the oxygen content, but that it does influence the oxidation state of the Pd cations. Specifically, the XPS spectra of Pd/BEA exhibited a significant shift in the Pd 3d5/2 peak compared to that of Pd/Fe/BEA, suggesting that more Lewis acid sites were introduced with the addition of La and Fe to the BEA structure.
Toluene-TPD experiments indicated that the Pd/BEA and Pd/Fe/La/BEA samples displayed lower desorption quantities of toluene compared to the pure zeolite beta sample.fe beta zeolite In addition, the adsorption peaks in the region around 1575 cm-1 of toluene in these samples are less pronounced compared with those of pure BEA. This is most likely due to competition between water and toluene for the adsorption sites.
Adding La and especially Fe to the BEA structure also improves the ability of the zeolite to store toluene, but does not significantly increase its adsorption capacity with propene.fe beta zeolite The underlying mechanism of this effect is unclear, but it may be associated with the formation of more Lewis acid sites within the zeolite. This result could potentially help to develop new HC-trapping strategies for reducing automotive pollution by lowering the ignition point of gasoline.
