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.     

Ammonia synthesis over multi‐promoted iron catalysts obtained by high‐energy ball‐milling

The feasibility of producing ammonia synthesis catalysts from highenergy ballmilling of a simple mixture of the constituent oxides has been investigated. The effect of ballmilling the fused oxidic precursor of the industrial KM1 ammonia synthesis catalyst has also been studied. The results show that highenergy ballmilling offers some interesting possibilities for preparing novel catalytic materials. It is observed that ballmilling of the powder oxides mixture leads to formation of solid solutions and the catalytic activity is significantly higher than that of the starting material. Furthermore, ballmilling of fused oxidic KM1 precursor is seen to give rise to more homogeneous promoter distribution and slightly higher activity. The quite small activity increase observed in this case probably reflects the fact that the fusion process has already resulted in a close to optimal promoter distribution. The choice of atmosphere during ballmilling is also seen to offer possibilities for regulating the phase composition.     

Enhancement of activity for NO removal of MFI‐type H‐Co‐silicate by high‐temperature pretreatment

The effect of high‐temperature pretreatment in the presence of steam on NO conversion of protonated cobalt‐incorporated silicate having MFI structure (H‐Co‐silicate) and copper‐ion‐exchanged MFI‐type zeolite (Cu/H‐ZSM‐5) was studied. The activity of Cu/H‐ZSM‐5 decreased with an increase of pretreatment temperature. In contrast with Cu/H‐ZSM‐5, the activity of H‐Co‐silicate for NO removal increased with the pretreatment temperature. As for H‐Co‐silicate, the pretreatment at 1000^°C was the optimum condition to enhance the conversion that was four times higher than that without pretreatment. The destruction of framework and loss of cobalt species were not observed after the pretreatment. Some parts of cobalt species migrated from the framework and became active sites that enhance the activity for NO removal. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Environmental high resolution electron microscopy of gas‐catalyst reactions

Environmental electron microscopy has become an important scientific method for fundamental studies of dynamic chemical reaction processes in heterogeneous catalysis and of catalytic growth of carbon nanotubes. Outstanding contributions are resulting from the ability to observe gas‐catalyst surface reactions in situ, on the atomic scale. A great deal of structural and chemical information including lattice modification of working catalysts is possible. This is key to understanding novel reaction processes, including release mechanism of structural oxygen in oxide catalysts in selective oxidation of hydrocarbons and to designing improved catalysts. This brief survey of the recent spectacular developments in environmental high resolution electron microscopy shows that new opportunities are being opened up in catalysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fabrication and characterization of the Ag‐based high‐technology model nanocluster catalyst for ethylene epoxidation manufactured by electron beam lithography

Nanocluster catalysis is an area where greater fundamental knowledge is needed to understand the behavior of aggregates of metal atoms in determining product selectivity of chemical reactions. While catalysis is practiced industrially with economic success there is still a great need to eliminate wasteful sidereactions which hurt overall yields. Here we report on fabrication of a Agbased hightechnology model nanocluster catalyst by using electron beam lithography (EBL) designed for systematic studies of the ethylene epoxidation reaction. The catalyst is made of a square array of cylindershaped Ag nanoclusters that are 200 Å in diameter, deposited on a four inch silicon wafer, precovered with a 100 Å thick film of alumina. The height of the particles and interparticle distance can vary, and were chosen to be 150–300 and 1000 Å, respectively. The high technology catalyst was characterized by Xray photoelectron spectroscopy (XPS), highresolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The thermal stability of Ag nanoclusters in vacuo was 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.     

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.     

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.     

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.     

Pt/CeO2 catalysts in selective hydrogenation of crotonaldehyde: high performance of chlorine‐free catalysts

The hydrogenation of crotonaldehyde was conducted in gaseous phase, at atmospheric pressure, on Pt/CeO₂ catalysts prepared from metal precursors containing or not chlorine. The activities and selectivities were studied, at 253 K, as a function of the reduction temperature of the catalyst (473–993 K). The Pt/CeO₂ catalyst, prepared from tetraammineplatinum nitrate, led to 5–20% crotyl alcohol selectivity when the catalyst was reduced at low temperature (473–673 K), while increasing the reduction temperature up to 973 K, the crotyl alcohol selectivity reached more than 80%. Repeating a series of experiments after a re‐calcination treatment at 673 K, the selectivity decreased to only 40% after 473 K reduction to reach again more than 80% after 673 K reduction temperature. A phase transformation of Pt to CePt₅ was observed by XRD analysis after 973 K reduction treatment. Differently on Pt/CeO₂ catalysts containing chlorine, prepared from either chloroplatinic acid or tetraammineplatinum chloride, the crotyl alcohol selectivity never exceeded 30% and did not form alloy up to 973 K reduction temperature. The main results are interpreted considering that the activity of CePt₅ for C=C hydrogenation is low compared to unmodified platinum catalyst and the activation of the carbonyl bond is induced by the presence of oxygen vacancies sites located at the interface between ceria and the metallic particles. The results are in good accordance with the information known at the present time on the metal–support interactions in Pt deposited on CeO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synergistic Extraction of Lanthanides(III) by Mixtures of N‐p‐Methoxybenzoyl‐N‐phenylhydroxylamine and 1,10‐Phenanthroline

Abstract

We conducted a study on the equilibrium extraction behavior of the trivalent lanthanide ions (M³⁺), La, Pr, Eu, Ho, and Yb, from tartrate aqueous solutions into chloroform solutions containing N‐p‐methoxybenzoyl‐N‐phenylhydroxylamine (Methoxy‐BPHA, HL) and 1,10‐phenanthroline (phen). The synergistic species extracted was found to be {ML₂(phen) (HL)}⁺(1/2)Tar^2?, where Tar^2? is tartrate ion. The extraction constants were calculated. The extraction separation behavior and extractability of lanthanides are discussed in comparison with the self‐adducted chelate, ML₃(HL)₂, which was extracted in the absence of phen, and synergistic extraction by mixtures of other extractants such as 2‐thenoyltrifluoroacetone, and neutral donors.     

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.     

Vapour phase O‐methylation of 2‐naphthol over the solid bases alkali‐loaded silica and Cs‐loaded MCM‐41

O‐alkylation of 2‐naphthol has been investigated in the vapour phase over alkali‐loaded fumed silica and Cs‐MCM‐41. Both SiO₂ and MCM‐41 had low C‐alkylation activities and no O‐alkylation activity. The introduction of alkali ions considerably increases 2‐naphthol conversion with 2‐methoxynaphthalene being the major product. The activity of the catalysts increases with alkali loading and the basicity of the metal (Cs > K > Na > Li). Very high conversion (∼99%) of 2‐naphthol and selectivity (>95%) for 2‐methoxynaphthalene are obtained over Cs‐loaded fumed silica and MCM‐41. A small amount of 1‐methyl‐2‐hydroxynaphthalene is also formed over the Li‐, Na‐ and K‐loaded silica. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stereoselective Formation of 1,4‐Anhydro‐2‐C‐carboxytetritols in the Degradation of 1,5‐Anhydroribitol and 1,5‐Anhydroxylitol with Oxygen in Aqueous Alkali

Abstract

In addition to other acid products, degradation of 1,5‐anhydroribitol (5) and 1,5‐anhydroxylitol (6) with oxygen in 1.25 M NaOH produced diastereomeric 1,4‐anhydro‐2‐C‐carboxy‐D‐erythritol (7) and 1,4‐anhydro‐2‐C‐carboxy‐D‐threitol (8) and their enantiomers as major products. However, the ratio of the diastereomers differed for the two reactants. Thus, their formation could not proceed solely by benzilic acid‐type rearrangements through α‐dicarbonyl intermediates as typically proposed for formation of alkyl C‐carboxyfuranosides from alkyl glycopyranosides in similar reactions. The α‐dicarbonyl species that can form from 5 and 6 are identical. Potential mechanisms to account for stereoselective formation of 7 and 8 are presented.     

FeAl/Al2O3 porous composite microfiltration membrane for highly efficiency high‐temperature particulate matter capturing

Journal of Porous Materials - Particulate matter (PM) pollution has raised serious concerns for public health. FeAl intermetallic porous membrane with extensive interconnected pores are potential...     

An Investigation into the Extraction of Americium(III), Lanthanides and D‐Block Metals by 6,6′‐Bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP)

Abstract

The tetradentate ligand (C₅‐BTBP) was able to extract americium(III) selectively from nitric acid. In octanol/kerosene the distribution ratios suggest that stripping will be possible. C₅‐BTBP has unusual properties and potentially offers a means of separating metals, which otherwise are difficult to separate. For example C₅‐BTBP has the potential to separate palladium(II) from a mixture containing rhodium(III) and ruthenium(II) nitrosyl. In addition, C₅‐BTBP has the potential to remove traces of cadmium from effluent or from solutions of other metals contaminated with cadmium. C₅‐BTBP has potential as a reagent for the separation of americium(III) from solutions contaminated with iron(III) and nickel(II), hence offering a means of concentrating americium(III) for analytical purposes from nitric acid solutions containing high concentrations of iron(III) or nickel(II).     

Pulsed Disc‐and‐Doughnut Column Performance

Abstract: A study of the hydrodynamic variables, drop size, continuous phase axial dispersion, and mass‐transfer coefficients of a pulsed annular disc‐and‐doughnut liquid extraction column are presented for three different systems. The results indicate that the characteristic velocity plot of Gayler et al. (1953) can be used to describe the variation of holdup with flow rate for a range of pulsation velocities. The existence of several different operating regimes, namely streamline, mixer‐settler, and emulsion regimes, was observed when the input energy was altered. Mass‐transfer data from 72.5 mm i.d. and 2.5 m i.d. columns were interpreted in terms of the differential axial‐dispersion model; the number of transfer units in a unit length of column is proposed as the basis for scale‐up of the mass‐transfer performance. By considering the free areas in the column, a method is proposed for the geometric scale‐up of pulsed disc‐and‐doughnut columns.