Crystal structure of zeolite X nickel(II) exchanged at pH 4.3 and partially dehydrated, Ni2(NiOH)35(Ni4AlO4)2(H3O)46Si101Al91O384

Complete Ni²⁺ exchange of a single crystal of zeolite X of composition Na₉₂Si₁₀₀Al₉₂O₃₈₄ per unit cell was attempted at 73°C with flowing aqueous 0.05 M NiCl₂ (pH=4.3 at 23°C). After partial dehydration at 23°C and ≈10⁻³ Torr for two days, its structure, now of composition Ni₂(NiOH)₃₅(Ni₄AlO₄)₂(H₃O)₄₆Si₁₀₁Al₉₁O₃₈₄ per unit cell, was determined by X-ray diffraction techniques at 23°C (space group Fd , a₀=24.788(5) Å). It was refined using all intensities; R₁=0.080 for the 236 reflections for which F_o>4σ(F_o), and wR₂=0.187 using all 1138 unique reflections measured. At four crystallographic sites, 45 Ni²⁺ ions were found per unit cell. Thirty of these are at two different site III′ positions. Twenty of those are close to the sides of 12-rings near O–Si–O sequences, where each coordinates octahedrally to two framework oxygens, to three water molecules which hydrogen bond to the zeolite framework, and to an OH⁻ ion. The remaining 10 are near O–Al–O sequences; only three members of a likely octahedral coordination sphere could be found. In addition, two Ni²⁺ ions are at site I, eight are at site I′, and five are at site II. Forty six H₃O⁺ ions per unit cell, 24 at site II′ and 22 at site II, each hydrogen bond triply to six rings of the zeolite framework. Each of the 22 H₃O⁺ ions also hydrogen bonds to a H₂O molecule that coordinates to a site III′ Ni²⁺ ion. Six of the eight sodalite cages each contain four H₃O⁺ ions at site II′; the remaining two each contains a tetrahedral orthoaluminate anion at its center. Each tetrahedral face of each orthoaluminate ion is centered by a site I′ Ni²⁺ ion to give two Ni₄AlO₄ clusters. The five site II Ni²⁺ ions each coordinate to a OH⁻ ion. With 46 H₃O⁺ ions per unit cell, the great tendency of hydrated Ni²⁺ to hydrolyze within zeolite X is demonstrated. With a relatively weak single-crystal diffraction pattern, with dealumination of the zeolite framework, and with an apparent decrease in long-range Si/Al ordering likely due to the formation of antidomains, this crystal like others treated with hydrolyzing cations appears to have been damaged by Ni²⁺ exchange and partial dehydration.     

In situ XPS investigations of Cu1−xNixZnAl-mixed metal oxide catalysts used in the oxidative steam reforming of bio-ethanol

A series of CuNiZnAl-multicomponent mixed metal oxide catalysts with various Cu/Ni ratios were prepared by the thermal decomposition of Cu_1−xNi_xZnAl-hydrotalcite-like precursors and tested for oxidative steam reforming of bio-ethanol. Dehydrogenation of EtOH to CH₃CHO is favored by Cu-rich catalyst. Introduction of Ni leads to CC bond rupture and producing CO, CO₂ and CH₄. H₂ yield (selectivity) varied between 2.6–3.0 mol/mol of ethanol converted (50–55%) for all catalysts at 300 °C. The above catalysts were subjected to in situ XPS studies to understand the nature of active species involved in the catalytic reaction. Core level and valence band XPS as well as Auger electron spectroscopy revealed the existence of Cu²⁺, Ni²⁺ and Zn²⁺ ions on calcined materials. Upon in situ reduction at reactions temperatures, the Cu²⁺ was fully reduced to Cu⁰, while Ni²⁺ and Zn²⁺ were partially reduced to Ni⁰ and Zn⁰, respectively. On reduction, the nature of ZnO on Cu-rich catalyst changes from crystalline to amorphous, relatively inert and highly stabilized electronically. Relative concentration of the Ni⁰ and Zn⁰ increases upon reduction with decreasing Cu-content. Valence band results demonstrated that the overlap between 3d bands of Cu and Ni was marginal on calcined materials, and no overlap due to metallic clusters formation after reduction. Nonetheless, the density of states at Fermi level increases dramatically for Ni-rich catalysts and likely this influences the product selectivity.     

A chronopotentiometric investigation of the dissociation of sulphate ions in molten equimolar NaCl-KCl at 750°C

The Lux—Flood acid—base equilibrium SO₃ + O²⁻ SO₄²⁻ in molten equimolar NaCl/KCl at 750°C has been investigated using conventional chronopotentiometry. The equilibrium constant for this reaction is shown to be very high (K > 10²). Thus the sulphate ion in solution in this melt does not decompose unless a very strong acid such as the metaphosphate ion is added to the melt. This removes oxide ions according to the reaction. 2PO₃⁻ + SO₄²⁻ → SO₃ + P₂O₇⁴⁻ The pyrophosphate anion is not a sufficiently strong acid to remove oxide from sulphate.     

Influence of chromium doping on the electrochemical performance of the 5 V spinel cathode LiMn1.5Ni0.5O4

With an aim to improve the 5 V capacity and cyclability of the LiMn_1.5Ni_0.5O₄ spinel oxide, three series of Cr substitutions have been pursued with y ≤ 0.2: LiMn_1.5Ni_0.5−yCr_yO₄, LiMn_1.5−0.5yNi_0.5−0.5yCr_yO₄, and LiMn_1.5−0.33yLi_0.33yNi_0.5−yCr_yO₄. While the first series involves an increase in the Mn³⁺ content, the second and third series are designed to maintain charge neutrality (Mn⁴⁺, Ni²⁺, Cr³⁺, and Li⁺) without introducing Mn³⁺ ions. The LiMn_1.5Ni_0.5−yCr_yO₄ series experiences a widening of the 4 V plateau and a decrease in the 5 V capacity compared to LiMn_1.5Ni_0.5O₄ due to an increase in the Mn³⁺ content. On the other hand, the LiMn_1.5−0.5yNi_0.5−0.5yCr_yO₄ series shows a suppression of the 4 V plateau and an increase in the 5 V capacity due to the elimination of the Mn³⁺ions. The LiMn_1.5−0.33yLi_0.33yNi_0.5−yCr_yO₄ series shows a suppression of the 4 V plateau at low Cr contents, but an increase in the 4 V plateau as the Cr content increases above 0.1. Among the various compositions investigated, LiMn_1.45Ni_0.45Cr_0.1O₄ exhibits the best combination of high 5 V capacity (128 mAh/g at 5–4.2 V) and excellent capacity retention (98% in 50 cycles) compared to 118 mAh/g and 92% for LiMn_1.5Ni_0.5O₄.     

Preparation of carbon-based adsorbents from sewage sludge pyrolysis to remove metals from water

The objective of this study was to evaluate the use of cheap carbon-based adsorbents from sewage sludge pyrolysis to remove Na⁺, K⁺, Ca²⁺ and Mg²⁺ from saline water. Four model solutions of NaCl, KCl, CaCl₂ and MgCl₂ that simulated seawater composition were used. The model solutions were 456.54 mmol_c L⁻¹ NaCl, 9.72 mmol_c L⁻¹ KCl, 19.96 mmol_c L⁻¹ CaCl₂ and 111.09 mmol_c L⁻¹ MgCl₂. Two carbon adsorbents, one with chemical activation, were prepared by a new method and evaluated for ion adsorption. The results indicated that carbon adsorbent without chemical activation was the most effective in removing ions from different solutions and the removal of metals followed the sequence: Na⁺ (76.78−69.66) >K⁺ (66.0−57.80) >Mg²⁺ (44.84−42.85) >Ca²⁺ (35.12−12.38). Results showed that it is to possible prepare carbon-based adsorbents from sewage sludge following inexpensive and environmentally acceptable methods.     

Decolorization of reactive brilliant red X-3B by heterogeneous photo-Fenton reaction using an Fe–Ce bimetal catalyst

Decolorization of reactive brilliant red X-3B was studied by using an Fe–Ce oxide hydrate as the heterogeneous catalyst in the presence of H₂O₂ and UV. The decolorization rate was in the order of UV–Fe–Ce–H₂O₂ > UV–Fe³⁺–H₂O₂ > UV–H₂O₂ > UV–Fe–Ce ≥ Fe–Ce–H₂O₂ > Fe–Ce. Under the conditions of 34 mg l⁻¹ H₂O₂, 0.500 g l⁻¹ Fe–Ce, 36 W UV and pH 3.0, 100 mg l⁻¹ X-3B could be decolorized at efficiency of more than 99% within 30 min. The maximum dissolved Fe during the reaction was 1 mg l⁻¹. From the fact that the decolorization rate of the UV–Fe–Ce–H₂O₂ system was significantly higher than that of the UV–Fe³⁺–H₂O₂ system at Fe³⁺ = 1 mg l⁻¹, it is clear that the Fe–Ce functioned mainly as an efficient heterogeneous catalyst. UV–vis, its second derivative spectra, and ion chromatography (IC) were employed to investigate the degradation pathway. Fast degradation after adsorption of X-3B is the dominant mechanism in the heterogeneous catalytic oxidation system. The first degradation step is the breaking down of azo and CN bonds, resulting in the formation of the aniline- and phenol-like compounds. Then, the breaking down of the triazine structure occurred together with the transformation of naphthalene rings to multi-substituted benzene, and the cutting off of sulphonic groups from the naphthalene rings. The last step includes further decomposition of the aniline structure and partial mineralization of X-3B.     

Interfacial Reaction Kinetics between Silver and Ceramic-Filled Glass Substrate

Interfacial reaction kinetics between Ag and ceramic-filled glass (CFG) substrate, containing borosilicate glass, high-silica glass, and alumina, has been investigated at 850°–925°C in different atmospheres. No chemical reaction at the interface of Ag/CFG is found when firing takes place in N₂ or N₂+ 1% H₂. Fired in air, however, an interfacial reaction zone is formed at the interface of Ag/CFG with Ag⁺ ion diffusing from silver and Al³⁺ ion dissolving from CFG, and both ions are always coupled together in the reaction zone. Microstructural and chemical analyses show that the reaction zone consists of two distinct layers; one is homogeneous, and the other, heterogeneous. The homogeneous layer, which is adjacent to Ag, is uniform in microstructure with a composition rich in Ag⁺ and Al³⁺. The heterogeneous layer is not uniform in microstructure with Si-rich and Ag–Al-rich phases. The reaction zone moves toward CFG with time, forming a heterogeneous layer first and then converting into a homogenous layer when diffusion of Ag⁺ ion into the CFG becomes significant. The growth kinetics for the homogeneous layer follows a linear rate equation, whereas the heterogeneous layer, a parabolic rate equation. Activation analyses suggest that the formation of the homogeneous layer is controlled by the combination of breakage and formation of M–O bonds, but the heterogeneous layer, by the diffusion of Ag⁺ ion in the BSG.     

Photodegradation catalyst screening by combinatorial methodology

In this work, a combinatorial methodology was developed for photodegradation catalyst screening. A fluorescence imaging detection system was designed for high throughput analysis, 1,6-hexamethylenediamine was used as the probe molecule for catalyst testing. The photodegradation activity of catalysts was evaluated by 1,6-hexamethylenediamine consumption during the photodegradation reaction. The methodology could provide reliable results. We found that pure TiO₂, ZrO₂, Nb₂O₅, MoO₃, and WO₃ did not show much activity for 1,6-hexamethylenediamine photodegradation under visible light. TiO₂ catalysts doped with different metal ions were tested. When TiO₂ was doped with Ta₂O₅, Nb₂O₅, V₂O₅, MoO₃, or WO₃, higher activity for photodegradation was observed. The doping of La³⁺, Ba²⁺, and Br⁻ to TiO₂ did not improve the catalytic activities. When doping TiO₂ with Mn²⁺, Cl⁻, Al³⁺, Cu²⁺, Fe³⁺, Na⁺, Mg²⁺, Li⁺, F⁻, Co²⁺, or K⁺, catalytic activity was lower than that of pure TiO₂. After elaborate catalysts screening, we discovered new catalysts, such as 50–70% TiO₂/0–20% WO₃/20–40% VO_2.5 and 20–30% TiO₂/30–50% MoO₃/40–60% VO_2.5 as well as 30% WO₃/20% ZrO₂/50% NbO_2.5 (synthesized from ZrCl₄, NbCl₅, and (NH₄)₅H₅[H₂(WO₄)₆]·H₂O in ethanol solution or suspension) and 60–70% WO₃/Nb₂O₅ (synthesized from WCl₆ and NbCl₅ in ethanol solution). We observed that the catalytic activity is sensitive to preparation methods and catalyst specific surface areas. When P123 (HO(CH₂CH₂O)₂₀(CH₂CH(CH₃)O)₇₀(CH₂CH₂O)₂₀H, designated EO₂₀PO₇₀EO₂₀) was used as template to synthesize mesoporous materials, the mesoporous catalysts showed higher activity than regular catalytic materials.     

Study of the impedance of a platinum electrode in the system Br2/Br (HClO4, aq.)—II. Mechanism of the electrode reaction

The Randles circuit well represents impedance measurements carried out with activated Pt electrodes. This enables us to study the variation of j_o for redox reactions with concentration of the reactants, at constant potential, and also the variation of j_o with potential, keeping constant the concentration of one of the reactants. The results thus obtained indicate that the step Br₂ + e Br₂⁻ is rate-determining; it is followed or preceded by the rapid equilibria Br₂⁻ Br⁻ + Br 2Br Br₂. The mechanisms proposed hitherto for the electrochemical behaviour of the halogen/halide systems at inert electrodes are discussed, and it is reasoned that the ‘reversibility’ of these systems increases in the order Cl₂/Cl⁻ < Br₂/Br⁻ < I₂/I.     

Nanosized perovskite-type oxides La1−xSrxMO3−δ (M = Co, Mn; x = 0, 0.4) for the catalytic removal of ethylacetate

Nanometer perovskite-type oxides La_1−xSr_xMO_3−δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m² g⁻¹, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn⁴⁺ and Mn³⁺ in La_1−xSr_xMnO_3−δ and Co³⁺ and Co²⁺ in La_1−xSr_xCoO_3−δ, Sr substitution induced the rises in Mn⁴⁺ and Co³⁺ concentrations; adsorbed oxygen species (O⁻, O₂⁻, or O₂²⁻) were detected on the catalyst surfaces. The O₂-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H₂-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h⁻¹, the catalytic activity (as reflected by the temperature (T_100%) for EA complete conversion) increased in the order of LaCoO_2.91 (T_100% = 230 °C) ≈ LaMnO_3.12 (T_100% = 235 °C) < La_0.6Sr_0.4MnO_3.02 (T_100% = 190 °C) < La_0.6Sr_0.4CoO_2.78 (T_100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn⁴⁺/Mn³⁺ and Co³⁺/Co²⁺ ratios), and rich lattice defects of the nanostructured La_1−xSr_xMO_3−δ materials.     

Synthesis of C2H4 by partial oxidation of CH4 over LiCl/NiO

Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO₂ + CO). However, addition of LiCl drastically improved the yield of C₂ compounds (C₂H₆ + C₂H₄). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH₄. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH₄ to C₂H₄ through C₂H₆ (2CH₄ → C₂H₆ → C₂H₄). The study on the oxidation of C₂H₆ over the LiCl/NiO showed that the oxidative dehydrogenation of C₂H₆ to C₂H₄ occurs very selectively, which is the main reason why partial oxidation of CH₄ over LiCl/NiO gives C₂H₄ quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH₄. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni^(2+δ)+ or Ni³⁺). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH₄---CD₄ exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide.     

Photocatalysis by polyoxometallates and TiO2: A comparative study

Polyoxometallates (POMs) as a homogeneous photocatalyst and TiO₂ as a heterogeneous photocatalyst seem to exhibit overall similar photocatalytic behavior. Both systems cause photodecomposition of a variety of organic pollutants via the formation and decay of several similar intermediates formed by OH addition (hydroxylation), dehalogenation, deamination, decarboxylation, etc. The final degradation products, for most organic substrates for both systems are CO₂, H₂O and inorganic anions. The similarity of behavior has been attributed to the formation of the common powerful oxidizing reagent, OH radical, from the reaction of the excited catalyst and water molecules.

On the other hand, lately, various laboratories have pointed out differences in reactivity and degradation mechanism between the two photocatalysts. The results are interesting and to a great extent contradictory.

This study compares the photodegradation of four substrates with diversified structures, namely, atrazine, fenitrothion, 4-chlorophenol (4-ClPh), and 2,4-dichlorophenoxyacetic acid (2,4-D) by both PW₁₂O₄₀³⁻ and TiO₂ and how their photodegradation is affected by the presence of strong OH radical scavengers, i.e., Br⁻ and isopropyl alcohol (i-prOH).

The results provide substantial evidence that the literature data on the apparent photooxidation mechanism of these two categories of photocatalysts is circumstantial, depending on substrate and the mode of investigation. Overall, though, the action of OH radicals relative to h⁺ appears to be more pronounced with PW₁₂O₄₀³⁻ than TiO₂.

With respect to thermal (dark) reaction of photoreduced catalysts, both systems can deliver their electrons to a variety of oxidants including metal ions. The advantages of POM relative to TiO₂ relates to the selective reduction precipitation of metal ions and to their unique ability to form metal nanoparticles in which POM serve both as reducing reagents and stabilizers.     

On the formation of pyronitrate in molten salts

N₂O₅ reacts with O²⁻ ion in LiCl---KCl eutectic at 450° to give NO₃⁻. By analogy to the salts of the other oxides of Group V, NO₃⁻ can be considered as metanitrate and is expected to give—under appropriate conditions—the corresponding pyro-salt. Experiments are described in which the O²⁻ ion in LiCl---KCl melt is potentiometrically titrated with KNO₃. The titration curves show an inflexion at the composition corresponding to pyronitrate, N₂O₇⁴⁻.

The formation of pyronitrate in KNO₃ melts is also established. Strong oxide-ion donors, eg Na₂O₂ or NaOH, or electrolytically generated O²⁻ ion, react slowly with the melt to produce a compound of less basic character. The reaction is zero-order with respect to O²⁻ and has an activation energy of ca 6·17 Kcal/mole.

Pyronitrate in molten KNO₃ possesses a basicity comparable to that of the carbonate ion in the same melt. It readily lends its oxide ion to strong acids eg, Cr₂O₇²⁻ and PO₃⁻. X-ray diffraction patterns of NO₃⁻-N₂O₇⁴⁻ mixtures show peaks that can be correlated to the new anion.     

Effective Au-Au-Clx/Fe(OH)y catalysts containing Cl for selective CO oxidations at lower temperatures

Supported Au catalysts Au-Au⁺-Cl_x/Fe(OH)_y (x < 4, y ≤ 3) and Au-Cl_x/Fe₂O₃ prepared with co-precipitation without any washing to remove Cl⁻ and without calcining or calcined at 400 °C were studied. It was found that the presence of Cl⁻ had little impact on the activity over the unwashed and uncalcined catalysts; however, the activity for CO oxidation would be greatly reduced only after Au-Au⁺-Cl_x/Fe(OH)_y was further calcined at elevated temperatures, such as 400 °C. XPS investigation showed that Au in catalyst without calcining was composed of Au and Au⁺, while after calcined at 400 °C it reduced to Au⁰ completely. It also showed that catalysts precipitated at 70 °C could form more Au⁺ species than that precipitated at room temperatures. Results of XRD and TEM characterizations indicated that without calcining not only the Au nano-particles but also the supports were highly dispersed, while calcined at 400 °C, the Au nano-particles aggregated and the supports changed to lump sinter. Results of UV–vis observation showed that the Fe(NO₃)₃ and HAuCl₄ hydrolyzed partially to form Fe(OH)₃ and [AuCl_x(OH)_4−x]⁻ (x = 1–3), respectively, at 70 °C, and such pre-partially hydrolyzed iron and gold species and the possible interaction between them during the hydrolysis may be favorable for the formation of more active precursor and to avoid the formation of Au–Cl bonds. Results of computer simulation showed that the reaction molecular of CO or O₂ were more easily adsorbed on Au⁺ and Au⁰, but was very difficultly absorbed on Au⁻. It also indicated that when Cl⁻ was adsorbed on Au⁰, the Au atom would mostly take a negative electric charge, which would restrain the adsorption of the reaction molecular severely and restrain the subsequent reactions while when Cl⁻ was adsorbed on Au⁺ there only a little of the Au atom take negative electric charge, which resulting a little impact on the activity.     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.     

Nickel(II) ion-intercalated MXene membranes for enhanced H2/CO2 separation

Hydrogen fuel has been embraced as a potential long-term solution to the growing demand for clean energy. A membrane-assisted separation is promising in producing high-purity H₂. Molecular sieving membranes (MSMs) are endowed with high gas selectivity and permeability because their well-defined micropores can facilitate molecular exclusion, diffusion, and adsorption. In this work, MXene nanosheets intercalated with Ni²⁺ were assembled to form an MSM supported on Al₂O₃ hollow fiber via a vacuum-assisted filtration and drying process. The prepared membranes showed excellent H₂/CO₂ mixture separation performance at room temperature. Separation factor reached 615 with a hydrogen permeance of 8.35 × 10⁻⁸ mol·m⁻²·s⁻¹·Pa⁻¹. Compared with the original Ti₃C₂T_x/Al₂O₃ hollow fiber membranes, the permeation of hydrogen through the Ni²⁺-Ti₃C₂T_x/Al₂O₃ membrane was considerably increased, stemming from the strong interaction between the negatively charged MXene nanosheets and Ni²⁺. The interlayer spacing of MSMs was tuned by Ni²⁺. During 200-hour testing, the resultant membrane maintained an excellent gas separation without any substantial performance decline. Our results indicate that the Ni²⁺ tailored Ti₃C₂T_x/Al₂O₃ hollow fiber membranes can inspire promising industrial applications.     

On the calculation of potential energy profile diagrams for processes in electrolytic metal deposition

The calculation of potential energy and free energy profile diagrams for successive and alternative steps in electrolytic metal deposition is described with reference to two extreme models of the entity resulting from the initial transfer of the metal particle from the solution to the surface of the metal.

Neutralization of the transferred ions to form adsorbed metal atoms is distinguished from ion-transfer processes in which the transferred entity maintains ionic character, with the appropriate number of stoichiometric electrons entering the metal lattice for each ion transferred.

The elementary processes considered are: transfer of ions from the solution to different types of surface sites upon the metal; surface diffusion of adsorbed ions; successive, dehydration of the adsorbed ions in lattice building.

The free energies of the transition states in successive steps in consecutive ion-transfer, surface-diffusion and lattice-building reactions are compared, and the probable rate-determining process in the over-all metal deposition reaction is deduced in the cases of Cu²⁺, Ni²⁺ and Ag⁺ ion deposition on to the respective metals. Uncertainties in the calculation are examined.

The heat of activation (ΔH^0≠) for transfer of ions from the solution to the metal surface depends upon the site to which transfer occurs, that to a planar site being significantly less than that to other sites (e.g., edges, kinks, etc.) Transfer to form completely non-polar neutral adatoms has prohibitively high values of ΔH^0≠

Direct deposition Of Cu²⁺ on to surface sites would be associated with a prohibitively high heat of activation. The path Cu²⁺ + e_M → Cu⁺ followed by Cu⁺ + e_M → (Cu_adion⁺+ e_M) is associated with heats of activation significantly lower than that for direct Cu²⁺ deposition in a single two-electron step. The free energy diagrams are consistent with the existence of a rate-determining reduction mechanism found experimentally. Near the Cu/Cu²⁺ reversible potential the free energy barrier for adion surface diffusion can become the highest. This is consistent with the experimental behaviour under these conditions. With Ag⁺ ion deposition the ion-transfer step has the highest free energy barrier at high negative overpotentials, whilst near the reversible potential the barrier for surface diffusion can become the highest. The kinetic behaviour found experimentally with silver supports the theoretical conclusions.

The low exchange current density for Ni²⁺ ion deposition is probably associated with the instability of the simple Ni⁺ ion in aqueous solutions.     

Ag exchange at Cds electrode surfaces

The inhibition effect of Ag⁺ ions on the photoanodic corrosion of CdS semiconductor electrodes has been studied in 0.5 M NaClO₄ + xM AgClO₄ solutions (0 x 10⁻², pH = 2) by means of potentiostatic current density-potential measurements, ac-impedance and atomic absorption. In the presence of Ag⁺ ions in the solution a thin Ag₂S film of ca. 30–300 nm thickness is formed on the CdS surface due to the heterogeneous cation exchange reaction CdS + 2Ag⁺ = Ag₂S + Cd²⁺. The Ag₂S film formation is a transport controlled process which can be described by a parabolic rate law. From kinetic investigations in the temperature range (298 T 348 K) the activation energy of this process was determined to be about 62 kJ mol⁻¹. Information about the morphology and composition of the surfaces was obtained from optical and scanning electron microscope investigations including EDAX.     

Two experiments for the introductory chemical reaction engineering course

This paper describes a pair of chemical reaction experiments developed for Rowan University's introductory course in chemical reaction engineering: an esterification reaction carried out in a packed bed, and a competitive reaction in which the kinetics were influenced by micromixing.

The first experiment is the esterification of ethanol and acetic acid to form ethyl acetate. Students first examine this reaction in their organic chemistry class. The experiment developed in this project re-examines this reaction from a chemical engineering perspective. For example, the reaction is reversible and equilibrium-limited, but in the organic chemistry lab, there is no examination of the kinetics. The complementary chemical engineering experiment examines the relationship between residence time and conversion.

The second experiment is a competitive system involving two reactions:

H₂BO₃⁻ + H⁺ ↔ H₃BO₃

5I⁻ + IO₃⁻ + 6H⁺ → 3I₂ + 3H₂O

The first reaction is essentially instantaneous. Thus, when H⁺ is added as the limiting reagent, a perfectly mixed system would produce essentially no I₂. Production of a significant quantity of I₂ is attributed to a local excess of H⁺; a condition in which all H₂BO₃⁻ in a region is consumed and H⁺ remains to react with I⁻ and IO₃⁻.

In the spring of 2005, for the first time, both experiments were integrated into the undergraduate chemical reaction engineering course. This paper describes the use of the experiments in the classroom and compares the performance of the 2005 students to the 2004 cohort, for whom the course included no wet labs at all.     

Catalytic performance of quaternary ammonium salts in the reaction of butyl glycidyl ether and carbon dioxide

The synthesis of cyclic carbonate from butyl glycidyl ether (BGE) and carbon dioxide was performed in the presence of quaternary ammonium salt catalysts. Quaternary ammonium salts of different alkyl group (C₃, C₄, C₆ and C₈) and anions (Cl⁻, Br⁻ and I⁻) were used for this reaction carried out in a batch autoclave reactor at 60–120 °C. The catalytic activity increased with increasing alkyl chain length in the order of C₃ < C₄ < C₆. But, the quaternary ammonium salt with longer alkyl chain length (C₈) decreased the conversion of BGE because it is too bulky to form an intermediate with BGE. For the counter anion of the tetrabutyl ammonium salt catalysts, the BGE conversion decreased in the order Cl⁻ > Br⁻ > I⁻. The effects of carbon dioxide pressure and reaction temperature on this reaction were also studied to better understand the reaction mechanism.