Acid catalyzed organic transformations by heteropoly tungstophosphoric acid supported on MCM-41

Green construction of eco-friendly phosphotungstic acid Sr-MOF catalysts for crystal violet removal and synthesis of coumarin and xanthene compounds

There is an urgent need to improve engineering and synthetic chemistry, either through the use of eco-friendly starting materials or the proper design of novel synthesis routes. This reduces the contamination of toxic chemicals and helps the disposal of organic dyes. In the current work, a metal–organic framework-based Sr(ii) was fabricated to achieve the desired goal for dye removal and catalysis. Sr-MOF-based phosphotungstic acid (PWA/Sr-MOF) was hydrothermally synthesized to study its adsorption and catalytic activities. Remarkably, about 99.9% of crystal violet (CV) dye was removed using PWA/Sr-MOF within 90 min at room temperature. Various factors have been studied to investigate the optimum conditions such as pH of solution, initial dye concentration, contact time, and temperature. The maximum adsorption capacity of CV dye was reached after 90 min and well fitted the pseudo-second kinetic order and Langmuir adsorption isotherm. Coumarin and xanthene reactions were chosen to test the catalytic activity of the prepared PWA/Sr-MOF at 373 K. Furthermore, structural and chemical characterization of the fabricated samples was obtained using FT-IR, XRD, TGA, DTA, TEM, EDX, and XPS. PWA/Sr-MOF can be considered as a promising and green framework in the material design used to study catalytic and adsorption performances.

There is an urgent need to improve engineering and synthetic chemistry, either through the use of eco-friendly starting materials or the proper design of novel synthesis routes.

Tungsten-substituted molybdophosphoric acid impregnated with kaolin: effective catalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones via biginelli reaction

A series of highly reusable heterogeneous catalysts (10-25 wt% PMo7W5/kaolin), consisting of tungsten-substituted molybdophosphoric acid, H3PMo7W5O40·24H2O (PMo7W5) impregnated with acid treated kaolin clay was synthesized by the wetness impregnation method. The newly synthesized catalyst was fully characterized using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform infrared (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis and thermal analysis (TG-DTA). The synthesized materials were shown to be efficient in the synthesis of 3,4-dihydropyrimidin-2(1H)-ones via Biginelli reaction under solvent-free conditions. The obtained results indicate that 20% PMo7W5/kaolin catalyst showed remarkably enhanced catalytic activity compared to the bulk PMo7W5 catalyst, and also the (10 and 15%) PMo7W5 catalyst supported on kaolin clay.

Study on heteropolyacid-based catalysts with high activity and reusability for isoprene synthesis from formaldehyde and isobutene

SiW/S-1 catalysts exhibited excellent catalytic activity and reusability due to the highly dispersed SiW and MFI structure of S-1.

A mesoporous SnO–γ-Al2O3 nanocomposite prepared by a seeding-crystallization method and its catalytic esterification performances

A mesoporous SnO–γ-Al₂O₃ nanocomposite was synthesized by a seeding-crystallization method and investigated in catalytic esterification of pentaerythritol and stearic acid to produce pentaerythrityl tetrastearate.

Ultrasonic-assisted preparation of highly active Co3O4/MCM-41 adsorbent and its desulfurization performance for low H2S concentration gas

Co₃O₄/MCM-41 adsorbents were successfully prepared by ultrasonic assisted impregnation (UAI) and traditional mechanical stirring impregnation (TMI) technologies and characterized by X-ray diffraction (XRD), N₂ adsorption desorption, Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry-differential thermal analysis (TG-DTA). The H₂S removal performances for a simulated low H₂S concentration gas were investigated in a fixed-bed. The effect of preparation and adsorption conditions on the H₂S removal over Co₃O₄/MCM-41 were systematically examined. The results showed that UAI promotes more and well defined highly dispersed active Co₃O₄ phase on MCM-41. As compared to the Co₃O₄/MCM-41-T prepared via TMI, the saturated H₂S capacity of Co₃O₄/MCM-41-U prepared via UAI improved by 33.2%. The desulfurization performance of adsorbents decreased in the order of Co₃O₄/MCM-41-U > Co₃O₄/MCM-41-T > MCM-41. The Co₃O₄/MCM-41-U prepared using Co(NO₃)₂ concentration of 10%, ultrasonic time of 2 h, calcination temperature of 550 °C and calcination time of 3 h exhibited the best H₂S removal efficiency. At adsorption temperature of 25 °C with model gas flowrate of 20 mL min⁻¹, the breakthrough time of Co₃O₄/MCM-41-U was 10 min, and the saturated H₂S capacity and H₂S removal rate was 52.6 mg g⁻¹ and 47.8%, respectively.

Co₃O₄/MCM-41 adsorbent with high surface area and more active sites was successfully prepared by ultrasonic assisted impregnation (UAI) technology and it has been found that the sulfur capacity was improved by 33.2% because of ultrasonication.

Study on the preparation of amine-modified silicate MCM-41 adsorbent and its H2S removal performance

A series of APTMS ((3-aminopropyl)trimethoxysilane)-modified silicate MCM-41 adsorbents ( x-APTMS/MCM-41, x is the volume of APTMS per 1 g of silicate MCM-41) with different APTMS contents was prepared, and the effects of APTMS content on the desulfurization performance of the APTMS/MCM-41 adsorbents were studied in a fixed adsorption bed using H2S and N2 mixture as a model gas. The as-prepared adsorbents were characterized by X-ray diffraction analysis, N2 adsorption–desorption, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The results showed that all the APTMS-modified x-APTMS/MCM-41 adsorbents retained the mesoporous silica structure of MCM-41. The Brunauer–Emmett–Teller-specific surface area of x-APTMS/MCM-41 increased slightly with increasing x at first and then decreased with further increasing APTMS content. The H2S removal performances of x-APTMS/MCM-41 adsorbents decreased in the order 0.6-APTMS/MCM-41 > 0.7-APTMS/MCM-41 > 0.5-APTMS/MCM-41 > 0.4-APTMS/MCM-41 > 0.8-APTMS/MCM-41. At x = 0.6, the maximum H2S removal rate of 54.2% and H2S saturated capacity of 134.4 mg g−1 were observed. The regeneration experiment of 0.6-APTMS/MCM-41 adsorbent after three times regeneration at 423 K for 3 h in nitrogen confirmed that it possessed a good regenerability.

Zn supported on titania-doped mesoporous silicate MCM-41 as efficient catalysts for acetylene hydration

A highly efficient grafting method to synthesise Ti-doped MCM-41 mesoporous supports and their respective Zn catalysts was investigated.

Amino-modified molecular sieves for adsorptive removal of H2S from natural gas

Amine-modified MCM-41 adsorbents (APTMS/MCM-41, PEI/MCM-41 and AAPTS/MCM-41) were prepared and characterized by XRD, N2 adsorption-desorption, FT-IR, TEM, SEM and TG-DTA. The performance of each adsorbent in a fixed adsorption bed for H2S removal was measured using a mixture of oxygen, nitrogen and hydrogen sulfide gases. It was found that the specific surface area decreased and the topography changed significantly after the use of each modified adsorbent. Nevertheless, all amine-modified MCM-41 adsorbents retained mesoporous silica of MCM-41. The H2S removal rate and saturated H2S capacity of APTMS/MCM-41 improved from 32.3% to 54.2% and 119.5 to 134.4 mg g-1, respectively, compared with that of MCM-41, and it showed the best performance among all adsorbents. APTMS/MCM-41, PEI/MCM-41 and AAPTS/MCM-41 were regenerated by maintaining at 423, 523 and 373 K in nitrogen for 3 h, respectively, and thus possessed high regenerability.

Gas phase dehydration of glycerol to acrolein on an amino siloxane-functionalized MCM-41 supported Wells–Dawson type H6P2W18O62 catalyst

A novel amino siloxane-functionalized MCM-41 supported Wells–Dawson type H₆P₂W₁₈O₆₂ (D-HPW) catalyst was synthesized by a two-step method and investigated in the gas phase dehydration of glycerol to acrolein, and the yield of acrolein was obviously improved.

Surface Properties of Al-Functionalized Mesoporous MCM-41 and the Melting Behavior of Water in Al-MCM-41 Nanopores

We report an experimental investigation of structural and adhesive properties for Al-containing mesoporous MCM-41 and MCM-41 surfaces. In this work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant. The incorporation of aluminum was evidenced simultaneously without any change in the hexagonal arrangement of cylindrical mesopores. The porous materials were examined by techniques such as low-temperature nitrogen sorption, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Surface properties were determined through X-ray photoelectron spectroscopy, potentiometric titration, and static contact angle measurements. It was shown that an increase in surface acidity leads to an increase in the wetting energy of the surface. To investigate the influence of acidity on the confinement effects, the melting behavior of water in Al-MCM-41 and MCM-41 with the same pore size was determined by using dielectric relaxation spectroscopy and differential scanning calorimetry methods. We found that the melting-point depression of water in pores is larger in the functionalized pores than in pure silica pores of the same pore diameter.

Ultrasound-assisted biodiesel production by a novel composite of Fe(III)-based MOF and phosphotangestic acid as efficient and reusable catalyst

In this work, esterification of oleic acid by various alcohols is achieved with high yields under ultrasonic irradiation. This reaction performed with a novel heterogeneous catalyst that fabricated by heteropoly acid and Fe(III)-based MOF, namely MIL-53 (Fe). Syntheses of MIL-53 and encapsulation process carry out by ultrasound irradiation at ambient temperature and atmospheric pressure. The prepared composite was characterized by various techniques such as XRD, FT-IR, SEM, BET and ICP that demonstrate excellent catalytic activities, while being highly convenient to synthesize. The obtained results revealed that ultrasound irradiation could be used for the appropriate and rapid biodiesel production.

Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy

Micro Raman spectroscopy was applied to investigate the speciation of heteropoly and isopoly molybdates in 0.05 and 0.005 M aqueous solutions of 12-molybdophosphoric acid at pH values between 1 and 6. For comparative purposes, (31)P NMR spectroscopy was applied too. It is shown that stability of Keggin anion is influenced both by pH and concentration of solution. The Keggin structure is stable in acidic solutions (pH<1.6) while defective Keggin structures are formed with further alkalization (up to pH5.6). Monolacunary anion PMo11O(39)(7-) is the main component in the pH region from 1.6 to 3.4. Further removal of molybdenyl species causes the appearance of other vacant Keggin structures such as PMo9O31(OH)(3)(6-) and PMo6O(25)(9-) at about pH4. At pH5.0, anion PMo6O(25)(9-) is the main species. In solutions with pH greater than 5.0, heteropolymolybdates disappear completely and isopolymolybdates Mo7O(24)(6-) and MoO(4)(2-) are formed in higher amounts. In more diluted solution of 0.005 M, the decomposition scheme of 12-molybdophosphoric acid solution with increasing of pH takes place without observation of significant amounts of Mo7O(24)(6-) species. If alkalinization is performed with 0.5 M instead of 5 M NaOH, there are no significant changes in the Raman spectra of solutions. It is shown that the spectra of evaporated samples may be used for the identification of molecular species in corresponding concentrated solutions. However, Raman spectra of dry residues of more diluted solutions differ from spectra of corresponding solutions due to the reactions performed during the process of drying and cannot be used for unambiguous identification of species in solution. Acidification of 0.05 M solution of Na2MoO4 shows that at pH>5.6, molybdate anion MoO(4)(2-) dominates, while in the pH range between 5.6 and 1, heptamolybdate anion Mo7O(24)(6-) is preferentially formed.

Fabrication of hierarchically mesoporous CuO nanostructures and their role as heterogenous catalysts and sensors

Tween-80 templated mesoporous CuO (mpCuO) nanostructures were explored via a facile, environmentally friendly and scalable sol–gel route for heterogeneous catalysis and sensor technology.

Preparation and characterization of NiW supported on Al-modified MCM-48 catalyst and its high hydrodenitrogenation activity and stability

Al-containing MCM-48 with different Si/Al ratios and aluminum free MCM-48 materials were successfully prepared with CTAB and P123 as a co-template.

Conversion of glucose into 5-hydroxymethylfurfural catalyzed by chromium(iii) Schiff base complexes and acidic ionic liquids immobilized on mesoporous silica

A series of novel catalysts were synthesized using immobilized chromium(iii) complexes and ionic liquids on the surface of MCM-41.

The comparison of two classes of bifunctional SBA-15 supported platinum–heteropolyacid catalysts for the isomerization of n-hexane

SBA-15 supported bifunctional acidic HSiW–Pt catalysts proved to be active, stable and highly selective in the isomerization of n-hexane.