Effective and selective adsorption of methyl tert-butyl ether on ZSM-5 zeolite: a comparative study.

The extensive use of methyl tert-butyl ether (MTBE) as a gasoline additive has caused serious environmental problems that need to be addressed urgently. The feasibility of remediation of MTBE-contaminated groundwater by ZSM-5 zeolite with SiO2/Al2O3 ratio of 50/130/360 was explored. The SiO2/Al2O3 ratio had a great influence on the physicochemical properties and structure, as well as the adsorption and mass transfer of MTBE on ZSM-5. The adsorption of MTBE on zeolites with SiO2/Al2O3 ratios of 50 and 130/360 followed the Langmuir and Freundlich models, respectively, and was controlled by different mass transfer processes. The morphology and adsorption capacity of ZSM-5 (50) and ZSM-5 (130) differed significantly, while the differences between ZSM5-(130) and ZSM-5 (360) were less pronounced. ZSM-5 (360) had higher adsorption capacity and adsorption efficiency for MTBE, and the larger BET surface area, pore volume and stronger hydrophobicity were the key factors to promote MTBE adsorption. Compared to activated carbon (AC), ZSM-5 (360) was more effective for MTBE removal at low concentrations (≤200 mg·L-1) and had the advantage of selective adsorption of MTBE with the addition of BTEX. In column adsorption, decreasing the concentration had opposite effects on MTBE removal by ZSM-5 and AC. At 5-10 mg·L-1, ZSM-5 (360) column reduced effluent concentration and improved bed utilization and removal efficiency.

Determination of Free Fatty Acids in Krill Oil during Storage Based on NH2-MMS.

In this study, amino-modified micro-mesoporous silica (NH2-MMS) with hierarchical pores was prepared by modifying micro-mesoporous silica ZSM-5 with 3-aminopropyltriethoxysilane and used as an adsorbent in solid-phase extraction to analyze free fatty acids (FFAs) in krill oil during storage for an initial time. The Brunner Emmet Teller adsorption experiment and Fourier transform infrared spectroscopy demonstrate that NH2-MMS, with a hierarchical pore structure, was successfully synthesized. The adsorption experiments, especially static adsorption, indicate that the absorption ability of the prepared NH2-MMS, with a hierarchical pore structure, toward FFAs was better than that of traditional amino-modified mesoporous silica (SBA-15) with a mesoporous structure at all temperature and concentrations. Fairly low limits of detection (0.06-0.15 µg g-1), acceptable recoveries (85.16-94.31%), and precision (0.08-5.26%) were attained under ideal circumstances. Moreover, NH2-MMS has the advantages of easy preparation and being environmentally friendly. As a result, this method offers an alternative to the current method for determining FFAs in different kinds of oil specimens.

Selective regulation of products for guaiacol hydrodeoxygenation by adjusting type and acidity of supports.

Upgrading lignin-oil into advanced fuels or chemicals has been widely studied in recent years. To understand the effect of support type and acidity on the hydrodeoxygenation (HDO) of guaiacol (lignin-oil model compound), Ni-based catalysts were prepared with SiO2, Al2O3 and ZSM-5 as supports, respectively. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption desorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Pyridine adsorption Fourier-transform infrared (Py-IR). The research results indicate that selective regulation of guaiacol hydrogenation products can be achieved by changing the type and acidity of support. Cyclohexanol is the main product over Ni/SiO2, while cyclohexane is the main product over Ni/ZSM-5 series catalysts. Moreover, as the Si/Al ratio increases, the catalytic activity of Ni/ZSM-5 slightly decreases, and the yield of cyclohexane also decreases. The Brønsted acidity of the support is the key to promoting the conversion of cyclohexanol to cyclohexane. The formation of NiAl2O4 is the main reason for the relatively low activity of Ni/Al2O3. The conversion of guaiacol is as high as 99.2 %, and the yield of cyclohexane is as high as 86.6 % over Ni/ZSM-5(Si/Al = 27). In addition, complete conversion of guaiacol and 92.6 % yield of cyclohexanol were achieved over Ni/SiO2. More importantly, Ni/SiO2 and Ni/ZSM-5(27) are suitable for aromatic substrates with different substituents, respectively.

Y and ZSM-5 Hierarchical Zeolites Prepared Using a Surfactant-Mediated Strategy: Effect of the Treatment Conditions.

Diffusional limitations associated with zeolite microporous systems can be overcome by developing hierarchical zeolites, i.e., materials with a micro- and mesoporous framework. In this work, Y and ZSM-5 zeolites were modified using a surfactant-mediated hydrothermal alkaline method, with NaOH and cetyltrimethylammonium bromide (CTAB). For Y zeolite, after a mild acidic pretreatment, the effect of the NaOH+CTAB treatment time was investigated. For ZSM-5 zeolite, different concentrations of the base and acid solutions were tested in the two-step pretreatment preceding the hydrothermal treatment. The properties of the materials were studied with different physical-chemical techniques. Hierarchical Y zeolites were characterized by 3.3-5 nm pores formed during the alkaline treatment through the structure reconstruction around the surfactant aggregates. The effectiveness of the NaOH+CTAB treatment was highly dependent on the duration. For intermediate treatment times (6-12 h), both smaller and larger mesopores were also obtained. Hierarchical ZSM-5 zeolites showed a disordered mesoporosity, mainly resulting from the pretreatment rather than from the subsequent hydrothermal treatment. High mesoporosity was obtained when the concentration of the pretreating base solution was sufficiently high and that of the acid one was not excessive. Hierarchical materials can be obtained for both zeolite structures, but the pretreatment and treatment conditions must be tailored to the starting zeolite and the desired type of mesoporosity.

Confined Cu Single Sites in ZSM-5 for Photocatalytic Hydroxylation of Benzene to Phenol.

Zeolites with band-like charge transport properties have exhibited their potential activities in sensing, optics, and electronics. Herein, a precisely designed Cu@ZSM-5 catalyst is presented with an ultra-wide bandgap of 4.27 eV, showing excellent photocatalytic activity in hydroxylation of benzene with benzene conversion 27.9% and phenol selectivity 97.6%. The SXRD and Rietveld refinement results illustrate that Cu@ZSM-5 has an average of 0.8 Cu atoms per unit cell and the single Cu atoms located in the cross-section of the sinusoidal and straight channels. XANES and EXAFS further demonstrate that the Cu atoms have an oxidation state of +2, coordinated with three OMFI-framework atoms and one ─OH group. Detailed characterizations demonstrate that the Cu@ZSM-5 with tailored bandgap is able to enhance the photoinduced electron-hole separation and hence promote selective hydroxylation of benzene to phenol via the superoxide radical route. This work may open a new way for designing electrically conductive zeolite-supported photocatalysts.

Introducing Molecular Sieve into Activated Carbon to Achieve High-Effective Adsorption for Ethylene Oxide.

Presently, ethylene oxide (EtO) is posing a significant threat to both human health and the environment due to occasional or deliberate emissions. However, few works so far have focused on this issue. It is urgent to explore novel and effective technology to protect against the threat of EtO. Herein, a series of AC/ZSM-5 composites were prepared to improve the adsorption performance for EtO, evaluated by dynamic breakthrough experiments. Particularly, the AC/ZSM-20% composite demonstrated a more excellent adsorption capacity of 81.9 mg/g at 25 °C and 50% RH than that of pristine AC and ZSM-5 with 32.5 and 52.3 mg/g, respectively. Moreover, the adsorption capacity of the AC/ZSM-20% composite remained constant even after five adsorption-desorption cycles. The adsorption mechanism of EtO on the composite is further revealed by density functional theory (DFT) calculations.

High-performance ratiometric fluorescence detection and removal of tetracycline in milk based on CDs@ZSM-5:Eu3.

Exploring materials with the dual functionality of detecting and removing tetracycline (TC) residues is crucial because of the environmental and health risks posed by antibiotic overuse. This study introduces a dual-emissive luminescent probe, CDs@ZSM-5:Eu3+, created through a solvent-free method combined with subsequent Eu3+ion exchange. The nanocomposite's blue emission, originating from carbon dots (CDs), is quenched by TC via an internal filtering effect, while an antenna effect triggers a strong red fluorescence of a TC-Eu3+chelate. The ratiometric fluorescence changes in CDs@ZSM-5:Eu3+ endow a self-calibrated sensing mechanism for TC, offering a low detection limit of 5.04 nM and a broad detection range of 0.01-50 µM. Demonstrated in real milk samples, the probe exhibits high selectivity and accuracy in detecting TC. The nanocomposite also displayed an impressive TC removal capacity of 238.1 mg g-1 in water, ascribing to the enrichment and electrostatic attraction effects of ZSM-5 toward TC molecules. This research offers a facile strategy for constructing multifunctional zeolite-based hybrids for simultaneous TC detection and removal from aqueous solutions.

Production of Jet Fuel Range Aromatics by Alkylation of Benzene with Olefins over Bifunctional Ga/ZSM-5 Catalyst.

Aromatic components of C8-C15 are playing indispensable roles in multi-functional properties of jet fuel. Here, we reported the controllable alkylation of benzene with mixed olefins of ethylene and propylene toward C8-C15 aromatic hydrocarbons for jet fuels over the bifunctional Ga/ZSM-5 catalyst. The resultant 2Ga/ZSM-5 exhibited a superior selectivity of 86.4% (yield of 55.5%) to C8-C15 range aromatics, at benzene conversion of 40.3%, ethylene and propylene conversion of 99.5% and 99.2%, respectively. The incorporation of Ga species could effectively weaken the strong acid sites of ZSM-5 and endow 2Ga/ZSM-5 catalyst with appropriate acidity, therefore facilitating the benzene alkylation process and suppressing the undesired hydrogen transfer or aromatization side reactions as well, thus improving the yield of desired C8-C15aromatics for jet fuels. This work provided insight into the development of promising bifunctional catalyst for the oriented transformation of biomass-derived chemicals to aviation fuels.

Tuning the morphology and textural properties of ZSM-5 additive for co-cracking of waste plastics with vacuum gas oil to light olefins.

Typical cracking catalysts, called equilibrium catalyst (E-Cat) are ultra-stable Y (USY) zeolite often used with 15% commercial ZSM-5 zeolite additive (ZSM-5(COM)) to boost olefin yield. In this study, similar additive zeolites with different pore sizes and acidic character were synthesized by rapid ageing of precursor solution and used in the co-cracking of low-density polyethylene (LDPE) and heavy vacuum gas oil (HVGO). Three ZSM-5 zeolites additives with Si/Al ratio 25 (ZSM-5(25)), 50 (ZSM-5(50)) and 75 (ZSM-5(75)) were synthesized and combined with E-Cat to form E-Cat/ZSM-5(25), E-Cat/ZSM-5(50) and E-Cat/ZSM-5(75) respectively. The E-Cat/ZSM-5(50) has slightly better endothermic conversion (cracking) of a mixture of dissolved LDPE and HVGO into H2, C1 to C4 gases and C2-C4 light olefins (total conversion of E-Cat 80.0%, E-Cat/ZSM-5(COM) 75.0% and E-Cat/ZSM-5(50) 83.7% respectively), with different gas, liquid and coke distributions. The E-Cat/ZSM-5(75) has 81% conversion, and highest yield of light olefins (38.4%). Structural (surface area, pore size) and chemical (acid sites) characteristics of the synthetized ZSM-5(75) zeolite explain the observed higher light olefin selectivity by different and competing catalytic routes. The ZSM-5(75) has demonstrated to be a good zeolite additive for converting dissolved plastic in HVGO into light olefins.

Pervaporation Dehydration Mechanism and Performance of High-Aluminum ZSM-5 Zeolite Membranes for Organic Solvents.

Membrane-based pervaporation (PV) for organic solvent dehydration is of great significance in the chemical and petrochemical industries. In this work, high-aluminum ZSM-5 zeolite membranes were synthesized by a fluoride-assisted secondary growth on α-alumina tubular supports using mordenite framework inverted (MFI) nanoseeds (~110 nm) and a template-free synthesis solution with a low Si/Al ratio of 10. Characterization by XRD, EDX, and SEM revealed that the prepared membrane was a pure-phase ZSM-5 zeolite membrane with a Si/Al ratio of 3.8 and a thickness of 2.8 µm. Subsequently, two categories of PV performance parameters (i.e., flux versus separation factor and permeance versus selectivity) were used to systematically examine the effects of operating conditions on the PV dehydration performance of different organic solvents (methanol, ethanol, n-propanol, and isopropanol), and their PV mechanisms were explored. Employing permeance and selectivity effectively disentangles the influence of operating conditions on PV performance, thereby elucidating the inherent contribution of membranes to separation performance. The results show that the mass transfer during PV dehydration of organic solvents was mainly dominated by the adsorption-diffusion mechanism. Furthermore, the diffusion of highly polar water and methanol molecules within membrane pores had a strong mutual slowing-down effect, resulting in significantly lower permeance than other binary systems. However, the mass transfer process for water/low-polar organic solvent (ethanol, n-propanol, and isopropanol) mixtures was mainly controlled by competitive adsorption caused by affinity differences. In addition, the high-aluminum ZSM-5 zeolite membrane exhibited superior PV dehydration performance for water/isopropanol mixtures.

Phosphorus-Water Interaction Drives Active Center Evolution into the Water-Adaptive Structure in the High-Humidity NH3-SCR Reaction.

The impact of water on catalyst activity remains inconclusive due to its dependence on the specific reaction environment. To maximize the exploitation of water's promoting effect, we employed ammonia selective catalytic reduction (NH3-SCR) as a probe reaction and proposed a phosphorus modification strategy for Cu-ZSM-5 catalysts. The objective of this approach was to construct water-adaptive microstructures through directional arrangement. To investigate the effect of phosphorus on the transformation of framework copper sites in humid environments, we conducted comprehensive characterizations and density functional theory calculation. Results reveal that water molecules cleave the oxygen bridges between phosphorus oxide and copper, leading to the formation of active isolated [Cu(OH)]+ groups and phosphate. The phosphate species weaken the interaction between exchanged Cu2+ groups and the zeolite framework, leading to the generation of highly migratory hydrated Cu2+ species. This work will potentially guide the rational design of water-adaptive catalysts for gas pollution abatement in a humid environment.

Mechanistic investigation of methanol-to-olefins conversion catalyzed by H-ZSM-5 zeolite: a DFT study.

CONTEXT: The mechanisms for the formation of the first C - C bond and lower olefins on methanol to olefins (MTO) conversion on H-ZSM-5 had been focused in dispute. In this paper, density functional theory has been used to study the reaction mechanisms of methanol to olefins on ZSM-5. The configurations of reactants, intermediates, products and transition state of the numerous reactions involved in such a process have been optimized, as well as the elementary reactions related to these configurations were determined by the calculation of corresponding activation energy barriers and reaction heats. Here, two different kinds of the mechanisms were proposed for the formation of dimethyl ether (DME), one involving an associative interaction of two methanol molecules with the zeolite Brønsted acid sites and the other occurring via a surface methoxy species and a methanol molecule. A critical intermediate of the methoxy methyl cation was theoretically verified by the reaction of the methoxy species and dimethyl ether. Besides, it was found that the first intermediates containing a C - C bond were 1,2-dimethoxyethane and 2-methoxy-ethanolare, in which the former was formed from methoxy species with dimethyl ether and the latter was formed from methanol by onium ions((CH3)2O+CH2CH2OCH3), respectively. For the whole reaction mechanism, the results in this paper indicated that the ethene formation is more favorable than propylene formation due to the low activation energy barrier for ethene formation (123.49 vs. 162.09 kJ.mol-1). From these calculations, it would be concluded that ethene is the first alkene product that induces the occurrence of the hydrocarbon pool mechanism. METHODS: All the periodic density function theory (DFT) calculations were performed by the Vienna Ab Initio Simulation package (VASP). The interaction between nucleus and valence electron was described using the pseudopotentials found in the projector augmented wave (PAW) method. PBE-D3 was used in the whole DFT calculations and CI-NEB was used to locate transition state.

Unraveling the Synergistic Mechanism of Ir Species with Various Electron Densities over an Ir/ZSM-5 Catalyst Enables High-Efficiency NO Reduction by CO.

Selective catalytic reduction using CO as a reducing agent (CO-SCR) has exhibited its application potential in coal-fired, steel, and other industrial sectors. In comparison to NH3-SCR, CO-SCR can achieve synergistic control of CO and NO pollutants, making it a powerful denitrification technology that treats waste with waste. Unfortunately, the competitive adsorption of O2 and NO on CO-SCR catalysts inhibits efficient conversion of NOx under O2-containing conditions. In this work, we obtained two Ir sites with different electron densities, Ir1 single atoms in the oxidized Irδ+ state and Ir0 nanoparticles in the metallic state, by controlled pretreatment of the Ir/ZSM-5 catalyst with H2 at 200 °C. The coexistence of Ir1 single atoms and Ir0 nanoparticles on ZSM-5 creates a synergistic effect, which facilitates the reduction of NO through CO in the presence of O2, following the Langmuir-Hinshelwood mechanism. The ONNO dimer is formed on the Ir1 single atom sites and then spills over to the neighboring Ir0 nanoparticles for subsequent reduction to N2 by CO. Specifically, this tandem reaction enables 83% NO conversion and 100% CO conversion on an Ir-based catalyst at 250 °C under 3% O2.

High valuable wax from multilayer film packaging wastes using solid catalyst via pyrolysis process.

Multilayer film packaging (MLP) waste was decomposed completely at 500 °C. Catalysts were employed to convert residue polymer to waxes via pyrolysis at 500 °C. The activities achieved from using mordenite (Si/Al = 10), H-ZSM-5 (Si/Al = 25), MCM-41, and Al-MCM-41 (Si/Al ratio of 25, 50, and 75) catalysts were studied. The yield and property of the wax were improved with the use of the catalysis with various acidity and porous structure. The low yield of the waxes, when using mordenite and H-ZSM-5 catalysts, was caused by the microporous structure and strong acidic properties of the catalysts resulting in larger amount of gas production. The MCM-41 catalyst modified with various aluminum content raised the wax yield to 60 %. Al-MCM-41(50) produced the largest amount of wax when compared to Al-MCM-41(25), Al-MCM-41(75), and MCM-41. The mild acidity and mesoporous structure of Al-MCM-41(50) significantly enhanced the paraffins structure of the obtained waxes over other structures, while lower Si/Al ratios favored the conversion of paraffins toward olefin structure. The pyrolysis of MLP with Al-MCM-41(50) produced paraffins and olefins with the middle carbon ranging (C11-20) which were similar quality to pharmaceutical grade of petroleum wax. The spent catalysts of Al-MCM-41 series gradually decreased in wax yield and paraffins composition during the sequential MLP pyrolysis; however, the activity of catalysts was recovered after calcination of the spent catalysts. Furthermore, the viscosity of waxes obtained from Al-MCM-41(50) was 2384 Pa.s at 25 °C similar to the viscosity from commercial petroleum jelly base of 2333 Pa.s.

Understanding the Structural and Catalytic Properties of Al(IV)-2 Acidic Sites of ZSM-5.

It is crucial to identify the structures of active sites to understand how catalysts function and to use that understanding to develop better catalytic materials. ZSM-5 zeolites with dominant Al(IV)-2 sites have been developed in this work. 1H-27Al 2D HMQC and 2D 1H TQ(DQ)-SQ NMR experiments have been performed to investigate the structural properties of this acidic site. The Al(IV)-2 sites have Brønsted and Lewis acid characteristics. The catalytic performance of Al(IV)-2 sites has been tested by n-dodecane cracking reactions. The catalytic results show that the Brønsted acidic strength of the Al(IV)-2 sites is comparable to that of the Al(IV)-1 sites, but the Al(IV)-2 sites' Lewis acid characteristics provide extra catalytic activity. We have gained valuable insights into the characteristics of Al(IV)-2 acid sites within these materials.

Selective Heterogeneous Fenton Degradation of Formaldehyde Using the Fe-ZSM-5 Catalyst.

As a toxic Volatile Organic Pollutant (TVOC), formaldehyde has a toxic effect on microorganisms, consequently inhibiting the biochemical process of formaldehyde wastewater treatment. Therefore, the selective degradation of formaldehyde is of great significance in achieving high-efficiency and low-cost formaldehyde wastewater treatment. This study constructed a heterogeneous Fe-ZSM-5/H2O2 Fenton system f or the selective degradation of target compounds. By immobilizing Fe3+ onto the surface of a ZSM-5 molecular sieve, Fe-ZSM-5 was prepared successfully. XRD, BET and FT-IR spectral studies showed that Fe-ZSM-5 was mainly composed of micropores. The influences of different variables on formaldehyde-selective heterogeneous Fenton degradation performance were studied. The 93.7% formaldehyde degradation and 98.2% selectivity of formaldehyde compared with glucose were demonstrated in the optimized Fenton system after 360 min. Notably, the resultant selective Fenton oxidation system had a wide range of pH suitability, from 3.0 to 10.0. Also, the Fe-ZSM-5 was used in five consecutive cycles without a significant drop in formaldehyde degradation efficiency. The use of reactive oxygen species scavengers indicated that the hydroxyl radical was the primary active species responsible for degrading formaldehyde. Furthermore, great degradation performance was acquired with high concentrations of formaldehyde for this system, and the degradation efficiency was more than 95.0%.

Rational Design of Fe Single Sites Supported on Hierarchical Zeolites via Atomic Layer Deposition for Few-Walled Carbon Nanotube Production.

Metal single-site catalysts have recently played an essential role in catalysis due to their enhanced activity, selectivity, and precise reaction control compared to those of conventional metal cluster catalysts. However, the rational design and catalytic application of metal single-site catalysts are still in the early stages of development. In this contribution, we report the rational design of Fe single sites incorporated in a hierarchical ZSM-5 via atomic layer deposition (ALD). The designer catalysts demonstrated highly dispersed Fe species, predominantly stabilized by oxygen atoms in the zeolite framework at terminal, isolated, and vicinal silanol groups within the micropores and external surfaces of the zeolite. The successful incorporation of highly thermally stable and uniform Fe single sites into hierarchical zeolite through ALD represents a significant advancement in few-walled carbon nanotube production. The inner and outer diameters of produced CNTs are approximately 4.4 ± 2.4 and 8.6 ± 1.8 nm, respectively, notably smaller than those produced via traditional impregnated catalysts. This example emphasizes the concept of rational design of a single Fe site dispersed on a hierarchical ZSM-5 surface, which is anticipated to be a promising catalyst for advancing catalytic applications.

Enhanced Lithium-Ion Transport in Lithium Metal Batteries Using ZSM-5 Nanosheets Hybridized Solid Polymer Electrolytes.

Solid polymer electrolytes (SPEs) are the key components of lithium metal batteries to overcome the obstacle of insecurity in conventional liquid electrolytes; however, the trade-off between their ionic conductivity and mechanical properties remains a significant challenge. In this work, two-dimensional ZSM-5 nanosheets as fillers are incorporated into a poly(ethylene oxide) (PEO) matrix and lithium salts to obtain composite polymer electrolytes (CPEs). The improved physicochemical and electrochemical properties of the CPE membranes are characterized in full detail. Stripping/plating measurements in symmetric Li/Li cells and cyclic charge/discharge tests are performed to investigate the cyclability and stability of the CPEs. All-solid-state LiFePO4/Li batteries deliver excellent cycling performance with an initial discharge capacity of 152.3 mAh g-1 and 91.4% capacity retention after 200 cycles at 0.2 C, with a discharge specific capacity of 118.8 mAh g-1 remaining after 350 cycles at 0.5 C. Therefore, CPEs containing ZSM-5 nanosheets are a promising option for all-solid-state lithium-ion batteries.

Enhancing the selectivity for light olefins through catalytic cracking of n-hexane by phosphorus doping on lanthanum-modified ZSM-5.

Naphtha, as the primary raw material in the production of light olefins, could well accommodate their increasing demand through the energy-efficient process of catalytic cracking with ZSM-5. In the current work, different amounts of lanthanum and phosphorous were loaded on ZSM-5 using the wet impregnation method to tune the acidic properties of ZSM-5 for selective catalytic cracking of n-hexane to produce light olefins. Various characterization techniques such as X-ray diffraction (XRD), Al nuclear magnetic resonance (NMR), temperature-programmed desorption of NH3 (NH3-TPD), Py-Fourier transform infra-red (Py-FTIR), inductively coupled plasma optical emission spectroscopy (ICP-OES), N2 adsorption-desorption, X-ray photoelectron spectra (XPS), and scanning electron microscopy were adopted to investigate the modified zeolites. It was found that adding La to ZSM-5 (0.25 wt% to 1 wt%) improved the catalytic life and increased the n-hexane conversion (to 99.7%), while the further addition had a negative impact, reducing the conversion rate and deviating the product selectivity towards a substantial, undesired benzene, toluene, and xylene (BTX) fraction (33%). On the other hand, a 64% selectivity for light olefins was achieved on phosphorous-doped ZSM-5 (at a loading amount of 1 wt%) while reducing the BTX fraction (2.3%) and converting 69% of the n-hexane. A dual metal-modified ZSM-5 with optimal loading amount, 1P0.25LaZ5 (phosphorus 1 wt% and La 0.25 wt%), helped boost the light olefin selectivity to 62% in the tuned Lewis acid sites at an n-hexane conversion of about 77% while decreasing the undesired BTX selectivity to 3% by reducing the number of Brønsted sites. Thus, the current study reveals that tuning the acidic sites of ZMS-5 by dual metal augmentation with P.La is an effective way of controlling the amount of undesirable BTX produced at a stable n-hexane conversion rate and substantial olefin selectivity.

Study on the mechanism of carbon nanotube-like carbon deposition in tar catalytic reforming over Ni-based catalysts.

The use of Ni-based catalysts is a common method for eliminating tar through catalytic cracking. Carbon deposition is the main cause of deactivation in Ni/ZSM-5 catalysts, with filamentous MWCNTs being the primary form of carbon deposits. This study investigates the formation and evolution of CNTs during the catalytic process of biomass tar to explore the mechanism behind carbon deposition. The effect of the 9Ni/10MWCNTs/81ZSM-5 on toluene reforming was investigated through a vertical furnace. Gases produced by tar catalysis were evaluated through GC analysis. The physicochemical structure, properties and catalytic performance of the catalyst were also tested. TG analysis was used to assess the accumulation and oxidation reactivity of carbon on the catalyst surface. An analysis was conducted on the mechanism of carbon deposition during catalyst deactivation in tar catalysis. The results showed that the 9Ni/91ZSM-5 had a superior toluene conversion of 60.49%, but also experienced rapid and substantial carbon deposition up to 52.69%. Carbon is mainly deposited as curved filaments on both the surface and pore channels of the catalyst. In some cases, tip growth occurs where both carbon deposition and Ni coexist. Furthermore, specific surface area and micropore volume are reduced to varying degrees due to carbon deposition. With the time increased, the amount of carbon deposited on the catalyst surface increased to 62.81%, which gradually approached saturation, and the overall performance of the catalyst was stabilized. This situation causes toluene molecules to detach from the active sites within the catalyst, hindering gas release, which leads to reduced catalytic activity and further carbon deposition. It provides both a basis for the development of new catalysts and an economically feasible solution for practical tar reduction and removal.