Synthesis and characterization of acidic properties of Al-SBA-15 materials with varying Si/Al ratios

Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, ²⁷Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH₃. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH₃ adsorption correlated well with activity indicate that acid sites with ΔH > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities.     

Synthesis of hierarchical MFI zeolite microspheres with stacking nanocrystals

MFI nanozeolite microspheres with intercrystal mesopores were synthesized by a steam-assisted crystallization–aggregation method, starting with close packed amorphous SiO₂ or Al-containing SiO₂ colloidal nanoparticles. The obtained samples with different Si/Al ratios were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) observations, nitrogen adsorption analyses and ²⁷Al magic angle spinning nuclear magnetic resonance (NMR). The SEM images clearly showed that the mean size of nanozeolite microspheres was ca. 0.5–3 μm, agglomerated from zeolite nanocrystals and varied with different Si/Al ratios. N₂ sorption analyses as well as TEM micrographs indicated the dual-porosity of samples, one is from intracrystal micropores, and the other is from intercrystal mesopores. ²⁷Al MAS-NMR suggested nearly all of the Al atoms were located at tetrahedral-coordinated sites in the framework. Furthermore, nanozeolite microspheres with various Si/Al ratios, even Si/Al equal to five, could be prepared by this facile route and less structure-directing agent was needed compared to conventional approach. This simple method could be easily extended to prepare other hierarchically structured zeolites.     

Influence of initial Si/Al ratios on the structural,acidic and catalytic properties of nanosized-ZSM-5/SBA-15 analog composites prepared from ZSM-5 precursors

Nano-ZSM-5/SBA-15 analog composites (ZSC) were prepared in a two-step process from ZSM-5 precursors with different Si/Al molar ratios (10–50) via high-temperature synthesis in mildly acidic media (200 °C, pH 3.5) aiming to evaluate the influence of the initial Si/Al ratio on their structural, acidic and catalytic properties. The resulting materials were characterized by SAXS, XRD, FTIR, TEM, N₂ sorption, ²⁷Al solid state-NMR, NH₃-TPD, FTIR spectroscopy of adsorbed pyridine, AAS and ICP-AES. Under the applied synthesis conditions, a ZSC material with controlled distribution of nano-ZSM-5 and SBA-15 analog phases can be prepared from ZSM-5 precursors by adjusting the initial Si/Al ratio in the range of 20–30. Increasing the initial Si/Al ratio to 50, only ZSM-5 nanocrystals were obtained whereas reducing the initial Si/Al ratio to 10 led to the formation of a disordered mesoporous SBA-15 analog. The total acidity increases with the crystallinity of the ZSM-5 phase as varying the Si/Al ratio from 10 to 30 despite the decreased amount of incorporated aluminum. However, the acidity declines slightly when raising the Si/Al ratio to 50 because of the low incorporated aluminum. The catalytic performance of the ZSC materials compared to the reference materials, i.e. purely mesoporous Al-SBA-15 and purely microporous H-ZSM-5 was assessed in the gas phase cracking of cumene and 1,3,5-tri-isopropylbenzene (TIPB) as test reactions. The results show that a balanced ratio of nano-ZSM-5 and SBA-15 analog phases obtained by tuning the initial Si/Al ratio is crucial to achieve superior catalytic performance of the ZSC materials in the cracking of both cumene and TIPB.     

Effect of different synthesis methods on the structural and catalytic performance of SBA-15 modified by aluminum

Two different aluminum-containing mesoporous Al/SBA-15 were prepared by post-synthesis method and direct synthesis method using P123 as structure directing agent and aluminum isopropoxide as the aluminum source. Samples were characterized in detail by XRD, N₂ adsorption, TEM,²⁷Al MAS NMR, and the acidic properties were performed by FT-IR of pyridine adsorption (Py-IR). The results show that Al/SBA-15 prepared by the direct synthesis method possessed higher BET surface area and larger pore volume. The acidic properties were investigated in Friedel–Crafts alkylation of phenol tert-butylation. The different synthesis method leads to distinct coordination of Al and intensity of acidity. Kinetics of the alkylation over Al/SBA-15 was also investigated. These results indicated that Al/SBA-15, prepared by post-synthetic grafting method, has more activity ability than the corresponding one synthesized by direct method since they contain more Lewis acid sites and Brönsted acid sites. The catalysts preserved almost their initial catalytic activity after four reuses.     

Optimization,synthesis and characterization of vanadium-substituted thick-walled three-dimensional SBA-16

A systematic study was carried out to examine the viable synthesis condition at high acidic condition for the direct incorporation of a high level of vanadium into the 3D cubic arrangement of SBA-16 molecular sieves. The extent of mesopore structural ordering was determined by X-ray diffraction, N₂ physisorption, SEM and TEM analysis. The coordination and nature of the V sites were characterized by FT-Raman, electron spin resonance, ²⁹Si nuclear magnetic resonance spectroscopy, UV–visible diffuse reflectance spectroscopy and NH₃–TPD analysis. The surface area of calcined V-SBA-16 was ～1000 m²/g, while the mesopore volume of the SBA-16 cage ranged from 0.3 to 0.6 cm³g^?1. The pore size distribution was ～3.0 nm with a wall thickness of ～9.7 nm at the maximum. The Si/V ratios as determined by ICP-OES technique was varied from 438 to 8, respectively. The calcined samples exhibited promising catalytic activity in the oxidation of styrene with tert-butyl hydroperoxide as an oxidant.     

Novel Pt/La1−xBixOF/SBA-16 catalysts for liquid-phase phenol oxidation

Novel catalysts of Pt/La_1−xBi_xOF/SBA-16 (SBA-16: Santa Barbara Amorphous No. 16) were synthesized, and their catalytic activities for phenol decomposition in the liquid phase were investigated. Lanthanum oxyfluoride (LaOF) was selected as the promoter due to its contribution to the smooth migration of oxygen species in the lattice and the acceleration of phenol adsorption on the catalyst surface. Reducible Bi³⁺ ions were introduced in the LaOF lattice to provide oxygen supply ability to LaOF. Among the prepared catalysts, the highest activity was obtained for the 7 wt% Pt/16 wt% La_0.99Bi_0.01OF/SBA-16 catalyst, which could remove 97% of phenol after 5 h of reaction at 80°C in an open-air atmosphere.     

Characterization and catalytic performance of mesoporous molecular sieves Al-MCM-41 materials

Mesoporous Al-MCM-41 materials of different Si/Al ratios have been synthesized and characterized by X-ray powder diffraction, ²⁷Al and ²⁹Si MAS NMR, differential thermogravimetric analysis, N₂ adsorption measurements, FT-IR and catalytic cracking of alkanes. The experimental results show that the incorporation of aluminium into the framework of MCM-41 has a great effect on the degree of long-distance order, the surface acidities and the mesoporous structures of the materials. With increase of the aluminium content, the amounts of tetrahedral framework aluminium and the acid sites on the samples increase, but the acid strength decreases. Al-MCM-41 materials exhibit high activity for n-C₁₆ ⁰ cracking and good selectivity for producing low carbon alkylenes, particularly for i-C₄ ⁼.     

One-pot Hydrothermal Synthesis of Mesoporous V-SBA-16 with a Function of the pH of the Initial Gel and its Improved Catalytic Performance for Benzene Hydroxylation

Abstract  

V-SBA-16 catalysts with uniform cubic mesoporous structure were prepared by direct hydrothermal method as a function of the pH of the initial gel and characterized by ICP, XRD, TEM, N₂ adsorption–desorption, DRUV—vis and Raman spectra. The pH of the initial gel in synthesis of V-SBA-16 show important effects on the maintenance of well ordered mesoporous structure, introduced vanadium content and the incorporation of vanadium into the network of SBA-16 type mesoporous material. The initial gel system with a pH value of 2.0 was found to be a suitable for incorporation of vanadium and retaining the mesostructure of SBA-16. The catalytic activities of V-SBA-16 catalysts were evaluated for the hydroxylation of benzene using molecular O₂ as the oxidant. The highest phenol yield of 30.4% with a selectivity of 90% and turnover number of 105 were obtained over the VS-2.0 (1.67) sample prepared at the initial gel system with pH value of 2.0, which is attributed to its high V content and uniform framework V species that highly dispersed on the well ordered SBA-16 type mesoporous materials.     

Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein

The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438 h^?1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of H_xNa_1–xZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol.     

One-Pot Synthesis and Characterization of Cu-SBA-16 Mesoporous Molecular Sieves as an Excellent Catalyst for Phenol Hydroxylation

Abstact  

Cu-SBA-16 has been prepared by one-pot synthesis method, and Characterized by XRD, TEM, and N₂ adsorption measurements. An extended study about the nature of copper species in the Cu-SBA-16 has been performed by FT-IR, UV-DRS, H₂-TPR and XPS. The copper species is mainly present on the mesoporous SBA-16 in the form of isolated mononuclear Cu²⁺ ions and highly dispersive CuO nanoclusters. The excellent catalytic activity has been obtained for phenol hydroxylation due to the presence of high amount of highly dispersive Cu species. The conversion to phenol and selectivity to diphenol are 29.4 and 91.5%, respectively.     

Effects of Fe addition on the structure and catalytic performance of mesoporous Mn/Al–SBA-15 catalysts for the reduction of NO with ammonia

Mesoporous Al–SBA-15 has been synthesized by a hydrothermal method and used as a support for Mn/Al–SBA-15, Fe/Al–SBA-15, and Mn–Fe/Al–SBA-15 catalysts. XRD, N₂ sorption, XPS, H₂-TPR and activity tests have been used to assess the properties of catalysts. The Mn–Fe/Al–SBA-15 catalyst exhibited a higher SCR activity than Mn/Al–SBA-15 or Fe/Al–SBA-15 due to a synergistic effect between Mn and Fe. After the addition of Fe, the binding energy of Mn 2p_3/2 on Mn–Fe/Al–SBA-15(573) decreased by about 0.4 eV and the Mn^4 +/Mn^3 + ratio decreased to 1.10. The appropriate Mn^4 +/Mn^3 + ratio may have a great effect on the reduction of NO over Mn–Fe/Al–SBA-15(573) catalyst.     

New mesoporous carbon materials synthesized by a templating procedure

The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀). SBA-15/cryogel carbon composites were obtained by sol–gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption–desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533–771 m² g^?1), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated.     

Facile tailoring of hierarchical mesoporous AlSBA-15 by ionic liquid and their applications in heterogeneous catalysis

Significant enhancement in the performance of incorporation of high content of aluminum within hierarchical mesoporous SBA-15 has been achieved by direct route using urea tetrachloroaluminate ionic liquid as novel aluminum source. The fabricated materials were fully characterized by N₂ sorption isotherms, powder X-ray diffraction (XRD), FT-IR, ²⁷Al MAS NMR, XRF, HRTEM and FESEM. The acidic properties of these materials have been examined using NH₃-TPD. The catalytic performance was investigated using cumene cracking and the esterification reaction as a probe molecules to estimate the acidity of the material. It is worth noting that the ionic liquid with accomplished Al–O–Si bonds is an efficient precursor to synthesis AlSBA-15 with high aluminum content (nSi/mAl?=?7) without destroying the structural order of the material in acidic medium. ²⁷Al MAS NMR spectra of AlSBA-15 show that all aluminum species were incorporated into the SBA-15 framework with nSi/mAl ratio up to 7. Overall, this work emphasize that the AlSBA-15 materials contain Bronsted and Lewis acid sites with medium acidity which makes them adequate to be adopted as acid catalysts in heterogeneous catalysis.     

Potassium-modified molybdenum-containing SBA-15 catalysts for highly efficient production of acetaldehyde and ethylene by the selective oxidation of ethane

Mo-incorporated SBA-15 (Mo-SBA-15) catalysts with different Mo:Si molar ratios were synthesized by a direct hydrothermal method, and SBA-15-supported Mo catalysts (Mo/SBA-15 and K-Mo/SBA-15) were prepared by an incipient-wetness impregnation method. The structures of the catalysts were characterized by means of N₂ adsorption–desorption, XRD, TEM, FT-IR, and UV-Raman, and their catalytic performance for the oxidation of ethane was tested. Turnover frequency and product selectivity are strongly dependent on the molybdenum content and catalyst preparation method. Furthermore, the addition of potassium promotes the formation of isolated tetra-coordination molybdenum species and potassium molybdate. The K/Mo-SBA-15 catalysts possess much higher catalytic selectivity to acetaldehyde in the selective oxidation of ethane than the supported molybdenum catalysts (Mo/SBA-15 or K-Mo/SBA-15). The highest selectivity of CH₃CHO + C₂H₄ 68.3% is obtained over the K/Mo-SBA-15 catalyst. Analysis of kinetic results supports the conclusion that ethane oxidation is the first-order reaction and ethane activation may be the rate-determining step for the oxidation of ethane. Ethylene is a possible intermediate for acetaldehyde formation.     

Grafting of lignin onto nanostructured silica SBA-15: preparation and characterization

The slow decline in oil reserves with mounting oil prices is pushing industry to find more sustainable sources for industrial manufacturing. Lignin is the second most abundant natural renewable biopolymer that is underutilized and has many functional groups (–OH, phenolics) that make the biopolymer a convenient substrate for materials manufacturing by the industry. The present study thus describes grafting of lignin onto nanostructured silica SBA-15 (Santa Barbara amorphous 15) by first silylating lignin with triethoxychlorosilane followed by treatment of silylated lignin with SBA-15. The resulting nanocomposite denoted as LIG–SBA-15-G was then characterized by powder X-ray diffraction, infra-red (FTIR), ³¹P nuclear magnetic resonance (³¹P NMR), N₂ adsorption (BET), scanning and transmission electron micrographs (SEM and TEM) and thermogravimetric analysis (TGA). X-ray data showed that LIG–SBA-15-G exhibited hexagonal structure closely similar to that observed for the SBA-15 host. FTIR of LIG–SBA-15-G showed characteristic absorption bands from lignin and attenuated Si–OH band due to its conversion to Si–O–Si ether bonds. Whereas, ³¹P NMR revealed that the majority of hydroxyl groups in lignin were replaced by Si–O–LIG ether bonds in LIG–SBA-15-G. SEM images of LIG–SBA-15-G displayed little changes in the macroscopic structure as compared to SBA-15. TEM images showed some disordered area in LIG–SBA-15-G and the grafted lignin appeared as black film on the silica surface. Using BET analysis the surface area of LIG–SBA-15-G was found to be 560 m² g^?1. Finally, TGA showed that LIG–SBA-15-G was more thermally stable than lignin and contained 13 % w/w lignin. Understanding the physicochemical and structural properties of the resulting lignin-nanosilica hybrid material should help engineer a robust and sustainable biomaterial suitable for various application, e.g. removal of contaminants from contaminated water.     

Functionalized Mesoporous SBA-15 with CeF<Subscript>3</Subscript>: Eu<Superscript>3+</Superscript> Nanoparticle by Three Different Methods: Synthesis,Characterization, and Photoluminescence

Luminescence functionalization of the ordered mesoporous SBA-15 silica is realized by depositing a CeF₃: Eu³⁺ phosphor layer on its surface (denoted as CeF₃: Eu³⁺/SBA-15/IS, CeF₃: Eu³⁺/SBA-15/SI and CeF₃: Eu³⁺/SBA-15/SS) using three different methods, which are reaction in situ (I-S), solution impregnation (S-I) and solid phase grinding synthesis (S-S), respectively. The structure, morphology, porosity, and optical properties of the materials are well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, N₂ adsorption, and photoluminescence spectra. These materials all have high surface area, uniformity in the mesostructure and crystallinity. As expected, the pore volume, surface area, and pore size of SBA-15 decrease in sequence after deposition of the CeF₃: Eu³⁺ nanophosphors. Furthermore, the efficient energy transfer in mesoporous material mainly occurs between the Ce³⁺ and the central Eu³⁺ ion. They show the characteristic emission of Ce³⁺ 5d → 4f (200–320 nm) and Eu^{3+ 5}D₀ → ⁷F _J (J = 1–4, with ⁵D₀ → ⁷F₁ orange emission at 588 nm as the strongest one) transitions, respectively. In addition, for comparison, the mesoporous material CeF₃: Eu³⁺/SBA-15/SS exhibits the characteristic emission of Eu³⁺ ion under UV irradiation with higher luminescence intensity than the other materials.     

Synthesis and characterization of the SBA-15/carbon cryogel nanocomposites

The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol–gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption–desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350–520 m² g^?1) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution.     

Uptake of decontaminating agent from aqueous solution: a study on adsorption behaviour of oxalic acid over Al-MCM-41 adsorbents

Hydrothermal method was followed to synthesis the mesoporous Al-MCM-41 (Si/Al = 25, 50, 75 and 100) and Si-MCM-41 molecular sieves using a cetyltrimethylammonium bromide as a surfactant and the materials were unambiguously characterized by XRD, N₂ sorption studies, ²⁷Al MAS-NMR and TEM. The removal of oxalic acid from aqueous solution was studied through an adsorption process because oxalic acid may cause complexes with radioactive cations during decontamination operation in nuclear industry, which resulting in interferences in their removal by conventional treatment. Adsorption of oxalic acid over Al-MCM-41 shows the applicability of Langmuir isotherm and follows first order kinetics. The effects of parameters such as contact time, concentration of oxalic acid, adsorbents (various Si/Al ratios of Al-MCM-41, Si-MCM-41 and activated charcoal) and pH have been investigated to yield higher removal of oxalic acid. The percentage of oxalic acid adsorbed per unit gram of adsorbent for Al-MCM-41 at Si/Al = 100, 75, 50 and 25, Si-MCM-41, and activated charcoal are 34.6, 40.9, 51.4, 61.3, 16.1 and 60, respectively. Retainment of crystallinity and absence of structural collapse of Al-MCM-41 after desorption and adsorption of oxalic acid, respectively has been achieved in this study.     

Effect of metal-support interaction on the structural and enhanced photocatalytic performance of mesoporous M–TiO<Subscript>2</Subscript>/SBA-16 (M = Ag and Fe)

In this paper, a series of metal supported TiO₂/SBA-16 photocatalysts were successfully synthesized by wet impregnation method. The synthesized samples were characterized by X-ray diffraction (XRD), Raman spectra, N₂ adsorption–desorption, transmission electron microscopy (TEM), UV–visible absorption spectra (UV-vis) and X-ray photoelectron spectroscopy (XPS). It was found that SBA-16 retained the ordered mesostructure after modification. The results shown that loading different metal elements was found to have significant influences on the crystallographic structure and physical properties. Moreover, the prepared materials were evaluated on photodegradation of Rhodamine B (RhB). Experiment results showed that the degradation of RhB by these catalysts follows the pseudo-first-order kinetic model. The effect of metal element on photocatalytic activity can be attributed that the appropriate amounts of metal concentration can enhance the photocurrent due to the reduced electron–hole recombination, which can improve the efficiency of photocatalytic reactions.     

Mesoporous beta zeolite obtained by desilication

Zeolite beta crystals (Si/Al = 35) synthesized in fluoride medium were treated in aqueous 0.2 M NaOH solution for mesopore formation by selective extraction of framework silicon. A 16 parallel-batch reactor was used to study the influence of the treatment time and temperature on the physico-chemical properties of the zeolites, which were characterized by ICP-OES, XRD, N₂ adsorption at 77 K, SEM, TEM, DRIFTS, and in situ ATR-IR. Alkaline treatment of H-beta within the optimal window of Si/Al ratios identified for other zeolite families leads to extensive silicon extraction at mild treatment conditions. This originates substantial mesoporosity and presumably improved transport, but negatively impacts on the microporous and acidic properties of the resulting sample. Consequently, the alkaline-treated beta zeolites show lower catalytic activity in the acid-catalyzed liquid-phase benzene alkylation than the purely microporous parent material. The relatively low stability of framework aluminum in BEA, compared to MFI and MOR, is detrimental for the controlled mesopore formation by Si dissolution, since aluminum cannot optimally exert its pore-directing role.