A nanocrystalline ZSM–5 aggregate having a hierarchical architecture for the catalytic cracking of waste cooking oil

doi:10.21203/rs.3.rs-3343882/v1

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A nanocrystalline ZSM–5 aggregate having a hierarchical architecture for the catalytic cracking of waste cooking oil

https://doi.org/10.21203/rs.3.rs-3343882/v1

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A series of hierarchical ZSM–5 nanocrystalline aggregates (HNZ–5) was synthesized using a hydrothermal method with tetrapropylammonium hydroxide as a structural guide. The morphologies and structures of these materials were characterized by X–ray diffraction, scanning electron microscopy, N₂–Brunauer–Emmett–Teller surface area analysis and assessment of pore size distribution. HNZ–5 specimens having different Si/Al molar ratios all showed suitable hierarchical architectures and the maximum surface area was found to be 329 m²/g. Temperature–programmed desorption with NH₃ indicated that the total acidity of this material increased with increases in the Al³⁺ content to a maximum of 0.47 mmol/g at a Si/Al ratio of 15. In addition, ²⁷Al magic angle spinning nuclear magnetic resonance spectra showed that the acid sites were associated with tetrahedral and octahedral Al sites. This HNZ–5 was applied to the catalytic cracking of a model waste cooking oil compound and gave a light olefins yield as high as 43.9% at 550°C. Extending the reaction time to 6000 min provided a yield of light olefins in excess of 30%. These data confirm that the hierarchical pore structure of this HNZ–5 resulting from the self–assembly of nanocrystals, together with exposed acidic sites, promoted the catalytic conversion of large molecules.

nanocrystalline aggregates

hierarchical molecular sieves

ZSM–5

waste cooking oil model compound

light olefins

Light olefins (that is, ethene, propylene and butene) are widely used in industry to produce polyethene, polypropylene, synthetic rubbers and other polymeric materials. At present, light olefins are primarily generated via the cracking of petroleum–based raw materials such as naphtha and light diesel oil. [1, 2] However, the production of these compounds from methanol or ethanol and from CO₂ hydrogenation or the catalytic cracking of biomass has also received extensive attention. [3–6] Biomass is the fourth largest energy source after coal, oil and natural gas, and is widely distributed while having a minimal environmental impact. [7] To date, lignocellulose, oil–rich microalgae and waste cooking oil (WCO) have all been used to produce light olefins on a laboratory scale. [8] The primary components of WCO are various free fatty acids and fatty acid triglycerides, comprising C₁₂–C₂₂ normal alkanes or alkenes with terminal ester/ carboxyl groups. Based on this composition, WCO is potentially an excellent raw material for cracking to produce light olefins. [9]

ZSM–5 molecular sieves have an MFI topology containing straight channels parallel to the b axis (channel diameters around 5.3−5.6 Å) and sinusoidal channels in the ac plane (around 5.1−5.5 Å). [10] These materials are often used to promote the catalytic cracking of WCO to generate light olefins because they exhibit significant selectivity for the desired products. As an example, Thanh–An et al.[11] synthesized HZSM–5 for use in the catalytic cracking of soybean oil and obtained the combined yield of both propylene and propane in the gas phase products of 41.7% at a reaction temperature of 450°C. Li et al.[12] applied a La₂O₃–modified ZSM–5 molecular sieves to the cracking of bio–oil model compounds and reported a light olefins yield of 128 mL/g. Vu et al. [13] used nanosized ZSM–5 and hierarchical ZSM–5 to catalyze the cleavage of triglyceride–rich biomass and obtained C₂–C₄ olefins concentrations of 88% using meso–ZSM–5 and 91% using the nanosized material, both of which were higher than the yield of 85% provided by a commercially available ZSM–5.

Typically, a ZSM–5 molecular sieves will have a largely microporous structure. Although such materials will show good selectivity for light olefins, the significant resistance to the diffusion of macromolecular reactants in these molecular sieves will lower their catalytic performance. [14, 15] The introduction of mesopores into a ZSM–5 molecular sieves can effectively reduce this resistance and improve the accessibility of reactants to acidic sites, thus improving activity. In particular, molecular sieves having hierarchical pore structures have been proven to showed improve reactant diffusion.[16] Vu et al. [17] synthesized hierarchical ZSM–5 specimens with mesoporous structures through treatments with bases and acids and applied these materials to the catalysis of the production of propylene and butene from triglycerides. The results showed that the selectivity for liquefied petroleum gas (LPG) olefins could be increased to 95 wt.% using these hierarchical ZSM–5 samples and so exceeded the values of 64–66 wt.% obtained using a commercially available molecular sieves. Li et al. [18] synthesized snowflake–shaped hierarchical Ca/ZSM–5 molecular sieves particles for the methanol to olefin reaction and this material exhibited higher selectivity for total light olefins (72%) and propene (39%) compared with a conventional ZSM–5 sample (which showed selectivities of 58.73% and 32.96%, respectively). This prior work demonstrated that the improved catalytic performance of such molecular sieves was primarily a consequence of the increased diffusion through the materials. This effect was attributed to the greater number of distortions and dislocations and the enhanced asymmetry of the molecular sieves frameworks. Miao et al. [19] prepared a hierarchical ZSM–5 molecular sieves from seeds functionalized with an organosilane using an N–[3–(trimethoxysilyl)propyl]–Nʹ–(4–vinylbenzyl) solution as the silylation agent. This specimen exhibited much higher activity during the benzylation of aromatics by benzyl chloride compared with a conventional ZSM–5. The isomeric selectivity for p–benzyltoluene in this previous study was 92.6% whereas that over the standard ZSM–5 molecular sieves (ZSM–5N) was only 27%.

At present, there are two general approaches to preparing hierarchical ZSM–5 molecular sieves. These comprise either the formation of secondary mesopore networks into single crystals to form intracrystalline mesopores or the self–assembly of nanocrystals to create intercrystalline mesopores. [20] The latter strategy can form mesoporous networks based on intercrystalline spaces in nanocrystal assemblies, thus producing a molecular sieves with improved reactant accessibility and better interconnectivity. [21] In the present work, a series of HNZ–5 specimens was synthesized using tetrapropylammonium hydroxide (TPAOH) as a template agent. These materials were characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM) and ammonia temperature programmed desorption (NH₃–TPD) to investigate their structural frameworks, pore structures and acidity. These samples were also applied to the cracking of a WCO model compound (WCOMC) to produce light olefins, and the effects of both the mesoporous volume/micropore volume (V_meso/V_micro) and weak acid/strong acid (WA/SA) ratios of the HNZ–5 as well as of the reaction temperature on the catalytic cracking reaction were investigated.

Materials

Tetrapropylammonium hydroxide (TPAOH, 25wt.%), sodium hydroxide (NaOH, 96%), sodium aluminate (NaAlO₂, 99%) ,tetraethyl orthosilicate (TEOS, 98%), soybean oil and oleic acid were spurchased from Aladdin Reagent Company (China). Animal fat provided by the local market. Preparation of WCOMC:90 g soybean oil and 5 g animal fat were heated at 150°C for 5 h, and then 5 g oleic acid was added to the mixture.

Synthesis of HNZ–5

An 18 g quantity of TEOS (98 wt.%) and 9.2 g TPAOH (25 wt.%) were combined with 60 g H₂O followed by stirring for 12 h at 25°C to obtain gel A. Following this, 0.458 g NaAlO₂ was dissolved in 10 g H₂O at 25°C and stirred until the powder was completely dissolved to obtain solution B. Finally, solution B was slowly added to gel A and the resulting mixture was stirred for 3 h to produce a gel in which the Al₂O₃: SiO₂: TPAOH: H₂O molar ratios were 0.5: 30: 4: 350 and the Si/Al molar ratio was 30. This gel was subsequently transferred to a hydrothermal reactor and held at 180°C for 24 h. After centrifugation and washing, the solid product was dried at 80°C for 12 h and then calcined at 550°C for 4 h to produce the HNZ–5–30 molecular sieves. The mass of NaAlO₂ used in solution B was changed to 0.229 or 0.687 g to give the products referred to herein as HNZ–5–15 and HNZ–5–45, respectively.

Characterization of HNZ–5

XRD patterns were obtained using a SmartLab diffractometer (Rigaku, Japan) equipped with a Cu Kα radiation source operating at 40 kV and 40 mA, applying a scanning speed of 8°/min. SEM images of the various samples were acquired with an EVO18 microscope (ZEISS, Germany) at acceleration voltages of either 5 or 2 kV. The specific surface areas and pore size distributions of the materials were determined using an ASAP 2020 HD88 instrument (Micromeritics, USA) based on the nitrogen adsorption–desorption technique at the liquid nitrogen temperature of 77 K. The specific surface area and pore volume data were calculated according to the Brunauer–Emmet–Teller (BET) method while the pore size distributions were determined based on nonlocal density functional theory. NH₃–TPD analyses were performed using an Autochem II 2920 apparatus (Micromeritics, USA). In each trial, a 60−80 mg sample was first heated to 200°C and then held at that temperature for 120 min under a flow of Ar (10 cm³/min). Following this, the temperature was lowered to 50°C and the gas flow was switched to 10% NH3 in He (30 cm³/min). These conditions were maintained for 120 min after which the gas flow was changed to pure Ar (10 cm³/min) for a further 120 min. After the baseline stabilized, the sample temperature was increased to 750°C at a rate of 10°C /min.

The ²⁷Al magic angle spinning nuclear magnetic resonance (NMR) spectra of these compounds were obtained using a 400 MHz instrument (Bruker, Germany) with a spin rate of 12 kHz, pulse length of 0.75 µs (π/8) and cycle delay of 2 s. The spent catalysts were assessed using thermogravimetric analysis with an STA 449 F5 instrument (NETZSCH–Gerätebau GmbH, Germany) over the temperature range of 50 to 850°C with heating at 10°C/min under gas (50% N₂ and 50% O₂).

Cracking apparatus and procedure

Trials involving catalytic cracking of the WCOMC were conducted using a lab–scale fixed bed apparatus. Prior to each trial, a 30 mL/min flow of N₂ was used to purge any residual air from the equipment. Following this, a 1 g HNZ–5 sample was placed in a reaction tube and the temperature was increased to the desired value at a rate of 8°C/min. The WCOMC was subsequently injected into a fixed bed at a rate of 0.04 mL/min. The gaseous reaction products (H₂, CO, CO₂, CH₄, light olefins and C₂–C₅ alkanes) were analyzed using a GC–7920 gas chromatograph equipped with HP–Al/KCl (30 m × 0.530 mm × 15 µm), 15–1 (3 mm × 1.5 m) and 15–5 (3 mm × 1 m) columns together with a flame ionization detector and a thermal conductivity detector (carrier gas: He). The yield of each gas phase product was calculated based on the equation:

$$\text{y}\left(\text{i}\right)\text{=}\frac{\text{Q×V(i)×M(i)×273.15}}{\text{22.4×G×Te×1000}}\text{×100%}$$

i: gas products. Q: volume of gas, L. V(i): percentage volume of gaseous substances in gas products, %. G: feed quality, Kg. Te: room temperature, K.

After cracking reaction, the collected liquid phase product was esterified and analyzed by a Pana A91 plus gas chromatograph equipped with a flame ionization detector to determine the amount of fatty acid methyl, which was the amount of unreacted raw material. The carrier gas was N₂ at a flow rate of 1.0 mL/min in conjunction with an FFAP capillary column (30 m × 0.132 mm × 0.33 µm). The injector and detector were both held at 250°C. The oven temperature was initially 100°C followed by a ramp to 230°C at 10°C/min with a subsequent hold for 5 min. The WCOMC conversion rate was calculated as

Conversion (%) = 100% – Fatty acid methyl esters content (%)

Characterization of catalysts

The wide angle XRD patterns obtained from the HNZ–5 specimens are shown in Fig. 1. The diffraction peaks at 7.78°, 8.80°, 23.10° and 23.74° are related to an MFI structure and are attributed to the (101), (200), (501) and (303) crystal planes, respectively. [22] As the Si/Al molar ratio was increased, the intensity of each peak was also increased, suggesting that the materials became more crystalline. However, an excess of NaAlO₂ produced a greater number of aluminum oxide tetrahedral (AlO^4–), reducing the probability that Si–O–Al bonds would be formed and providing HNZ–5 with a lower degree of crystallinity. [23]

Figure 1 XRD patterns of HNZ–5 specimens having different Si/Al molar ratios.

Figure 2 demonstrates that the HNZ–5 crystals synthesized in this work each had a structure comprising typical nanocrystalline aggregates. The surfaces of these HNZ–5 samples were composed of uneven crystal particles, as opposed to the coffin–like morphologies of conventional ZSM–5 crystals. The HNZ–5–15 evidently had a low degree of crystallinity and contained a high proportion of the amorphous aluminosilicate precursor. Increasing the Si/Al molar ratio to 30 or 45 provided more ordered crystal structures along with aggregated nanoparticles. The crystal size of the HNZ–5–45 was larger than those of the other two specimens, possibly because the greater number of silicon oxide tetrahedra (SiO^4–) in this material promoted crystal growth to give larger particle sizes. It is evident from these data that the Si/Al molar ratio greatly affected the morphology of material by modifying the nanocrystalline stacking pattern. [24]

Figure 2 SEM images of HNZ–5 specimens having different Si/Al molar ratios. (a) HNZ–5–15, (b) HNZ–5–30, and (C) HNZ–5–45.

Figure 3a presents the adsorption–desorption isotherms obtained from the HNZ–5 samples. The rapid increase in the quantity of adsorbed N₂ at low relative pressures (P/P₀ < 0.1) indicates the presence of numerous micropores. In the medium relative pressure region (0.3 < P/P₀ < 0.8), N₂ was condensed and accumulated in the mesopores, resulting in the formation of a hysteresis loop. [25] Moreover, the HNZ–5–45 isotherm exhibits an H₃ type hysteresis loop, suggesting the presence of mesopores formed by particle stacking. In the corresponding SEM image (Fig. 2c), crystal particles with lengths on the order of 50 nm can be seen on the surface of the HNZ–5–45. From this image, it is apparent that a mesoporous structure was formed between nanocrystalline aggregates in this material. Figure 3b demonstrates that the HNZ–5–45 contained both mesopores (2–80 nm in size) and micropores (0–2 nm in size). In contrast, the HNZ–5–15 did not generate a significant hysteresis loop in the medium relative pressure region, indicating a low number of mesopores in this sample. The corresponding SEM image (Fig. 2a) confirms that this material had a low degree of crystallinity with many amorphous structures, resulting in fewer intergranular mesopores. The pore size distribution of the HNZ–5–15 shows a wide range of pore sizes and is uneven.

Table 1 summarizes the BET surface areas of the catalysts and confirms that increasing the Si/Al ratio increased the area. The BET surface area of the HNZ–5–15 was much lower than those of the HNZ–5–30 and HNZ–5–45 because the former material underwent limited nanocrystal aggregation.

Figure 3 Adsorption–desorption curves and pore size distributions of HNZ–5 specimens having different Si/Al molar ratios.

Table 1

BET surface areas, pore volumes, average pore diameters and acidity of HNZ–5.
Samples	S_BET (m²/g)	S_micro (m²/g)	S_external (m²/g)	V_total (cm³/g)	V_micro (cm³/g)	Average pore diameter (nm)	Acid amount (mmol NH₃/g)
Samples	S_BET (m²/g)	S_micro (m²/g)	S_external (m²/g)	V_total (cm³/g)	V_micro (cm³/g)	Average pore diameter (nm)	Weak acid	Strong acid	Total
HNZ–5–15	90	72	18	0.12	0.04	5.18	0.45	0.02	0.47
HNZ–5–30	321	226	95	0.20	0.12	2.50	0.31	0.05	0.36
HNZ–5–45	329	241	88	0.11	0.09	2.04	0.23	0.04	0.27

Figure 4 provides the NH₃–TPD curves of the HNZ–5 specimens. These materials generated NH₃ desorption peaks within the ranges of 100–290 and 290–400°C, corresponding to weak and strong acid sites, respectively. [26] In general, weak acid sites can be attributed to non–framework aluminum atoms or Si–OH groups associated with structural imperfections in these materials. In contrast, strong acid sites are primarily associated with Si–O–Al groups in molecular sieves. [27] The number of weak acid sites increased with decreases in the Si/Al molar ratio (Table 1). This was a consequence of increases in the concentration of Al³⁺ ions in the initial gel, which in turn increased the proportion of non–framework aluminum atoms in the product. The HNZ–5–30 was found to have the highest number of strong acid sites, indicating that the use of a suitable Si/Al molar ratio promoted the formation of Si–O–Al bonds. As such, more Al³⁺ ions were embedded in the catalyst skeleton to act as strong acid sites. Conversely, the HNZ–5–15 had the lowest proportion of strong acid sites because of the poor crystallinity of the sample. As a result, the majority of the Al³⁺ ions originally present in the gel were not embedded in the HNZ–5–15 skeleton but rather became non–framework aluminum, generating more weak acid sites and fewer strong acid sites.

Figure 4 NH₃–TPD profles of HNZ–5 specimens having different Si/Al molar ratios.

Figure 5 shows the ²⁷Al magic angle spinning NMR spectra acquired from the various HNZ–5 samples. Each spectra contains a peak at approximately 54 ppm representing framework tetrahedral aluminum (FAl) along with a much weaker, broader peak at approximately 0 ppm typical of extra–framework octahedral aluminum (EFAl). [28, 29] These data confirm that Al³⁺ ions in these materials were present at tetrahedral sites in the same manner as Si. It should be noted that the four Al–O groups in each tetrahedra provided a net negative charge to the framework that could be compensated for by the presence of protons. These protons were situated in hydroxyl bridges next to aluminum ions, providing strong acid sites. [30] The HNZ–5–30 produced the most intense peak at 55 ppm, establishing that this specimen contained the greatest number of four–coordinated skeleton aluminum ions. The corresponding NH₃–TPD results (Table 1) confirmed that the HNZ–5–30 had the largest quantity of strong acid sites.

Figure 5 ²⁷Al MAS NMR spectra of HNZ–5 specimens having different Si/Al molar ratios.

Catalytic cracking of the WCOMC

The effects of the V_meso/V_micro ratio on the selectivity for light olefins and the conversion of the WCOMC are summarized in Fig. 6. The total selectivity for light olefins was found to initially increase and then decrease as this ratio was increased, with the highest selectivity (71.3%) at a V_meso/V_micro ratio of 0.76 in the case of the HNZ–5–30. Using this material, the selectivity for butene reached the highest value of 16.8%. The HNZ–5–30 had a BET specific surface area of 321 m²/g with mesopores accounting for 29.6% of this area. The weak and strong acid sites in ZSM–5 molecular sieves are typically found in micropores while the main function of mesopores is to reduce the resistance to the diffusion of reactants. The latter effect limits the occurrence of secondary reactions of the desired products. [31, 32] An excess of mesopores will reduce the residence time of reactants at the acid sites and hence lead to an incomplete reaction such that the selectivity for light olefins is lowered. Therefore, the most suitable catalyst will have an optimal V_meso/V_micro ratio.

Figure 6 also summarizes the effect of the WA/SA ratio on the conversion of the WCOMC and shows that, as the WA/SA value was increased, the conversion increased. The present WCOMC was primarily composed of triglycerides and free fatty acids, and triglycerides were cracked at high temperatures to form fatty acids, acrolein and ketones. Subsequently, these compounds underwent decarbonylation and dehydration at acid sites on the catalyst to generate additional products such as C₂H₄ and long–chain alkanes. The latter then underwent C–C bond cleavage and isomerization to produce short–chain alkanes and olefins. [33, 34] Some of the ester groups contained in the triglycerides also participated in deoxygenation reactions at strong acid sites that produced small molecule substances such as CO₂, CO, H₂O and coke precursors. [35] Therefore, neither high nor low WA/SA values were conducive to the formation of light olefins through WCOMC cracking.

Figure 6 Influence of pore structure on the selectivity of light olefins and WA/SA on the conversion of WCOMC. Temperature = 600°C, WCOMC flow rate = 0.04 mL/min, reaction time = 500min.

Figure 7 demonstrates the effects of temperature on reactions using the HNZ–5–30 and shows that the highest yields of gaseous products and of light olefins (57.6% and 37.1%, respectively) were obtained at 550°C. The product distribution varied with temperature while the ethene and butene yields increased and decreased, respectively, along with temperature. At 650°C, the ethene yield reached 11.9% and the butene yield was only 2.7%. These data indicate that the cleavage of long carbon chains was promoted at elevated temperatures. [36] Fig. 7b also shows that higher temperatures increased the selectivity for ethene but decreased that for butene. It is possible that ethene originated from monomolecular cracking reactions while propylene was generated by bimolecular cracking reactions and that higher temperatures enhanced the former while suppressing the latter. [37]

Figure 7 Influence of the reaction temperature: (a) gas product yield (b) light olefins selectivity.

Catalyst: HNZ–5–30, WCOMC flow rate = 0.04 mL/min, Reaction time = 500 min.

Figure 8a and b show the effects of the WCOMC flow rate on the yields of and selectivities for gas phase products using the HNZ–5–30. It can be seen that the highest yield of light olefins (43.9%) was obtained at a flow rate of 0.02 mL/min. Increasing the WCOMC flow rate decreased the yields of gaseous products and of light olefins, from 43.9–31.1% in the case of the latter. Figure 8b demonstrates that the flow rate affected the ethene and butene outputs although in opposite ways. The selectivities for ethene and propylene decreased by 1.4% and 2.2%, respectively, while the selectivity for butene increased by 1.3%. These changes are attributed to decomposition of the WCOMC at high temperatures to produce pyrolysis vapors, non condensable gases (mainly CO, CO₂, H₂ and CH₄) and carbon deposits. The pyrolysis vapors eventually contacted the catalyst surfaces and diffused into the HNZ–5 pores. In this manner, these compounds interacted with acidic sites and underwent a series of reactions such as dehydration, decarbonylation and oligomerization to generate light olefins. A high flow rate reduced the fracture rate of long–chain alkanes at catalytic sites, leading to a decrease in selectivity for ethene and propylene but an increase in selectivity for butene.[38]

Figure 8 Influence of the feed flow rate: (a) gas product yield, (b) light olefins selectivity.

Catalyst: HNZ–5–30, temperature = 550°C, reaction time = 500 min.

Figure 9 plots the product outputs over time from a reaction using the HNZ–5–30 at 550°C that proceeded for 6000 min. The yields of ethene, propylene and butylene were initially high and then remained stable as the reaction time was extended. These data also reveal a slight decrease in the cracking performance after 3500 min. This effect occurred because some active sites on the catalyst were covered by coke precursors as the reaction progressed. This would have prevented access of reactants to acidic sites in the micropore channels to some extent and thus degraded the catalytic performance.[17]

Figure 9 Influence of the reaction time. Temperature = 550°C, WCOMC flow rate = 0.04 mL/min, reaction time = 6000 min.

Figure 10 showed the thermogravimetric data acquired from fresh catalyst and spent fresh catalyst and spent catalyst. These data indicate that both specimens exhibited mass loss due to the reaction between carbon deposits and oxygen. The used HNZ–5–30 showed a mass loss of 16.67% in the range of 450–600°C, suggesting a high H/C ratio related to so–called “soft coke” in the catalyst pore system. [39] This coke corresponded to adsorbed hydrocarbon molecules inside the catalyst pores that had been generated by coke precursors. However, the spent HNZ–5–30–6000 (having been applied to the reaction for 6000 min) showed a mass loss of 28.17% within the range of 500–650°C. This result indicates the formation of “hard coke” associated with the polymerization of soft coke to produce more bulky carbonaceous compounds having low H/C ratios. [40]

Figure 10 TG curves of the spent catalysts.

The present work synthesized a series of HNZ–5 molecular sieves with different Si/Al ratios and applied these materials to the catalytic cracking of a WCOMC to produce light olefins in a lab–scale fixed bed. SEM images showed that the HNZ–5 surfaces were made of uneven crystalline particles that had assembled to form nanocrystalline aggregates. This assembly produced hierarchical architectures. The NH₃–TPD results demonstrated that the HNZ–5 contained both strong and weak acid sites and ²⁷Al magic angle spinning NMR spectra indicated that these acidic sites originated from both framework tetrahedral aluminum and typical extra–framework octahedral aluminum. During the catalytic cracking of a WCOMC to produce light olefins, the molecular sieves having a Si/Al molar ratio of 30 exhibited the highest activity. At a reaction temperature of 550°C and feed flow rate of 0.02 mL/min, the yield of light olefins reached 43.9%. These data confirm that a suitable pore structure and optimized WA/SA ratio are conducive to the generation of light olefins.

Ethical Approval

not applicable

Competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this manuscript.

Authors' contributions

H.L. and G.Z. wrote the main manuscript text and prepared figures 1-10. All authors reviewed the manuscript.

Funding

This study was funded by the National Natural Science Foundation of China (21962001), China; the Ningxia Key Research and Development Project (2023BDE03009), China; the Ningxia Scientific and Technological Innovation Leading Personnel Training (KJT2017006), China; Innovative team for transforming waste cooking oil into clean energy and high value–added chemicals, China; Ningxia low–grade resource high value utilization and environmental chemical integration technology innovation team project, China are gratefully acknowledged.

Availability of data and materials

All data generated or analysed during this study are included in this published article.

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A nanocrystalline ZSM–5 aggregate having a hierarchical architecture for the catalytic cracking of waste cooking oil

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Abstract

Figures

Introduction

Materials and method

Materials

Synthesis of HNZ–5

Characterization of HNZ–5

Cracking apparatus and procedure

Results and discussion

Characterization of catalysts

Catalytic cracking of the WCOMC

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1