Dealumination Treatment Research Articles

Facile Creating a Hierarchical and Hydrophobic Fe-Co/LZSM-5 Catalyst for the Oxidative Desulfurization Process

This research involved top-down dealumination and steam treatment methods to design the hierarchical pores of ZSM-5, which is then wet-impregnated with a Fe-Co. This method overcomes the steric barrier that hinders the oxidative desulfurization (ODS) process and makes the catalyst hydrophobic, thereby allowing it to overcome the biphasic hindrance caused by the difference in polarity between the fuel oil and the oxidant. Characterization of the catalyst's properties based on BET and BJH, XRF, and contact angle, as well as testing its performance on DBT model oil in n-hexadecane and Indonesian commercial diesel were conducted. Simulation of the reaction energy profile using density functional theory calculations was also carried out to deepen insight into the mechanism of the reaction. Results of this study show that the catalyst has excellent catalytic reactivity in the long-chain hydrocarbon ODS process, with a TOF number of 183 h−1.

Valorisation of waste biomass and plastics toward light aromatics: Co-catalytic fast pyrolysis of torrefied bamboo and polyethylene over alkali and acid treated hierarchical HZSM-5

Light aromatics are extremely important building blocks which can be prepared from the co-catalytic fast pyrolysis (Co-CFP) of biomass and polyethylene. In this study, the bamboo was torrefied to remove part of oxygen element prior to pyrolysis, then being co-fed with polyethylene (HDPE, PE and LDPE) during CFP over alkali (NaOH and Na2CO3) and acid (H3PO4 and HCl) treated HZSM-5. 40.3% oxygen element in bamboo could be eliminated at torrefaction temperature of 300 °C. After the acid dealumination or alkali desilication treatments, the mesopore was creased in HZSM-5, transforming into hierarchical structure with larger pore size and lower acidity. The effect of torrefaction temperature, the species of alkali or acid solutions and their concentrations, the mass ratio of HDPE-to-torrefied bamboo, the CFP temperature on the yields of light aromatics was systematically discussed. The maximum yield of BTX was 4.39 × 108 a.u./mg which was obtained by Co-CFP of torrefied bamboo (250 °C) and HDPE at mass ratio of 1:2 with 800 °C over 0.2 M NaOH treated hierarchical HZSM-5. The aromatization reaction of olefins, the deoxygenation reaction of oxygenates, and the Diels-Alder reaction between furans and olefins were key reactions for the formation of BTX during Co-CFP of torrefied bamboo and polyethylene.

Tuning the Structure and Acidity of Pt/Hierarchical SSZ-32 Catalysts to Boost the Selective Hydroisomerization of n-Hexadecane

Developing highly selective and efficient bifunctional catalysts is an important issue for the hydroisomerization of long-chain n-alkanes. It is vital to tailor the balance of isomerization and cracking reactions in hydroisomerization. Herein, a bifunctional Pt/hierarchical SSZ-32 catalyst was fabricated with a sequential desilication–dealumination treatment to boost the selective hydroisomerization of n-hexadecane (C16). The pore structure and acid sites of SSZ-32 zeolite were tailored. More mesopore and Brønsted acid sites were generated, and the ratio of weak to strong Brønsted acidity (Bw/Bs) was increased by the sequential desilication–dealumination. The generated hierarchical structure had little effect on the selectivity of the reaction pathways of hydroisomerization versus cracking. The ratio of isomers/cracking products increased almost linearly with the increase in the Bw/Bs ratios. Meanwhile, the synergetic effect of the hierarchical structure and acidity regulation promoted the selectivity of monobranched i-C16 products. Therefore, the resulting Pt/SSZ-0.6AS exhibited the highest activity with a total isomer yield of 71.5% at 255 °C and the enhanced formation mechanism of monobranched isomers occurred via the pore mouth.

Nonoxidative propane dehydrogenation by isolated Co2+ in BEA zeolite: Dealumination-determined key steps of propane C[sbnd]H activation and propylene desorption

With BEA (Si/Al = 20) zeolite and dealuminated Si-BEA as supports, the non-noble metal Co catalysts are prepared by vacuum impregnation method to study the correlation between the catalyst structure and catalytic performance in propane dehydrogenation (PDH) reaction . The optimal 0.5 wt% Co@Si-BEA catalyst exhibits over 93 % selectivity to propylene, high single-pass yield and great regeneration stability in the recycling PDH reactions at 590 °C. The isolated Co2+ cations are anchored in the micropores of Si-BEA zeolites through interacting with the silanol groups generated by dealumination treatment, and serve as the catalytically active sites to selectively activate the CH bonds of propane rather than dissociate the CC bonds. Furthermore, Co@Si-BEA catalyst adsorbs propylene in a favorable configuration, leading to desired adsorption features with respect to less amount and weaker strength in comparison with that on non-dealuminated Co@BEA catalyst. Therefore, the facile propylene desorption can be achieved on Co@Si-BEA catalyst, which is responsible for its high propylene selectivity, activity, and long-term stability in PDH reaction. By contrast, Co@BEA catalyst with higher density of surface Brønsted acid sites, facing with severe issues of propane CC bond scission, strong propylene adsorption and coke deposition-caused deactivation.

VOCs catalytic removal over hierarchical porous zeolite NaY supporting Pt or Pd nanoparticles

The present work reports the impregnation of palladium (Pd) or platinum (Pt) on hierarchical porous zeolite catalysts for Volatile Organic Compounds (VOCs) oxidation. The hierarchical porous zeolite (NaYmod) was synthesized via a top-down approach to incorporate mesoporosity into the microporous zeolite NaY. This process was achieved through a three steps synthesis: dealumination, desilication and alkaline treatment. 0.5 wt% of Pd and Pt precursors were then added to NaY and NaYmod supports by wet impregnation in order to elaborate efficient catalysts for the total oxidation of two types of VOCs, ethanol and toluene, which are probe molecules for oxygenated VOCs and BTEX compounds respectively. The supported and unsupported samples were characterized by X-Ray Diffraction (XRD), N2-physisorption, Transmission Electron Microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS). The modified mesostructured support ensures a better dispersion of the active phases and led to a partial presence of highly reactive Pt(II) species in the case of platinum-based samples. Whatever the oxidation reaction, these latter demonstrate higher conversions compared to palladium-based ones. The presence of Pt(II) species provided a high catalytic performance, with a total degradation of both VOC probe molecules at temperatures lower than 170 °C. Such temperatures have not been recorded before for NaY supported materials.

On understanding the sequential post-synthetic microwave-assisted dealumination and alkaline treatment of Y zeolite

Systematic investigation was performed to understand the change of physiochemical properties in Y zeolite after the microwave (MW)-assisted dealumination (using mineral acid, HCl, and chelating agent, EDTA4−) and the subsequent alkaline treatment (of the dealuminated zeolites). The findings show that the combination of EDTA4− and hydrogen ions was effective to achieve dealumination of zeolite Y under MW irradiation, which formed complexed framework Al, instead of extra-framework Al (EFAl), to be extracted readily by the sequential alkaline treatment for mesopore formation. Conversely, under the same MW condition, the use of HCl encouraged the formation of EFAl species in the defective Y framework, which did not benefit the mesopore formation. The disclose of the distinct dealumination mechanisms of the MW-assisted method using different agents can benefit the further development of effective MW methods for dealumination of zeolites and/or making mesoporous zeolites.

Thermo-catalytic co-pyrolysis of ironbark sawdust and plastic waste over strontium loaded hierarchical Y-zeolite

The objective of this research is to synthesize hierarchical strontium loaded Y-zeolite and study its application for ironbark (IB) and plastic waste (PW) co-pyrolysis. Commercial parent Y-zeolite (Si/Al = 2.48) was modified via sequential dealumination-desilication using citric acid and NaOH. Further, strontium (8 wt %) was loaded into the modified Y-zeolite via wet and dry impregnation methods. The prepared catalyst was characterized by N2 adsorption-desorption isothermal, field emission scanning electron microscopy (FESEM) combined with energy dispersive x-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analyzer (TGA). After dealumination (treatment using 0.1 M of citric acid), the external surface area and Si/Al ratio increased from 53.5 to 147.4 m2/g and 2.48 to 5.36, respectively. However, the sequential desilication treatment reduced Si/Al ratio from 5.36 to 2.57. In addition, Y-zeolite enhanced the total aromatic percentage and reduced the acidic group in co-pyrolysis oil.

Selective conversion of methanol to propylene over highly dealuminated mordenite: Al location and crystal morphology effects

The growing consumption of light olefins has stimulated intensive researches on methanol to olefin (MTO) process which possesses great advantages for coal conversion to value-added chemicals in an environmentally benign way. The catalysts commonly used for MTO process faces several challenges such as poor selectivity control, low hydrothermal stability and short lifetime. In the present study, we prepared a series of mordenite zeolites with variable Al contents (Si/Al molar ratios of 51−436) by a sequential dealumination treatment of air-calcination and acid leaching. The textural properties, acidity and Al location before and after the dealumination treatment have been systematically studied and their effect on MTO especially the methanol to propylene (MTP) performance was thoroughly investigated. The mordenite zeolites with the Si/Al ratios over 150 selectively catalyzed methanol conversion in the MTP pathway, providing a high propylene selectivity of 63% and propylene/ethylene ratio of > 10. Compared to the low-silica MOR catalysts, highly dealuminated MOR showed much higher stability and longer lifetime, which can be further enhanced via harsh hydrothermal pretreatment. Furthermore, the lifetime was highly related to the crystal size along c-axis. The excellent performance of highly dealuminated MOR is likely ascribed to the mesopores formed upon dealumination and the scarce Al sites located in the T sites shared by the 8-member ring (MR) side pockets and 12-MR pore channels.

Correction to: Sequential Microwave-Assisted Dealumination and Hydrothermal Alkaline Treatments of Y Zeolite for Preparing Hierarchical Mesoporous Zeolite Catalysts

The original version of this article unfortunately contained an error. The authors would like to correct the error with this erratum.

Sequential Microwave-Assisted Dealumination and Hydrothermal Alkaline Treatments of Y Zeolite for Preparing Hierarchical Mesoporous Zeolite Catalysts

A novel post-synthetic method combining the microwave (MW)-assisted dealumination and hydrothermal (HT) alkaline treatment for obtaining mesoporous Y zeolite catalysts is presented. In the first-step MW-assisted dealumination of the pristine Y zeolite, both the mineral acid (i.e. hydrochloric acid, HCl) and organic carboxylic acids (e.g. oxalic and diethylenetriaminepentaacetic acid) were used (all at 0.16 M), and their effects on the physical and chemical properties of the resulting modified zeolites (after the identical HT alkaline treatment using 0.2 M sodium hydroxide solution) are studied in detail by comprehensive characterisation of the bulk silicon-to-aluminium (SAR) ratio, crystallinity and textural properties. The findings show that, in the developed sequential method, (i) HCl was only effective to achieve the hydrolysis of the zeolite, (ii) carboxylic acids with the function of chelation was very capable of extracting Al species and creating mesopores, and (iii) the mesopores formation is a function of the number of coordination sites in the carboxylic acid. The hierarchical feature of the mesopores in the modified zeolites (using carboxylic acids) was probed by the model reaction of aldol condensation of 1-heptanal with benzaldehyde for the selective formation of jasminaldehyde. The normalised selectivity to jasminaldehyde (with respect to the strong acidity) was proportionally related to the specific mesopores volume of the zeolites, revealing hierarchical porous networks in the relevant modified Y zeolites and indicating the effect of hierarchical mesopores in the zeolites on their catalytic performance.

Effect of the Post‐Treatment of HZSM‐5 on Catalytic Performance for Methanol to Aromatics

AbstractThe preparation of aromatic by methanol was the most effective way for rational utilization of resources. However, the catalyst for MTA reaction has not yet been successfully studied. Therefore, highly active and shape‐selective HZSM‐5 zeolite‐based catalysts were designed and synthesized by post‐treatments of desilication, dealumination, surface‐passivation and hydrothermal treatment tuning pore structure and acid amount and acid concentration of catalysts. XRD, SEM, TEM, BET, NH3‐TPD and Py‐IR were used for research and analysis the structure‐activity relationship between the catalysts and MTA reaction. The results showed that the total acid amount of catalyst shown a significant role in increasing the BTX selectivity. The selectivity of aromatics increased from 33 % to 58.1 % after hydrothermal treatment compared to the parent HZSM‐5 zeolite due to the decreased of total acid amount. Nevertheless the weak acid sites were crucial in increasing the p‐xylene selectivity. The selectivity of p‐xylene reached 63.8 % and 70.1 % after hydrothermal treatment and surface‐passivation due to the increased of weak acid sites, respectively. Modified HZSM‐5 zeolite‐base catalysts showed good application prospects in producing aromatics from methanol.

Using ultrasound to improve the sequential post-synthesis modification method for making mesoporous Y zeolites

Mesoporous Y zeolites were prepared by the sequential chemical dealumination (using chelating agents such as ethylenediaminetetraacetic acid, H4EDTA, and citric acid aqueous solutions) and alkaline desilication (using sodium hydroxide, NaOH, aqueous solutions) treatments. Specifically, the ultrasound-assisted alkaline treatment (i.e., ultrasonic treatment) was proposed as the alternative to conventional alkaline treatments which are performed under hydrothermal conditions. In comparison with the hydrothermal alkaline treatment, the ultrasonic treatment showed the comparatively enhanced efficiency (with the reduced treatment time, i.e., 5 min vs. 30 min, all with 0.2 mol·L−1 NaOH at 65°C) in treating the deal-uminated Y zeolites for creating mesoporosity. For example, after the treatment of a dealuminated zeolite Y (using 0.1 mol·L−1 H4EDTA at 100°C for 6 h), the ultrasonic treatment produced the mesoporous zeolite Y with the specific external surface area (Sexternal) of 160 m2·g·−1and mesopore volume (Vmeso) of 0.22 cm3·g−1, being slightly higher than that by the conventional method (i.e., Sextemal= 128 m2·g−1 and Vmeso = 0.19 cm3·g−1). The acidic property and catalytic activity (in catalytic cracking of n-octane) of mesoporous Y zeolites obtained by the two methods were comparable. The ultrasonic desilication treatment was found to be generic, also being effective to treat the dealuminated Y zeolites by citric acid. Additionally, the first step of chemical dealumination treatment was crucial to enable the effective creation of mesopores in the parent Y zeolite (with a silicon-to-aluminium ratio, Si/Al = 2.6) regardless of the subsequent alkaline desilication treatment (i.e., ultrasonic or hydrothermal). Therefore, appropriate selection of the condition of the chemical dealumination treatment based on the property of parent zeolites, such as Si/Al ratio and crystallinity, is important for making mesoporous zeolites effectively.

Novel hierarchical HZSM-5 zeolites prepared by combining desilication and steaming modification for converting methanol to propylene process

The effect of mesoporosity formation and acidity modification have been investigated by desilication and combined desilication–dealumination treatments over highly siliceous zeolite HZSM-5 (Si/Al = 200) and its catalytic performance has been studied in the conversion of methanol to propylene (MTP) reaction. Desilication of a conventional microporous HZSM-5 catalyst was performed using NaOH, mixtures of NaOH and tetrapropylammonium hydroxide (TPAOH), and mixtures of NaOH and tetrabutylammonium hydroxide (TBAOH) with different ratios. Subsequent mild steaming treatment has been used to modify acidity of the selected samples. The physicochemical properties of all samples were characterized by XRD, FE-SEM, BET and NH3-TPD methods. Textural and acidity properties confirmed that TBAOH is more effective than TPAOH in the mesoporosity formation, micropore volume preservation, and acidity modification. Steaming treatment after desilication over the sample with TPAOH/(NaOH + TPAOH) ratio of 0.4, led to increase in selectivities to propylene from 38.4 to 41.3%, and total light olefins from 69.4 to 76.6%, while it led to decrease in C5+ components selectivity from 14.8 to 10.1%. The combined alkaline-steam treatment over the sample with TBAOH/(NaOH + TBAOH) ratio of 0.2 compared to the parent one led to considerable higher selectivities to propylene (44.8 vs. 30.7%), total light olefins (84.1 vs. 57.9%), as well as lower selectivities to C5+ components (7.4% vs. 27.1%). Moreover, this sample showed double lifetime (830 h) in MTP reaction compared to the conventional micropore ZSM-5 catalyst (425 h). The results showed that desilication led to a remarkable mesoporosity development, while steaming treatment generally influenced on the HZSM-5 acidity. Therefore, the combined alkaline-steam treatment leads to HZSM-5 zeolite formation with tailored pore architecture and surface acidic properties.

Origin and Structural Characteristics of Tri-coordinated Extra-framework Aluminum Species in Dealuminated Zeolites.

Post-synthetic dealumination treatment is a common tactic adopted to improve the catalytic performance of industrialized zeolitic catalysts through enhancements in acidity and stability. However, among the possible extra-framework aluminum (EFAL) species in dealuminated zeolites such as Al3+, Al(OH)2+, Al(OH)2+, AlO+, AlOOH, and Al(OH)3, the presence of tri-coordinated EFAL-Al3+ species, which exhibit large quadrupolar effect due to the lack of hydrogen-bonding species, was normally undetectable by conventional one- and two-dimensional 1H and/or 27Al solid-state nuclear magnetic resonance (SSNMR) techniques. By combining density functional theory (DFT) calculations with experimental 31P SSNMR using trimethylphosphine (TMP) as the probe molecule, we report herein a comprehensive study to certify the origin, fine structure, and possible location of tri-coordinated EFAL-Al3+ species in dealuminated HY zeolite. The spatial proximities and synergies between the Brønsted and various Lewis acid sites were clearly identified, and the origin for the observed EFAL-Al3+ species with ultra-strong Lewis acidity was deduced to be at the expense of adjacent Brønsted acid sites. The excellent performance of such tri-coordinated EFAL species was furthermore confirmed by glucose isomerization reactions.

Optimization of Preparation of Zeolite Y Dealuminate Catalysts for Glycerol Conversion to Glycerol Mono Laurate

This Research has been done to analyze Zeolite Y CBV 712 as a catalyst. Zeolite Y CBV 712 was dealuminated by treating it with H2SO4 solution, with 3 – 8 M concentration at 40 – 60 oC. The dealumination treatment runs for 4 hours. Then, dealuminated zeolite was calcinated with a furnace for 3 hours with temperature range between 500 – 600 oC. Dealuminated zeolit Y then tested to synthesize Glycerol Mono Laurate (GML). By Analysis of Variance (ANOVA) analyze, indicated that the higher Glycerol Monolaurate yield, X2 factor is the most significance factor, indicating with high F-value (29.60768) and low P-value (0.001600). Objective function from this tests, is used to determine the optimum value between dealumination temperature (X1), acid concentration used (X2) and calcinating temperature (X3). The relation between each operating variables and the responses is shown in mathematical equation below : [see formula in PDF] The optimum condition obtained is 43.25oC for dealumination temperature, 5.45 M for acid concentration and 614oC for calcination temperature. According to the optimum condition obtained, the glycerol monolaurate yield obtained is 59.470%.

Selective Isomerization of n-Butane over Mordenite Nanoparticles Fabricated by a Sequential Ball Milling–Recrystallization–Dealumination Route

For the first time, a sequential fabrication step involving mechanochemistry, recrystallization, and dealumination was developed to convert low-cost natural zeolites to mordenite (MOR) nanoparticles. Natural zeolites are mostly found having poor textural properties and a high aluminum content, which are not suitable for most industrial catalytic reactions. The parent natural zeolites within the size of 1–10 μm were treated by ball milling to obtain nanosized particles with size in the range of 20–160 nm. The nitrogen physisorption study revealed that the external surface area and intercrystalline mesopore volume of the milled nanoparticles increased by 4- and 7-fold, respectively. Recrystallization by hydrothermal treatment in basic silicate solution was applied to recover the MOR crystallinity at 170 °C for 6 h. The recrystallized MOR samples were further subjected to acid dealumination treatment over different periods. The H-MOR samples were evaluated in a fixed-bed reactor for n-butane isomerization. T...

Ethylene production via catalytic dehydration of diluted bioethanol: A step towards an integrated biorefinery

After a preliminary thermodynamic investigation, proper operating conditions have been selected to maximise ethylene productivity by ethanol dehydration and limit side products such as coke and higher olefins or oxygenates. We focused on the possibility to operate with a diluted bioethanol solution (ca. 50wt%), which represents a promising and convenient raw material, obtainable by simple flash concentration of the fermentation broth. Furthermore, water addition to the ethanol dehydration reactor may help preventing catalyst coking and diethyl ether formation, although affecting the thermodynamic products distribution. A proof of concept for an ethanol dehydration process using diluted ethanol is also provided through process simulation.Catalysts based on a BEA zeolite have been compared, characterised by different acidity imparted by dealumination treatments. Ni addition in variable loading helped suppressing undesired byproducts, difficult to separate from ethylene. For instance, no trace of diethyl ether nor acetaldehyde has been observed for the Ni-loaded samples under optimised working conditions.Catalyst characterisation by FT IR allowed correlating a high selectivity to ethylene with the acid sites nature of the catalyst, whereas the presence of extraframework Lewis acidic sites induced faster coke formation.Durability was finally checked on the most active and selective catalyst evidencing stable operation for 80h-on-stream and without evidence of coke deposition, as determined after characterisation of the spent samples. A γ-Al2O3 catalyst has been tested as benchmark under the same conditions.

Effect of multi-step desilication and dealumination treatments on the performance of hierarchical EU-1 zeolite for converting methanol to olefins

Multi-steps sequential alkaline and acid treatments were applied on EU-1 zeolite to develop more mesoporosity surface area and to offer more active sites. Different concentrations of NaOH (0.1, 0.25 and 0.5 M) were used to treat parent EU-1 with different cyclic times, followed by a treatment with HNO3 (4 M) also for different cycles. The treated and the parent EU-1 samples were assessed on the conversion of methanol to olefins. The multi-step sequential treatments succeed to create more mesopores as compared with single-step treatment. This improvement was confirmed by BET analysis and NLDFT calculations for pore size distribution. The total acidity was measured using TPD and the quality of the active sites was characterized by in situ FTIR spectroscopy of adsorbed pyridine. Solid state NMR was used to study the position of Al in the EU-1 framework. The main advantage of this multi-step treatment is the preservation of EU-1 crystallinity, which was calculated using XRD. The multi-step treatment yielded an increase in the mesoporosity surface area by 24% and an enhancement of the total acidity, up to five times larger than the parent EU-1 crystals. Furthermore, the selectivity of propylene was increased from 0%, in the case of parent EU-1, to 50% of the product stream together with large enhancement of the stability of methanol conversion and life time.

Effect of hierarchical porosity and phosphorus modification on the catalytic properties of zeolite Y

The zeolite Y is considered as a leading catalyst for FCC industry. The acidity and porosity modification play important roles in determining the final catalytic properties of zeolite Y. The alkaline treatment of zeolite Y by dealumination and alkaline treatment with NaOH and NaOH&TBPH was investigated. The zeolites were characterized by X-ray diffraction, low-temperature adsorption of nitrogen, transmission electron microscope, NMR, NH3-TPD and IR study of acidity. Accordingly, the hierarchical porosity and acidity property were discussed systematically. Finally, the catalytic performance of the zeolites Y was evaluated in the cracking of 1,3,5-TIPB. It was found that desilication with NaOH&TBPH ensured the more uniform intracrystalline mesoporosity with higher microporosity, while preserving higher B/L ratio and moderate Brønsted acidities resulting in catalysts with the most appropriated acidity and then with better catalytic performance.

Hierarchical NaY Zeolites for Lactic Acid Dehydration to Acrylic Acid

AbstractThe industrial viability of heterogeneous catalysts for the gas‐phase conversion of lactic acid to acrylic acid will strongly depend on their selectivity and durability. Here, we initially screened various aluminum‐rich zeolites confirming that NaY is the most efficient catalyst for this reaction. This material was modified by sequential dealumination and alkaline treatment attaining a solid featuring a hierarchical distribution of micro‐ and mesopores, reduced Lewis acidity, and increased basicity owing to the presence of well‐dispersed sodium ions interacting with external siloxy groups, as evidenced by in‐depth characterization. These properties were crucial for determining higher selectivity (75 %) and minimizing the activity loss in a 6 h run. Remarkably, the catalyst gained in selectivity and stability upon reuse in consecutive cycles. This was ascribed to the depletion of the stronger basic sites and the clustering of sodium into oxidic particles upon the intermediate calcination.