Abstract
H-ZSM-5 materials embedded in an amorphous silica were successfully synthesized with three different Si/Al ratios (i.e., 40, 45, and 50). The presence of the MFI structure in the synthesized samples was confirmed by X-ray diffraction (XRD), Fourier transform infra-red (FT-IR), and solid state-nuclear magnetic resonance (SSNMR) techniques. The morphology and textural properties of the samples were investigated by scanning electron microscopy (SEM), TEM, and N2-physisorption measurements. Furthermore, acidic properties of the synthesized catalysts have been studied by NH3-TPD and FT-IR spectroscopy of CO adsorption studies. Variation of the Si/Al ratio affected the crystal morphology, porosity, and particle size, as well as the strength and distribution of acid sites. The synthesized zeolite materials possessed low acid-site density and exhibited high catalytic activity in the methanol-to-olefin (MTO) reaction. To study the intermediate species responsible for catalyst deactivation, the MTO reaction was carried out at high temperature (500 °C) to accelerate catalyst deactivation. Interestingly, the synthesized catalysts offered high selectivity towards the formation of propylene (C3=), in comparison to a commercial microporous crystalline H-ZSM-5 with Si/Al = 40, under the same reaction conditions. The synthesized H-ZSM-5 materials offered a selectivity ratio of C3=/C2= 12, while it is around 2 for the commercial H-ZSM-5 sample. The formation of hydrocarbon species during MTO reaction over zeolite samples has been systematically studied with operando UV-vis spectroscopy and online gas chromatography. It is proposed that the strength and type of acid sites of catalyst play a role in propylene selectivity as well as the fast growing of active intermediate species. The effective conversion of methanol into propylene in the case of synthesized H-ZSM-5 materials was observed due to possession of weak acid sites. This effect is more pronounced in H-ZSM-5 sample with a Si/Al ratio of 45.
Highlights
Propylene is one of the most important base chemicals in chemical industries
Fourier transform infra-red (FT-IR) spectral analysis was used to confirm the presence of the MFI structure in the synthesized samples, since Jacobs et al [28] indicated that X-ray diffraction (XRD) should be used
It is clear from the activity results that the active hydrocarbon pool (HCP) species formation rate and the propylene selectivity are higher for all synthesized H-ZSM-5 samples, due to fact that these samples possessed low density of Brønsted acid sites
Summary
Propylene is one of the most important base chemicals in chemical industries. Due to the high demand for propylene, the development of more selective catalysts for the methanol-to-olefin (MTO). In addition to the effort of forming high selectivity towards propylene, Palčić et al [10] studied the effect of crystallization temperature (170, 150, 120, and 100 ◦ C) on the ZSM-5 properties They observed that the decrease in the crystallization temperature 100 ◦ C led to significant changes in zeolite properties exhibiting many framework defects with decrease in acid-site density, decrease in their strength, and larger external surface area. Yarulina et al [27] studied the effect of acidity on the catalytic activity of the ZSM-5 for the MTO process; the authors observed that the introduction of Lewis acid sites averts coke formation, enhancing the lifetime of the catalyst and observing that the isolation of Brønsted acid sites is essential to increase propylene selectivity. UV-vis spectroscopy and online at gas500 chromatography to correlate elucidate theof catalytic activity spectroscopy and online gas chromatography to correlate and elucidate thegenerated catalytic in activity with the with the formation of different active and deactivating hydrocarbon species the catalyst bed. of different active and deactivating hydrocarbon species generated in the catalyst bed
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
