Steady‐state N2O decomposition on Pt and Rh surfaces using a free‐jet molecular‐beam excited by nozzle heating

Steady‐state N₂O decomposition reaction on polycrystalline Pt and Rh surfaces has been studied using a supersonic free‐jet molecular beam (2.1 × 10¹⁸ molecules/cm² s). The energy of the incident N₂O beam was controlled by a nozzle heating technique in conjunction with a seeding technique. The decomposition rate shows both translational and vibrational energy dependence on the Pt surface. However, there is also the surface temperature dependence of the decomposition rate even varying the incident beam energy, indicating precursor‐mediated dissociation of N₂O on the Pt surface. On the other hand, no energy dependence was observed on the Rh surface, suggesting that the decomposition dynamics are different between Pt and Rh surfaces. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simultaneous removal of N2O and CH4 as the strong greenhouse‐effect gases over Fe‐BEA zeolite in the presence of excess O2

Simultaneous catalytic removal of N₂O and CH₄ as the strong greenhouse‐effect gases was found to be possible over an Fe‐ion‐exchanged BEA zeolite (Fe‐BEA) by the selective catalytic reduction (SCR) of N₂O with CH₄. The direct decomposition of N₂O (2N₂O → 2N₂ + O₂) and the oxidation of CH₄ (CH₄ + 2O₂ → CO₂ + 2H₂O) over Fe‐BEA zeolite required high temperature above 400 and 450 °C, respectively. Nevertheless, the catalytic reduction of N₂O by adding CH₄ over Fe‐BEA zeolite readily occurred at much lower temperatures (ca. 250–350 °C) whether in the presence of O₂ or not. No oxidation of CH₄ by O₂ took place at these temperatures. On the basis of these results and the kinetic studies, it was concluded that CH₄ reacted selectively with N₂O to produce N₂, CO₂ and H₂O over Fe‐BEA zeolite even in the presence of excess O₂. Overall stoichiometry of the SCR of N₂O with CH₄ was determined as follows: 4N₂O + CH₄ → 4N₂ + CO₂ + 2H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

High activity and stability of the Rh‐free Co‐based ex‐hydrotalcite containing Pd in the catalytic decomposition of N2O

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over calcined hydrotalcite‐like compounds containing different combinations of bivalent (Co, Pd, Mg) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co‐precipitation under low supersaturation conditions and characterized by XRD and TG/DSC. The mixed oxides derived after calcination at 723 K were characterized by XRD, N₂ adsorption at 77 K, and XRF. The presence of Rh, La, or Pd in the Co‐based HTlc's improves considerably the catalytic activity. Co–Rh,Al‐HTlc (Co/Rh/Al==3/0.02/1) proved to be a very active catalyst, although the presence of the noble metal Pd in this catalyst ex‐Co,Pd–La,Al‐HT (Co/Pd/La/Al=3/1/1/1) produces a similar catalytic activity to that of Rh‐containing catalyst, both in a N₂O‐containing stream and in one containing also SO₂ and O₂, but with a better performance in stability tests. PdO phase has been identified by XRD as being responsible for the considerable improvement in the activity. The presence of Mg as spinel structure exerts a stabilizing effect in the more active catalysts when mixtures of SO₂ and O₂ are considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ozone formation with (V)UV‐enhanced dielectric barrier discharges in dry and humid gas mixtures of O2, N2/O2, and Ar/O2

The effect of (V)UV illumination at 172 run and 253.7 run on ozone formation with dielectric barrier discharges in air‐like mixtures of nitrogen/oxygen and argon/oxygen as function of the water concentration is presented. Although (V)UV at these wavelengths efficiently cleaves ozone, the ozone concentration in a combined (V)UV/dielectric barrier discharge in oxygen‐containing gases is reduced only very little. This corresponds to an enhanced concentration of atomic singlet oxygen, which, in presence of water, increases the production of hydroxyl radicals. This is confirmed by measurements of the removal rates of 2‐propanol and of its byproducts in dry and humid air in a combined (V)UV/dielectric barrier discharge treatment.     

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.     

Carbonyl‐precursor‐based W/Al2O3 and CoW/Al2O3 catalysts: characterization by temperature‐programmed methods

Carbonyl‐precursor‐based W/Al₂O₃ and bimetallic CoW/Al₂O₃ catalysts were prepared by gas‐phase adsorption in a fluidized‐bed reactor. The surface species formed during the gradual and controlled preparation process were studied by temperature‐programmed methods. Interactions on the surface were investigated as a function of metal loading by temperature‐programmed oxidation (TPO) and oxygen pulse chemisorption (PCO). A clear relationship was observed between decarbonylation treatment and the tungsten species formed. Total acidity of the samples was determined by temperature‐programmed desorption of ammonia (NH₃‐TPD). The NH₃‐TPD measurements, together with previous activity studies, suggest a relationship between total acidity and hydrotreating activity. The results of PCO and NH₃‐TPD measurements indicate that when the controlled gas‐phase preparation method is applied to zerovalent carbonyl precursor, the unfavourable formation of tungsten oxide can be minimized. This revised version was published online in July 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.     

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.     

Synergistic Extraction of Lanthanides(III) with N‐p‐Methoxybenzoyl‐N‐Phenylhydroxylamine and Neutral Nitrogen Donors

Abstract

We investigated the extraction equilibrium behavior of a series of trivalent lanthanide ions, (M³⁺), La, Pr, Eu, Ho, and Yb, from tartrate aqueous solutions using a chloroform solution containing N‐p‐methoxybenzoyl‐N‐phenylhydroxylamine (Methoxy‐BPHA or HL) combined with an adductant, 1,10‐phenanthroline (phen) or 2,2′‐bipyridyl (bipy). The synergistic species extracted were found to be {ML₂(phen)(HL)}⁺(1/2)Tar^2? and {ML₂(bipy)(HL)₂}⁺(1/2)Tar^2?, where Tar^2? is the tartrate ion. The stoichiometry, the extraction constants, and the separation factors of these systems were determined. We discuss the extractability and the separation factors in comparison with self‐adduct chelates, ML₃(HL)_2,(o), which were formed in the absence of phen or bipy.     

On the reactivity of K2O‐, CaO‐ and P2O5‐doped nickel molybdate catalysts in a periodic‐flow reactor

The propane oxydehydrogenation with monolayer lattice oxygen of undoped and K₂O–, CaO– and P₂O₅–NiMoO₄ was investigated by using a periodic‐flow reactor (PFR). The influence of the nature and the extent of the promoter has been emphasized relative to the doped catalysts with respect to pure NiMoO₄ phases. It was observed that calcium and potassium promoters satisfactorily enhance propylene selectivity, and phosphorus promoter specifically increases the total activity while maintaining the propylene selectivity. Evidence found by thermogravimetric (TG) analyses (oxygen depletion rate) has shown a dependence on lattice oxygen mobility due to the presence of promoters. This dependence has been correlated to the propane conversion while the propylene selectivity was attributed to the acid–base properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Labeled 15NO Study on N2 and N2O Formation Over Pt–Ba/Al2O3 NSR Catalysts

Mechanistic aspects involved in the formation of N₂ and of N₂O during the reduction of NO, stored nitrites and stored nitrates in the presence of NO are investigated in this work by means of isotopic labeling experiments over a model PtBa/Al₂O₃ NSR catalyst. The reduction of gaseous labeled NO with unlabelled NH₃ leads to the formation of N₂O at low temperature (below 180 °C), and of N₂ at high temperature. All N₂ possible isotopes are observed, whereas only labeled molecules have been detected in the case of N₂O. Hence the formation of nitrous oxide involves undissociated NO molecules, whereas that of N₂ can be explained on the basis of the statistical coupling of ¹⁵N- and ¹⁴N-adatoms on Pt. However, due to a slight excess of the mixed ¹⁵N¹⁴N isotope, a SCR-like pathway likely operates as well. The reduction of the stored labelled nitrates is very selective to N₂ and all isotopes are observed, confirming the occurrence of the recombination pathway. However also in this case a SCR-like pathway likely occurs and this explains the abundance of the ¹⁴N¹⁵N species. When the reduction of the stored nitrates is carried out in the presence of NO, this species is preferentially reduced pointing out the higher reactivity of gaseous NO if compared to the nitrates.     

Sol–Gel Pd Exhaust Catalysts and N2O Production

Al₂O₃, CeO₂–Al₂O₃, CeO₂–Tb₄O₇–Al₂O₃ and ZrO₂–Al₂O₃ supported Pd samples have been prepared by sol–gel methods. Extents and mechanisms of N₂O production in CO–NO and CO–NO–O₂ reactions on these have been considered. This occurs most selectively under oxidising (lean-burn) conditions or in the presence of CeO₂ and CeO₂–Tb₄O₇ promoters near the CO–NO light off temperature. Over Pd/ZrO₂–Al₂O₃ the CO–NO reaction at 573 K has CO and NO conversions that are second order with respect to p _CO and p _NO. Over this catalyst NO conversion is faster than that of CO until O_2(g) is added, causing CO conversion and N₂O production at 573 K to rise simultaneously. CeO₂ or CeO₂–Tb₄O₇ incorporation into a Pd/Al₂O₃ catalyst enhances N₂O production near the CO–NO light-off temperature in the absence of added O₂ without CO conversion being raised. There is current attention on pollution control opportunities through lean-burn conditions, Pd catalysts and oxygen storage capacity enhancement. The present work suggests that their role in N₂O production may need to be better understood and controlled. For the moment N₂O formation provides a window on mechanisms of TWC operation.     

Degradation of orange G by H2O2、S2O82－、S2O82－-H2O2with ferrous ion

以偶氮染料橙黄G（OG）为目标污染物,研究Fe2+分别催化H2O2、S2O82－、H2O2-S2O82－降解0.1 mmol/L OG Fe2+/H2O2体系,[Fe2+]=1 mmol/L, pH=3, [H2O2]0=10 mmol/L,降解30 min OG脱色率为96%,随着pH值增大和[H2O2]0＞10 mmol/L,OG脱色率减小,呈线性变化。Fe2+/S2O82－体系,随着S2O82－初始浓度增加OG脱色率增大,随着pH值增大OG脱色率减小,呈非线性变化。Fe2+/H2O2-S2O82－体系,pH=3, [H2O2]0=2 mmol/L, [S2O82－]0＞10 mmol/L时OG脱色率持续增大。Fe2+/H2O2-S2O82－体系矿化率最高。利用乙醇和硝基苯作为分子探针,采用分子探针竞争实验鉴定该体系中产生的SO4?和OH?。     

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.     

N2O分解催化剂的制备

中国石油辽阳石化分公司尼龙厂己二酸装置年排出N2O约45 kt,本文介绍了该厂N2O排放气的组成、对环境的危害和治理方案,并研究开发出两类N2O分解催化剂——低温高活性含钴-镁-铝类水滑石煅烧催化剂和载Ni蜂窝型规整催化剂。对组成为Co∶Mg∶Al=3∶0.5∶1(摩尔比)的类水滑石催化剂,当反应气中N2O的摩尔分数为0.13%(其余为N2),空速为4000 h-1时,在220℃下N2O开始分解,到400℃时分解完全。负载金属氧化物蜂窝型规整催化剂N2O的分解温度较高:当反应气中N2O的摩尔分数为0.34%,空速为2400 h-1时,对3次浸渍的载Ni催化剂(NiO负载量9.4%),在360℃下N2O开始分解,480℃分解完全,但蜂窝型规整催化剂流体阻力小,对大气量处理有竞争力。     

313.15 K四元体系Na+// S O 4 2 - ， C O 3 2 - ， N O 3 - -H2O固液相平衡研究

采用等温溶解法研究313.15 K下四元体系Na⁺// \mathrm{S} {\mathrm{O}}_4^{2-} , \mathrm{C} {\mathrm{O}}_3^{2-} , \mathrm{N} {\mathrm{O}}_3^{-} -H₂O的固液相平衡关系。测定了平衡溶液的溶解度数据及物理性质数据,包括密度、黏度、折射率。根据实验数据,绘制了相应的干盐相图、水图及物理性质-组成图。实验结果表明：313.15 K下,此四元体系相图包括两个共饱和点,六条单变曲线以及五个单盐结晶区域(分别为NaNO₃,Na₂SO₄,Na₂CO₃·H₂O, Bur(Na₂CO₃·2Na₂SO₄),Da(NaNO₃·Na₂SO₄·H₂O)),其中Bur的结晶区域最大,最容易从混合溶液中结晶析出。实验中的物理性质(黏度、密度、折射率)随J(Na₂SO₄)的变化呈现相似性规律。该体系中存在复盐碱芒硝Bur(Na₂CO₃·2Na₂SO₄)、钠硝矾Da(NaNO₃·Na₂SO₄·H₂O),结晶水合物(Na₂CO₃·H₂O),没有固溶体存在,故该体系是一个复杂的共饱和型。实验所获数据和结论对煤化工过程产生的高盐废水结晶析盐工艺开发及实现资源梯级综合利用具有重要意义。     

Coupling of N2O Decomposition and Ethylbenzene Dehydrogenation over γ-Al2O3-Supported Transition Metal Oxide Catalysts

Transition metal (Cr, Cu, Fe, Co and Ni) oxides supported on -alumina were characterized with respect to their textural parameters and reducibility and used as catalysts in decomposition of nitrous oxide and ethylbenzene (EB) dehydrogenation as well as coupling of both processes. High activity of -Al₂O₃ in N₂O decomposition coupled with EB dehydrogenation has been found. An increase in EB and N₂O conversion was observed when transition-metal-containing catalysts were used. The activity of catalysts depended on their reducibility. Maximum N₂O efficiency was observed for the Cr/-Al₂O₃ sample, whereas -Al₂O₃-supported Cu and Fe oxide systems showed about 50% efficiency of N₂O in the reaction. An influence of the molar ratio of N₂O/EB on activity and selectivity of the catalysts was found. An excess of N₂O resulted in an increase in CO₂ formation at nearly constant styrene yield.