Presence Of MCM-41 Research Articles

Pyrolytic Decomposition of Polyethylene in the Presence of Aluminosilicate Materials Containing Nickel Oxide

The work is devoted to the study of the pyrolysis of high-density polyethylene (PE) in the presence of aluminosilicate materials containing nickel oxide. The process of catalytic pyrolysis of plastics makes it possible to convert polymers into chemical compounds, which can later be used as an additional source of fuels, raw materials for the chemical industry or polymer production. The physicochemical parameters of materials containing nickel oxide have been established using the following methods: IR-Fourier spectroscopy; x-ray diffraction analysis; N2 physical adsorption method; thermogravimetric analysis; pyrolytic gas chromatography. The dependences of the chemical composition of PE pyrolysis products on the type of support used and the presence of nickel oxide. The presence of nickel oxide in the studied aluminosilicates increases the Lewis acidity, which increases the content of aromatic compounds in the pyrolysis products. The activation energy of the PE pyrolysis process in the presence of MCM-41 containing nickel oxide was calculated from experimental data.

Catalytic Ozonation of Pesticide Wastewater by Using MCM-41 and ZSM-5/MCM-41 as Catalysts

In the present study, two catalysts, MCM-41 and ZSM-5/MCM-41, were prepared by the hydrothermal synthesis method and their catalytic ozonation performances on pesticide wastewater were investigated. MCM-41 and ZSM-5/MCM-41 were proved to be a mesoporous structure and a micro-mesoporous structure, respectively, by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption measurements. The experimental results indicated that the chemical oxygen demand (COD) removal rate increased from 57.46% without catalysts to 79.35% and 87.56%, respectively, in the presence of MCM-41 and ZSM-5/MCM-41 after 100 min of catalytic ozonation. The catalytic activity of ZSM-5/MCM-41 was found to be greater than that of MCM-41. OH· played an important role in the catalytic ozonation, which was verified by the tert-butanol test. The catalysts had highest activity at pH of 7, and both higher and lower pH values reduced the catalytic ozonation. The optimal ozone dosage was found to be 22.0 mg L−1 min−1 for the COD removal of the pesticide wastewater. The catalysts could be reused five times without significant loss of the catalytic activity, suggesting that the catalysts could be promising catalysts for the catalytic ozonation of the pesticide wastewater.

MCM-41/PVA Composite as a Separator for Zinc-Air Batteries.

Membrane separators are one of the critical components in zinc–air batteries (ZABs). In the control of mass transfer, and hence, electrochemical reaction, membrane separators have an important role to play. This work addresses the issue of battery performance in a ZAB via a new composite membrane separator based on polyvinyl alcohol (PVA). To enhance the electrolyte uptake and ionic conductivity, mesoporous Mobil Composition of Matter No. 41 (MCM-41) is incorporated as a filler in the membrane while maintaining its integrity. The presence of MCM-41 is seen to reduce the number of cycles of secondary ZABs due to the uninvited drawbacks of increased zincate crossover and reduced triple phase boundary at the air cathode, which is pivotal for oxygen reduction reaction. Overall, results suggest that the application of the MCM-41/PVA composite has the potential for use as a separator in high-capacity primary ZABs.

Nicotine/mesoporous solids interactions at increasing temperatures under inert and air environments

In this work, the pyrolysis of nicotine under N2 and air atmospheres and in the presence of three mesoporous materials (SBA-15 and two different forms of MCM-41) has been studied by TGA-FTIR. The results obtained show that, in the absence of a catalyst, the thermal evolution of nicotine mainly results in the volatilization of the compound. In an air atmosphere, nicotine evolves at a slightly lower temperature than in N2 and the oxidation of the small solid residue at around 475°C is observed. The results obtained suggest that the main interaction of SBA-15 with nicotine is related to adsorption processes, with slight modifications of the reaction pathways in an N2 atmosphere and enhanced oxidation in the presence of air. The thermal decomposition of nicotine in an inert atmosphere and in the presence of MCM-41 indicates that, besides the desorption processes, an early decomposition step takes place, yielding several derivatives of nicotine. This phenomenon seems to be enhanced in an air atmosphere, where the presence of MCM-41 appears to markedly modify the evaporation and desorption of nicotine processes.

Morphology and properties of poly(methyl methacrylate) (PMMA) filled with mesoporous silica (MCM-41) prepared by melt compounding

This paper reports on the morphologies of poly(methyl methacrylate) (PMMA)/mesoporous silica (MCM-41) composites prepared by melt compounding with various MCM-41 contents in the range of 0.1–5 wt%, the interactions between the polymer and filler in these composites, and their thermomechanical, mechanical and thermal degradation properties. The composites formed transparent films at low filler loadings (<0.5 wt%) because of well-dispersed, unagglomerated particles. The presence of polymer did not alter the pore dimensions in the MCM-41 structure and it maintained its hexagonal structure, even though the polymer chains partially penetrated the pores during composite preparation. The PMMA interacted with the MCM-41 through hydrogen bonding. The glass transition temperature, as well as storage and loss modulus of PMMA increased with addition of, and increase in the amount of, MCM-41 due to the interaction of the polymer chains with the porous filler which restricted the mobility of the polymer chains and increased the stiffness of the composites. The thermal stability of PMMA apparently increased in the presence of MCM-41, although this observation probably was the result of delayed mass loss because of the trapping of volatile degradation products in the pores of MCM-41. The presence of MCM-41, up to 1.0 wt%, increased the impact strength of PMMA.

Manganese meso-tetra-4-carboxyphenylporphyrin immobilized on MCM-41 as catalyst for oxidation of olefins with different oxygen donors in stoichiometric conditions

Oxidation of olefins with tert-butyl hydroperoxide (TBHP), tetra-n-butylammonium periodate (TBAP) and potassium peroxomonosulfate (Oxone) in the presence of MCM-41 immobilized meso-tetra-4-carboxyphenylporphyrinatomanganese(III) acetate has been studied. The results of this study show better catalytic performance of the heterogonous catalyst using TBHP as oxidant in comparison with Oxone and TBAP in oxidation of the used olefins with the exception of cyclooctene. However, different order of reactivity of various olefins has been observed in the presence of Oxone and TBHP. In spite of the absence of good electron-withdrawing groups at the periphery of porphyrin ligand, the catalyst was recovered and reused (at least four times) without detectable catalyst leaching or a significant loss of the catalytic efficiency. All results have been obtained in the absence of using excess molar ratios of olefin to the oxidant, commonly employed as a strategy to overcome the instability of metalloporphyrins in oxidative conditions.

Study of the oxidative pyrolysis of tobacco–sorbitol–saccharose mixtures in the presence of MCM-41

In this work, the oxidative pyrolysis of a reference tobacco and of two ingredients widely used as cigarette ingredients, i.e.: sorbitol and saccharose, as well as that of the mixtures of these materials has been studied by thermogravimetric analysis. The comparison of the results obtained with these corresponding to the pyrolysis processes under inert atmosphere shows the existence of reaction steps corresponding to pure pyrolysis or cracking processes and others corresponding to the combustion or other oxidative processes. The presence of mesoporous MCM-41 as catalyst seems to have more significant influence on the non-oxidative pyrolysis stages. Moreover, the pyrolysis processes taking place at temperatures lower than 400 °C seem to be practically independent of the oxidative character of the atmosphere used.

Kinetic study of degradation of heavy oil over MCM-41

Thermogravimetry was applied in order to investigate the catalytic degradation of heavy oil (15.4oAPI) over silica-based MCM-41 mesoporous molecular sieve. This material was synthesised by the hydrothermal method, using cetyltrimethylammonium bromide as organic template. The physicochemical characterization by nitrogen adsorption, X-ray diffraction, and thermogravimetry, showed that the obtained material presents well-defined structure, with a uniform hexagonal arrangement. The thermal and catalytic degradation of heavy oil was performed by thermogravimetric measurements, in the temperature range from 30 to 900 °C, at heating rates of 5, 10, and 20 °C min−1. By using the model-free kinetics, proposed by Vyazovkin, it was determined that the activation energy to degrade the heavy oil was ca. 128 kJ mol−1, and for degradation of oil in presence of MCM-41, this value decreased to 69 kJ mol−1, indicating the performance of the mesoporores catalyst for the degradation process.

Study on the Mechanical Properties of PP/EPDM/Mesoporous MCM-41 Composites

Nano-sized as-synthesized MCM-41 (with template) particle, whose pore channels and outer surface are full of organic CTAB template, is used as compatibilizers for immiscible polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends. The mechanical properties of PP/EPDM/mesoporous MCM-41 ternary composites are investigated. The nano-structured MCM-41 (without template) material constituted by an ordered network of hexagonal channels is selected to compare with as-synthesized MCM-41 (with template) in mechanical properties of PP/EPDM blend. The results shows that tensile strength of the blend is increased by 13.6% and the impact strength is increased by 71.6% by addition 2 wt% content of as-synthesized MCM-41 (with template) compared to pure PP/EPDM. The presence of MCM-41(without template) in the blend cannot improve the mechanical properties obviously. SEM reveals that the enhancement of the interface is obtained by adding MCM-41 (with template). SEM also indicates that incorporation of as-synthesized MCM-41 (with template) into PP/EPDM blend can act as compatibilizer, which results in a decreased particle size of dispersion phase together with morphological evidence of interfacial adhesion. However, with the presence of MCM-41 (without template), the interface do not show clearly change compared with the PP/EPDM blend. The PP/EPDM/MCM-41 (with template) composites show higher tensile strength and impact strength than the PP /EPDM / MCM-41 (without template).

MCM‐41 Catalyzed Efficient Regioselective Synthesis of β‐Aminoalcohol under Solvent‐free Conditions

Abstractβ‐Aminoalcohols were synthesized in high yields by reaction of epoxides with amines in the presence of MCM‐41 as a green and reusable catalyst under solvent‐free conditions.

Accelerated Oxidation of Epinephrine by Silica Nanoparticles

We have measured the influence of mesoporous silica (MCM-41 and SBA-15) nanoparticles and dense silica nanoparticles on epinephrine oxidation, a pH-dependent reaction, whose rate is small in acidic or neutral solutions but much greater at higher pH. The reaction was measured by monitoring adrenochrome at 480 nm, the product of epinephrine oxidation. In distilled water (dH(2)O) with no particles present, the oxidation of epinephrine occurs slowly but more rapidly at higher pH. The presence of MCM-41 or silica spheres does not accelerate the oxidation, but SBA-15 does, showing that the difference in the structures of nanomaterials leads to differing effects on the epinephrine oxidative process. In phosphate buffered saline (PBS, pH = 7.4), epinephrine undergoes a much quicker oxidation, and, in this case, the presence of SBA-15 and MCM-41 makes it even more rapid. Silica spheres have no noticeable influence on the oxidation in PBS or in dH(2)O. The possibility that the catalytic effect of mesoporous silica nanoparticles (MSN) could result from the residue of templating chemicals, however, can be excluded due to the postsynthesis calcinations. Experiments with dithionite, added either earlier than or at the same time as the epinephrine addition, show that fast oxidation takes place only when dithionite and epinephrine are simultaneously added into PBS solution. This confirms a vital role of oxygen radicals (probably *O(2)(-)) in the oxidation of epinephrine. These oxygen radicals are likely to form and accumulate within the phosphate buffer or in the presence of MSN. Comparing the three kinds of silica nanoparticles applied, we note that mesoporous SBA-15 and MCM-41 materials own much larger surface area than solid silica particles do, whereas MCM-41 possesses a much narrower pore size (0.4-fold) than SBA-15. It seems, therefore, that large surface area, characteristic mesoporosity, and surface structures aid in the deposit of oxygen radicals inside MSN particles, which catalyze the epinephrine oxidation in a favorable phosphate environment.

Efficient solid-base catalysts for aldol reaction by optimizing the density and type of organoamine groups on nanoporous silica

A highly efficient solid-base catalyst for aldol condensation reaction was synthesized by grafting site-isolated secondary amines onto the channel walls of mesoporous silica, MCM-41, in a polar-protic solvent. These site-isolated organoamines pair up with the neighboring residual surface silanol (weak acid) groups to form optimized acid and base groups, which cooperatively catalyze the aldol condensation reaction with high TON (turn over number) and selectivity (alcohol products over alkene products). The organoamine samples grafted in a polar-protic solvent, isopropanol, showed higher catalytic efficiency toward aldol reaction than those grafted in a non-polar solvent, toluene, because the former gave a sample with less dense loading of grafted organoamines (or more silanols present in it). To elucidate the role of surface silanols as acidic sites and their ability to activate the substrates in aldol condensation, control experiment with diethylamine as a homogeneous catalyst in the presence of MCM-41, silica microspheres, methyl-capped MCM-41 or methyl-capped catalyst was carried out. MCM-41 resulted in significant enhancement of catalytic activity compared to the corresponding reactions conducted in the absence of MCM-41, or in the presence of methyl-capped catalysts or silica spheres. By testing materials with different grafted organoamine groups as catalysts, we also found that secondary amine functionalized sample produced the best acid and base pairs and most efficient catalytic activity in aldol reaction. This was followed by primary amines, while the tertiary amine functionalized samples showed negligible catalytic property.

Oxidative degradation of EVA copolymers in the presence of catalysts

A study of the catalytic degradation of EVA copolymers under air atmosphere has been carried out using thermogravimety (TG). Three commercial EVA copolymers and five zeolites and related materials catalysts have been selected. The degradation process in air atmosphere involves four main decomposition steps (as observed in TG), being more complex than the corresponding process in inert atmosphere. The presence of MCM-41, HY and H-β does not seem to noticeably affect to the overall degradation temperature, despite the temperature of maximum reaction rate for the second decomposition step being slightly displaced towards lower temperatures. Contrarily, the presence of HZSM-5 and HUSY zeolites seems to displace the main stage of the oxidative degradation process towards higher temperatures. Moreover, the relative importance of the second and third decomposition step is different depending on the amount and the nature of the zeolite mixed with the EVA sample. The results obtained show that the presence of the catalyst also enhances the formation of the carbonous residue.

Novel method for aroma recovery from the bioconversion of lutein to β-ionone by Trichosporon asahii using a mesoporous silicate material

In this work, we report on the synthesis and ability of the mesoporous material MCM-41 to adsorb the norisoprenoid beta-ionone. This compound, with a violet aroma note, can be produced from lutein by the yeast Trichosporon asahii through a bioconversion process. We found that beta-ionone inhibited the yeast growth and constrained aroma formation. Growth inhibition was overcome using silicate MCM-41 as sorbent device in a fermentation system that allowed product removal from the culture medium by headspace manipulation. Compared to a commercial silica gel, the mesoporous material exhibited a 4.5-fold higher beta-ionone adsorption. Contrasting to cultures without the sorbent device, the presence of MCM-41 allowed a marked increase (14-fold) in beta-ionone production. Our results suggested that confinement of the norisoprenoid into the sorbent material bypassed its toxicity which allowed a better beta-ionone production. This study represents the first report on the use of MCM-41 to recover an aroma produced by fermentation and therefore, a novel application for a mesoporous material.

Effect of MCM-41 on the physicochemical properties of Mo and NiMo catalysts and their performance in DBT conversion

The influence of mesoporous materials on the properties and HDS activity of Mo and NiMo catalysts was investigated for supports containing 50 wt.% of MCM-41. A series of catalysts was characterized by different techniques (S BET, TPD-NH 3, TPR, SEM, XPS) and tested in dibenzothiophene (DBT) conversion. On the surface of the catalysts containing mesoporous materials, agglomerations of the Mo oxo-species were observed. The presence of MCM-41 in the support visibly weakened the promoting effect of TiO 2 on the reducibility of Mo oxides. The results of DBT HDS showed that the NiMo catalyst supported on MCM-41 was not only less efficient than that supported on Al 2O 3 but also that supported on Al 2O 3–TiO 2. From the distribution of DBT HDS products we can conclude that over catalysts containing MCM-41 the desulphurization of DBT runs mostly via the DDS route.

Oxidative degradation of EVA copolymers in the presence of MCM-41

In this work, a study of the degradation of PE and an EVA copolymer under air atmosphere, in the presence and absence of mesoporous MCM-41, was carried out using thermogravimetric analysis (TGA), focusing on the analysis of the EVA behaviour during this the process. The results obtained show that the air atmosphere causes an increase of the complexity of the process, with respect to the thermal and catalytic pyrolysis in N 2 atmosphere, exhibiting more decomposition steps. The results obtained for both polymers show that the presence of MCM-41 does not practically affect the temperature of the oxidative decomposition processes, but a clear effect has been found on the main step of degradation, that supports the existence of cracking or incomplete oxidation reactions, and clearly it enhances the carbonaceous residue formation.

TGA/FTIR study of the catalytic pyrolysis of ethylene–vinyl acetate copolymers in the presence of MCM-41

The evolution of gas during the catalytic pyrolysis of three commercial ethylene–vinyl acetate copolymers in the presence of mesoporous MCM-41 has been studied by TGA/FTIR. The results have been compared with those corresponding to the thermal pyrolysis carried out under the same experimental conditions, and showed that the formation of alkenes and aromatics and shorter and/or more branched hydrocarbons is favoured in the presence of the catalyst.

Condensation of pyrrole with aldehydes in the presence of Y zeolites and mesoporous MCM-41 aluminosilicate: on the encapsulation of porphyrin precursors

Condensation of pyrrole and benzaldehyde was carried out in isooctane or cyclohexane in the presence of MCM-41, HY (Si/Al 15) and CoY (Si/Al 2.6). In all cases, formation of tetraphenylporphyrin (TPP) was observed in the organic solutions, even after dissolving with hydrofluoric acid the resulting MCM-41 solid employed in the condensation. In addition, some reaction intermediates containing one to two pyrrole heterocycles were also characterized in these solutions. In spite of this, the diffuse reflectance and IR spectra of the organic material adsorbed in the aluminosilicates after the condensation reaction were remarkably different from those characteristic of TPP. This discrepancy indicates that the material adsorbed inside the solid pores is not TPP but most probably any of its immediate porphyrinogen precursors. In this regard, the coincidence of the diffuse reflectance spectra obtained after the synthesis with those characteristic of porphomethenes and porphodimethenes was noted. Condensation of pyrrole and acetaldehyde follows the same pattern: lack of formation of meso-tetramethylporphyrin (TMP) inside the pores according to diffuse reflectance and IR spectroscopies, but detectable amounts of TMP in the organic solutions.