H-ZSM-5 Materials Embedded in an Amorphous Silica Matrix: Highly Selective Catalysts for Propylene in Methanol-to-Olefin Process

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.

Boron-Modified Mesoporous ZSM-5 for the Conversion of Pyrolysis Vapors from LDPE and Mixed Polyolefins: Maximizing the C2–C4 Olefin Yield with Minimal Carbon Footprint

“…Therefore, the benefit of boron incorporation may be attributed to the addition of Lewis acidic sites, aiding in the cracking of C 5+ aliphatics toward lighter olefins. While aromatization activity was also low with Conv-Z_med Si/Al , this is attributed to the higher fraction of EFAL from the synthesis compared to Meso-Z_med Si/Al , , in line with the results from 27 Al and 29 Si MAS NMR analysis (Table ). Using MPO as the feed instead of LDPE resulted in a similar yield distribution.…”

Si–OH Nest and Al Distribution of Silicalite-1 Core/Al-ZSM-5 Shell Zeolites for Methane Dehydroaromatization Reaction

“…Commercial Al-ZSM-5 with an SAR of 120 was also characterized for comparison. The zeolites showed three distinct peaks around 3750, 3600, and 3500 cm −1 (Figure 7a), corresponding to the external Si-OH group, Brønsted acid sites, and internal Si-OH nests, respectively, [36]. Highly siliceous MFI zeolites often accompany Si-OH nests [36,37].…”

“…The zeolites showed three distinct peaks around 3750, 3600, and 3500 cm −1 (Figure 7a), corresponding to the external Si-OH group, Brønsted acid sites, and internal Si-OH nests, respectively, [36]. Highly siliceous MFI zeolites often accompany Si-OH nests [36,37]. The commercial Al-ZSM-5 exhibited two distinct bands at 3750 cm −1 and 3600 cm −1 , and its IR absorption was lower than that of the core-shell zeolite, as shown in Figure 7a.…”

Effect of Steaming on Waste‐Derived Zeolite ZSM‐5 as Methanol‐To‐Hydrocarbons Catalyst

“…It is known that BAS promotes hydride transfer reactions, which form aromatic compounds as well as C 1-5 paraffins. [62,79]…”

“…As shown in Figure 7(a–c), the S10 sample shows relatively lower aromatic hydrocarbon species, which is related to the lower amount of BAS present in this sample compared to the commercial and S3 parent samples. It is known that BAS promotes hydride transfer reactions, which form aromatic compounds as well as C 1–5 paraffins [62,79] . Regarding the parent samples, it can be noted that waste‐derived zeolite ZSM‐5 materials contain a relatively higher amount of poly‐condensed aromatic species than the commercial sample, which can be attributed to the different morphologies of the samples.…”