The sorption and reduction of nitrogen oxides by 12-tungstophosphoric acid and its ammonium salt

Nitrogen dioxide is removed from the gas phase by 12-tungstophosphoric (HPW), 12-tungstosilicic and 12-molybdophosphoric acids, with the two solid acids containing tungsten sorbing significantly larger quantities of NO₂ than that containing molybdenum, indicating the dependence on acidic strength. NO₂ interacts with the water contained on and in HPW to form HNO₃ which desorbs. On depletion of the water additional NO₂ remains held on HPW as

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In contrast the ammonium salt of HPW reduces NO₂ to N₂ , NO and N₂O at an optimal temperature of 175°C for the reduction to N₂. The interaction process occurs between NO₂ and the reductant NH₃ while it is bound as

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on the solid. Thus NH₃ is not lost to the gas phase during the reduction process, and ammonia slip is effectively eliminated. The ammonium salt can be regenerated by exposure of HPW to gaseous NH₃ or by precipitation from aqueous solution.     

The effects of pH on the molecular distribution of water soluble ruthenium(II) hydrides and its consequences on the selectivity of the catalytic hydrogenation of unsaturated aldehydes

The effect of pH on the formation and equilibrium distribution of the water soluble ruthenium hydrides [HRuCl(TPPMS)₂]₂, [HRuCl(TPPMS)₃] and [H₂Ru(TPPMS)₄] (TPPMS=(3-sulfonatophenyl)diphenylphosphine sodium salt) was studied in aqueous solution by pH-potentiometric and

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and

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NMR methods. Depending on the pH, [RuCl₂(TPPMS)₂]₂ and its hydrido-derivatives hydrolyse extensively, giving rise to formation of hydroxo-ruthenium complexes. It was established that at pH≤3.3 the dominant ruthenium(II) species was [HRuCl(TPPMS)₃], while at pH≥7 it was [H₂Ru(TPPMS)₄]. While [HRuCl(TPPMS)₃] catalyzed the slow, selective hydrogenation of the C=C bond in trans-cinnamaldehyde, [H₂Ru(TPPMS)₄] was found an active and selective catalyst for C=O reduction. Consequently, the selectivity of the hydrogenation of trans-cinnamaldehyde could be completely inverted by minor changes in the solution pH, shifting the equilibrium between [HRuCl(TPPMS)₃] and [H₂Ru(TPPMS)₄].     

Palladium(0) allylic alkylation in a two-phase system or with a supported aqueous phase catalyst

The reaction of allylic carbonates with various acyclic and cyclic carbonucleophiles is catalyzed by the system Pd(OAc)₂ and P(C₆H₄-m-SO₃Na)₃ (or tppts) in a two-phase liquid medium H₂O-nitrile, the activity of the catalyst depending mainly on the nature of the nitrile, the temperature of the reaction and the ratio palladium/tppts. The same system Pd(OAc)₂ and P(C₆H₄-m-SO₃Na)₃ supported on silica catalyzes also this reaction. The formation of the active palladium species in the two cases is followed by

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NMR spectroscopy and discussed.     

Sulfonic acid functionalized periodic mesostructured organosilica as heterogeneous catalyst

Periodic mesostructured organosilicas (PMO) were first synthesized using 1,2-bis(triethoxysilyl)ethylene (BTENE) under acidic conditions using Pluronic 123 as surfactant. The ethylene bridges were then arylated with benzene using AlCl₃ as catalyst. These materials were further treated with sulfuric acid for the sulfonation of the phenyl moieties yielding a new preparation of sulfonic acid functionalized PMO. Ordered hexagonal mesostructures with surface areas up to 440 m²/g and narrow pore size distribution (around 5.3 nm) were obtained. This work thus provides a new example of chemical modification for the conception of functionalized PMO catalysts. Liquid phase self-condensation of heptanal was performed at 75 °C in the presence of these catalysts and the results were compared with those obtained with several other heterogeneous acid catalysts.

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Structures of H3PO4/SiO2 catalysts and catalytic performance in the hydration of ethene

The hydration of ethene was carried out over H₃PO₄/SiO₂ having various amounts of H₃PO₄. The rate of the ethanol formation increased markedly with the increasing H₃PO₄ loadings, in particular above 60–70 wt%. By X-ray diffraction (XRD), and

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and

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MAS NMR methods, it was revealed that various silicon phosphates were produced in the preparation of the catalysts. The structures of the phosphates depended on the H₃PO₄ loadings. It was suggested that Si(HPO₄)₂·H₂O species which formed at higher H₃PO₄ loadings were hydrolyzed to H₃PO₄ and SiO₂ during the course of the reaction, yielding the catalysts with high performance. The bulk phase of the H₃PO₄ was involved in the reaction.     

Alinite — Chemical composition, solid solution and hydration behaviour

The chemical composition of alinite was investigated in the system CaO--- SiO₂---Al₂O₃---MgO---CaCl₂. Solid solution was observed. The formula should be written as Ca₁₀Mg_1−x/2□_x/2[(SiO₄)_3+x(AlO₄)_1−x/O₂Cl] with 0.352 (chloride not combined with alinite) which is present after synthesis influences the hydration. Calorimetric and SEM investigations lead to the following equation:

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Mie scattering of electromagnetic radiation by a sphere: A computer program

A computer program for calculating the Mie scattering of electromagnetic radiation by a sphere is described. The program will evaluate, amongst other parameters, the Mie scattering functions a_m and b_m, the extinction, scattering, back-scattering, absorption and radiation pressure efficiencies, the intensity functions, I₁ and I₂ and the polarisation ratios

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. The program can be made available to other users and computations can be commissioned on a repayment basis. A library of results is being established.     

Kinetic study of the photocatalytic recovery of Pt from aqueous solution by TiO2, in a closed-loop reactor

The photocatalytic recovery of platinum

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ions from aqueous solution by TiO₂ (anatase) at conditions met in hydrometallurgical practice (low platinum concentration, low pH values and high chloride concentration) was studied. A continuous flow system with recirculation of the TiO₂ suspension through an illuminated column was applied. The addition of methanol as a “hole scavenger” was proved essential for the reaction to proceed. The influence of various parameters, such as initial platinum and methanol concentration, TiO₂ concentration, pH and flow rate, on the recovery rate was studied. The rate determining stage was found to be the adsorption of methanol molecules on the particles surface. The process seems to be effective and recovery yields up to 95% were achieved.     

NO reduction by H2 over perovskite-like mixed oxides

Perovskite-like mixed oxides

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(A′=Ce or Eu; B=Mn or Co) and La_0.8Sr_0.2BO_3+δ (B=Mn, Fe, Co or Ni) prepared by the amorphous citrate method were used as catalysts for NO reduction by hydrogen. XRD patterns showed a fully crystalline perovskitic structure only in the case of Ce- and Eu-substituted samples. The results suggest that the presence of structural defects is important for the activity of these catalysts, as shown by pretreatment under different atmospheres (He and O₂). La_0.9Ce_0.1CoO_3+δ was the most active of the mixed oxide catalysts investigated and its activity was influenced by the presence of both anion vacancies and Co²⁺ species. La_0.8Sr_0.2NiO_3+δ showed a particular catalytic behaviour, attributed to surface Ni reduction.     

Epoxide–tertiary amine combinations as efficient catalysts for methanol carbonylation into methyl formate in the presence of carbon dioxide

The influence of CO₂ on the carbonylation of methanol into methyl formate was investigated with two classes of catalytic systems: MeO⁻ and epoxide–amine combinations. In the absence of CO₂, NaOMe is the more active, but its efficiency is rapidly destroyed by CO₂. On the other hand, the epoxide–amine system is much less sensitive to the presence of CO₂. Different classes of amines and epoxides have been tested. Tertiary alkyl amines and terminal epoxides are the most efficient. Phosphines associated with an epoxide have also been found to be able to catalyse this reaction. On the basis of

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NMR studies, a plausible mechanism which can also be applied to amines is proposed for the reaction.     

Catalytic dehydrofluorination of CF3CH3(HFC143a) into CF2CH2(HFC1132a)

The catalytic dehydrofluorination of CF₃CH₃ was studied over various metal phosphate catalysts in a fixed-bed reactor. The Mg₂P₂O₇ catalyst exhibited the moderate activity and high selectivity of CF₂CH₂, and it is the most suitable catalyst for the dehydrofluorination of CF₃CH₃. Deactivation did not take place during the 100 h reaction over the Mg₂P₂O₇ catalyst, and XRD patterns of the catalyst were unchanged after 100 h reaction. However, small amounts of F⁻ ions were present on the surface of the catalyst from results of XPS. The active sites for CF₂CH₂ formation are weak acid sites of the catalysts, and carbon deposition and/or polymerization take place on strong acid sites. Results of CF₃CH₃-TPD indicated that the dehydrofluorination proceeds through a

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carbonium-ion mechanism over Mg₂P₂O₇ catalyst, and the rate-determining step is the cleavage of the C–F bond.     

Oxide ion concentration dependence of the potential of stabilized zirconia-air electrode in a molten LiF-KF system

This paper describes oxide ion concentration dependence of the potential of stabilized zirconia-air electrode in a molten LiF-KF eutectic system at 823–973 K. Experimental results can be explained well by the theoretical equation of the zirconia-air electrode potential,

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derived by the authors.

As an example of the application of the equation, solubility product of Al₂O₃ in a molten LiF-KF eutectic system has been determined to be (1.0–3.0) × 10⁻¹⁷ at 823 K, by the use of the zirconia-air electrode.     

The application of chronoamperometry to the study of the kinetic parameters of electron-donor-acceptor (EDA) complexes. The N,N,N′,N′-tetramethyl-p-phenylenediamine-m-dinitro-benzene complex in acetonitrile

The kinetic parameters of the Electron-Donor-Acceptor (EDA) complex between N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and m-dinitrobenzene (MDB) in acetonitrile have been determined by chronoamperometry. The CE_rev system studied and represented by

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was chosen as a model to test the applicability of this electrochemical technique to determine k_f and k_b. Three different methods of calculation are proposed and their scope is discussed. The values of k_f and k_b obtained, although relatively large, are well below diffusion control values. The calculated activation parameters allowed to presume an entropic control for the association process and suggest that the formation of this EDA complex may require a preferred orientation of the donor and acceptor. Moreover, solvation effects seem to play an important role for the dissociation process. The results obtained with this model allowed to consider that chronoamperometry may be a very valuable technique for this type of studies, with the condition that the lifetimes of complexation are within the time constant of the technique.     

Desulphurization of coals and chars by treatment in various atmospheres between 400 and 600 °C

Desulphurization of fifteen US coals of rank ranging from anthracite to sub-bituminous B and five high-temperature chars by carbon monoxide and other gases and gas mixtures between 400 and 600 °C has been studied. The sulphur content of the parent coals ranged between 3.0 and 7.3% and that of the chars between 1.3 and 3.8% by weight. A comparison between air, nitrogen, carbon monoxide, and steam-carbon monoxide mixtures as desulphurizing gases shows the order of desulphurizing ability as

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.     

Mossgas “gas-to-liquid” diesel fuels—an environmentally friendly option

This paper presents a brief summary and comparison of heavy vehicle emissions using Mossgas synthetically derived diesel as opposed to a US Regular Federal 49-state number 2 diesel fuel. A series of engine dynamometer and heavy-duty chassis dynamometer tests were performed at West Virginia University early in 1999.

The Mossgas gas-to-liquid (GTL) low sulphur diesel fuel is produced primarily by the conversion of olefins to distillate (COD) process in conjunction with a high temperature Fisher–Tropsch technology process.

Findings were that there were significant emission benefits when using Mossgas GTL diesel fuel. Oxides of nitrogen (NO_x) and particulate matter (PM) emissions were substantially lower when compared to normal fossil fuel-derived diesel. Additionally the benefits have been found to cut across different engine technologies, various test cycles, engine age (1991–1999), as with or without engine aftertreatment catalysts.

The Mossgas GTL diesel meets the world-wide challenge to produce environmentally friendly transportation fuels and sets the benchmark for future diesel specifications. Accordingly Mossgas has petitioned the US Department of Energy to register this fuel as an alternative fuel under its EPACT program [1 and 2].     

Adsorption and electrokinetics of glucose reduction

The kinetics of cathodic reduction of glucose were studied by a rotating disk electrode at rotation speeds from 500 to 6000 rpm and zero to 2.0 M concentration of glucose. Sodium sulfite was used as the supporting electrolyte as well as the reducing mediator. Both the experimental results and the theoretical analysis indicated that several reaction steps occurred for the cathodic reduction of glucose. The results also revealed that the adsorption of glucose on a cathode played an important role during the electrolysis. The reaction mechanism was proposed and a mathematical model was developed. The model correlated well with the experimental results. The rate determining step was found to be the cathodic reduction of the sodium cation. The rate current of the electroreduction of glucose can be expressed as

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Determination of optimized membrane area from long-term flux decline data

Due to membrane fouling, long-term flux decline follows a general trend: it starts with a steep decline followed by a gradual decrease and approaches its final value asymptotically. Coupled with the concentration effect, our data indicate that this flux behavior can be represented with the equation F = f(t) (k₁ 1n r + k₂) with f(t) = a₀ + exp [a₁ + a₂t + a₃t²] where t is time, a₀, a₁, a₂, a₃, k₁, and k₂ are constants and r is the concentration ratio.

To take advantage of early high flux, ultrafiltration is usually discontinued after a period of time t_u, to be replaced by membrane cleaning period of time t_c. Only then the ultrafiltration cycle is repeated. The total membrane area required for multistage ultrafiltration can be shown as

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where Q₀ is the ultrafiltration capacity, n is the number of stages, and rr_i is the concentration ratio at stage i. An optimization method can be utilized to determine minimum value of A_T. Results will be presented for the case of ultrafiltration of palm oil mill effluent.     

Methanol in microporous materials from first principles

Zeolites are amongst some of the most important heterogeneous catalysts in use commercially today, combining acid–base catalysis due to the presence of Brønsted acid sites with shape selectivity resulting from the microporous environment [1]. Despite this, there is still a great deal of uncertainty concerning the mechanisms of many of the processes which are known to occur and the way in which the zeolite accelerates them. While much information has been obtained from experimental techniques, including infra-red spectroscopy and magic angle spinning NMR [2], there is presently a need for models and reaction pathways to aid in their interpretation. Here theoretical methods are playing a major role in the field of microporous materials.     

Syngas in perspective

Syngas manufacture is an important part of a Fischer–Tropsch (FT) plant as it is responsible for ca. 60% of the investments. The developments of syngas technologies are summarized in Section 1. The present choice for large-scale FT plants based on natural gas is autothermal reforming. The requirements to the syngas and the state of art are summarized. The main costs of an ATR unit are related to the manufacture of oxygen. Air-blown technologies are discussed and compared with ATR.     

Solid solution of ettringites part I: incorporation of OH and CO3 in 3CaOA12O332H2O

Solid solutions of ettringites containing SO₄^2-, OH⁻ and CO₃^2- were investigated. The compositions of the solid solutions are represented by:

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The properties of the different solid solution series are given. By X-ray measurements it is possible to distinguish between the different solid solutions of ettringites.