Mesostructured Aluminosilicates Research Articles

On the role of the nature and density of acid sites on mesostructured aluminosilicates dehydration catalysts for dimethyl ether production from CO2

In this work, we designed four different mesostructured acidic materials to be used as methanol dehydration catalysts for the one-pot CO2-to-DME process, in the form of physical mixtures with a Cu/ZnO/Al2O3-based commercial redox catalyst (CZA). The studied systems consist in a mesostructured γ-Al2O3 and three mesostructured aluminosilicates (namely Al-MCM-41, Al-SBA-15, and Al-SBA-16) with the same Si/Al ratio (= 15) but significantly different textural properties. The main goal of this work is to understand how the textural features can influence the acidic properties (typology, amount, strength, surface density) and, consequently, how catalytic performances can be correlated with acidic features. On this note, we found that the systems presenting both Brønsted and Lewis sites (namely the three aluminosilicates) show much better catalytic performances than γ-Al2O3, that only features Lewis sites, thus implying that Brønsted sites are more active towards methanol dehydration than Lewis sites. The three aluminosilicates, despite presenting comparable amounts of Brønsted sites, show significantly different performances in terms of selectivity to DME; particularly, Al-SBA-16, the system with the lowest surface area, proved to be the most efficient catalyst. This finding led us to infer that, besides Brønsted acidity, a high surface density of acid sites is a key factor to obtain a high dehydration activity; being methanol dehydration a bi-molecular reaction, the close proximity of two acid sites would indeed favor the kinetics of the process.

SYNTHESIS AND PHYSICOCHEMICAL CHARACTERISTICS OF MESOPOROUS ALUMINOSILICATES

In the article, the synthesis of mesoporous aluminosilicates was carried out according to the developed methods, in which tetraethylorthosilicate Si(OC2H5)4 was used as a source of silicon, secondary aluminum butoxide (sec-BuO)3Al and aluminum triisopropoxide Al(i-OPr)3 were used as aluminum's sources. The synthesis of mesostructured aluminosilicate is based on the method of copolycondensation of silicon and aluminum sources in the presence of alcohol. Hexadecylamine (HDA, C16H33NH2) was used as a template for the formation of a porous structure. The physicochemical characteristics of the synthesized structured mesoporous aluminosilicates have been studied. It was found that the synthesized materials MAS-1 and MAS-2 possess high specific surface area from 511 to 1170.0 m2/g. The presence of a mesoporous and ordered structure in the synthesized aluminosilicates is confirmed by the data of low-temperature nitrogen adsorption/desorption, X-ray diffraction and FT-IR. To determine the relative strength of Brønsted and Lewis acid sites on the surface of mesoporous aluminosilicates, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of adsorbed pyridine samples was carried out. DRIFT analysis data demonstrated a majority of Lewis acid sites on the surface of the synthesized materials. We are currently studying the possibility of applying these materials as acidic components of bifunctional catalysts for petrochemical N E W S OF THE NATIONAL ACADEMY OF SCIENCES OF THE REPUBLIC OF KAZAKHSTAN SERIES CHEMISTRY AND TECHNOLOGY ISSN 2224-5286 https://doi.org/10.32014/2020.2518-1491.94 Volume 6, Number 444 (2020), 22 – 29 UDC 665.64.097.3 MRNTI 61.51.17, 61.51.19 К.M. Umbetkaliyeva1,2, G.K. Vassilina1,2, А.К. Abdrassilova1 , А.R. Khaiyrgeldinova2, Т.К. Vassilina2,3, Zh.Y. Zakirov1, М.Kh. Taliyeva2 , А.К. Kaldybayeva2 1al-Farabi Kazakh National University, Almaty, Kazakhstan; 2SRIfor New Chemical Technologies and Materials, Almaty, Kazakhstan; 3Кazakh National Agrarian University, Almaty, Kazakhstan. E-mail: kamilla.u.m21@mail.ru, v_gulzira@mail.ru, albina06.07@mail.ru, asyltas_2008@mail.ru, v_tursunai@mail.ru, abuzhassulan@gmail.com, taliyevamadina@gmail.com, kaldybayeva.assylai@gmail.com SYNTHESIS AND PHYSICOCHEMICAL CHARACTERISTICS OF MESOPOROUS ALUMINOSILICATES Abstract. In the article, the synthesis of mesoporous aluminosilicates was carried out according to the developed methods, in which tetraethylorthosilicate Si(OC2H5)4 was used as a source of silicon, secondary aluminum butoxide (sec-BuO)3Al and aluminum triisopropoxide Al(i-OPr)3 were used as aluminum's sources. The synthesis of mesostructured aluminosilicate is based on the method of copolycondensation of silicon and aluminum sources in the presence of alcohol. Hexadecylamine (HDA, C16H33NH2) was used as a template for the formation of a porous structure. The physicochemical characteristics of the synthesized structured mesoporous aluminosilicates have been studied. It was found that the synthesized materials MAS-1 and MAS-2 possess high specific surface area from 511 to 1170.0 m2/g. The presence of a mesoporous and ordered structure in the synthesized aluminosilicates is confirmed by the data of low-temperature nitrogen adsorption/desorption, X-ray diffraction and FT-IR. To determine the relative strength of Brønsted and Lewis acid sites on the surface of mesoporous aluminosilicates, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of adsorbed pyridine samples was carried out. DRIFT analysis data demonstrated a majority of Lewis acid sites on the surface of the synthesized materials. We are currently studying the possibility of applying these materials as acidic components of bifunctional catalysts for petrochemical processes.

Microwave-assisted synthesis of mesostructured aluminosilicates (MA) for the preparation of nano-MoS2/MA catalysts active in decalin hydrocracking

Aluminosilicates with disordered hexagonal mesostructure leading to wormhole-like porosity (MA, Si/Al = 50) were obtained using BEA-seeds and CTABr as directing agent of the hexagonal mesopores. A microwave-assisted synthesis was proposed as an alternative to the time-consuming conventional hydrothermal synthesis. Time of microwave irradiation was evaluated, and it was found that aluminosilicates were successfully synthesized in 5 min via microwave heating as compared to 2 days required in the conventional hydrothermal synthesis without sacrificing material properties. Mesoporous aluminosilicates with Si/Al molar ratio between 24 and 42 were obtained with a yield of about 95% and they were used as the acidic function in bifunctional MoS 2 /MA catalysts, where nano-MoS 2 was formed in-situ during the decalin hydrocracking. The acidic properties of the aluminosilicates, specifically, number and strength of Brønsted acid sites have an impact on the catalytic activity of the bifunctional catalysts measured for decalin hydroconversion, leading mostly skeletal isomerization and single-ring opening products. • Mesostructured aluminosilicates with different Si/Al were obtained by microwave-assisted hydrothermal synthesis in 5 min. • Mesoporous aluminosilicates were successfully used as acidic function in bifunctional catalyst for decalin hydrocracking. • Bifunctional MoS 2 -MA catalysts were obtained in-situ during decalin hydrocracking. • Decalin conversion was influenced by the number and the strength of the Brønsted acid sites.

In-situ and ex-situ catalytic pyrolysis/co-pyrolysis of empty fruit bunches using mesostructured aluminosilicate catalysts

Mesostructured aluminosilicates of Al-MSU-F (commercial), Al-SBA-15 (home-made), and mesoMFI (a mesoporous aluminosilicate with MFI structure, home-made), with a silica-to-alumina ratio of 40, were used as catalyst for the in-situ catalytic pyrolysis (CP) of empty fruit bunches (EFB) at 600 °C. The highest selectivity to aromatic hydrocarbons in bio-oil was obtained over mesoMFI due to its higher acidity than Al-SBA-15 and Al-MSU-F. In addition, ex-situ CP of EFB using mesoMFI was compared with in-situ CP; the ex-situ configuration produced higher aromatic hydrocarbons than the in-situ configuration. Meanwhile, in-situ and ex-situ catalytic co-pyrolysis (CCP) of EFB (with a H/Ceff ratio less than 0.3) and polypropylene (PP) (with a high H/Ceff ratio about 2) were carried out using the mesoMFI at 600 °C to investigate the supplementary effect of PP on the deoxygenation of EFB-derived pyrolyzates for producing aromatic hydrocarbons. Ex-situ CCP of EFB/PP (with the mass ratios of 75/25, 50/50, and 25/75) resulted in a lower formation of aromatic hydrocarbons than the in-situ CCP. In addition, the thermal decomposition behavior of EFB, PP, and EFB/PP in non-catalytic and catalytic (mesoMFI) pyrolysis/co-pyrolysis was investigated using thermogravimetric analysis (TGA); use of catalyst reduced the temperature of PP thermal degradation, but did not change the maximum reactivity temperature of EFB degradation.

Rh/Ni wet-impregnated Ia3d mesostructured aluminosilicate and r-GO catalysts for hydrodeoxygenation of phenoxybenzene

Rh/Ni bimetallic supported bifunctional 3D porous aluminosilicate and Rh/Ni supported reduced graphene oxide (r-GO) catalysts were synthesised and their structural properties evaluated by XRD, BET-surface area, FT-IR, NH3-TPD, H2-TPR, ICP-OES, HRTEM-EDAX and XPS analysis.

Synthesis of Mesoporous Alumosilicates

Synthesis techniques of the mesostructured alumino-silicates were developed. Synthesis with various Si/Al ratios was carried out. Textural characteristics and structure's orderliness of the mesostructured alumino-silicates' synthesized samples were investigated.

Strongly acidic mesoporous aluminosilicates prepared via hydrothermal restructuring of a crystalline layered silicate

Crystalline layered silicates may be hydrothermally restructured to generate mesostructured aluminosilicates with retained molecular ordering and strong acidity via benign template removal routes.

Acidic mesostructured aluminosilicates assembled from economic acidic template characterized by catalytic cracking reactions

Mesoporous 3D aluminosilicates, denoted as AlMFA-8, were one-pot synthesized with two different nSi/nAl ratios using linear alkylbenzene sulfonic acid, LASH, as template. The AlMFA-8 materials were characterized using XRD, N2-adsoption, SEM, HRTEM, XRF, XPS and FT-IR. The results showed that AlMFA-8(x) has large-pore mesoporous solids. The pore volume increases from 1.28 to 1.45cm3/g without significant concomitant decrease of the surface area (≈659m2/g). On the other hand, AlSBA-15(x) materials with the same nSi/nAl ratios were one-pot synthesized by adjusting the molar of nH2O/nHCl in synthesis gel at 276 using P123 as template.The surface acidity of AlMFA-8(x) and AlSBA-15(x) were evaluated and confirmed by NH3-TPD, Pyr-FT-IR, TGA-wax-catalytic cracking, 1,3,5-triisopropylbenzene and n-hexadecane cracking. In addition, commercial silica–alumina (CSi–Al) was characterized and its catalytic activity is compared with the different acid mediated synthesis route, AlMFA-8(x) and AlSBA-15(x). The AlMFA-8(x) showed the higher activity under equivalent conditions in comparison to AlSBA-15(x) and CSi–Al materials.

Anhydrous Proton Conducting Hybrid Proton Exchange Membrane by Phase Mode Atomic Force Microscopy

Hybridization of inorganic pillars and proton exchange membrane have been studied for increasing performance of proton exchange membrane fuel cell such as working under low relative humidity. For developing hybrid membrane, understanding of morphological structure is crucial. In this study, we synthesize silica meso-structured cellular foam (Si-MSU-F) and meso-structured aluminosilicate with hexagonal network (Al-MCM-41) and study morphological evolution of the membrane by using atomic force microscopy. When Nafion is composited with Si-MSU-F and Al-MCM-41, the hybrid membrane surface is evolved to different structure compare with the pristine Nafion. In addition, Si-MSU-F/Nafion shows different morphological structure as Al-MCM-41/Nafion hybrid membranes due to different hybridization mechanism between pillars and Nafion.

Shaping adsorption properties of nano-porous molecular sieves for solar thermal energy storage and heat pump applications

The water adsorption properties of modified porous sorbents for solar thermal energy storage and heat transformation have been investigated by measurements of water adsorption isotherms, microcalorimetry and storage tests. A chabazite type SAPO, a dealuminated faujasite type zeolite, and a mesostructured aluminosilicate, have been synthesized and compared with common zeolites NaX, NaY and silica gel. It has been found that optimized lattice composition and pore architecture contribute to well adapt hydrophilic properties and a beneficial steep isotherm.

Mesostructured-aluminosilicate-Nafion hybrid membranes for direct methanol fuel cells

Organic–inorganic hybrid membranes are prepared from Nafion and acid functionalized aluminosilicate with varying structures and surface areas. Acid-functionalized mesostructured aluminosilicate with cellular foam framework (Al-MSU-F type) of surface area 463m2g−1, acid-functionalized aluminosilicate molecular sieves (Al-HMS type) of surface area 651m2g−1 and acid-functionalized mesostructured aluminosilicate with hexagonal network (Al-MCM-41 type) of surface area 799m2g−1 have been employed as potential filler materials to form hybrid membranes with Nafion. The structural behavior, water uptake, ion-exchange capacity, proton conductivity and methanol permeability of the hybrid membranes are extensively investigated. Direct methanol fuel cells (DMFCs) with Al-HMS-Nafion and Al-MCM-41-Nafion hybrid membranes deliver respective peak power-densities of 170mWcm−2 and 246mWcm−2, while a peak power-density of only 48mWcm−2 is obtained for the DMFC employing pristine recast-Nafion membrane under identical operating conditions. The unique properties associated with hybrid membranes could be exclusively attributed to the presence of pendant sulfonic-acid groups in the filler materials, which provide proton-conducting pathways between the filler and matrix in the hybrid membranes, and facilitate proton transport with adequate balance between proton conductivity and methanol permeability.

Adsorption properties of porous materials for solar thermal energy storage and heat pump applications

The water adsorption properties of modified porous sorbents for solar thermal energy storage and heat transformation have been investigated by thermogravimetry (TG) differential thermogravimetry (DTG), microcalorimetry, measurements of water adsorption isotherms, and storage tests. A chabazite type SAPO, a dealuminated faujasite type zeolite, and a mesostructured aluminosilicate, have been synthesized and compared with common zeolites X, Y and silica gel. It has been found that optimized lattice composition and pore architecture contribute to well adapt hydrophilic properties and a beneficial steep isotherm.

Selective Isobutene Oligomerization by Mesoporous MSU-SBEA Catalysts

Hydrolytically stable mesostructured aluminosilicates assembled from protozeolitic precursors are examined as acid catalysts in the isobutene oligomerization reaction. Steady state conversions as high as 80% at 60 °C are achieved, depending on the isobutene:butane feed composition and space velocity. Most notably, the product selectivity to dimeric C8= and trimeric C12= olefins is readily fine-tuned simply by changing the feed composition. Undesirable high molecular weight oligomers are not produced in any case. The superior catalytic performance of the mesostructured aluminosilicates in comparison to commercial USY and BEA zeolites is clearly established. The improvement in catalytic performance is attributed to a combination of textural and acidic properties, as judged by N2 adsorption and pyridine adsorption studies.

Valorization of Waste Agricultural Polyethylene Film by Sequential Pyrolysis and Catalytic Reforming

This paper deals with the potential of using sequential pyrolysis and catalytic reforming for the conversion of agriculture film waste into useful hydrocarbon products. The experiments were conducted in a two-step reaction system consisting of a pyrolytic batch reactor (450 °C) connected in series to a secondary fixed bed reactor where the organic vapors were reformed at temperatures between 425 and 475 °C. Two conventional zeolites (HZSM-5 and Beta) and a mesostructured aluminosilicate Al-MCM-41 were used as catalysts in the reforming stage. Conversion values were not affected by the temperature in the reforming stage and remained fairly constant in all the experiments (89−92 wt %). In the absence of catalyst, the process generated a high proportion of hydrocarbons in the gasoline (C5−C12) and diesel (>C13) range (between 51 and 56 wt % and between 18 and 19 wt %, respectively) and a consequently lower amount of light hydrocarbon products (between 17 and 23 wt %), all of which consisted essentially of a ...

Direct Aerosol Synthesis of Large‐Pore Amorphous Mesostructured Aluminosilicates with Superior Acid‐Catalytic Properties

An old dream comes true: A direct and environmentally benign synthetic strategy was developed for the aerosol-based mass production of large-pore mesostructured aluminosilicate powders (see TEM image). Although amorphous, some powders exhibit higher activity towards m-xylene isomerization and lower coke formation than a Y-zeolite based industrial reference catalyst.

Direct Aerosol Synthesis of Large‐Pore Amorphous Mesostructured Aluminosilicates with Superior Acid‐Catalytic Properties

AbstractKatalysatoren en masse: Eine direkte und umweltverträgliche Synthesestrategie für die Aerosol‐basierte Massenproduktion großporiger mesostrukturierter Alumosilicatpulver wurde entwickelt (siehe TEM‐Bild). Obgleich amorph, zeigen einige Pulver eine höhere Aktivität für die Isomerisierung von m‐Xylol sowie eine geringere Koksbildung als ein industrieller Y‐Zeolith‐Referenzkatalysator.magnified image

Efficient dehydration of cinnamaldoxime to cinnamonitrile over H3PO4/Al-MCM-41

Abstract Cinnamonitrile was synthesized via the environmentally benign liquid-phase dehydration of cinnamaldoxime over Al-MCM-41 modified with H 3 PO 4 . FT-IR experiments with pyridine have indicated that these mesostructured aluminosilicates contain both Bronsted and Lewis acid sites. The catalytic properties of their H 3 PO 4 treated derivatives for dehydration of cinnamaldoxime have been evaluated. An aprotic solvent with a higher dielectric constant was preferred for this transformation. The conversion of cinnamaldoxime to cinnamonitrile increased with increasing the H 3 PO 4 content in the catalysts up to a maximum value of 30% and decreasing if H 3 PO 4 content was higher. The influence of other operating parameters was also investigated.

Adsorption of aniline onto hexagonal mesoporous silicate monoliths (HOM-2)

Hexagonally highly ordered monolithic mesoporous silica and aluminosilicate composites (HOM-2 and Al/HOM-2, respectively) were used as adsorbents for removal of aniline in aqueous solution. These HOM-adsorbents were fabricated by using a simple, reproducible and direct synthesis strategy in which instantly preformed liquid crystalline phase of Brij 56 (C16EO10) surfactant was used as templates. Extensive characterisation studies showed that Al/HOM-2 composites revealed higher surface area, smaller pore sizes and thicker pore wall than those of unloaded-HOM-2 monoliths, indicating that Al might be impregnated into the inner pores and the wall frameworks of HOM-2 silica monoliths. The adsorption experiments of aniline were investigated by using batch techniques. The results obtained showed that the aniline molecule strongly adsorbed onto the aluminosilicate mesostructures. In addition, the HOM-adsorbent exhibited high efficiency for aniline removal after several uses without loss of structural ordering, permitting the reusability for further selective separation of organic molecules from water.

Assembly of nanosized mesostructured aluminosilicates by in situ hydrolysis of inorganic precursors

This work emphasizes the influence of the addition of inorganic aluminum salt on the macroscopic properties of mesoporous aluminosilicates. It was found that upon the addition of an optimal amount of aluminum salt followed by a basic catalyst into the system, mesoporous aluminosilicate nanoparticles could be obtained, an observation that had barely been mentioned before. The assembly of nanosized mesostructures was explained by the separate control of silica hydrolysis and condensation in the system, each of which can be effectively manipulated by the aluminum salt and basic catalyst, respectively.

Hydrothermal synthesis of mesostructured aluminosilicate nanoparticles assisted by binary surfactants and finely controlled assembly process

Mesostructured aluminosilicate nanoparticles with narrow grain size distribution have been hydrothermally prepared for the first time with assistance of binary surfactants and separate hydrolysis and assembly of inorganic precursors. Compared to the sample assembled at room temperature, condensation degree and aluminum stability were greatly improved using hydrothermal treatment. The formation of nanoparticles consists of two steps, that is, the hydrolysis of silica precursor via catalysis by an acidic aluminum salt, followed by facile assembly into mesostructured nanocomposites with cationic micelles by addition of condensation catalyst. Simultaneously, nonionic polyethylene glycol (PEG-4000) present in this process would surround the formed nanoparticles through hydrogen-bonding interactions, thereby tailoring the grain size distribution and preventing aggregation and growth of inter-nanoparticles during the hydrothermal treatment process. The microstructure and chemical compositions of these products were thoroughly characterized by XRD, SEM, TEM, N 2 sorption and 27Al MAS NMR techniques.