Methanol-to-olefins over FeHZSM-5: Further transformation of products

The catalytic activity of FeHZSM-5 was investigated for the conversion of both methanol and mixed C₃° + C₄ hydrocarbons. For methanol conversion at WHSV = 1 h^− 1 and 470 °C, 0.35% FeHZSM-5 showed increased selectivity for propylene and C₂⁼–C₄⁼ olefins by 21% and 4%, respectively, compared with HZSM-5. The selectivity of propane and butylene decreased. High temperature favored the conversion of C₃° + C₄ mixture while the selectivity of ethene + propylene achieved a maximum at 470 °C. Improved olefins selectivity for methanol conversion was attributed to FeHZSM-5 with more weak acid but less strong acid amount and to further transformation of the products.     

Yield of gasoline-range hydrocarbons as a function of uniform ZSM-5 crystal size

Uniform ZSM-5 nanocrystals were synthesized by a single-templating procedure. The samples were then characterized by a variety of physical techniques such as XRD, SEM, BET, ICP and TPD. The dehydration of methanol over synthesized ZSM-5 zeolite was studied in a fixed-bed continuous flow reactor at 370 °C and WHSV of 2.6 gg⁻¹ h under ambient pressure. The effect of crystal size of zeolite catalysts on product distribution in methanol dehydration reaction was investigated. Good correlation was observed between catalytic performance, product distribution and size of ZSM-5 crystals. It was found that the decrease in crystal size significantly influences light olefins (ethylene and propylene) and paraffins (C₁–C₄) selectivity in methanol dehydration reaction. Furthermore, nanocrystal ZSM-5 showed long-term catalytic stability compared with conventional ZSM-5 provided that the reaction activity is strongly dependent on the crystal size in methanol dehydration process. The results indicated that crystal size significantly affects the catalyst lifetime and hydrocarbon distributions in product stream. Based on the obtained results, it is concluded that the use of uniform ZSM-5 nanocrystals improves the yield of propylene and alkyl aromatics in methanol conversion reaction at mild conditions.     

Gas-phase epoxidation of propylene through radicals generated by silica-supported molybdenum oxide

It was found that silica-supported molybdenum oxide was high effective for the epoxidation of propylene among various silica-supported metal oxides. The post-catalytic bed volume played an important role in its formation. On a MoO_x/SiO₂ with 0.255 mmol/g-SiO₂, a propylene conversion of 17.6% and a PO selectivity of 43.6% were obtained at 5 atm, 573 K and flow rates of C₃H₆/O₂/He = 10/5/10 cm³ min⁻¹. The characterization studies indicated that crystalline MoO₃ nano-particle species was more effective for propylene epoxidation to PO than molecularly dispersed Mo oxide species. The reaction mechanism of propylene epoxidation on MoO_x/SiO₂ catalysts is hypothesized to involve gas-phase radicals generated at relatively low temperature by the dispersed molybdenum oxide species. These radicals participated in homogeneous reactions with molecular oxygen to produce propylene oxide.     

Size controlled ZSM-5 on the structure and performance of Fe catalyst in the selective catalytic reduction of NOx with NH3

Fe/ZSM-5 catalysts with various morphologies and sizes were prepared and the catalytic properties in NH₃-SCR were also investigated. The different ZSM-5 morphologies and sizes indeed influence the dispersion of Fe species. The Fe/ZSM-5 catalyst, which was cauliflower-like morphology of ZSM-5 support aggregated by small nano-crystal zeolite with crystallite size of about 50 nm, exhibited the best NH₃-SCR activity (T_≥ 90% = 280–650 °C). This specific morphology and size of ZSM-5 support were considered to benefit the distribution of isolated Fe^3 + species, which was proved to be the main active sites in SCR reaction.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

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).     

Effects of particle size on catalytic conversion of ethanol to propylene over H-ZSM-5 catalysts—Smaller is better

In this study, H-ZSM-5 catalysts with different particle sizes were prepared by adding different amount of water to the starting gel before crystallization. These H-ZSM-5 catalysts were characterized by scanning electron microscopy, N₂ adsorption/desorption measurements, X-ray fluorescence, X-ray diffraction, and temperature programmed desorption of ammonia. It was found that the olefin (ethylene, propylene and butene) yield decreased with the increase in the particle size of the catalysts. The paraffin (ethane, propane and butane) yield trended to increase with the increase of particle size. The C₅ + products yield increased considerably with the increase of particle size. The results implied that the formation of the C₅ + products and hydrogen was inhibited over the smaller particle size catalyst, furthermore the formation of paraffin decreased. So the propylene yield could be increased over smaller H-ZSM-5 catalyst.     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

Characterization and application of a Pt/ZSM-5/SSMF catalyst for hydrocracking of paraffin wax

The microstructured Pt/ZSM-5/SSMF catalysts, for hydrocracking of paraffin wax, have been developed by impregnation method to place Pt onto thin-sheet ZSM-5/SSMF composites obtained by direct growth of ZSM-5 on the sinter-locked stainless steel microfibers (SSMF). The best catalyst is the one with ZSM-5 having a SiO₂/Al₂O₃ weight ratio of 200, delivering ~ 95% conversion with 77.5% selectivity to liquid products or 64.4% selectivity to naphtha at 280 °C. This new approach is capable of increasing the naphtha selectivity with high activity maintenance in comparison with the literature catalysts.     

Aromatization of n-hexane over Ga,Mo and Zn modified H-ZSM-5 zeolite catalysts

n-Hexane aromatization was investigated at 500 °C on parent and metal (i.e. Ga, Mo and Zn) modified H-ZSM-5 zeolite catalysts. Conversion reached 88% over H-ZSM-5 and was stable. Addition of metal resulted in lower conversion (< 80%). Formation of aromatic compounds was favored on Ga/H-ZSM-5 (> 35%) and Zn/H-ZSM-5 (> 40%) while H-ZSM-5 and Mo/H-ZSM-5 showed higher cracking activity. Gallium and zinc favored aromatization. At 600 °C a decrease in activity with increasing TOS was observed. A decrease in aromatics selectivity was also observed. The aromatics selectivity with increase in TOS of Ga/H-ZSM-5 (43–27%) and Mo/H-ZSM-5 (35–27%) catalysts was higher than for Zn/H-ZSM-5 (46–7%).     

High selective and stable performance of catalytic aromatization of alcohols and ethers over La/Zn/HZSM-5 catalysts

The catalytic conversions of methanol, ethanol, dimethyl ether and diethyl ether to aromatic hydrocarbons (especially benzene, toluene and xylene) were achieved over 0.8%Zn/0.6%La/HZSM-5 catalyst with a BTX selectivity as high as over 50% at reaction conditions of 710 K, WHSV 0.8 h^?1. The selectivity of BTX hydrocarbons in methanol aromatization reaction could remain 35% in 40 h.     

Ultrasound assisted synthesis of Gd and Nd doped ceria electrolyte for solid oxide fuel cells

In this study, the ceramic powders of Ce_1?xGd_xO_2?x/2 and Ce_1?xNd_xO_2?x/2 (x=0.05, 0.10, 0.15, 0.20 and 0.25) were synthesized by ultrasound assisted co-precipitation method. The ionic conductivity was studied as a function of dopant concentration over the temperature range of 300–800 °C in air, using the impedance spectroscopy. The maximum ionic conductivity, σ_800 °C=4.01×10^?2 Scm^?1 with the activation energy, E_a=0.828 kJmol^?1 and σ_800 °C=3.80×10^?2 Scm^?1 with the activation energy, E_a=0.838 kJmol^?1 were obtained for Ce_0.90Gd_0.10O_1.95 and Ce_0.85Nd_0.15O_1.925 electrolytes, respectively. The average grain size was found to be in the range of 0.3–0.6 μm for gadolinium doped ceria and 0.2–0.4 μm for neodymium doped ceria. The uniformly fine crystallite sizes (average 12–13 nm) of the ultrasound assisted prepared powders enabled sintering of the samples into highly dense (over 95%) ceramic pellets at 1200 °C (5 °C min^?1) for 6 h.     

A facile synthesis of water-soluble BaYF5:Ln3 + NCs with excellent luminescent properties as promising contrast agent for dual-modal bioimaging

Monodisperse, water-dispersible lanthanide (Ln^3 +)-doped BaYF₅ nanocrystals (NCs) are synthesized through a fast, facile and environmentally–friendly microwave-assisted modified polyol process with polyethyleneimine as the surfactant. The TEM images illustrate the sphere-like and flower-like morphologies of the obtained NCs. Intense multicolor down conversion (DC) luminescence is also achieved in Ce^3 +/Ln^3 + (Ln = Tb, Dy) doped BaYF₅ NCs. Then, upon excitation at 980 nm, upconversion (UC) luminescent properties of BaYF₅:Yb^3 +/Ln^3 + (Ln = Er, Tm, Ho) NCs and energy transfer between Yb^3 + and Ln^3 + are systematically surveyed. Furthermore, a layer of SiO₂ is coated on the surface of the NCs and the methyl thiazolyl tetrazolium (MTT) assays are performed to test the cytotoxicity of BaYF₅:Ln^3 + NCs. Due to the X-ray absorption property of Ba element, a proof-of-concept CT imaging with BaYF₅:Ln^3 + NCs is conducted. These results indicate that the obtained NCs have great potential as optical/CT bioprobe.     

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.     

NO reduction over nanostructure M-Cu/ZSM-5 (M: Cr,Mn, Co and Fe) bimetallic catalysts and optimization of catalyst preparation by RSM

The selective catalytic reduction (SCR) of NO with NH₃ in the presence of oxygen over a series of H-ZSM-5 supported transition metal oxides (Co, Mn, Cr, Cu and Fe) was investigated. Among them, Cu/ZSM-5 nanocatalyst was found to be the most promising catalyst based on activity. The modification of Cu/ZSM-5 by adding different transition metals (Co, Mn, Cr and Fe) to improve the efficiency of NO conversion was studied. The results indicated that the Fe–Cu/ZSM-5 bimetallic nanocatalyst was the highest active catalyst for NO conversion (67% at 250 °C and 93% at 300 °C). Response surface methodology (RSM) involving central composite design (CCD) was employed to evaluate and optimize Fe–Cu/ZSM-5 preparation parameters (Fe loading, calcinations temperature, and impregnation temperature) in SCR of NO at 250 °C. The optimum condition for maximum NO conversion was estimated at 4.2 wt.% Fe loading, calcinations temperature of 577 °C and impregnation temperature of 43.5 °C. Under these condition, experimental NO conversion efficiency was 78.8%, which was close with the predicted value (79.4%).     

Highly active and selective ethylene oligomerization catalysts: Asymmetric 2,6-bis(imino)pyridyl iron (II) complexes with alkyl and halogen substitutients

A series of asymmetric 2,6-bis(arylimino)pyridines with alkyl and halogen substitutients on different iminoaryl rings and corresponding iron (II) complexes ([2-(Ar₁N = CCH₃)-6-(Ar₂N = CCH₃)C₅H₃N]FeCl₂, 3a–3j) are synthesized and characterized. These Fe(II) complexes are highly active for ethylene oligomerization with high selectivity for linear α-olefins. The oligomer distributions can be tuned by the synergism of alkyl-steric effect and halogen electronic effect, and the production of C₆–C₁₆ can reach more than 80% with the highest selectivity being 87.5% for 3 g (Ar₁ = 2-ethylphenyl, Ar₂ = 2-fluorophenyl), which is 15–30% higher than that catalyzed by their methyl or fluoro-substituted symmetric counterparts.     

Photocatalytic reduction of Cr(VI) to Cr(III) in solution containing ZnO or ZSM-5 zeolite using oxalate as model organic compound in environment

Photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solution containing ZnO or ZSM-5 zeolite under ambient condition was studied by using oxalate as model organic compound in the natural environment. ZSM-5 zeolite was characterized by X-ray diffraction (XRD), and point of zero net proton charge (PZNPC) titration. The effect of illumination time, mass content of catalyst (m/V), Cr(VI) initial concentrations, pH, ionic strength, and oxalate concentrations on the photocatalytic reduction of Cr(VI) was determined. The results indicate that the PZNPC of ZSM-5 zeolite is at pH 3.6 ± 0.1. At C[Cr(VI)_(initial)] = 2.00 × 10^?4 mol/L, pH 7.5 ± 0.1 and after illumination time of 24 h, the reduction of Cr(VI) were 1.1 × 10^?5 mol/L (no ZSM-5 zeolite, 4.0 × 10^?3 mol/L oxalate) and 1.0 × 10^?5 mol/L (0.4 g/L ZSM-5 zeolite, no oxalate), respectively; whereas the reduction of Cr(VI) achieved 1.0 × 10^?4 mol/L in the presence of 0.4 g/L ZSM-5 zeolite and 4.0 × 10^?3 mol/L oxalate. The removal of Cr(VI) from solution is dependent on pH value. The results are important for the application of zeolites in the treatment of Cr(VI) polluted solution in the natural environment.     

Liquid-phase dehydrocondensation of 1-pentanol to di-n-pentyl ether (DNPE) over medium and large pore acidic zeolites

The present paper deals with the liquid-phase synthesis of di-n-pentyl ether (DNPE) by dehydration of 1-pentanol over H-Beta, H-ZSM-5, H-mordenite and H-Y zeolites. Their SiO₂/Al₂O₃ ratios were about 25 for H-Beta, 28 for H-ZSM-5, 35 for H-mordenite and 6 for H-Y. Experiments were performed in a batch reactor in the temperature range 140–180 °C at 1.6 MPa. Comparison of the catalysts behaviour shows that H-Beta is the most active and selective to DNPE, although it is less active than microporous ion-exchange resins. Kinetics of DNPE synthesis was studied. The best kinetic model for all the catalysts stems from a reaction mechanism whose rate-limiting step is the surface reaction between two 1-pentanol molecules adsorbed on adjacent sites, to yield DNPE and water both adsorbed on single site. Activation energy, on each single catalyst, was estimated to be in the range 94–118 kJ mol^?1.     

The effect of surface passivation on the preparation and stability of the graphite intercalation compounds containing tetra-n-alkylammonium cations

The kinetic stability of graphite intercalation compounds (GICs) is markedly increased by a surface passivation reaction that occurs under strong reducing conditions in the presence of long-chain tetra-n-alkylammonium cations. A simple alkylation model is proposed. Surface alkylation allows the formation of a stable, isolable, graphite intercalation compound of tetra-n-ethylammonium, (C₂H₅)₄N⁺ for the first time, by chemical surface passivation of [Na(en)_1.0]C₁₅ (en = ethylenediamine) with R₄N⁺, R = C₆H₁₃, C₇H₁₅ or C₈H₁₇, followed by an ion exchange reaction to displace the Na(en)⁺ complex with (C₂H₅)₄N⁺. One GIC thus obtained using dimethylsulfoxide (DMSO) as solvent has composition [(C₂H₅)₄N]C₅₇ 0.5DMSO, and is a stage-1 compound with a gallery expansion of 0.47 nm. This relatively small expansion indicates a monolayer of intercalate and additionally requires an unusually flattened cation conformation. Electrophoretic analyses indicate that the ion exchange within the graphene galleries goes to completion. Additionally, the passivated GIC surfaces afford a dramatic increase in the stability of GICs, in protic solvents, aqueous media, and the ambient environment.     

Self-assembly and magnetic behavior of 2-aldehyde-8-hydroxyquinolinate-based lanthanide complex

Self-assembly reaction of Ln(NO₃)_3.6H₂O, 2-aldehyde-8-hydroxyquinoline and histamine dihydrochloride affords two mononuclear complex [Ln(hma)(NO₃)₂(CH₃OH)]∙0.5C₄H₁₀ (Ln = Tb (1), Dy (2); Hhma = N-(2-(8-hydroxylquinolinyl)methane(2-(4-imidazolyl)ethylamine)). The structural analysis indicates that they are isomorphous where the Ln^3 + is ligated to one ligand, two nitrates and one methanol molecule. Variable temperature magnetic susceptibility studies reveal the presence of antiferromagnetic interactions in 2 and the dynamic measurement reveals that 2 displays single molecular magnet behavior below 10 K under an applied field of 2000 Oe.