Dealumination of zeolite Y by H4EDTA

Solid-state NMR shows that the treatment of zeolite Y by H₄EDTA dealuminates the zeolite framework. Since no extra-framework aluminium is found, all the Al removed from the framework is subsequently washed out of the crystallites in the form of an H₄EDTA complex. Unlike with hydrothermal dealumination or treatment with SiCl₄, H₄EDTA gives defective crystals in which framework vacancies created by the expulsion of aluminium are not healed by silicon from other parts of the framework. The likely reason for this is the slow intracrystalline diffusion of Si(OH)₄ at low temperatures.²⁹Si CP/MAS NMR and infrared spectra confirm the creation of hydroxyl nests in the zeolitic framework. A small amount of disordered siliceous phase responsible for a low intensity²⁹Si MAS NMR shoulder at –110 ppm is produced in the process.On leave from the Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30-239 Krakow, Niezapominajek 1, Poland.     

Non‐isothermal crystallization behavior of stereo diblock polylactides with relatively short poly(d‐lactide) segments from the melt

Stereo diblock polylactides (SDB‐PLAs) composed of relatively short poly(d ‐lactide) (PDLA) segments and relatively long poly(l ‐lactide) (PLLA) segments were synthesized to have a wide number‐average molecular weight (M_n) range of 2.5 × 10⁴–2.0 × 10⁵ g mol^?1 and d ‐lactyl unit content of 0.9–38.6%. The effects of incorporated short PDLA segments (M_n = 2.0 × 10³–7.7 × 10³ g mol^?1) on crystallization behavior of the SDB‐PLAs were first investigated during heating after complete melting and quenching or during slow cooling after complete melting. Stereocomplex (SC) crystallites can be formed at d ‐lactyl unit content as low as 4.3 and 5.8% for heating and slow cooling, respectively, and for M_n of PDLA segments as low as 2.0 × 10³ and 3.5 × 10³ g mol^?1, respectively. With decreasing M_n and increasing d ‐lactyl unit content, the cold crystallization temperature during heating decreased and the crystallization temperature during slow cooling increased. With increasing d ‐lactyl unit content, the melting enthalpy (ΔH_m) of SC crystallites during heating and the crystallinity (X_c) of SC crystallites after slow cooling increased, whereas ΔH_m of PLLA homo‐crystallites during heating and X_c of PLLA homo‐crystallites after slow cooling decreased. The total ΔH_m of SC crystallites and PLLA homo‐crystallites during heating and the total X_c after slow cooling became a minimum at d ‐lactyl unit content of 10–15% and gave a maximum at d ‐lactyl unit content of 0%. Despite the accelerated crystallization of some of SDB‐PLAs, the low values of total ΔH_m and X_c at d ‐lactyl unit content of 10–15% are attributable to the formation of two crystalline species of SC crystallites and PLLA homo‐crystallites.     

Hydrothermal conversion of FAU zeolite into aluminous MTN zeolite

The hydrothermal conversion of FAU zeolite into aluminous MTN zeolite is described here. In the presence of both benzyltrimethylammonium hydroxide (BTMAOH) and sodium chloride (NaCl) the highly crystalline and pure MTN zeolites with Si/Al ratios of 21-23 could be obtained from the hydrothermal conversion of FAU zeolite. Based on powder XRD refinement and ¹³C CP/MAS NMR spectra, BTMA⁺ ions were not present in cages of the obtained zeolites, but TMA⁺ ions existed instead. It means that BTMAOH underwent degradation during the conversion. Moreover, the effects of Si/Al ratio of starting FAU zeolite, synthesis parameters (BTMAOH/SiO₂ and H₂O/SiO₂ ratios) and the addition of alkali metal chlorides on the hydrothermal conversion of FAU zeolite into MTN zeolite are discussed. As compared to amorphous SiO₂/γ-Al₂O₃, which produced impurity, the hydrothermal conversion of FAU zeolite showed a fast crystallization rate and a high selectivity to MTN zeolite formation. These phenomena indicate that the assembly of locally ordered aluminosilicate species coming from the decomposition or dissolution of FAU zeolite should be taking part in the conversion process.     

Synthesis and characterization of hollow zeolite microspheres with a mesoporous shell by O/W/O emulsion and vapor-phase transport method

Hollow microspheres of ZSM-5 with a mesoporous shell have been synthesized through formation of amorphous hollow SiO₂/Al₂O₃ microspheres by sol–gel process in multiple oil–water–oil emulsions and transformation of the amorphous species into zeolite by water–organic vapor-phase transport treatment at 160 °C for 8 days. The morphology of the amorphous and zeolite spheres observed by scanning electron microscopy shows no significant change whereas the molar ratio of Si/Al increases from 6 to 20 during the transformation. The structural feature of zeolite was characterized by X-ray diffraction and ²⁹Si and ²⁷Al magic-angle spinning nuclear magnetic resonance. Transmission electron microscopy and N₂ adsorption–desorption isotherms indicate that uniform mesopores in the shell of zeolite spheres arise from the interstices among zeolite crystallites.     

Removal of Ammonium from Wastewater by Pure Form Low-Silica Zeolite Y Synthesized from Halloysite Mineral

Pure form, single phase, and highly crystalline low-silica zeolite Y was synthesized from natural nanotubular halloysite mineral by the hydrothermal method. In the synthesis process, the halloysite consisted of SiO₂ and Al₂O₃ was used as starting material with adding supplementary silica and alumina sources. Ammonium adsorption properties of the as-synthesized zeolite Y were studied using batch experiments and the results revealed that its adsorption properties were strongly dependent on contact time, adsorbent dosage, pH, ionic strength, temperature, and initial concentration. The equilibrium data fit well with the Langmuir isotherm compared with the Freundlich isotherm. Kinetic studies showed that the adsorption followed the pseudo-second-order model. Thermodynamic parameters such as change in free energy (ΔG ⁰), enthalpy (ΔH ⁰), and entropy (ΔS ⁰) were also determined, which indicated that the adsorption of ammonium on zeolite Y was a spontaneous and exothermic process at ambient conditions. Due to its low cost, high adsorption capacity and fast adsorption rate, the zeolite Y synthesized from halloysite has the potential to be utilized for the cost-effective removal of ammonium from wastewater.     

Redox Potentials of High-Valent Iron-, Cobalt-, and Nickel-Oxido Complexes: Evidence for Exchange Enhanced Reactivity

The ferrocene titration method has been employed to determine the one-electron reduction potentials of a series of oxido-iron(IV), oxido-cobalt(IV) and oxido/hydroxido-nickel(III) complexes based on the same tetradentate TMG₃tren ligand (TMG₃tren=tris[2-(N-tetramethylguanidyl)ethyl]amine). The S=2 ground state of the [(TMG₃tren)Fe^IV=O]²⁺ complex allows an exchange enhanced reactivity, which enables it to perform efficient oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) reactions with a low one-electron reduction potential of 270 mV vs. SCE. In the absence of exchange enhanced reactivity, the OAT and HAA abilities of the S=3/2 [(TMG₃tren)Co^IV−O(Sc(OTf)₃)]²⁺, S=1/2 [(TMG₃tren)Ni^III−O(H)]²⁺ and the previously reported S=1 [(TMC)(CH₃CN)Fe^IV=O]²⁺ and [(N4Py)Fe^IV=O]²⁺ complexes can be directly correlated to their reduction potentials. Notably, [(N4Py)Fe^IV=O]²⁺ and [(TMG₃tren)Fe^IV=O]²⁺ exhibit similar OAT and HAA reactivities although the reduction potential of [(N4Py)Fe^IV=O]²⁺ is 0.24 V more positive than that of [(TMG₃tren)Fe^IV=O]²⁺. The present study therefore provides experimental evidence for exchange enhanced reactivity and rationalizes nature's choice for employing S=2 oxido-iron(IV) cores to achieve difficult oxidation reactions at biologically viable potentials.     

The Kinetics of Melting Crystallization of Poly-L-Lactide

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min^?1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min^?1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of K_g(II)/K_g(III) is 2.17 [K_g(II) = 6.025 × 10⁵K², K_g(III) = 1.307 × 10⁶ K²].     

Phosphorus sorption in relation to soil properties in some cultivated Swedish soils

Phosphorus (P) sorption properties are poorly documented for Swedish soils. In this study, P sorption capacity and its relation to soil properties were determined and evaluated in 10 representative Swedish topsoils depleted in available P. P sorption indices were estimated from sorption isotherms using Langmuir and Freundlich equations (X_m and a_F, respectively) and P buffering capacity (PBC). X_m ranged from 6.0 to 12.2 mmol kg^–1. All indices obtained from sorption isotherms were significantly correlated with each other (r=0.96^*** to r=0.99^***). Two single-point sorption indices (PSI₁ and PSI₂) were also determined, with additions of 19.4 and 50 mmol P kg^–1 soil, respectively. Both PSI indices were well correlated with X_m (r0.98^***), with PSI₁ giving the highest correlation. As isotherms for determining P sorption capacities involve laborious analytical operations, PSI₁ would be preferable for routine analyses. X_m was significantly correlated with Fe extracted by sodium pyrophosphate and ammonium oxalate, to Al extracted by ammonium oxalate and dithionite-citrate-bicarbonate and to organic c. X_m was also significantly correlated with the sum of Fe and Al extracted by ammonium oxalate. The best prediction of X_m through multiple regression was obtained when Fe extracted in ammonium oxalate and Al extracted in dithionite-citrate-bicarbonate were used. Based on the results obtained, both PSI₁ and oxalate-extractable Fe plus Al can be used for predicting P sorption capacity in Swedish soils.     

Upgrading of Lignin-Derived Compounds: Reactions of Eugenol Catalyzed by HY Zeolite and by Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Abstract  

The conversion of eugenol (4-allyl-2-methoxyphenol), a compound derived from the lignin in woody biomass, was catalyzed by HY zeolite at 573 K and atmospheric pressure. The main products were isoeugenol and guaiacol, formed by isomerization and by deallylation, respectively. Substituted guaiacols with saturated side-chains (4-methylguaiacol, 4-ethylguaiacol, and 4-propylguaiacol) were also formed, by hydrogen transfer and alkylation reactions. The pseudo-first-order rate constant for the overall disappearance of eugenol was found to be 12.4 L (g of catalyst)/h. When the catalyst was Pt/γ-Al₂O₃ used in the presence of H₂, significant hydrogenation of the propenyl side-chain took place, accompanied by isomerization, and hydrodeoxygenation. Under similar operating conditions, the reaction catalyzed by Pt/γ-Al₂O₃ in the presence of H₂ gave a higher eugenol conversion (X = 0.70) than the reaction catalyzed by HY zeolite (X = 0.11), primarily because of the dominant hydrogenation observed with the former catalyst. In the absence of H₂ as a co-reactant, the acidic γ-Al₂O₃ support in Pt/γ-Al₂O₃ evidently catalyzed all the classes of reactions catalyzed by HY zeolite.     

Chemical transformations of functional polycarbosilanes

The functional polycarbosilane [Si(X ₂)C₂H₄] _n , whereX ₂=Cl₂ (1), was chemically transformed into the corresponding polymers, whereX ₂=F₂ (3), (2-N, N-dimethylbenzylamino)(H) (5), (9-N,N-dimethyl-1-naphthylamino)(H) (6), (1-C₁₀H₇)(H) (7), Me₂ (8a), (Me₃SiNH)₂ (10), and (vinyl)(H) (11). The functional polycarbosilane, whereX ₂=H₂ (2), was converted into the polymers, whereX ₂=Me(H) (8b) and (OMe)₂ (9). Reaction of3 with KF in the presence of 18-crown-6 gave rise to the poycarbosilane4 containing both pentacoordinate and tetracoordinate silicons in the proportion of 1:15 as shown by quantitative¹⁹F and²⁹Si NMR. Conversion of a greater proportion of silicon atoms to the pentacoordinate state was not possible because of insolubility of the resulting ionomer in the reaction medium.     

Adsorption isotherms in bleaching hazelnut oil

Adsorption isotherms in bleaching hazelnut oil were determined to investigate the applicability of the Langmuir and Freundlich equations and to elucidate the adsorption characteristics of oil on bentonite EY-09 (Bensan Co. Ltd., Edirne, Turkey). The degree of bleaching was monitored spectrophotometrically. Absorbance measurements were carried out to investigate the adsorption force of clay during bleaching of hazelnut oil with 0.3, 0.5, 0.7, and 0.9 wt% clay at 50, 60, 70, 80, and 90°C. Bentonite EY-09 was used as the bleaching clay (adsorbent). Plots of log(x/m) vs. log X _e (for the Freundlich isotherm) and X _e /(x/m) vs. X _e (for the Langmuir isomtherm) were made (where x is the amount of pigment removed per unit mass of the adsorbent, m, and X _e is the equilibrium concentration of the pigment). The Freundlich constants were found to increase with temperature for a given oil/bleaching agent ratio, showing the formation of more active sites on the adsorbent with a rise in temperature. Since the heat evolved during adsorption (0.32–1.03 kJ mol⁻¹) was less than 20 kJ mol⁻¹, the forces between the adsorbent and adsorbate appeared to be van der Waals forces. This type of adsorption is defined as physical or van der Waals adsorption. The results obtained show good agreement with the Freundlich isotherm, indicating that the adsorption of the pigment from the oil proceeds by monolayer formation on the surface of the adsorbent.     

Synthesis of zeolite L crystals with different shapes

Zeolite L crystals were synthesized hydrothermally from aqueous mixtures of potassium hydroxide, metallic aluminum, and colloidal silica. The influence of hydrothermal conditions and the addition of triethanolamine (N(C₂H₄OH)₃; H₃tea) upon the formation and shape of the resulting zeolite L crystals was examined. When the mixtures of KOH:Al:SiO₂:H₂O = 2.2 or 2.5:1.0:4.5:80 were hydrothermally treated at 130 or 175 °C, the zeolite L crystals had a columnar shape. Decrease in the added amount of KOH facilitated crystal growth in the axial direction, whereas a decrease in hydrothermal temperature inhibited it. For the synthesis using H₃tea, a silica-rich starting composition of KOH:Al:SiO₂:H₂O:H₃tea = 10:1.0:15:250:x and a hydrothermal temperature of 120 °C was used. When no H₃tea was added, the obtained zeolite L crystals had an indistinct shape. H₃tea addition at x = 2 led to the formation of zeolite L crystals with a well-defined, clam-like shape. The formation of the well-defined shape is due to the coordination of H₃tea to aluminate ions. The starting composition has some influence on the formation of the clam-like shape. The zeolite L crystal morphologies obtained in this study ranged from stick-like shapes to clam-like ones. The length-to-diameter ratios ranged from 0.2 to 5.8.     

Gas‐ versus liquid‐phase α-pinene transformation over faujasite‐like zeolites and an amorphous silicoaluminate

The transformation of α-pinene was studied in both gas and liquid phase over a series of faujasite‐like zeolites having different framework composition. A comparison with an amorphous silicoaluminate having 13 wt% of Al₂O₃ (SA) was made. Camphene + limonene were the major products observed in liquid phase at 393 K at conversion levels lower than 90%. At 473 K, where the reaction in gas phase took place, limonene suffered an ulterior transformation mainly into terpinenes and terpinolenes and a faster deactivation of the zeolite catalysts as compared to the one in liquid phase was observed. This behaviour contrasts with the high stability shown by SA in gas phase. Over the wider pore system of SA undesired heavy products were formed in liquid phase at the expenses of the terpene isomers. However, in gas phase this ulterior transformation of monoterpenes was minimised. A maximum activity for the zeolite catalysts was observed when the number of Al^IV per unit cell reached about 17, a value where the population of Si(0Al) sites has been shown to reach the maximum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acid Strength of Pt-Zeolite Catalysts: Evidence of Metal-Support Interaction from Linear Free-Energy Relationship

Abstract  

The acid strength of Pt-HBeta and Pt-HMordenite zeolite catalysts were estimated by H/D exchange of substituted benzenes with the use of linear free-energy relationship, through the use of the Hammet–Brown equation. The results indicated that compared with the parent acidic zeolite, the incorporation of Pt metal leads to a significant decrease in the acid strength, estimated by the slope (ρ) of the logarithm of the relative rate (k _X/k _H) with the σ⁺ constant of the substituent, indicating a lower degree of proton transfer to the ring in the transition state. The results support the model of metal-support interaction in Pt-zeolite catalyst, with formation of a metal-proton adduct.     

Influence of aluminium hydroxide and lime on the hydration of tricalcium silicate

Experiments by isothermal calorimetry, indicate that the hydration of 3CaO·SiO₂ (C₃S) is influenced very little by gibbsite; it is influenced by bayerite to a somewhat larger extent. In the presence of amorphous Al(OH)₃ the reaction of C₃S with water shows a very complicated course and gives four heat peaks. If CaO is added in addition to this Al(OH)₃, the third and the fourth heat peaks are more pronounced. From qualitative d.t.a., infra-red, electron-microscope and X-ray investigations, as well as from quantitative X-ray analysis, a reaction mechanism is proposed. The quantity of C₃S reacted, determined by means of quantitative X-ray analysis, is greater during the reaction of 2·00 g C₃S with 0·40 g amorphous Al(OH)₃, 0·08 g CaO and 2·00 ml water, than during the reaction of 2·00 g C₃S with 2·00 ml water.     

NO Adsorption on Ex-Framework [Fe,X]MFI Catalysts: Novel IR Bands and Evaluation of Assignments

IR spectra of NO adsorbed on isomorphously substituted [Fe,Al]MFI, [Fe,Ga]MFI and [Fe]MFI after steaming at 873 K in 30 vol% H₂O are presented. On ex-[Fe,Al]MFI, NO adsorption leads to bands at 2133 cm^-1 and a doublet at 1886 and 1874 cm^-1. The 2133 cm^-1 band is assigned to NO⁺ occupying cationic positions in the zeolite structure. Of the doublet, the 1874 cm^-1 band is much more susceptible to reaction with O₂ than the 1886 cm^-1 band, yielding adsorbed NO₂ with an absorption frequency of 1635 cm^-1. After evaluation of the constitution of the catalyst and (sometimes contradictory) literature assignments, the 1886 cm^-1 band is assigned to NO adsorbed on Fe ions located in isolated positions, and/or (FeO)_n clusters inside the zeolite channels, whereas the 1874 cm^-1 band is proposed to be induced by 2 nm FeAlO_x nano-particles. The ex-[Fe,Ga]MFI catalyst showed a similar absorption pattern (doublet), which is shifted to lower wavenumbers (1881 and 1867 cm^-1), suggesting that both frequencies are affected by the vicinity of Ga (or Al) to the Fe site involved. The absence of bands at 1765 and 1835 cm^-1 suggests that the isolated sites causing these absorptions are in the Fe^III state in ex-[Fe,Al]MFI and ex-[Fe,Ga]MFI. For the ex-[Fe]MFI sample, which did not contain any 2 nm FeO_x nano-particles, an NO absorption band at 1854 cm^-1 is assigned to mono-nitrosyl on extra-framework oligonuclear (Fe^IIO)_n species in the zeolite channels.     

Photooxidation of N,N-bis(3,5-di-tert.-butylsalicylidene)-1,2-diamino hexane-manganese(III) chloride (Jacobsen catalyst) in chloroform

Mn^III(J-salen)Cl (Jacobsen catalyst) with J-salen=N,N^′-bis(3,5-di-tert.-butylsalicylidene)-1,2-diaminocyclohexane dianion in CHCl₃ is photooxidized by the solvent to a Mn^IV(J-salen) complex, presumably Mn^IV(J-salen)Cl₂, with φ=0.002 at λ_irr=333 nm.     

Blends of aliphatic polyesters. I. Physical properties and morphologies of solution-cast blends from poly(DL-lactide) and poly(ε-caprolactone)

Effects of the mixing ratio of poly(DL-lactide) (PDLLA) and poly (ε-caprolactone) (PCL) on the thermal and mechanical properties and morphologies of the solution-cast blends were investigated by differential scanning calorimetry (DSC), polarizing microscopy, tensile tests, and dynamic mechanical analysis. The presence of amorphous PDLLA did not disturb crystallization of PCL over the PDLLA content [X_PDLLA = PDLLA/(PCL + PDLLA)] from 0.1 to 0.9 and allowed PCL to form spherulites over X_PDLLA ranging from 0.1 to 0.6. The spherulite radius was larger for the blends than for the nonblended PCL. Phase separation occurred for the blends with X_PDLLA between 0.1 and 0.9 T^m of PCL remained unchanged in the X_PDLLA range up to 0.6 but decreased at X_PDLLA above 0.6, whereas the crystallinity of PCL was constant around 60%, irrespective of X_PDLLA. The tensile strength (σ_B, the yield stress (σ_Y), the Young's modulus(E), and the storage modulus (G′) of the blends increased monotonously with X_PDLLA if σ_B at X_PDLLA = 0 and 0.6 and σ_Y at X_PDLLA = 0.6 were excluded. Elongation-at-break (ε_B) of PDLLA increased dramatically, while ε_B of PCL decreased remarkably when a small amount of the other component was added. Equations and parameters predicting σ_Y, E, and G′ of the PCL-PDLLA blends were proposed as a function of X_PDLLA. © 1996 John Wiley & Sons, Inc.     

Some thermodynamic properties of tetrafluoroethene-hexafluoropropene copolymers

Copolymers of tetrafluoroethene (TFE) with hexafluoropropene (HFP) have been prepared in the 0-14mol% HFP composition range. Their melting temperatures (T_m), enthalpies (ΔH_f) and entropies (ΔS_f) of first and second fusion, and crystallinities (X) according to x-ray diffraction(x.r.d.) and differential scanning calorimetry (d.s.c.) have been determined. The results indicate that ΔH_f/X_x.r.d of the polymer crystals decreases with higher HFP content.     

Efficient ring-opening polymerization of -caprolactone using anilido-imine–aluminum complexes in the presence of benzyl alcohol

A number of new anilido-imine–Al complexes ortho-C₆H₄(CHNAr¹)(NAr²)AlMe₂ [Ar¹ = C₆H₅, Ar² = C₆H₅ (2a); Ar¹ = 2,6-Me₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2b); Ar¹ = 2,6-Et₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2c); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2d); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2e)] were synthesized, characterized and used as initiators for the ring-opening polymerization of -caprolactone in the presence of benzyl alcohol. The effect of initiator structure and reaction conditions, such as benzyl alcohol/Al molar ratio and reaction temperature on the reactivity, and polymer molecular weight were investigated. The polymerization of -caprolactone initiated by these complexes was found to take place in an immortal fashion.