Extrusion of AlSBA-15 molecular sieves: An industrial point of view

AlSBA-15 in the powder form with different n_Si/n_Al ratios (45, 136 and 215) were synthesized by hydrothermal technique. The powdered materials were made into cylindrical extrudates with the addition of bentonite as a binder. The AlSBA-15 materials were characterized by XRD, N₂ adsorption, AAS and thermogravimetric analysis. The orderly growth of AlSBA-15 is evidenced by its XRD. The surface area of the powder catalyst is around 950 m²/g and that of extrudate is close to 600 m²/g. Vapor phase alkylation of phenol with tert-butanol was carried out over the extrudates of AlSBA-15 as a model reaction. The activity of AlSBA-15 extrudates follows the order: AlSBA-15 Si/Al = 45 > AlSBA-15 Si/Al = 136 > AlSBA-15 Si/Al = 215. The reaction products were found to be 2-TBP, 4-TBP and 2,4-DTBP. The selectivity to para tertiary butylation is higher than other reactions.     

Thermal-catalytic degradation kinetics of polypropylene over BEA,ZSM-5 and MOR zeolites

In this study, thermal degradation of additive-free polypropylene powder over different type of zeolite catalysts was investigated. BEA, ZSM-5 and MOR with different surface areas, pore structures, acidities and Si/Al molar ratios were used as solid catalysts for degradation of polypropylene (PP). Degradation rate of the PP over zeolites was studied by thermogravimetric analysis (TGA) employing four different heating rates and apparent activation energies of the processes were determined by the Kissinger equation. The catalytic activity of zeolites decreases as BEA > ZSM-5a (Si/Al = 12.5) > ZSM-5b (Si/Al = 25) > MOR depending on pore size and acidity of the catalysts. On the other hand, initial degradation is relatively faster over MOR and BEA than that over both ZSM-5 catalysts depending on the apparent activation energy. It can be concluded that acidity of the catalyst is the most important parameter in determining the activity for polymer degradation process as well as other structural parameters, such as pore structure and size.     

Internal versus external surface active sites in ZSM-5 zeolite: Part 2: Toluene alkylation with methanol and 2-propanol catalyzed by modified and unmodified H3PO4/ZSM-5

Vapor-phase methylation of toluene with methanol and isopropylation of toluene with 2-propanol has been investigated in a down flow reactor under atmospheric conditions using N₂ gas carrier over a series of surface modified and unmodified ZSM-5 (Si/Al = 60–170) loaded with H₃PO₄, differing in the external surface treatment of the zeolites. The feed molar ratios of toluene/methanol and toluene/2-propanol were varied over a wide range (8–0.125), and the optimum feed ratio of toluene/alcohol was less than 0.5 in both cases. Space velocity employed in toluene methylation reported as WHSV (toluene) = 1.2 h⁻¹, and the space velocity employed in toluene isopropylation reported as WHSV (toluene) = 0.8 h⁻¹. The methylation reactions were carried out in the temperature range of 623–773 K, and the isopropylation reactions were carried out in the temperature range of 483–583 K. Atmospheric pressures was maintained in all runs. Catalysts containing 0–4.9 wt.% P were prepared using modified and unmodified ZSM-5 zeolites, and their catalytic performance for vapor-phase alkylation of toluene with methanol and 2-propanol were investigated. The optimum phosphorous content for methylation was 2.1 wt.% P which was greater than the optimum phosphorous loading for isopropylation (0.7 wt.% P).     

Kinetics of reductive alkylations of phenylenediamines: Influence of substrates isomeric structure

Reductive alkylation of ortho-, meta- and para-phenylenediamines (PDAs) with methyl ethyl ketone (MEK) has been studied in a semi-batch slurry reactor in the presence of a commercial 3% Pt/Al₂O₃ catalyst. It was observed that the PDA isomers differ remarkably from each other in their activity in reductive alkylation and product distribution. The activity was found to decrease in the following order: PPDA>OPDA>MPDA. To understand the substrate structure–activity correlation, the homogeneous equilibrium reactions involved in the alkylation step and the overall catalytic reactions were studied separately. Kinetics of reductive alkylation of PDAs with MEK as a solvent and alkylating agent with 3% Pt/Al₂O₃ catalyst was studied in a semi-batch slurry reactor over a temperature range of 373–453 K and pressure range of 2.07–6.21 MPa. Semi-batch slurry reactor models were developed and kinetic parameters were estimated by fitting the integral batch reactor data at different temperatures to understand the influence of different reaction steps on the activity and selectivity of different products.     

Solid acid-catalyzed conversion of furfuryl alcohol to alkyl tetrahydrofurfuryl ether

The acidic zeolite HZSM-5 (Si/Al = 25) achieved 58.9% selectivity of methyl furfuryl ether (MFE) and 44.8% selectivity of ethyl furfuryl ether (EFE) from etherification of furfuryl alcohol with methanol and ethanol. MFE and EFE were quantitatively hydrogenated into methyl tetrahydrofurfuryl ether (MTE) and ethyl tetrahydrofurfuryl ether (ETE) using a Raney Ni catalyst.     

Enhanced production of high octane gasoline blending stock from methanol with improved catalyst life on nano-crystalline ZSM-5 catalyst

Methanol value addition reaction has been studied on lab-synthesized nano-crystalline ZSM-5, Si/Al = 13 (NZ) possessing particle size of ∼29–51 nm and a micro-crystalline ZSM-5 (MZ) of similar atomic ratio is also taken as standard for comparison studies. The NZ sample exhibited excellent catalytic activity to produce 50.7 wt.% of high octane (Research Octane Number = 137) gasoline blending stock rich in desired toluene and xylene components, while the undesired benzene is very low, suitable for fuel applications. The superior performance of NZ to MZ catalyst reflected in three fold increase in gasoline yield and considerably high time-on-stream performance.     

Reductive dehydration of butanone to butane over Pt/γ-Al2O3 and HZSM-5

We show that butanone can be reacted to form n-butane in an isothermal reactor containing a 1 wt.% Pt/γ-Al₂O₃ and an HZSM-5 catalyst (total mass of 12–400 mg, Si/Al = 11.5) below 160 °C with up to 99% selectivity and 67% yield. The catalyst loading (12–400 mg) and temperature (100–250 °C) were varied to obtain primary products whose selectivities decreased with conversion and secondary/tertiary products whose selectivities increased with conversion. As conversion increased, the selectivities of butanol and butene decreased, showing the formation of butane from butanone through a series reaction pathway: butanone → 2-butanol → butene → butane. Butane selectivity increased as the temperature was increased from 100 to 200 °C when compared at similar conversions due to higher dehydration rates over the zeolite. Processing ketones at low temperatures over bifunctional catalysts may be an efficient means of obtaining high yields of stable paraffins from reactive oxygenates.     

The effect of Si/Al ratio and moisture on an organic/inorganic hybrid material: Thioindigo/montmorillonite

Colored Organic/Inorganic Hybrid Materials (OIHM) with reversible properties were prepared by a solid-state reaction between several montmorillonites (MMT) with different Si/Al ratio (Bentolite L^®, Texas, Wyoming and Kunipia deposits) and a neutral organic dye (thioindigo) at 413 K for nine hours. Spectroscopic and thermogravimetric analysis of the above mentioned interactions were evaluated. Results obtained by these techniques revealed an influence of Si/Al ratio in dehydrated MMT, where the intramolecular charge-transfer (IMCT) in thioindigo progressively red-shifted and increased in intensity in the following order: BentoT (Si/Al = 8.2) > TexasT (Si/Al = 7) > WyomingT (Si/Al = 5.6) > KunipiaT (Si/Al = 4.8). Moreover, a disturbance of thioindigo C=O at 1654 cm^?1 to lower frequencies occurred due to C=O---Lewis acid sites (LAS) and Brønsted (B) interaction in MMT with high Si/Al ratio. In the presence of water, a smaller C=O shift due to C=O---(H₂O)LAS or B interaction was identified. In addition, displacement of the basal spacing (001) in all MMT confirmed the effect of water on the reversible color changes displayed by UV–Vis diffuse reflectance spectroscopy. The existence of different binding strengths in OIHM was also evaluated by TGA and UV–Vis spectroscopy of their ethanol Soxhlet extractions.     

Catalytic activity of FeZSM-5 zeolites in benzene hydroxylation by N2O: The role of geometry characterized by fractal dimensions

The fractal dimensions of FeZSM-5 zeolites were used to characterize the change in their geometry depending on different post-synthesis treatments. The fractal dimension values were estimated from the Dubinin–Astakhov isotherms of nitrogen adsorption and related to the activity of these zeolites in the benzene hydroxylation to phenol by nitrous oxide. The zeolites had two different iron contents (350 and 5800 ppm) and a Si/Al ratio of 42. The catalysts were activated by steaming (823 K) and/or calcinations in He (1323 K). The FeZSM-5 activated by steaming exhibited fractal dimensions lower than the samples activated by calcinations. The steamed samples also had activities in the benzene hydroxylation per Fe(II) site (TOF values) somewhat higher as compared to the zeolites activated by calcinations. This indicates the importance of the zeolite geometry for the reaction of bulky benzene molecule within a confined space.     

Enhancing the selectivity of Pare-dihydroxybenzene in hollow titanium silicalite zeolite catalyzed phenol hydroxylation by introducing acid–base sites

A facile and effective method for enhancing the selectivity of Pare-dihydroxybenzene in phenol hydroxylation has been developed by introducing acid–base sites (MgO–Al₂O₃ binary oxide) to the micropores of hollow titanium silicalite (HTS, Ti/Si = 25) zeolite. For MgO–Al₂O₃ modified HTS zeolites, the biggest ratio of para- to ortho-dihydroxybenzene is over 2, while that is close to 1 for conventional HTS zeolite. The high pare-dihydroxybenzene selectivity is ascribed to the steric hindrance and the synergistic effect between acid–base sites of mixed oxide and tetrahedral framework Ti species in HTS zeolite.     

Alkylation of benzene with propene over HBeta zeolites near supercritical conditions

The alkylation of benzene with propene to produce cumene over HBeta zeolites was carried out near supercritical conditions, where the reaction conditions were determined with considering the changes in the critical properties of reacting mixture along with the reaction extent. The results demonstrate that the reaction behaviour, especially the catalyst lifetime is sensitive to the reaction conditions. Catalysts deactivate much more rapidly when the reactions are carried out under such conditions far from the critical region of the reacting mixture, while they exhibit much longer lifetimes under the conditions near the critical region of the reacting mixture (290–310 °C, about 5.7 MPa). Performing the alkylation of benzene with propene on HBeta zeolites under supercritical conditions rather than in gas or liquid phase can be an interesting option for increasing throughput and prolonging catalyst lifetime; however, the reaction conditions should be determined according to the critical properties of reacting mixture along the reaction course.     

Diesel-like hydrocarbons obtained by direct hydrodeoxygenation of sunflower oil over Pd/Al-SBA-15 catalysts

Hydrodeoxygenation of sunflower oil was performed in an autoclave over 5.0 wt.% Pd/Al-SBA-15 (Si/Al molar ratios from 22 to 300) and Pd/HZSM-5(22). The effects of acidity of the catalysts and the reaction temperatures on the activity of the catalysts were investigated. Pd/Al-SBA-15(Si/Al = 300) showed a high activity as 74.4% liquid yield and 72.9% C15–C18 diesel-like hydrocarbons yield at 250 °C. At 300 °C, the higher activity over Pd/Al-SBA-15(Si/Al = 50, 100 and 300) catalysts compared with that over Pd/Al-SBA-15(22) and Pd/HZSM-5(22) indicated that strong acidity of the catalysts was not favorable for converting sunflower oil into C15–C18 diesel-like hydrocarbons at a high temperature.     

Benzylation of benzene to diphenylmethane using zeolite catalysts

The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl chloride (BC) is investigated over a number of zeolite catalysts at 358 K and under atmospheric pressure. Conventional homogeneous Lewis acid catalyst, AlCl₃, is also included for comparison. Zeolite H-β is found to be more selective but less active compared to HY and H-ZSM-5 zeolites in the benzylation of benzene. The conversion of BC, rate of BC conversion and selectivity to DPM over H-β after 6 h of reaction time are 33.3 wt%, 4.7 × 10⁻³ mmol g⁻¹ h⁻¹ and 89.1 wt%, respectively. For comparison, the conversion of BC, rate of BC conversion and selectivity to DPM over AlCl₃, under identical reaction condition, are found to be 100 wt%, 170 × 10⁻³ mmol g⁻¹ h⁻¹ and 58 wt%, respectively. Higher amounts of consecutive products are obtained over AlCl₃ due to its non shape selectivity. The acidity of the zeolite catalysts is measured by temperature programmed desorption method. The effect of the duration of the run, SiO₂/Al₂O₃ ratio of H-β, catalyst concentration, reaction temperature and benzene to BC molar ratio on the catalyst performance is also investigated in order to optimize the conversion of BC and selectivity for DPM. The conversion of BC using H-β is increased with the increase in the reaction time, catalyst concentration, reaction temperature and molar ratios whereas it decreases with the increase in SiO₂/Al₂O₃ molar ratio of H-β. H-β is recycled two times and a slight decrease in BC conversion is observed after each cycle, which is related to the minor dealumination of the zeolite catalyst by HCl, which is produced during the reaction as by product. The formation of DPM is explained by an electrophilic attack of the benzyl cation (C₆H₅CH₂⁺) on the benzene ring, which is produced by the polarization of BC over acidic sites of the zeolite catalysts.     

Synthesis of 3,3′-dimethyl-4,4′-diaminodiphenylmethane catalyzed by zeolites replacing mineral acids

Synthesis of 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDT) from o-tolylamine and formaldehyde over zeolites was investigated. Among the three tested zeolites, Hβ showed higher catalytic activity than HY and HZSM-5 for MDT synthesis. In the case of Hβ as a catalyst, the effects of feed composition, reaction time and temperature on the yield and selectivity of product MDT were further examined to optimize process conditions. In an o-tolylamine:formaldehyde = 8:1 molar ratio, the two-step reaction running at 413 K for 0.5 h and then 433 K for 0.5 h gave the MDT yield of 87.5%.     

Suitable acidity of ZSM-5 for the isomerization of styrene oxide to phenylacetaldehyde

The effect of acidity of HZSM-5 (SiO₂/Al₂O₃ = 25–360) on isomerization of styrene oxide to phenylacetaldehyde was investigated under gas–phase free of solvents. The reaction was mainly catalyzed by the strong acid sites of HZSM-5 and catalyst lifetimes were affected by both acid strength and concentration. Trimerization of phenylacetaldehyde occurred at external acid sites, leading to a sharp decline in product selectivity. High Si/Al HZSM-5 (e.g., SiO₂/Al₂O₃ = 360), which contains weaker acid sites inside pores and trace amount of external acid sites, was found to be more effective with a higher stability and phenylacetaldehyde yield up to 95%.     

Catalytic oxidation of benzene with ozone over Mn ion-exchanged zeolites

Catalytic oxidation of benzene with ozone was carried out over Mn ion-exchanged zeolites at 343 K. Benzene was oxidized on Mn-Y to form CO_x without the release of organic byproducts, whereas formic acid was formed with supported manganese oxide catalysts, Mn/SiO₂ and Mn/SiO₂–Al₂O₃. Mn-Y showed higher activity and selectivity to CO₂ than other zeolite catalysts, Mn-β, Mn-MOR, and Mn-ZSM-5. Linear relationship was observed between benzene consumption, CO_x formation and ozone consumption. Formic acid adsorbed on Mn-Y catalyst was completely oxidized to CO₂ with ozone at around 343 K.     

Characterization and catalytic application of MnCl2 modified HZSM-5 zeolites in synthesis of aromatics from syngas via dimethyl ether

The conversion of syngas to aromatics via dimethyl ether was investigated over MnCl₂ modified HZSM-5 zeolites. The results demonstrated that 2%MnCl₂ modified HZSM-5 (SiO₂/Al₂O₃ = 38) exhibited higher p-xylene selectivity than other catalysts and further decreased 1,2,4,5-tetramethylbenzene selectivity. The CO conversion was obviously increased after 5%MnCl₂ modification to HZSM-5. The catalysts were characterized by XRD, BET, XPS, FT-IR, NH₃-TPD, SEM, element analysis and O₂-TPO. The loading amount of MnCl₂ affected the adsorption and reaction of DME molecules on zeolites. Appropriate amount of MnCl₂ introduction could adjust the acidity and pore volume of HZSM-5 to increase p-xylene selectivity and CO conversion.     

PFG NMR self-diffusion of propylene in ITQ-29, CaA and NaCaA: Window size and cation effects

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy was used to measure and rationalize the self-diffusion coefficients of propylene in various LTA materials having different framework composition and varying proportions of charge balancing cations: ITQ-29 (Si/Al = ∞), CaA (Si/Al = 1), and six NaCaA (Si/Al = 1) samples at greater than 50% Na⁺ exchange. The critical role of the framework Si/Al ratio on the self-diffusivity of propylene is demonstrated. Changes in self-diffusion driven by changes in framework composition are well documented in the literature. Diffusion frequency response experiments in the pure silica and alumino-phosphate forms of the CHA structure are included in this work to illustrate such situation.For the LTA structures, propylene was chosen as a very sensitive probe molecule because its size is comparable to the size of the 8-ring window apertures in the materials. A clear increase in self-diffusivity with the size of the window apertures, which increases with Al content in the framework, is shown. Thus, ITQ-29 and CaA exhibit the lowest and highest self-diffusivities, respectively. The self-diffusivities in the NaCaA samples lie in between those of ITQ-29 and CaA and increase with the Ca²⁺ content. Thus, the presence of extra-framework balancing cations in either CaA or NaCaA does not lead to lower self-diffusivities than in the cation-free ITQ-29. The lower self-diffusivities in ITQ-29, instead, can be largely attributed to its smaller window size, which is a more dominant effect than any reduction in self-diffusivity caused by the cations, at the levels of Na⁺ exchange studied.     

Liquid-phase oxidation of benzene to phenol by molecular oxygen over transition metal substituted polyoxometalate compounds

Transition metal substituted polyoxometalate (TMSP) compounds were used as catalysts for the liquid-phase oxidation of benzene to phenol by molecular oxygen with ascorbic acid as a reducing agent in an acetone/sulfolane/water mixed solvent. [(C₄H₉)₄N]₅[PW₁₁CuO₃₉(H₂O)] is the best catalyst tested in this study. It showed 9.2% benzene conversion (TON = 25.8) and 91.8% selectivity to phenol for the oxidation of benzene at 323 K for 12 h. The effect of the substituted transition metal in the TMSP compounds on the benzene conversion is in the order: Cu > V > Fe ≫ Mn > Ti > Cr > Co > Ni > Zn. The effect of the central atom in the TMSP compounds on the benzene conversion is in the order: P ≈ Si > Ge > B. [SiW₁₁O₃₉]⁸⁻ is a good polyoxometalate ligand for transition metal ions as [PW₁₁O₃₉]⁷⁻ for the oxidation of benzene. The selectivity to phenol was dramatically improved by adding the sulfolane solvent, but the benzene conversion decreased when a large amount of sulfolane was used in the mixed solvent. Ascorbic acid is indispensable for forming phenol from benzene oxidation by O₂ over TMSP compounds. Higher O₂ pressure in the catalytic system ensured more oxygen molecules solving in the solvent, and promoted the benzene conversion.     

Immobilization of Cs,Cd, Pb and Cr by synthetic zeolites from Spanish low-calcium coal fly ash

This report describes a study of the immobilization of Cs⁺, Cd²⁺, Pb²⁺ and Cr³⁺ by synthetic zeolites formed as a result of the hydrothermal treatment of Spanish class F coal fly ash in a 1 M solution of NaOH. The majority zeolite formed at 150 °C was a gismondine-type P1-Na species (Na₆Al₆Si₁₀O₃₂·12H₂O), which at 200 °C transformed into analcime-C zeolite (Na(Si₂Al)O₆H₂O). The shift in pore size distribution towards pores with diameters of about 2.2 nm observed after the zeolites were washed entailed an increase in the specific surface area, to values nearly double the figures recorded prior to washing. With a high selectivity for Cs, the gismondine type Na zeolite P was found to be the best candidate for immobilizing radioactive waste. Gismondine and analcime-C zeolites also exhibited high Cd selectivity.