Synthesis, characterization and acidic properties of nanopowder ZSM-5 type ferrisilicates in the Na/K alkali system

In this study Aluminium-free ZSM-5 type nanopowder ferrisilicates (as K-FZ or Na-FZ) were synthesized successfully from silicic acid, potassium (or sodium) carbonate and iron (III) nitrate using hydrothermal procedure (in relatively low crystallization time) in the presence of tetrapropylammonium bromide (TPABr) as a template. Prepared samples have been characterized by XRD, TEM, EDAX, NH₃-TPD, BET surface area, FTIR, TGA/DTA, SEM and ICP analysis. FTIR spectra confirm the production of ZSM-5 type ferrisilicates by the zeolite pentacycle peak at 547 cm^− 1 and the symmetric stretching peak of Si-O-Fe at 656 cm⁻¹. XRD diffractograms confirmed ZSM-5 crystal phase. The results clearly show that K⁺ cation (like Na⁺) plays a role of structure directing as well as a role of charge balancing agent. This could be assigned from NH₃-TPD analysis that ferrisilicate pretreatment procedure and iron-exchanging can significantly affect the strength of acidic sites. NH₃-TPD indicates that using potassium instead of sodium, leads to an increasing of the global acidity. Furthermore Na-FZ exchanging with iron ions (as Fe-NaFZ) leads to the same results. Thermal analysis revealed 14.7% weight loss due to the decomposition of TPABr template. Scanning electron microscope revealed that there is clustering of spherical particles in dry state. The TEM images confirm the particle size of the ferrisilicates in the range of 15-30 nm and show that iron-exchanged ferrisilicate has well-dispersed nano-sized iron oxide particles with various sizes in the range of 5-15 nm.     

The promotional effect of Cr on catalytic activity of Pt/ZSM-35 for H2-SCR in excess oxygen

Selective catalytic reduction of NO by hydrogen was studied over Cr modified Pt/ZSM-35 catalysts. The preparation process greatly influenced catalytic activity and sample prepared by co-impregnation method exhibits the best activity. In situ DRIFT studies revealed that on Pt–Cr/ZSM-35, (1) new Pt-NO^δ+ and NO species adsorbed on Pt were detected upon NO + O₂ adsorption; (2) much more ammonia species were formed under reaction condition. Cr addition not only enhanced the adsorption of NO_x but also promoted the formation of surface NH₄⁺ species, which should be the origin of promotional effect of Cr on Pt/ZSM-35 for H₂-SCR reaction.     

Fate of Fertilizer15N applied as urea and ammonium sulphate in opium poppy (Papaver somniferum L.) grown under greenhouse conditions

Laboratory incubation and greenhouse experiments were conducted to investigate the comparative effectiveness of urea and ammonium sulphate in opium poppy (Papaver somniferum L.) using¹⁵N dilution techniques. Fertilizer treatments were control (no N), 600 mg N pot^–1 and 1200 mg N pot^–1 (12 kg oven dry soil) applied as aqueous solution of urea or ammonium sulphate. Fertilizer rates, under laboratory incubation study were similar to that under greenhouse conditions. A fertilizer¹⁵N balance sheet reveals that N recovery by plants was 28–39% with urea and 35–45% with ammonium sulphate. Total recovery of¹⁵N in soil-plant system was 77–82% in urea. The corresponding estimates for ammonium sulphate were 89–91%. Consequently the unaccounted fertilizer N was higher under urea (18–23%) as compared to that in ammonium sulphate (9–11%). The soil pH increased from 8.2 to 9.4 with urea whereas in ammonium sulphate treated soil pH decreased to 7.3 during 30 days after fertilizer application. The rate of NH₃ volatilization, measured under laboratory conditions, was higher with urea as compared to the same level of ammonium sulphate. The changes in pH of soil followed the identical trend both under laboratory and greenhouse conditions.     

Potential reaction paths in NOx reduction over Cu/ZSM-5

The reaction of NO with adsorbed acetone oxime has been studied over Cu/ZSM-5 employing FTIR and MS. It is found that¹⁵NO_gas reacts with¹⁴N labelled acetone oxime and/or its hydrolysis product, hydroxylamine, to form¹⁴N¹⁵NO and¹⁴N¹⁵N at 40°C. As acetone oxime is easily formed from alkyl radicals and NO via alkylnitroso compounds, the results indicate possible reaction paths for the SCR of NO _x by hydrocarbons over zeolite based catalysts. The isotopic data suggest predominant formation of N-N bonds occurs via interaction of gaseous NO with a nitrogen containing adsorbed complex.     

Storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere by the sealing of the micropore outlet

The storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere was examined by hydrogen filling into the micropore and the following sealing of the micropore outlet to prevent the release of hydrogen to the outside. The surface grafting of 1,4-bis(hydroxydimethylsilyl)benzene onto ZSM-5 zeolite was applied to the sealing of the micropore outlet. Pressurized hydrogen (10 MPa) was filled into the micropore of ZSM-5 at liquid nitrogen temperature (−196 °C), and then the sample was heated at 150 °C for forming strong binding between the zeolite surface and the disilane compound under the hydrogen pressure. The hydrogen sorption isotherm at −196 °C showed that the adsorption of hydrogen onto the disilane-grafted ZSM-5 thus obtained was reduced to less than 20% from the original ZSM-5. The remarkable hysteresis between the adsorption and desorption branches of the isotherm indicated that the kinetic trap of hydrogen occurred by the narrowed outlets of the micropores of ZSM-5 with the disilane compound. Even after exposing the disilane-grafted ZSM-5 to the atmosphere over a few months, hydrogen could be discharged by heating over 150 °C. This result demonstrated that molecular hydrogen was successfully stored into ZSM-5 zeolite in the ambient atmosphere for a long time.     

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.     

Effect of thermal treatment on states of molybdenum in Mo/H–ZSM-5 catalyst for methane dehydroaromatization: ESR and UV–VIS study

Valence and coordination states of molybdenum ions formed upon thermal treatment of Mo/H–ZSM-5 catalyst for methane dehydroaromatization in Ar and Ar/CH₄ media at 573–973 K have been studied by ESR and UV–VIS spectroscopy. For comparison, the characteristic ESR spectra of thermolyzed bulk ammonium heptamolybdate have been studied and analyzed in detail. The nature of earlier observed Mo⁵⁺ ions has been verified, and new paramagnetic states of molybdenum in Mo/H–ZSM-5 catalysts have been detected: Mo³⁺ ions, and Mo⁵⁺ ions in tetrahedral coordination with delocalization of unpaired electron to Al and H or Al and N atoms.     

Synthesis of nano-sized YAG:Eu phosphor in continuous supercritical water system

Luminescent yttrium aluminum garnet (Y₃Al₅O₁₂) nanoparticles doped with Eu (YAG:Eu³⁺) were continuously synthesized by directly feeding potassium hydroxide solution and metal salt solution to supercritical water (SCW). Effects of Eu concentration, pH, and residence time on photo-luminescence were studied using a continuous tubular reactor. Residence time played a key role in producing single-phase YAG:Eu³⁺ nanoparticles. The residence time of 20 s under SCW conditions (400 °C and 280 bar) was enough to form YAG:Eu³⁺ phosphor without any intermediate phases. At this residence time, the Eu concentration and pH condition under SCW contributed to improving the size, morphology and luminescent property of YAG: Eu³⁺ nanoparticles. The average size of the prepared phosphor nanoparticles at 10 at.% and pH of 9.10 was 74 nm and the morphology was identified as nearly uniform and spherical-like in shape. Without further thermal treatment, the phosphor YAG:Eu³⁺ synthesized in the continuous reactor under SCW conditions showed strong luminescence properties and red emission spectra.     

Effects of Water and Ion-Exchanged Counterion on the FTIR Spectra of ZSM-5. II. (Cu+–CO)-ZSM-5: Coordination of Cu+–CO Complex by H2O and Changes in Skeletal T–O–T Vibrations

The 2157 cm^–1 (strong) and 2108 cm^–1 (very weak) (CO) IR bands due to Cu⁺–CO in ZSM-5 zeolite with ¹²C and ¹³C isotopes, respectively, are reversibly red-shifted by subsequent adsorption of H₂O at 293 K. On the contrary, the locally perturbed internal (T–O–T) asymmetric stretching framework vibration [ _as ^int (TOT)(Cu⁺–CO)=965 cm^–1] is reversibly blue-shifted. The courses of the band shifts revealed notable features. Charge transfers from water to Cu⁺ ions, changes in coordination spheres of Cu⁺(CO)(H₂O) _n aqua complexes and secondary (solvent-like) effects were considered to explain the results.     

Direct synthesis of mesoporous M-SBA-15 (M = Al, Fe, B, Cr) and application to 1-hexene oligomerization

M-SBA-15 materials (M = Al, B, Cr, Fe) were prepared by different direct synthesis methods, characterized and tested catalytically in the 1-hexene oligomerization reaction at 125 °C. Al-SBA-15 were synthesized within the range Si/Al = 12–86 using aluminium isopropoxide as aluminium source. ²⁷Al MAS NMR spectra point out that the three Al-SBA-15 samples contain more tetrahedral aluminium than octahedral and the ratio tetrahedral/octahedral diminished with increasing aluminium contents. B-SBA-15 was prepared with a Si/B = 51–106 using two direct synthesis methods (sol–gel and hydrothermal) and three different boron sources (solid boric acid, aqueous boric acid and boron isopropoxide). The best results in terms of boron incorporation (Si/B = 51) were achieved with solid boric acid and the sol–gel method, although a lower degree of mesoscopic ordering was obtained compared to the hydrothermal procedure. ¹¹B MAS NMR showed that trigonal boron is the principal coordination state obtained after calcination. Cr-SBA-15 was also achieved by direct synthesis method at different pH (1.5, 3, 5) but the incorporation degree was low, at best Si/Cr = 240 at pH 5. UV–vis spectroscopy indicated that all Cr species were Cr⁶⁺ formed during the calcination step. Oligomerization of 1-hexene at 125 °C showed that the highest conversion (30%) was attained over Al-SBA-15 (Si/Al = 30) although Cr-SBA-15 material exhibited close conversion (21%) despite its low heteroatom content (Si/Cr = 240). Dimers were the major products over Al-SBA-15, Cr-SBA-15 and Fe-SBA-15 catalysts (selectivity ≥ 40%) while strikingly, sol–gel B-SBA-15 lead mostly to heavy oligomers (>60%), with less than 10% of dimers.     

Aromatization of pentane catalyzed over various metallosilicates

Various metallosilicates were synthesized using a hydrothermal method and characterized by SEM, XRD,²⁹Si MAS NMR, chemical analysis and surface area measurements. These results showed that they had a MFI structure. The pentane aromatization reaction was carried out over these metallosilicates in a continuous flow reactor at 550 °C, He/pentane=3, WHSV=1.5 h⁻¹ and 1 atm. Among the various metallosilicates, [Ga]ZSM-5(20) (52.3%) and [Zn]ZSM-5(40) (37.6%) showed higher aromatic selectivities for pentane aromatization. When [Al] ZSM-5(40) was ion-exchanged with gallium nitrate and zinc chloride, the selectivities for aromatics increased from 23.0% to 35.5% and to 32.7%, respectively. The Si/metal mole ratios of [Ga]ZSM-5 and [Al]ZSM-5 were changed from 20 to 250 and NH₃ temperature programmed desorption (TPD) was carried out. As the Si/metal ratio was changed from 250 to 20, the selectivities for aromatics were increased from 5.3 % to 52.3 % over [Ga]ZSM-5 and from 10.1% to 25.7% over [Al]ZSM-5. NH₃ TPD of [Ga]ZSM-5 indicated that the sites of medium acidity play an important role in the formation of aromatics. When H₂ and CO were added to the reactant of pentane, the production of methane and ethane increased and that of aromatics decreased.     

Electrical properties of V2O5–WO3/TiO2 EUROCAT catalysts evidence for redox process in selective catalytic reduction (SCR) deNOx reaction

Electrical conductivity measurements on EUROCAT V₂O₅–WO₃/TiO₂ catalyst and on its precursor without vanadia were performed at 300°C under pure oxygen to characterize the samples, under NO and under NH₃ to determine the mode of reactivity of these reactants and under two reaction mixtures ((i) 2000 ppm NO + 2000 ppm NH₃ without O₂, and (ii) 2000 ppm NO + 2000 ppm NH₃ + 500 ppm O₂) to put in evidence redox processes in SCR deNO_x reaction.It was first demonstrated that titania support contains certain amounts of dissolved W⁶⁺ and V⁵⁺ ions, whose dissolution in the lattice of titania creates an n-type doping effect. Electrical conductivity revealed that the so-called reference pure titania monolith was highly doped by heterovalent cations whose valency was higher than +4. Subsequent chemical analyses revealed that so-called pure titania reference catalyst was actually the WO₃/TiO₂ precursor of V₂O₅–WO₃/TiO₂ EUROCAT catalyst. It contained an average amount of 0.37 at.% W⁶⁺dissolved in titania, i.e. 1.07 × 10²⁰ W⁶⁺ cations dissolved/cm³ of titania. For the fresh catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved in titania were found to be equal to 1.07 × 10²⁰ and 4.47 × 10²⁰ cm⁻³, respectively. For the used catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved were found to be equal to 1.07 × 10²⁰ and 7.42 × 10²⁰ cm⁻³, respectively. Since fresh and used catalysts have similar compositions and similar catalytic behaviours, the only manifestation of ageing was a supplementary progressive dissolution of 2.9 × 10²⁰ additional V⁵⁺ cations in titania.After a prompt removal of oxygen, it appeared that NO alone has an electron acceptor character, linked to its possible ionosorption as NO⁻ and to the filling of anionic vacancies, mostly present on vanadia. Ammonia had a strong reducing behaviour with the formation of singly ionized vacancies. A subsequent introduction of NO indicated a donor character of this molecule, in opposition to its first adsorption. This was ascribed to its reaction with previously adsorbed ammonia strongly bound to acidic sites. Under NO + NH₃ reaction mixture in the absence of oxygen, the increase of electrical conductivity was ascribed to the formation of anionic vacancies, mainly on vanadia, created by dehydroxylation and dehydration of the surface. These anionic vacancies were initially subsequently filled by the oxygen atom of NO. N^o atoms, resulting from the dissociation of NO and from ammonia dehydrogenation, recombined into dinitrogen molecules. The reaction corresponded to

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. In the presence of oxygen, NO did not exhibit anymore its electron acceptor character, since the filling of anionic vacancies was performed by oxygen from the gas phase. NO reacted directly with ammonia strongly bound on acidic sites. A tentative redox mechanism was proposed for both cases.     

SCR of NOx with NH3 over Cu/NaZSM-5 and Cu/HZSM-5 in the presence of decane

The selective catalytic reduction of NO_x with NH₃ in the presence of decane over Cu/ZSM-5 catalysts prepared from H⁺ and Na⁺ZSM-5 precursors were investigated. Cu/NaZSM-5 catalyst showed significantly higher NO_x conversion compared to Cu/HZSM-5. However, the presence of decane decreased the activity of both the catalysts, due to coke formation. Cu/HZSM-5 catalyst showed a larger decline in NO_x conversion with time on stream compared to Cu/NaZSM-5. The higher activity of Cu/NaZSM-5 is attributed, to the promoting effect of Na⁺ cations in the formation of active Cu⁺ and nitrite and nitrate intermediates species and retardation of coke formation.     

Conversion of methane to benzene over Mo2C and Mo2C/ZSM-5 catalysts

The activation and dehydrogenation of CH₂ on Mo₂C and MO₂C/ZSM-5 have been investigated under non-oxidizing conditions. Unsupported Mo₂C exhibited very little activity towards methane decomposition at 973 K. The main reaction pathway was the decomposition of methane to give hydrogen and carbon with a trace amount of ethane. Mixing Mo₂C with ZSM-5 support somewhat enhanced its catalytic activity, but did not change the products of the reaction. A dramatic change in the product formation occurred on partially oxidized Mo2C/ZSM-5 catalyst; besides some hydrocarbons benzene was produced with a selectivity of 70–80% at a conversion of 5–7%. Carburization of highly dispersed MoO₃ on ZSM-5 also led to a very active catalyst: the conversion of methane at the steady state was 5–6% and the selectivity of benzene formation was 85%.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Studies on the mechanism of ZSM-5 formation

The nucleation of (Al-free) zeolite precursor gels was studied using X-ray diffraction,²⁹Si FT-NMR, and ion exchange. Results suggest that in ZSM-5 nucleation, the channel intersections are first formed. These clathrate-like units, each containing essentially one TPA⁺ cation, are initially randomly connected, but progressively anneal with rearrangement under the influence of OH^– ions to form the ZSM-5 framework.     

Estimation of the effectiveness factor of an outer-sphere redox couple (Fe3+/Fe2+) using rotating disk Ti/IrO2 electrodes of different loading

The effectiveness factor; E _f , defined as the fraction of the surface that participates effectively in a given reaction, is an important parameter when operating three-dimensional (3D) electrodes. The rotating disk electrode (RDE) technique with the Fe³⁺/Fe²⁺ redox couple as a probe reaction has been used for the evaluation of the effectiveness factor of 3D Ti/IrO₂ electrodes with different IrO₂ loading. For this purpose, steady-state polarization measurements using Ti/IrO₂ rotating disk electrodes in 0.5 M Fe³⁺/Fe²⁺ in 1 M HCl were carried out under well-defined hydrodynamic conditions. The low-field approximation relation has been used for the estimation of the exchange current densities j ₀, of the Fe³⁺/Fe²⁺ redox couple. It was found for this redox couple that the effectiveness factor is very low (<2%) and essentially the 2D electrode surface area works effectively in the steady-state polarization measurements.     

Hydrocracking of heavy oil using zeolites Y/Al-SBA-15 composites as catalyst supports

A series of Y/Al-SBA-15 composites were prepared by a two-step synthesis procedure in mild acidic medium. The materials were characterized by powder X-ray diffraction (XRD), N₂ sorption isotherms and TEM techniques. Catalytic cracking of cumene and 1,3,5-tri-isopropylbenzene was carried out as the probing reactions on these composites. The XRD results showed that these materials are composites of Al-SBA-15 and Y zeolite. N₂ sorption isotherms and TEM displayed that these composites were abundant in micropores and mesopores. At the same time, the mesopores may communicate with the␣micropores in some domains, which may result in the high catalytic activities of Y/Al-SBA-15 composites for the␣cracking of both small-molecule (cumene) and large-molecule (1,3,5-tri-isopropylbenzene) hydrocarbons. The existence of mesopores may also make the acid sites easily accessible for reactants. Catalysts of W–Ni supported on Y/Al-SBA-15 and modified Y zeolites with mesopores were prepared by impregnation method, and the hydrocracking of heavy oil was performed on these catalysts. The catalyst using zeolite Y/mesoporous Al-SBA-15 composites as support gave higher yield of diesel compared to the catalysts using modified zeolite Y as support. In addition, the higher aromatics potential of heavy naphtha and the significantly lower BMCI (U.S. Bureau of Correlation Index) of tail oil revealed Y/Al-SBA-15 composite catalyst possessed integrated performance in the hydrocracking of heavy oil. These results proved that the combination of Y zeolites and mesoporous Al-SBA-15 plays a great role in improving the performance of catalysts for hydrocracking heavy oils.     

Synthesis and structure of Mu-33, a new layered aluminophosphate

Mu-33, a new layered aluminophosphate with an Al/P ratio of 0.66, was obtained from a quasi non-aqueous synthesis in which tert-butylformamide (tBF) was the main solvent and only limited amounts of water were present. During the synthesis, tBF decomposed and the resulting protonated tert-butylamine is occluded in the as-synthesized material. The approximate structure was determined from data collected on a microcrystal (200 × 25 × 5 μm³) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, but the quality of these data did not allow satisfactory refinement. Therefore the structure was refined using high-resolution powder diffraction data, also collected at the ESRF. The structure (P2₁/c, a = 9.8922(6) Å, b = 26.180(2) Å, c = 16.729(1) Å and β = 90.4(1)°) consists of anionic aluminophosphate layers that can be described as a six-ring honeycomb of alternating corner-sharing AlO₄ and PO₄ tetrahedra with additional P-atoms above and below the honeycomb layer bridging between Al-atoms. The tert-butylammonium ions and water molecules located in the interlayer spacing interact via hydrogen-bonds with the terminal oxygens of the P-atoms. The characterization of this new aluminophosphate by ¹³C, ³¹P, ¹H–³¹P heteronuclear correlation (HETCOR) and ²⁷Al 3QMAS solid state NMR spectroscopy is also reported.     

Enhancement of Sm3+ emission by SnO2 nanocrystals in the silica matrix

Silica xerogels containing Sm³⁺ ions and SnO₂ nanocrystals were prepared in a sol–gel process. The image of transmission electron microscopy (TEM) shows that the SnO₂ nanocrystals are dispersed in the silica matrix. The X-ray diffraction (XRD) of the sample confirms the tetragonal phase of SnO₂. The xerogels containing SnO₂ nanocrystals and Sm³⁺ ions display the characteristic emission of Sm³⁺ ions (⁴G_5/2 → ⁶H _J (J = 5/2, 7/2, 9/2)) at the excitation of 335 nm which energy corresponds to the energy gap of the SnO₂ nanocrystals, while no emission of Sm³⁺ ions can be observed for the samples containing Sm³⁺ ions. The enhancement of the Sm³⁺ emission is probably due to the energy transfer from SnO₂ nanocrystals to Sm³⁺ ions.     

采用不同模板剂控制合成较大晶粒的ZSM-5分子筛

采用不同模板剂以及模板剂组合比较,研究了合成较大晶粒ZSM-5分子筛的过程。通过XRD表征产物的晶相结构,采用SEM观察了产物分子筛的晶粒大小。在分析不同模板剂的模板效应以及合成较大晶粒分子筛影响因素的基础上,提出了能够控制合成中等粒度ZSM-5分子筛的合成方法。结果表明,采用模板剂的不同组合可以控制合成出晶粒粒径在10 μm左右的均匀的较大晶粒分子筛。