External Surface Area Research Articles

Synthesis of Nanocrystalline Mordenite Zeolite with Improved Performance in Benzene Alkylation and n‐Paraffins Hydroconversion

AbstractNanocrystalline mordenite (MOR) zeolites were hydrothermally synthesized in a single step with commercial cetyltrimethylammonium (CTA) hydroxide as the sole organic template, while the aluminum source was varied in a typical synthesis gel. CTA can effectively reduce the crystal growth of MOR zeolites, in some cases selectively in the a‐ and b‐directions of the unit cell. These nanocrystalline MOR zeolites do not only have a larger external surface area than their bulk counterparts prepared without CTA, but the Brønsted acid sites in the side‐pockets are also more accessible. The combination of the use of CTA and AlCl3 ⋅ 6H2O afforded the best‐performing catalyst with much improved activity in benzene alkylation and hydroconversion of n‐hexadecane (n‐C16). Modifying MOR synthesis with CTA hydroxide is a cheap and effective method to open up the one‐dimensional micropore system of mordenite, increasing the catalytic performance in hydrocarbon reactions.

Controlled synthesis of hierarchically porous SAPO-34 zeolites with tailored crystal size and morphology

A series of hierarchically porous SAPO-34 zeolites with tunable crystal sizes varying from 40 to 200 nm were synthesized with different morphologies from well-dispersed ultra-small nanocrystals to compact spherical-like polycrystalline aggregates by only changing the Si/TEAOH (TEAOH: tetraethylammonium hydroxide) molar ratios in the gel precursors without using any meso-templates. The hierarchical samples were systematically characterized by XRD, FT-IR, SEM, TEM, XRF, 29Si MAS NMR spectra and N2 adsorption–desorption. It reveals that hierarchical SAPO-34 nanocrystals with high crystallinities, larger external surface areas (61 – 125 m2/g) and mesopore volumes (0.15 – 0.29 cm3/g) were obtained under current synthesis condition.

Carbon Aerogel Based Thin Electrodes for Zero‐Gap all Vanadium Redox Flow Batteries – Quantifying the Factors Leading to Optimum Performance

AbstractDirect growth of resorcinol−formaldehyde carbon aerogels (CAGs) on carbon paper electrodes was achieved using a new approach. Materials with variations in density, mesoporosity and microporosity were prepared. Microstructural properties of the resultant thin electrodes are shown to directly influence performance in zero‐gap redox flow battery (RFB). BET analysis shows a total surface area between 643 to 931 m2 g−1. Deposition of only ≈15 wt.% CAG on the carbon electrode leads to a 320‐fold increase in electrochemical surface area. Analysis of the results saw a strong positive correlation of RFB performance with surface area. The best performing electrodes had a good balance between microporous and external surface area, and on the macroscopic scale had sufficiently large pores to allow efficient electrolyte permeation. The poorest performing electrodes which had the highest surface area, also had poor macroscopic porosity leading to large mass transport and solution resistance losses. The best performing electrodes were tested in a zero‐gap setup using polarization curves, showing a 25 % increase in power density at 100 mA cm−2 and a peak power density of 706 mW cm−2 at 1 V using thin electrodes.

STUDY THE SPECIFICATIONS OF ACTIVATED CARBON PREPARED FROM AVOCADO SEEDS USING CARBONATION AND CHEMICAL ACTIVATION

Activated carbon was prepared from Avocado Seeds using different percentages of sodium hydroxide and under the same conditions. Through the study, it was found that increasing the base leads to the production of new good varieties of a neutral nature. The study proved through physical and chemical examinations of the prepared samples that gave the best results when compared with other samples for activated carbon produced by well-known companies, the most important tests conducted for the prepared samples are the determination of the density, the iodine number (IN), the low ash content, the measurement of the external surface area by the adsorption method of the methylene blue dye from its aqueous solution, the measurement of moisture and ash content.

Fe-doped porous Co3O4 nanosheets with highly efficient catalytic performance for soot oxidation

A series of CoxFe1-x-PNS materials were synthesized at room temperature through the one-pot MgO-mediated method and were then used as catalysts for soot oxidation. Of all the catalyst samples prepared, the porous Co0.8Fe0.2-PNS nanosheets exhibited the highest catalytic performance for soot oxidation under both loose and tight contact modes. The 2D nanosheets provided a larger external surface area for contact between the catalyst and soot, and the porous structure was beneficial to the adsorption and diffusion of reactant gas. It was found that Fe was successfully doped in the lattice of Co3O4, and the mechanism regarding how Fe doping enhances intrinsic activity was investigated by a series characterization and DFT calculations. The results indicated that Fe doping made it easier to form oxygen vacancies and adsorb gaseous O2, which effectively improved the catalytic activity of soot oxidation. Hence, it is believed that the synergy between the well-defined porous nanosheets morphology and the properties induced by the doping of Fe resulted in better catalytic activity. This study also provided insight into the design of 2D transition metal oxides nanosheets as catalysts for soot oxidation.

Unlocking Zinc-Ion Energy Storage Performance of Onion-Like Carbon by Promoting Heteroatom Doping Strategy.

Onion-like carbon (OLC) is one kind of a quasi-nanosphere with a concentric graphite shell structure and abundant mesopores, which is appropriate for a high rate of charging/discharging and long-lifespan cycling. However, the moderate specific surface area seriously impeded its capacitance performance in comparison with activated carbon and porous carbon. Herein, we have unlocked the Zn ion storage performance of OLC material through introducing N and P dopants. Benefitting from the fabricated N,P-OLC with a fully accessible external surface area for ion adsorption, high proportion of mesopores for fast ion migration, and synergistic effect of N and P co-doping in a carbon matrix favoring chemical adsorption of Zn2+ ions, when applied as a cathode electrode for Zn ion hybrid supercapacitors (ZHSCs), such a device can deliver a high specific capacitance of 420.3 F g-1 (184.5 mA h g-1) at 0.5 A g-1, an outstanding capacitance retention capability of 262.7 F g-1 even at 20 A g-1 (∼63% capacitance retention), a high energy density of 149.5 W h kg-1, and a high power density of 26.7 kW kg-1. Furthermore, this N,P-OLC material can in situ tightly integrate with a carbon cloth (CC) or carbon fiber to construct a freestanding and flexible electrode. The fabricated Zn//N,P-OLC@CC device achieved a high energy density of 85.3 mW h cm-2, a high power density of 24.3 W cm-2, and a long-term cycling lifespan (77.8% after 50 000 cycles). At last, the assembled quasi-solid-state fiber-shaped ZHSCs also present excellent flexibility and practicality. Our study exhibits that OLC can act as a promising carbon electrode for ZHSCs.

Nickel on two-dimensional ITQ-2 zeolite as a highly active catalyst for carbon dioxide reforming of methane

The physicochemical properties of the support material are important parameters that determine the activity and stability of supported metal catalysts in chemical reactions. In this study, we investigated the influence of the support dimensionality and nickel loading (5, 15, and 30 wt%) of supported-Ni catalysts for the carbon dioxide reforming of methane (CDR) by comparing the three-dimensional (3D) Ni/MCM-22 and its delaminated two-dimensional (2D) Ni/ITQ-2 catalyst. Owing to its delaminated nature, Ni/ITQ-2 exhibited a large external surface area (319 m2 g−1) and a high proportion of the nickel phyllosilicate phase, even for 30 wt% Ni loading. In addition, the strong interaction of Ni clusters with phyllosilicate resulted in a high dispersion of Ni. The 2D Ni/ITQ-2 catalysts generally exhibited a higher catalytic performance than the 3D Ni/MCM-22 catalysts. The relative proportion of the nickel phyllosilicate phase in the catalyst also played a promoting role in achieving a high catalytic performance for CDR. Unlike Ni/γ-Al2O3, Ni/ITQ-2 exhibited high conversions of CH4 and CO2, regardless of pre-reduction, which is advantageous for catalyst handling.

Comparison of Dynamic Charge Acceptance Tests on Lead–Acid Cells for Carbon Additive Screening

Including a certain amount of carbon in the negative active material is currently the state‐of‐the‐art method to improve the dynamic charge acceptance (DCA) of lead–acid batteries. The DCA is a key parameter of batteries used in microhybrid cars where brake energy recuperation is implemented. To find the optimal carbon additive, it is essential to test the carbon both in short‐term and long‐term tests. This work investigates the long‐term and short‐term DCA of 2 V, 2.5 Ah lead–acid cells and correlates the results with the external surface area of the carbon. Five different carbons with tailored particle size (27–633 nm) and external surface area (7.1–159.3 m2 g−1) are employed as additives in the negative electrodes. The charge acceptance of cells according to the charge acceptance test 2 (SBA), the DCA (EN) test, and the run‐in DCA test (Ford) is increased via an increase in the carbon external surface area. A correlation between the short‐term tests and the first week of the run‐in DCA test is established for the carbon impact. After several weeks of run‐in DCA test, the carbon effect is diminished and only a differentiation between high and low DCA cells is possible.

3D mathematical modeling of external mass transfer effect in high-rate adsorption process

The effect of external mass transfer on the high-rate adsorption system was evaluated in the present study. In the experimental section, the removal of methyl orange (MO) was carried out by using surfactant modified chitosan-clinoptilolite at specific conditions such as the optimum adsorbent dosage of 11 g L−1, solution pH of 3.5, contact time of about 3 min and constant temperature of 30 °C. The characterization of adsorbent showed the porosity value of 0.064 and the BET surface area of 10.5 m2 g−1. These features of adsorbent established the high-rate adsorption process in which the shape of decay curves is not smooth and the concentration of adsorbate falls quickly. In high-rate adsorption processes, the external mass transfer mechanism has a significant effect on total mass transfer at early time of adsorption. The pore volume and surface diffusion model (PVSDM) were applied for predicting MO concentration decay curves. This model and its parameters could not estimate properly the concentration of MO at the early time of the adsorption process. To overcome this problem, in addition to optimization of surface diffusion coefficient (Ds), the external mass transfer coefficient (ke) was optimized and the effect of those parameters was studied in three dimensions. The optimization provided a better agreement between the model and experimental data in such a way to reduce the error rate. To show better the effect of external mass transfer, Biot number (between (2.15 and 24.05) × 10−3) was applied and it revealed that the adsorption mechanism was controlled by external mass transport. The high external surface area illustrated that in all values of ke and initial concentration of MO, surface diffusion is the dominant mechanism in intraparticle diffusion and the low porosity of adsorbent limited the penetration of adsorbate species into the adsorbent cavities, whereby the pore volume diffusion could be considered negligible.

Direct synthesis of ultrathin FER zeolite nanosheets via a dual-template approach.

The synthesis of zeolites with nanosheet morphology has been attracting extensive attention. Despite the steady progress, the direct synthesis of ultrathin nanosheets of FER zeolite with thickness of less than 10 nm is still a great challenge. Herein we report a facile synthesis of FER zeolite nanosheets (named SCM-37) by using octyltrimethylammonium chloride (OTMAC) and 4-dimethylaminopyridine (4-DMAP) as dual organic templates. The effects of synthesis parameters, including initial molar ratio of SiO2/Al2O3, crystallization temperature and time were investigated. It turned out that the crystallization field of SCM-37 was narrow. A two-step crystallization method was utilized to obtain pure and completely crystallized SCM-37 zeolite. SCM-37 was characterized by multiple techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption, Fourier transform infrared (FTIR), ammonia-temperature programmed desorption (NH3-TPD) and nuclear magnetic resonance (NMR), and compared with the conventional FER zeolite (C-FER). The two most significant features of SCM-37 are the ultrathin crystal nanosheet and extremely high external surface area. The thickness of SCM-37 along the a-axis is 4∼7 nm, while that of C-FER is over 20 nm. The external surface area reaches 198 m2 g−1, which is over ten times larger than that of C-FER. The catalytic performances of the FER zeolites were evaluated by the cracking of 1,3,5-triisopropylbenzene (TiPB). Although possessing a lower amount of total acid sites, SCM-37 showed higher conversion of TiPB, as well as selectivity to the deep cracking products. The superior performance of SCM-37 was attributed to the higher external surface area arising from the ultrathin nanosheets.

Influence of Internal and External Surface Area on Impregnation and Activity of 3d Printed Catalyst Carriers

Influence of Internal and External Surface Area on Impregnation and Activity of 3d Printed Catalyst Carriers

Preparation of nanocrystalline ZSM-5 and its catalytic performance in fast pyrolysis of cellulose to produce aromatic hydrocarbons

A series of nanocrystalline ZSM-5 zeolites with abundant intercrystalline mesopores was fabricated by a hydrothermal crystallization method without any mesopore template. The ZSM-5 zeolite was characterized by XRD, XRF, N2 adsorption, NMR, SEM, TEM and NH3-TPD and used for the catalytic fast pyrolysis (CFP) of cellulose. The external surface area of the nanocrystalline ZSM-5 zeolite reached 146.6 m2/g, larger than the external surface area of conventional ZSM-5 (57.9 m2/g). The product yields of the CFP reaction were studied over different Si/Al ratios of nanocrystalline ZSM-5, and the aromatic yield of nanocrystalline ZSM-5 was generally higher than the aromatic yield of conventional ZSM-5. The relationship between the surface area, acid amounts and product yields was established by drawing a linear fitting curve. The results show that both pore structure and acidity have important effects on aromatic yield and coke yield. Aromatics are generated in micropores, and the increase in external surface area caused by reducing the particle size improves the pyrolysis of cellulose to generate bio-oil vapours, which further diffuse into micropores to generate aromatics.

Preparation of core-shell ZSM-5@Beta molecular sieve and catalytic alkylation to 2,6-Dimethylnaphthalene

ZSM-5@Beta core-shell molecular sieve was prepared by dynamic hydrothermal synthesis method using ZSM-5 adhered Beta seed crystals as the core phase, and polydiallyl dimethyl ammonium chloride (PDDA) was used as a coupling agent to adhere Beta seed crystals on the surface of ZSM-5. The structure and physical properties of composite molecular sieves were characterized by XRD, N2 adsorption-desorption, SEM, TEM, ICP, NH3-TPD and Py-FTIR. The catalytic performance of composite molecular sieves for alkylation of 2-methylnaphthalene (2-MN) with methanol was investigated. The results showed that ZSM-5@Beta composite molecular sieve prepared by this method had a core-shell structure, and the particle size was about 500 nm. Compared with mechanically mixed binary molecular sieve, core-shell molecular sieve had higher specific surface area and external surface area, lower acid strength and stronger acid center density. Through the construction of core-shell interface and hierarchical porous, the catalytic activity was improved by shell phase Beta molecular sieve with 12-membered ring channel, and the catalytic selectivity was improved by core phase ZSM-5 molecular sieve with 10-membered ring channel in the alkylation reaction of 2-MN with methanol. The 2,6-/2,7-DMN ratio in the products reached 1.35, and the yield of 2,6-DMN reached 4.29%.

Multiscale storage and transport modeling in unconventional shale gas: A review

Several studies have been performed to model the storage and transport in organic matter present in shale gas. However, the unconventional formation does not only contain organic matter but also inorganic mineral matrix. The studies necessitated by this research gap showed that quartz pores contribute more to the amount of free gas present in shale while clay minerals play a significant role to the adsorbed gas storage capacity, especially in rocks containing low total organic content. Interestingly, methane and a small amount of carbon dioxide, ethane, propane, nitrogen, and water are trapped within the mineral pores and the interphase between two or more minerals. The gases present are stored in a sorbed and free state at different pore scales, which makes the modeling challenging. More so, the adsorbed gas layer influences gas transport through the pore structure. In this work, an extensive review of experimental and simulation outlook to these subjects was considered, with emphasis on key highlights and limitations to previous studies. Besides, there was a recap of commonly utilized field perspectives to compute the producible gas from shale reservoirs, and an insight into an experimental validation point of view. Analytical and numerical transport description methods were broadly debated. Furthermore, there was an overview of the widely availed relationship between heat with chemical and physical adsorption, including the process for evaluating the efficiency of CO 2 sequestration and enhanced gas recovery projects in shale reservoirs alongside the possible drawbacks in their application. • In addition to kerogen, bitumen and other semi-solids organics in shale impact on gas storage and transport. • Crushed samples with variable grain sizes are widely utilized for experimental adsorption and diffusion studies. • Clay has a complex mineralogy, microstructure and charged interlayer and external surface area. • The uncertainty in shale reserves can be reduced by integrating field and experimental approach. • Most existing volume models ignore capillary gas in shale confined pores.

Electrocatalytic oxygen reduction of COF-derived porous Fe-Nx nanoclusters/carbon catalyst and application for high performance Zn-air battery

The development of non-previous-metal electrocatalyst with low cost, high activity and stability towards oxygen reduction reaction (ORR) remains a challenge. Covalent organic frameworks (COFs) have emerged as promising candidates for the preparation of porous metal/nitrogen co-doped carbon catalysts. In the present work, porous Fe-Nx nanoclusters/carbon catalysts are prepared by pyrolyzing iron-containing covalent-triazine organic frameworks. It is found that the synthesis conditions including pyrolysis temperature and pressure have great impacts on the surface area of micropores, mesopores and macropores, which in turn influences the ORR activity of catalysts by varying the mass diffusion and the contact of active centers with electrolytes. The optimized catalyst (denoted as Fe1.2NC-0.02-800), having the highest both BET and external surface areas, shows much higher kinetic current density and catalytic stability than commercial Pt/C catalyst in ORR process. When being assembled into Zn-air battery, it also exhibits excellent performances in terms of open circuit voltage (1.45 V), power density (210 mW cm−2 at 330 mA cm−2) and specific capacity (713.1 mA h gZn−1), which outperform the corresponding values of Pt/C-based Zn-air battery. Moreover, 15 light-emitting diodes can be powered by two series-connected Zn-air batteries with Fe1.2NC-0.02-800 as the air-cathode catalyst, implying its promising application in clean energy conversion field.

An efficient green protocol for the synthesis of 1,2,4,5-tetrasubstituted imidazoles in the presence of ZSM-11 zeolite as a reusable catalyst.

In this study, we have synthesized a series of ZSM-11 zeolite catalysts using tetrapropyl ammonium hydroxide as a structure-directing agent through a highly efficient hydrothermal method. The series of catalysts were studied by different techniques such as FT-IR spectroscopy, XRD, FE-SEM, HR-TEM, EDS, pyridine-FT-IR spectroscopy, and BET analysis. We focused on varying reaction time intervals from 18 to 48 hours to investigate the effect on catalytic activities of the synthesized series of catalysts. The percentages of aluminum increased in the framework of zeolites with increasing crystallinity, surface area, external surface area, and acidity in the series of ZSM-11 zeolites by increasing the time from 18 to 48 h. Then, we studied the catalytic activity of a series of ZSM-11 zeolites and found that the ZSM-11 zeolite (48 h) possesses higher catalytic activity towards the synthesis of 1,2,4,5-tetrasubstituted imidazoles under solvent-free conditions. The present protocol scored well with excellent yield, short reaction time, clean reaction profiles, low catalyst loading, and no tedious workup. The catalyst (ZSM-11 zeolite 48 h) was recycled and reused in five runs without any considerable loss of activity and product yield.

Optimization of Preparation Conditions of Activated Carbons Based on the Shells of <i>Ricinodendron heudoltii</i>

The purpose of this work is to prepare better activated carbons from the shells of Ricinodendron Heudelotii by chemical activation with sulfuric acid (H2SO4) and sodium hydroxide (NaOH). The process was optimized by a full factorial design (2K) based on the analysis of the external specific surface area of sixteen (16) activated carbons prepared according to the parameters of the preparation. This active analysis reveals that under the preparation conditions, good carbons are obtained for a sodium hydroxide concentration equal to 1 M, an impregnation time of 24 h and carbonization at 500˚C for 1 h. The external specific surface of this carbon is 358 m2 • g-1. The characteristics of this prepared carbon are as follows: a pH at zero point charge (pHpzc) of 8.2, a predominantly amorphous structure, a basic character and a low ash content (4.2%). It also has surface functions; the lactonic and carbonyl groups (C=O) at 1600 cm-1 and the carboxylate groups (O-H or C-O) at 1340 cm-1.

High-efficiency hydrocracking of phenanthrene into BTX aromatics over a Ni-modified lamellar-crystal HY zeolite.

A new Ni-HY zeolite with lamellar-crystals was prepared as a catalyst for phenanthrene hydrocracking. It showed significantly improved reactivity and BTX (benzene, toluene and xylene) selectivity (up to 99.1% and 75.6%, respectively), depending on a reasonable synergistic effect between its excellent internal-diffusion and the high-efficiency concerted catalysis of surface metal-Ni active sites and acid sites. In particular, compared with a conventional Ni-HY with diamond-shaped crystals, its significantly shortened diffusion-reaction path of the micropore system in the lamellar crystals greatly enhanced the diffusion-reaction efficiency of large-molecule phenanthrene and polycyclic intermediates and remarkably improved the utilization of both pores and internal reactive sites, powerfully promoting phenanthrene into benzene series conversion. The much decreased diffusion-residence time of benzene-series products in shortened channels also effectively weakened the further cracking loss of the benzene-ring, leading to enhanced BTX selectivity. Moreover, this shorter-channel Ni-HY catalyst with a higher external surface area and mesoporous volume also exhibited greatly improved catalytic stability attributed to its stronger capabilities of accommodating coke and resisting coke-deposition. The phenanthrene conversion of >76.3% and the BTX yield of >46.3% were obtained during a 60 h on-stream reaction.

Improved accessibility of Na-LTA zeolite catalytic sites for the Knoevenagel condensation reaction

The use of zeolites in basic catalysis is limited when large molecules are involved, such as in the manufacture of fine chemicals, due to difficulty in accessing the micropores of the catalyst. A solution to this problem is to synthesize zeolites containing mesopores that improve the accessibility of the active sites. This work investigates the synthesis of zeolites 4A according to a bottom-up method employing the organosilane surfactant [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride (TPOAC), at different concentrations in the synthesis mixture (TPOAC/Al2O3 = 0–0.09), to produce mesopores. The zeolites were evaluated in the Knoevenagel condensation reaction, which is strongly influenced by the accessibility of the catalytic sites, due to the large sizes of the molecules involved. Zeolites 4A with mesopores, showing higher external surface areas, were formed in the presence of TPOAC at the different concentrations tested. Higher conversions were achieved using the zeolites with mesopores, compared to conventional zeolite 4A, due to improved access of the reactant molecules to the catalytic sites. In addition, the reaction catalyzed by the zeolite with mesopores had lower activation energy, compared to use of the conventional zeolite 4A.

Ethylene production via ethanol dehydration over desilicated ZSM-5 catalyst

The catalytic dehydration of ethanol is a potential alternative route to synthesize ethylene apart from the traditional method which depends on fossil fuels. This report successfully prepared modified ZSM-5 with mesopores using desilication methods to enhance ethanol catalytic dehydration performance and ethylene production at lower temperature. The modified zeolite have the external surface area increased by 3.5 times and a higher dehydration efficiency compared with the original sample especially at temperatures below 220°C. Increasing reaction temperatures and gas houly space velocity (GHSV) increased the dehydration efficiency while increasing the inlet ethanol concentration had opposite effect. Significantly, the ethanol conversion over modified zeolite remained above 90 % when the GHSV increased to 36000 h‑1 after the time-on-stream of 24 h.