Hydrothermal deactivation of Ce‐ZSM‐5, Ce‐beta, Ce‐mordenite and Ce‐Y zeolite deNOx catalysts

The hydrothermal stability of Ce³⁺ zeolite catalysts used for selective catalytic reduction of NO _x was investigated. Aging of Ce‐ZSM‐5, Ce‐beta, Ce‐mordenite and Ce‐Y catalysts consisted of steaming in 10 or 12 vol% water at 600°C for 3–99 h. Ce‐ZSM‐5 (Si/Al ratios: Si/Al = 17.1, 22.6 and 146.6) and Ce‐mordenite (Si/Al = 6.4, IE = 77.2%) showed fast deactivation. Ce‐beta (Si/Al = 12, IE = 68.4%) and Ce‐Y (Si/Al = 2.8, IE = 122%) are significantly more stable zeolite catalysts, Ce‐beta being the most active of these two. Ce‐beta and Ce‐ZSM‐5 catalysts – both having high initial activities – were characterized with ²⁹Si‐NMR and ²⁷Al‐NMR. Especially Ce‐ZSM‐5 showed an increase of non‐framework Al, meaning that the zeolite suffered from dealumination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of Extraction of Chromatographic Materials Containing Bis(2‐ethyl‐1‐hexyl)Phosphoric Acid, 2‐Ethyl‐1‐Hexyl (2‐Ethyl‐1‐Hexyl) Phosphonic Acid,and Bis(2,4,4‐Trimethyl‐1‐Pentyl)Phosphinic Acid

Abstract

This work describes the uptake of a wide range of metal ions, including alkaline earths, transition metals, post‐transition metals, lanthanides and actinides, from acidic nitrate and chloride media on extraction chromatographic resins prepared from three different acidic organophosphorus compounds: bis(2‐ethyl‐1‐hexyl) phosphoric acid (HDEHP), 2‐ethyl‐1‐hexyl(2‐ethyl‐1‐hexyl)phosphonic acid, (HEH[EHP]) and bis(2,4,4‐trimethyl‐1‐pentyl)phosphinic acid (H[DTMPP]). The data is plotted in a format allowing for the easy comparison of the uptake of all metal ions under a given condition. Additionally, examples of several novel separations using the three extraction chromatographic materials are discussed.     

Extraction of Actinide(III,IV, V,VI) Ions and TcO4 − by N,N,N′,N′‐Tetraisobutyl‐3‐Oxa‐Glutaramide

Abstract

The extraction behavior of U(VI), Np(V), Pu(IV), Am(III), and TcO₄ ^? with N,N,N′,N′‐tetraisobutyl‐3‐oxa‐glutaramide (TiBOGA) were investigated. An organic phase of 0.2 mol/L TiBOGA in 40/60% (V/V) 1‐octanol/kerosene showed good extractability for actinides (III, IV, V VI) and TcO₄ ^? from aqueous solutions of HNO₃ (0.1 to 4 mol/L). At 25°C, the distribution ratio of the actinide ions (D _An) generally increased as the concentration of HNO₃ in the aqueous phase was increased from 0.1 to 4 mol/L, while the D _Tc at first increased, then decreased, with a maximum of 3.0 at 2 mol/L HNO₃. Based on the slope analysis of the dependence of D _M (M=An or Tc) on the concentrations of reagents, the formula of extracted complexes were assumed to be UO₂L₂(NO₃)₂, NpO₂L₂(NO₃), PuL(NO₃)₄, AmL₃(NO₃)₃, and HL₂(TcO₄) where L=TiBOGA. The enthalpy and entropy of the corresponding extraction reactions, Δ_r H and Δ_r S, were calculated from the dependence of D on temperature in the range of 15–55°C. For U(VI), Np(V), Am(III) and TcO₄ ^?, the extraction reactions are enthalpy driven and disfavored by entropy (Δ_r H<0 and Δ_r S<0). In contrast, the extraction reaction of Pu(IV) is entropy driven and disfavored by enthalpy (Δ_r H>0 and Δ_r S>0). A test run with 0.2 mol/L TiBOGA in 40/60% 1‐octanol/kerosene was performed to separate actinides and TcO₄ ^? from a simulated acidic high‐level liquid waste (HLLW), using tracer amounts of ²³⁸U(VI), ²³⁷Np(V), ²³⁹Pu(IV), ²⁴¹Am(III) and ⁹⁹TcO₄ ^?. The distribution ratios of U(VI), Np(V), Pu(IV), Am(III) and TcO₄ ^? were 12.4, 3.9, 87, >1000 and 1.5, respectively, confirming that TiBOGA is a promising extractant for the separation of all actinides and TcO₄ ^? from acidic HLLW. It is noteworthy that the extractability of TiBOGA for Np(V) from acidic HLLW (D _Np(V)=3.9) is much higher than that of many other extractants that have been studied for the separation of actinides from HLLW.     

Effect of Anions on the Extraction of Lanthanides (III) by N,N′‐Dimethyl‐N,N′‐Diphenyl‐3‐Oxapentanediamide

Abstract

The extraction of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y by N,N′‐dimethyl‐N,N′‐diphenyl‐3‐oxapentanediamide (DMDPhOPDA) in 1,2‐dichloroethane from aqueous media containing ClO₄ ^?, PF₆ ^?, (CF₃SO₂)₂N^? anions or by DMDPhOPDA in 1,2‐dichloroethane in the presence of 1‐butyl‐3‐methylimidazolium bis[(trifluoremethyl)sulfonyl]imide ([C₄mim][Tf₂N]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) from HNO₃ solutions has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes has been determined. The addition of HPF₆ and (CF₃SO₂)₂NH or their salts to the aqueous HNO₃ or HCl solutions leads to an enchancement of lanthanides (III) extraction by DMDPhOPDA. A considerable synergistic effect was observed in the presence of ionic liquids (IL) in the organic phase containing DMDPhOPDA. This effect is connected with the hydrophobic nature of the IL anion. The distribution of ILs between the equilibrium organic and aqueous phases can govern the extractability of lanthanides (III) in DMDPhOPDA‐IL systems.     

Acid‐Base and Organic‐Water Distribution Equilibria for Symmetrically‐Substituted P,P′‐Dialkyl Alkylenebisphosphonic Acids

Abstract

P,P′‐dialkyl alkylenebisphosphonic acids are powerful metal extraction reagents. The acid dissociation constants for a homologous series of aqueous‐insoluble P,P′‐di‐3‐(trimethylsilyl)‐propyl and aqueous‐soluble P,P′‐diethyl methylene‐, ethylene‐ and propylene‐ bisphosphonic acids were determined in a 70∶30 w/w methanol‐water solvent by potentiometric titration and ³¹P NMR spectrometry. The values obtained for the diethyl‐substituted acids were compared with those determined in water and used to assess the effect of the medium on the aqueous acid dissociation constants of the lipophilic series of P,P′‐di‐3‐(trimethylsilyl)propyl alkylenebisphosphonic acids. The dependence of the organic/aqueous distribution equilibrium on the aqueous acid concentration was also investigated using electrospray ionization mass spectrometry. The acid dissociation and organic/aqueous distribution properties of the substituted alkylenebisphosphonic acids are discussed in terms of their influence on metal ion extraction.     

Comparison of Hydrometallurgical Parameters of N,N‐Dialkylamides and of Tri‐n‐Butylphosphate

Straight‐chain N,N‐dihexyloctanamide (DHOA) and branched‐chain N,N‐di(2‐ethylhexyl)isobutyramide (D2EHIBA) have been identified as promising alternatives to tri‐n‐butylphosphate (TBP) for the reprocessing of spent uranium based fuels, and selective extraction of ²³³U from irradiated thorium fuels, respectively. The present work deals with the effects of different hydrodynamic parameters such as viscosity, density, and interfacial tension (IFT) on the phase‐separation time (PST) under uranium and thorium loading conditions. The IFT values have been determined under varying experimental conditions such as the aqueous nitric acid concentration, n‐dodecane purity, ligand concentration, and thorium/uranium loading conditions. These studies have suggested that the quality of n‐dodecane affects the IFT values of different solutions. The IFT values of D2EHIBA changed marginally (23.3 ± 0.9 mNm^?1) against THOREX feed solution for the wide range of D2EHIBA concentration (0.1–1.0 M). However, IFT, viscosity, and PST values increased with uranium loading of 1.1 M DHOA. These studies suggested that a lower phase‐disengagement rate with increased uranium loading was mainly due to the increased viscosity of the loaded 1.1 M DHOA solution.     

Proton‐poor, gallium‐ and indium‐loaded zeolite dehydrogenation catalysts

The catalytic (propane dehydrocyclization) and reduction behaviors of near 1:1 cation (Ga, In)/framework‐Al MFI zeolites were examined under conditions where the materials were initially either in fully protonated or zero−protonated states. Reductions at appropriate temperatures proceeded up to ∼100% exchange of protons for reduced univalent cations. Further aqueous exchange of alkali (K⁺>) or alkaline earth (Ba²⁺) cations increased the selectivity for dehydrogenation reactions at little or no sacrifice in overall activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

15N solid state NMR study of the reactions of propane or propene, 15NO and oxygen on Na‐, H‐, and CuZSM‐5

Ni- and Co-based catalysts derived from NiAl- and CoAl-layered double hydroxides were tested in four kinds of reactions of methanol, namely decomposition of methanol (DCM), partial oxidation of methanol (POM), steam reforming of methanol (SRM), and oxidative steam reforming of methanol (OSRM), for the purpose of H₂ production for fuel cells. H₂, CO and/or CO₂ were the predominant products with minor amounts of dimethyl ether (DME) and CH₄ depending on the reaction temperature. Among the four kinds of reactions tested, the OSRM reaction was found to be more effective in terms of MeOH conversion and H₂ selectivity over these catalysts. Higher selectivity of H₂ and CO₂ with only traces of CO could be obtained at about 100% methanol conversion around 300 °C in the OSRM reaction over the catalyst derived from CoAl-LDH. Substitution of a part of Al by Sn in the NiAl- and CoAl-LDH systems was found to be inhibiting the methanol conversion. On the other hand, the selectivities to DME and CH₄ were declined with a consequent increase in the selectivity to H₂. In addition, considerable amount of formaldehyde was also noticed, especially over the catalyst derived from CoAlSn-LDH at lower reaction temperatures. The observed difference in the catalytic performance upon Sn incorporation was attributed to an improved redox capability of the Ni- and Co-based oxide catalysts, as determined by temperature-programmed reduction (TPR) experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal Extraction by Sulfur‐Containing Symmetrically‐Substituted Bisphosphonic Acids. Part I. P,P′‐di(2‐ethylhexyl) Methylenebisthio‐Phosphonic Acid

Abstract

P,P′‐dialkyl methylenebisphosphonic acids are powerful metal extraction reagents exhibiting strong affinity for a variety of metal ions, especially lanthanides and actinides. While the affinity of gem‐bisphosphonic acids is generally high for most metal ions because of their relative high acidity and ability to form six‐member chelate rings, the selectivity often is low. Thus, a strategy of incorporating soft‐donor atoms such as sulfur into gem‐bisphosphonic acids has been adopted to obtain enhanced metal selectivity while retaining high extraction efficiency. To this end a new class of sulfur‐containing gem‐bisphosphonic acid solvent extraction reagents was designed, synthesized, and evaluated for heavy element separations. Specifically, the novel sulfur‐containing P,P′‐di(2‐ethylhexyl) methylenebisthiophosphonic acid, H₂DEH[MBTP], was synthesized, characterized and its aggregation, metal extraction and acid‐base behavior assessed. Vapor phase osmometry measurements indicate that H₂DEH[MBTP] is less aggregated than its P,P′‐di(2‐ethylhexyl) methylenebisphosphonic acid analogue, H₂DEH[MBP], existing in toluene primarily as an equilibrium mixture of monomer and dimer in the concentration range studied. The acid dependency data for the extraction of Am³⁺ and Eu³⁺ from aqueous perchlorate solutions by H₂DEH[MBTP] in o‐xylene exhibit slopes close to ?3 at low acidity, consistent with extraction of a trivalent metal ion. The extractant dependency data exhibit pH dependent slopes, suggesting different stoichiometry of metal extraction under different acidities.     

Highly Copper(II) Ion‐Selective Transport Through Liquid Membrane Containing N,N′‐bis(salicylidene)‐1,2‐phenyldiamine

Abstract

N,N′‐bis(salicylidene)‐1,2‐phenyldiamine was synthesized for examining their ability to extract and transport Cu²⁺ through a liquid membrane. By using hydrazine sulfate and potassium thiocyanate as reducing agent and acceptor respectively in the receiving phase at the optimum pH of 1.5, the amount of copper transported across the liquid membrane after 3.5 hours was 96%. The selectivity and efficiency of copper transport from aqueous solution containing various metal ions were investigated.     

Para‐substituted 1‐Phenyl‐3‐methyl‐4‐aroyl‐5‐pyrazolones as Selective Extractants for Vanadium(V) from Acidic Chloride Solutions

Abstract

Para‐substituted 4‐aroyl derivatives of 1‐phenyl‐3‐methyl‐5‐pyrazolones (HX), namely, 1‐phenyl‐3‐methyl‐4‐(4‐fluorobenzoyl)‐5‐pyrazolone (HPMFBP) and 1‐phenyl‐3‐methyl‐4‐(4‐toluoyl)‐5‐pyrazolone (HPMTP) were synthesized and examined with regard to the extraction behavior of multivalent metal ions such as magnesium(II), aluminum(III), titanium(IV), vanadium(V), chromium(III), manganese(II), iron(II), and iron(III) that are present in titania waste chloride liquors. For comparison, studies have also been carried out with 1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone (HPMBP). The results demonstrate that vanadium(V) and iron(III) are extracted into chloroform with 4‐aroyl‐5‐pyrazolones as VO₂X · HX and FeX₃, respectively. On the other hand, magnesium(II), aluminum(III), titanium(IV), chromium(III), manganese(II), and iron(II) were not found to be extracted into the organic phase. The equilibrium constants of vanadium(V) and iron(III) with various 4‐aroyl‐5‐pyrazolones follow the order HPMFBP>HPMBP>HPMTP, which is in accordance with their pKa values. The selectivity between vanadium(V) and iron(III) increases with increasing hydrochloric acid concentration. Further, it is clear from the results that iron(III) is not getting extracted above 1.0 mol dm^?3 hydrochloric acid solution. The electronic and IR spectra of the extracted complexes of vanadium(V) and iron(III) were used to further clarify the nature of the extracted complexes. The potential of these reagents for the selective extraction and separation of vanadium(V) from titania waste chloride liquors has also been discussed.     

Synthesis,Characterization, and Evaluation of Gel‐Type Poly(4‐Vinylpyridine) Resins for Plutonium Sorption

Abstract

Three different cross‐linked (4, 8, and 12%) gel‐type strong‐base poly(4‐vinylpyridine) resins (PVP) have been synthesized and characterized by elemental analysis, IR, exchange capacity, and moisture content. The uptake of plutonium and uranium was measured as a function of nitric acid concentration using all the three PVP resins. Plutonium sorption and elution kinetics experiments were also performed on all three PVP resins and compared with the benchmark, a gel‐type quarternary ammonium type anion‐exchange resin. The plutonium sorption rate decreases with the increase in cross‐linkage of the resin. All the three PVP resins exhibit better elution kinetics compared to the benchmark. The results on kinetic experiments performed on all three‐gel‐type resins indicated 8% gel‐type PVP resin with 50–100 mesh as a better candidate for plutonium processing or purification. Radiation degradation studies were carried out on the 8% PVP resin by gamma irradiation up to 200 MRad. The irradiated resins were characterized by IR, TGA, and SEM.

The exchange capacity, moisture content, and plutonium uptake were also evaluated for the irradiated PVP resins in comparison with the benchmark. The results indicated a better radiation stability for PVP resin over the benchmark.     

Extraction Properties of 6,6′‐Bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP)

Abstract

The extraction of americium(III) and europium(III) into a variety of organic diluents by 6,6′‐bis‐(5,6,‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) has been investigated. In addition to determining the stoichiometry for the extraction, the dependence of extraction on contact time and temperature was also studied. The resistance of the ligand to gamma irradiation and the possibility to recycle the organic phase after stripping were tested to determine how the molecule would perform in a radiochemical process. Different organic diluents gave different extraction results, ranging from no extraction to distribution ratios of over 1000 for americium(III). In 1,1,2,2‐tetrachloroethane, the extraction and separation of americium from europium and the extraction kinetics were good; a separation factor above 60 was obtained at equilibrium, ～5 min contact time. The extraction capabilities are adequate for C5‐BTBP to be used in a process for separating trivalent actinides from lanthanides. However, C5‐BTBP is susceptible to radiolysis (americium extraction decreases ～80% after a dose of 17 kGy) and may not be the best choice in the processing of spent nuclear fuel. Nonetheless it is a useful starting point for further development of this type of molecule. It could also prove useful for analytical scale separations for which radiolytic instability is less important.     

Extraction of Palladium(II) from Nitric Acid Solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea

The extraction of palladium (II) from HNO₃ solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea (Ia) and several monodentate thiourea derivatives in 1,2‐dichloroethane has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant in the organic phase on the Pd(II) extraction is considered. The stoichiometry of the extracted complexes has been determined. The increasing number of thioamide groups in the molecule of Ia increases its extraction efficiency towards Pd(II). The potentialities of a polymeric resin impregnated with compound Ia for selective extraction of Pd(II) from nitric acid solutions are demonstrated.     

Application of N,N′‐Dimethyl‐N,N′‐Di(4‐Chlorophenyl)Tetradecyl Malonamide for the Selective Recovery of Iron(III) from Concentrated Chloride Solutions

Abstract

The feasibility of using two new diamides namely; N,N′‐dimethyl‐N,N′‐di(4‐chlorophenyl)malonamide (DMDPhClMA) and N,N′‐dimethyl‐N,N′‐di(4‐chlorophenyl)tetradecylmalonamide (DMDPhClTDMA), as agents for the selective extraction of iron(III) from chloride solution was investigated. A systematic investigation has been carried out on the detailed extraction properties of iron(III) with these extractants from chloride media. The extraction of iron(III) from an aqueous chloride solution in the presence of metal ions, such as Zn(II), Co(II), Mn(II) Cu(II), Pb(II), Ni(II) and Ag(I) was carried out using DMDPhClMA or DMDPhClTDMA in binary and multicomponent mixtures. The quantitative extraction of iron(III) with DMDPhClMA and DMDPhClTDMA in toluene is observed at 4 and 7 M HCl, respectively. The quantitative stripping of Fe(III), from the loaded organic phase was successfully achieved by simple contact with water.     

Extraction of Actinides with Different 6,6′‐Bis(5,6‐Dialkyl‐[1,2,4]‐Triazin‐3‐yl)‐[2,2′]‐Bipyridines (BTBPs)

Abstract

The extraction of Am(III), Th(IV), Np(V), and U(VI) from nitric acid by 6,6′‐bis(5,6‐dialkyl‐[1,2,4]‐triazin‐3‐yl)‐[2,2′]‐bipyridines (C2‐, C4‐, C5‐, and CyMe₄‐BTBP) was studied. Since only americium and neptunium extraction was dependent on the BTBP concentration, computational chemistry was used to explain this behavior. It has been shown that the coordination of the metal played an important role in forming an extractable complex into the organic phase, thus making it possible to extract pentavalent and trivalent elements from tetravalent and hexavalent elements. This is very important, especially because it shows other possible utilizations of a group of molecules meant to separate the actinides from the lanthanides. In addition, the level of extraction at very low or no BTBP concentration was explained by coordination chemistry.     

Combinatorial chemistry, high‐speed screening and catalysis

Combinatorial and high‐speed screening techniques, which have revolutionized the search for new drug molecules, are now finding broader application in the chemical and materials development areas. The ability to generate large “libraries” of samples and to evaluate their performance simultaneously reduces the time and cost per sample and enables multicomponent parameter spaces to be explored. In the area of catalyst development, the impact of this technology promises to be substantial, not only in synthesis and performance evaluation, but also for the optimization of operating parameters. In this review, the major experimental approaches are described; for heterogeneous catalysts, especially, the parallel approach proves the most useful, rather than the “split‐and‐mix” methods of drug screening. Novel techniques for the high‐speed, parallel performance evaluation of catalyst arrays are reviewed with numerous recent examples. Indications are provided of expected future trends in this rapidly developing area. This revised version was published online in July 2006 with corrections to the Cover Date.     

A high‐resolution solid‐state NMR study on nano‐structured HZSM‐5 zeolite

Variations in the structure and acidity properties of HZSM‐5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid‐state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of ²⁷Al MAS NMR, ²⁹Si MAS, CP/MAS NMR and ¹H MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the ²⁷Al, ²⁹Si MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM‐5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of ¹H MAS NMR obtained using Fluorinert^® FC‐43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Brønsted acid sites on the external surface of the nano‐structured zeolite appears to be distinctly higher than that of the microsized zeolite.     

C,N‐Pyridylpyrazole‐Based Ligands: Synthesis and Preliminary Use in Metal Ion Extraction

Abstract

The synthesis of new N‐donor pyridylpyrazole ligands with a functionalized arm is described. The complexation capabilities of these compounds towards bivalent metal ions (Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺) and alkali metal ions (K⁺, Na⁺, and Li⁺) were investigated using the liquid‐liquid extraction process. The percentage limits of extraction were determined by atomic absorption measurements.