Pyrolysis of biomass in the presence of Al-MCM-41 type catalysts

Al-MCM-41 type mesoporous catalysts were used for converting the pyrolysis vapours of spruce wood in order to obtain better bio-oil properties. Four Al-MCM-41 type catalysts with a Si/Al ratio of 20 were tested. The catalytic properties of Al-MCM-41 catalyst were modified by pore enlargement that allows the processing of larger molecules and by introduction of Cu cations into the structure.Spruce wood pyrolysis at 500 °C was performed and the products were analysed with the help of on-line pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). In addition, thermogravimetry/mass spectrometry (TG/MS) experiments were applied for monitoring the product evolution under slow heating conditions (20 °C/min) from 50 to 800 °C.Levoglucosan is completely eliminated, while acetic acid, furfural and furanes become quite important among cellulose pyrolysis products over the unmodified Al-MCM-41 catalyst. The dominance of phenolic compounds of higher molecular mass is strongly cut back among the lignin products. Both the increase of the yield of acetic acid and furan and the decrease of large methoxyphenols are repressed to some extent over catalysts with enlarged pores. The Cu modified catalyst performed similarly to the catalyst with enlarged pore size in converting the pyrolysis vapours of wood, although its pore size was similar to the unmodified Al-MCM-41.     

Efficient catalysis of mesoporous Al-MCM-41 for Mukaiyama aldol reactions

Mesoporous aluminosilicates, Al-MCM-41 (Si/Al = 20 and 50), efficiently catalyzed Mukaiyama aldol reaction of benzaldehyde with 1-(trimethylsiloxy)cyclohexene in CH₂Cl₂ at 0 °C to afford the corresponding β-trimethylsiloxy ketone in quantitative yield. On the other hand, mesoporous silica (MCM-41), amorphous SiO₂–Al₂O₃, and H–Y and H-ZSM-5 zeolites barely catalyzed the reaction. Additionally, the less ordered Al-MCM-41 prepared by mechanical compression exhibited much lower catalytic activity compared with Al-MCM-41, indicating that the presence of the ordered mesoporous structure in aluminosilicates is crucial for the catalysis. The Al-MCM-41 catalyzed Mukaiyama aldol reaction was applicable to a wide range of aldehydes and silyl enol ethers. Furthermore, the Al-MCM-41 catalyst could be recycled at least three times without any loss in the yield. Thus, mesoporous aluminosilicates are promising heterogeneous catalysts for fine chemicals synthesis.     

Liquid phase catalytic hydrodechlorination of aryl chlorides over Pd–Al-MCM-41 catalyst

Supported Pd catalysts were prepared by direct hydrothermal (DHT) or template-ion exchange (TIE) method on Al-substituted MCM-41 as the support and tested in the hydrodechlorination of aryl chlorides such as 4-chloroanisole in liquid phase, together with impregnated Pd catalysts as references. When Pd was loaded on Al-MCM-41 with the Si/Al ratio of 150 by the TIE method, the catalyst showed the highest activity among the Pd catalysts prepared. PdO originally formed on the catalyst surface was in situ reduced to Pd metal during the reaction as the active form for the dechlorination. The activities of the supported Pd catalysts well correlated with the Pd dispersion on the TIE or impregnated Pd catalysts, whereas the DHT catalysts showed relatively high activities independently on the Pd dispersions. It was confirmed that the dechlorination proceeded by a heterogeneous mechanism catalyzed by Pd metal particles sized less than 10 nm on the surface of the catalyst. Al substitution for Si on MCM-41 was effective for the loading of Pd metal with the high dispersion, none the less Pd was located on the surface of the TIE catalyst particles and no significant effect of mesoporous structure on the reaction was observed. Methanol was the most profitable as the solvent among the various solvents tested. Various types of arylchlorides bearing hydroxy, methoxy, methyl, nitro and phenylcarbonyl group at the p-position were efficiently dechlorinated over Pd–Al-MCM-41 catalyst at 40 °C. Electrophilic attack of arylchloride was proposed as the rate determining step, where ionic mechanism positively worked and electron-releasing substituents increased the catalytic activity.     

Near-infrared luminescent mesoporous MCM-41 materials covalently bonded with ternary thulium complexes

Two β-diketones 4,4,4-trifluoro-1-2-thenoyl-1,3-butanedione (Htta) and 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (Htfnb), which contain trifluoroalkyl chain, were selected as the main sensitizer for synthesizing Tm(L)₃phen (L = tta, tfnb) complexes. The two near-infrared (NIR) luminescent thulium complexes have been covalently bonded to the ordered mesoporous material MCM-41 via a functionalized 1,10-phenanthroline (phen) group 5-(N,N-bis-3-(triethoxysilyl)propyl)ureyl-1,10-phenanthroline (phen-Si) [The resultant mesoporous materials are denoted as Tm(L)₃phen–MCM-41 (L = tta, tfnb)]. The Tm(L)₃phen–MCM-41 (L = tta, tfnb) mesoporous materials were characterized by small-angle X-ray diffraction (XRD) and N₂ adsorption/desorption, and they show characteristic mesoporous structure of MCM-41. Luminescence spectra of the Tm(L)₃phen–MCM-41 (L = tta, tfnb) mesoporous materials were recorded and the corresponding luminescence decay curves were obtained. After ligand-mediated excitation, the emission spectra of the Tm(L)₃phen–MCM-41 (L = tta, tfnb) mesoporous materials show the characteristic NIR-luminescence of the Tm³⁺ ion. The full width at half maximum (fwhm) of the 1474-nm emission band are 96 and 100 nm for Tm(tta)₃phen–MCM-41 and Tm(tfnb)₃phen–MCM-41, respectively. The good luminescent performances enable these NIR-luminescent mesoporous materials to have potential applications in optical amplification [broadening amplification band from C band (1530–1560 nm) to S⁺ band (1450–1500 nm)]. Furthermore, the comparison of the luminescence behavior for Tm(tta)₃phen–MCM-41 and Tm(tfnb)₃phen–MCM-41 mesoporous materials was investigated. It shows that Tm(tfnb)₃phen–MCM-41 is somewhat superior to Tm(tta)₃phen–MCM-41 as optical amplifier.     

Synthesis of mesoporous molecular sieves as catalytic template for the growth of single walled carbon nanotubes

Mesoporous Mo MCM-41 and Nb MCM-41 molecular sieves were synthesized in various ratios by hydrothermal method and were characterized by XRD, N₂ adsorption isotherm and DRS-UV spectroscopy. The calcined samples were used as catalysts for the growth of carbon nanotubes using acetylene by chemical vapor deposition technique at 700–900 °C. The deposited carbon materials by acetylene decomposition, were found to be more in the case of Nb MCM-41 than in Mo MCM-41, and their catalytic activity was found to be in the order as Si/Nb = 100 > 75 > 50 > 25, and the same trend is followed for Mo MCM-41 molecular sieves. The catalytically synthesised carbon materials were characterized with Raman spectroscopy, SEM and TEM. We have obtained single walled carbon nanotubes in bundles with a tube diameter of 1.06–2.9 nm and 1.08–2.3 nm formed over Mo MCM-41 and Nb MCM-41, respectively, according to Raman spectra. Similarly well graphitised single walled carbon nanotubes formation was observed from TEM. From this observation, it is confirmed that Mo MCM-41 (100) and Nb MCM-41 (100) exist as stable catalysts for the synthesis of single walled nanotube.     

Unique vapor phase synthesis of 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine selectively over Co–Al-MCM-41

Cyclization of cyclopentanone, formaldehyde and ammonia in vapor phase gives 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine (HHDCP) and spiro[cyclopentane-1,8′-(1′,2′,3′,5′,6′,7′,8′,8′a) octahydrodicyclopenta[b,e]]pyridine (SCOHDCP) over zeolites HY, HZSM-5, Hβ and mesoporous Al-MCM-41 molecular sieves. The preliminary screening of catalysts clearly shows that Al-MCM-41 is more suitable for the vapor phase synthesis of HHDCP. As the NH₃-TPD profiles of Al-MCM-41 show wide range distribution of acid sites in the temperature range of 200–600 °C (weak–medium–strong), Al-MCM-41 is further modified with transition metal ions like V(V), Mn(II), Fe(III), Co(III), Cu(II), La(III) and Ce(III) to fine tune the acid sites. Correlation of activity and selectivity of transition metal modified Al-MCM-41 with the NH₃-TPD profiles show that though the conversions are high, selectivity of either HHDCP or SCOHDCP is a preference of acid site strength formed on metal ion modification. Interestingly Co²⁺ ion modification of Al-MCM-41 resulted distinctly into two sets of acid sites with T_max around 218 °C (weak–medium) and 673 °C (strong). The reaction is studied on Co–Al-MCM-41 by adsorbing pyridine at 300 °C. The typical acidity available on pyridine adsorbed Co–Al-MCM-41 around 300 °C is showing cyclization activity forming only HHDCP indicating that weak–medium acid sites are responsible for the formation of HHDCP. Based on the product distribution plausible reaction mechanism is proposed.     

Mesoporous silicas containing carboxylic acid: Preparation,thermal degradation,and catalytic performance

The calcination and thermal degradation behaviors of surfactants in mesoporous silicas SBA-15 and MCM-41 were investigated by FT-IR, ¹³C CP/MAS NMR, TG/DTA, and GPC. It was found that carboxylic acid-containing products were generated as active components in the mesopores of SBA-15 and MCM-41 from the triblock copolymer (PEO)₂₀(PPO)₇₀(PEO)₂₀ and cetyltrimethylammonium bromide (CTAB), respectively; the latter materials were used as templates. The carboxylic acid-containing mesoporous silica obtained showed a catalytic activity for hydrolysis of sucrose. The acidity was evaluated by means of NaOH titration. The acidity sensitively depended on both the calcination temperature and the atmosphere; the maximum appeared at 150 °C in air for SBA-15 where the highest activity was observed. However, the product in MCM-41 showed a lower catalytic activity than that in SBA-15. The SBA-15 product was easily leached from the mesopores of SBA-15 into the solution, but the degree of leaching for MCM-41 was considerably smaller than that for SBA-15.     

Vapor-Phase Isopropylation of Phenol over Fe-Containing Al-MCM-41 Molecular Sieves

Al-MCM-41 and Fe-containing MCM-41 molecular sieves are hydrothermally synthesized. The low-angle XRD analysis shows that iron incorporation in Al-MCM-41 retains the hexagonal structure of MCM-41. The higher d-spacing values of Fe-Al-MCM-41 catalysts than those of Al-MCM-41 indicate the incorporation of iron into the framework. The mesoporous nature of the materials was confirmed by nitrogen adsorption isotherms. Electron paramagnetic resonance (EPR) and diffuse reflectance spectra (DRS) techniques confirm the tetrahedral coordination of iron into the Al-MCM-41 framework. Acidity of the synthesized catalysts was analyzed by both TPD of ammonia and pyridine-adsorbed FT-IR spectroscopy. The acidity measurements indicate that iron incorporation increases both Lewis and Brønsted acidity of the catalysts. Vapor-phase isopropylation of phenol with the new'alkylating agent isopropyl acetate was carried over the H-forms of the above catalysts. The phenol to isopropyl acetate ratio of 1?:?2 and the phenol space velocity of 1.1 h^-1 were found to be the optimum conditions for better phenol conversion and para isomer (4-isopropyl phenol) selectivity. On comparison, the Fe-incorporated Al-MCM-41 catalysts show significantly higher phenol conversion and selectivity toward the important product 4-isopropyl phenol (4-IPP) may be due to stronger Brønsted acid sites generated by the strengthening effect of nearby Lewis acid sites. Further, the undesired and dialkylated products selectivity are found to be lower over Fe-incorporated Al-MCM-41 than pure Al-MCM-41 catalysts.     

Effect of SiO2 pore size on catalytic fast pyrolysis of Jatropha residues by using pyrolyzer-GC/MS

Catalytic fast pyrolysis of Jatropha residue was performed over SiO₂ catalysts with different pore sizes (SiO₂-Q3, -Q10, -Q30, and -Q50 with pore diameters of 3, 16, 45, and 68 nm, respectively) at 500 °C using a pyrolyzer-gas chromatography/mass spectrometry system. SiO₂-Q10, which combined weak acidity and medium porosity, was the most effective catalyst in removing oxygenated compounds such as acids, ketones, and aldehydes, which are the principal reason for the polymerization of hydrocarbons from bio-oil, and in inhibiting coke and polycyclic aromatic compound formation. SiO₂-Q10 is also useful for stabilizing bio-oil and has potential for catalytic fast pyrolysis.     

Photophysical properties of a naphthalimide derivative encapsulated within Si-MCM-41, Ce-MCM-41 and Al-MCM-41

4-Piperazinyl-N-methyl-1,8-naphthalimide (PMN) was synthesized and encapsulated into mesoporous molecular sieves. The fluorescent emission spectra and fluorescence decay of PMN/M-MCM-41 (where M = Si, Ce, Al) were used to investigate the photophysical properties of the hybrid composites. The emission intensity of 4-piperazinyl-N-methyl-1,8-naphthalimide can be increased by decreasing the pH environment of the hybrid composites; the emission intensity varied with different MCM-41 hosts in the order: PMN/Al-MCM-41 > PMN/Si-MCM-41 > PMN/Ce-MCM-41; the fluorescence lifetime of PMN molecules followed the same order. The reasons for the improved fluorescence intensity and the prolonged lifetime of PMN in a low pH environment and Al-MCM-41 are discussed.     

On the Confinement Effect During Catalytic Reaction Over Al-MCM-41

A comprehensive study has been made on the cracking abilities of mesoporous aluminosillicate MCM-41 materials with different Si/Al ratios (15–∞) and pore diameters (1.6–3.0 nm) by using 1,3,5-triisopropylbenzene (1,3,5-TiPB) cracking as the test reaction. The roles of Al content and pore diameter on the catalytic features of the samples were evaluated by the conversion of 1,3,5-TiPB, coke content and deactivation parameters. It is found that the catalytic activity is mainly controlled by adsorptive properties towards the reactant and the dispersion of acid sites. In terms of their catalytic performances, cracking reaction over aluminosilicate mesoporous materials is more favorable for catalysts with smaller pore size and higher Al concentration. Moreover, coking is found responsible for catalyst deactivation during 1,3,5-TiPB cracking reaction over Al-MCM-41.     

Synthesis of dypnone using SO4/Al-MCM-41 mesoporous molecular sieves

The mesoporous molecular sieves Al-MCM-41 with Si/Al ratio equal to 16, was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTMA⁺Br⁻) as surfactant. The same ratio of Al-MCM-41 materials was impregnated using sulfuric acid, the materials as sulfated Al-MCM-41 (SO₄²⁻/Al-MCM-41). The mesoporous materials viz Al-MCM-41 and SO₄²⁻/Al-MCM-41 were characterized using several techniques e.g. ICP-AES, Nephelometer, XRD, FT-IR, TG/DTA, N₂-adsorption, solid-state-NMR, SEM and TPD-pyridine. ICP-AES studies indicated the presence of Al in the mesoporous materials. Nephelometer studies indicated the SO₄²⁻ presence of the SO₄²⁻/Al-MCM-41. XRD studies indicated that the calcined materials of Al-MCM-41 and SO₄²⁻/Al-MCM-41 had the standard MCM-41 structure. The surface area, pore diameter, pore volume and wall thickness of the mesoporous materials were calculated by BET and BJH equations, respectively. Crystallinity, surface area, pore diameter and pore volume of SO₄²⁻/Al-MCM-41 decreased except wall thickness and the expelling aluminum from the Al-MCM-41 framework increased the Lewis acidity. FT-IR studies indicated that Al-ions were incorporated in the hexagonal mesoporous structure of Al-MCM-41 and sulfuric acid was impregnated into hexagonal Al-MCM-41 materials. The thermal stability of as-synthesized Al-MCM-41 materials and SO₄²⁻/Al-MCM-41 materials were studied using TG/DTA. The environments of the Al-ions coordinated in the silica matrix were determined by ²⁷Al-MAS-NMR. The morphology of Al-MCM-41 and SO₄²⁻/Al-MCM-41 was determined by SEM. The total acidity of Al-MCM-41 and SO₄²⁻/Al-MCM-41 materials was determined by TPD-pyridine. The catalytic results were compared with those obtained by using sulfuric acid, amorphous silica–alumina, H-β, USY and H-ZSM-5 zeolites. The SO₄²⁻/Al-MCM-41 catalyst exclusively forms the product of dypnone from self-condensation of acetophenone molecules due to higher number of Lewis acid sites and has much higher yields than other catalysts except USY.     

The selective catalytic reduction activity of Cu/MCM-41 catalysts prepared by using the Cu2+–MCM-41 mesoporous materials with copper ions in the framework as precursors

The Cu²⁺–MCM-41 mesoporous materials with different loadings of copper species in the framework have been prepared by hydrothermal method and characterized by using various physico-chemical methods combined with the selective catalytic reduction of NO by NH₃. It has been shown that the particle size of metallic copper formed after hydrogen reduction is much smaller than that in the supported catalysts prepared by impregnation method, and that the SCR activity of catalyst increases obviously with the increase of Cu content to 10 wt.% because of its higher dispersion of copper metal in the mesoporous catalyst even at higher Cu loading.     

Pyrolysis of two different biomass samples in a fixed-bed reactor combined with two different catalysts

Pyrolysis of Euphorbia rigida and sesame stalk biomass samples with two selected commercial catalyst, namely DHC-32 and HC-K 1.3Q, have been conducted in a fixed-bed reactor. The effect of different catalysts and their ratio (5, 10 and 20% w/w) and pyrolysis temperature (500 and 750 °C) on the pyrolysis product yields were investigated and the obtained results were compared with similar experiments without catalyst. Bio-oil yield was increased comparing with non-catalytic experiments, at final pyrolysis temperature of 500 °C for both biomass samples and catalysts. In the catalytic experiments; when the temperature reached to 750 °C, although bio-oil product yield was reduced, the gas product yield was increased comparing with non-catalytic experiments.The pyrolysis oils were examined using spectroscopic and chromatographic analyses and then fractioned by column chromatography. Although the aliphatic and aromatic fractions were decreased and polar fraction was increased with catalytic pyrolysis of E. rigida; an opposite trend was observed in the sesame stalk pyrolysis oil, comparing with non-catalytic results.Obtained results were compared with petroleum fractions and determined the possibility of being a potential source of renewable fuels.     

H2SO4和Al2（SO4）3改性中孔分子筛Al-MCM-41及其催化性能

用SO24-物质的量相同的H2SO4和Al2(SO4)3分别对Al-MCM-41进行改性,得到样品SO42-/Al-MCM-41和Al/SO24-/Al-MCM-41。采用X射线多晶衍射(XRD)、红外光谱(FTIR)、N2吸附-脱附和NH3程序升温脱附(NH3-TPD)等测试技术对样品进行表征。分别用H2SO4、MCM-41、Al-MCM-41、SO42-/Al-MCM-41和Al/SO24-/Al-MCM-41催化合成丙酸香叶酯,比较了它们的催化性能。结果表明,H2SO4和Al2(SO4)3改性对Al-MCM-41中孔分子筛结构影响不明显,都可提高其酸性,改性后中孔分子筛的骨架仍保持着六方介孔结构,孔径、孔容和比表面积有所降低,但用Al2(SO4)3改性的分子筛酸性和催化性能更强;SO42-/Al-MCM-41的酸催化活性主要源于SO42-与分子筛表面硅羟基作用形成的双齿螯合配位结构,而Al/SO42-/Al-MCM-41的酸催化活性一方面来自SO24-与分子筛表面硅羟基作用形成的双齿螯合配位结构,另一方面,也来自与分子筛骨架接枝的铝,使其产生了更多的Brnsted酸中心。     

Vapor-phase alkylation of toluene by benzyl alcohol on H3PO4-modified MCM-41 mesoporous silicas

Several mesoporous aluminosilicate molecular sieves with the MCM-41 structure (SiO₂/Al₂O₃ = 20–200) have been synthesized using different aluminum sources and modifying several synthesis parameters during the preparation process, such as the temperature and the content of water and sulfuric acid in the gel mixture. All samples were characterized by element chemical analysis, X-ray diffraction, N₂ physisorption, thermal analyses, and electron microscopy. These Al-MCM-41 materials have BET surface areas up to 940 m² g⁻¹. The catalytic properties of their H₃PO₄-treated derivatives for Friedel–Crafts alkylation of toluene with benzyl alcohol have been evaluated. Toluene benzylation preferentially gave p-benzyl-toluene. The conversion of toluene to monoalkylated products increased with increasing the H₃PO₄ content in the catalysts and reached a maximum value for a H₃PO₄ loading of 25%, a further increase in H₃PO₄ leading to a decrease in the activity for alkylation. The influence of H₃PO₄ loading and of the operating parameters on the performance of the catalysts was also investigated.     

Synthesis of high-stability acidic Ce3 + (La3 + or Sm3 +)~β/Al-MCM-41 and the catalytic performance for the esterification of oleic acid

Ce^3 + (La^3 + or Sm^3 +)~β/Al-MCM-41 molecular sieves were synthesized by impregnation and used to catalyze the esterification of oleic acid with short chain alcohols, such as methanol, ethanol, isopropanol, and isobutanol, to obtain biodiesel. Ce^3 +(La^3 + or Sm^3 +)~β/Al-MCM-41 was found to exhibit excellent catalytic activity and stability. The effect of rare earth elements on the acidity of catalysts was examined in detail by NH₃-TPD and Py-FTIR. The optimum conditions for the esterification of oleic acid with methanol were determined. Moreover, the kinetics of the esterification showed that the average reaction order (n) was 1.92, with an activation energy of 51.46 kJ/mol.     

Vapor-phase tert-butylation of p-hydroxytoluene over Al-MCM-41 and PWA supported Al-MCM-41 mesoporous molecular sieve catalysts

Mesoporous Al-MCM-41 and PWA, impregnated with different weight percent catalysts have been prepared and investigated by combining structural and textural properties of both the catalysts. The catalytic behavior of both the Al-MCM-41 and PWA impregnated catalysts were evaluated for tert-butylation of p-hydroxy toluene. Among the series of catalysts, 20 wt% PWA impregnated catalyst was found to have superior activity for the alkylation of p-hydroxytoluene. The activity was increased with more PWA content upto 20 wt%. This implied that the PWA loaded Al-MCM-41catalysts had enhanced acid strength, thereby increasing the Bronsted acid sites for the tertiarybutylation of p-hydroxytoluene. Various parameters viz. feed rate, temperature, feed ratio of p-HT and MTBE, Time on stream and WHSV were optimized for the reaction.     

废聚烯烃催化裂解研究进展

综述了废聚烯烃催化裂解反应中所用的主要催化剂及反应器的研究进展。指出中孔分子筛由于其大而均匀的孔结构以及较高的比表面积有望成为处理废聚烯烃的有效催化剂,流化床反应器是处理废聚烯烃的有效反应器。与传统的小孔分子筛相比,目前所用的全硅型中孔分子筛还存在酸性弱、催化活性低等缺点,建议应通过在全硅型中孔分子筛骨架中引入某些过渡金属元素和某些能产生超强酸的基团,进一步提高该类催化剂的酸强度、催化活性及稳定性。     

Influence of alcohol addition on properties of bio-oil produced from fast pyrolysis of eucalyptus bark in a free-fall reactor

Fast pyrolysis of eucalyptus bark was carried out in a free-fall pyrolysis unit at different temperatures ranging from 400 to 550 °C to produce bio-oil, char and gas. The bio-oil produced at optimum temperature was mixed with alcohols with an aim to improve its properties. The results showed that the maximum bio-oil yield of 64.65 wt% on dry biomass basis could be obtained at the pyrolysis temperature of 500 °C. The addition of a small proportion (2.5–10%) of alcohol into the bio-oil could improve its viscosity, stability and heating value. These effects were further enhanced when increasing the alcohol.