Activation of methane, oxygen and nitrous oxide over surface-doped MgO materials: I. Conversions in N2O, (N2O + CH4) and (O2 + CH4) reactants

The following materials have been prepared having monolayer equivalent loadings of the indicated dopants: Li⁺/MgO, Ca²⁺/MgO, Sr²⁺/MgO and Ba²⁺/MgO. A continuous-flow microcatalytic reactor system has been used to compare activities of these surface-doped materials for : (a) the catalytic dissociation of N₂O alone at 760K and 958K; (b) N₂O dissociation accompanied by methane coupling and oxidation in a flow of (N₂O + CH₄) reactants at temperatures 760–958K; (c) Methane coupling and oxidation in (O₂ + CH₄) at temperatures 760–993K. The methane-activation roles proposed for various surface sites/intermediates on MgO-based materials are reconsidered in the light of these results.     

Impurity-Dependent Morphology and Grain Growth in Liquid-Phase-Sintered Alumina

The alumina grains in liquid-phase-sintered (LPS) materials prepared from different commercial sources have a predominantly platelet morphology. Generally, the MgO:(CaO + BaO + Na₂O + K₂O) ratio in the chemical composition controls the morphology in LPS alumina that is 91–94 wt% pure. Within a given range of SiO₂ content (i.e., 4.3–5.2 wt% in the chemical composition), a low MgO:(CaO + BaO + Na₂O + K₂O) ratio (i.e., <1.0) in the LPS compositions favors the formation of elongated grains, whereas ratios of >1.0 result in equiaxed grains. SiO₂ contents outside the 4.3–5.2 wt% range favor the formation of elongated grains. A tendency to form platelike grains is observed for LPS alumina with a purity of 91–94 wt% when both the MgO:(CaO + BaO + Na₂O + K₂O) ratio and the SiO₂ content are relatively low. The sintered density generally increases as the SiO₂ content in the chemical composition decreases.     

Study on the active centers of methane coupling catalysts by means of fluorescence emission of Eu

Eu³⁺ ion was adopted as a probe to detect the probability of entrance of alkali elements into the crystal lattice of MgO, CaO and La₂O₃ by means of its characteristic emission. Based on the experimental data it is concluded that Li⁺ and Na⁺ ions can substitute Mg²⁺ and Ca²⁺ ions and only a small amount of K⁺ ion can enter into the lattice of CaO. Whilst Li⁺ ion can not enter into the lattice of lanthana. The conclusion of this investigation is in good agreement with that obtained by Lunsford by ESR studies.     

固相法制备掺杂型高色度CoxM1-xAl2O4/高岭土复合颜料

为了制备低成本、高色度的钴蓝颜料,本文以高岭土为载体,以Al₂O₃和Co₃O₄为主要原料,通过引入ZnO、CaO及MgO不同金属氧化物,采用固相法制备了高色度(Co_xM_1-xAl₂O₄)/高岭土复合颜料(M为Ca²⁺、Mg²⁺或Zn²⁺)。系统考察了研磨时间、煅烧温度、煅烧时间和不同金属氧化物掺量对复合颜料呈色性能的影响规律。研究表明,在煅烧温度1 200 ℃、研磨时间12 h和n(Co²⁺)/n(M²⁺)为3:2时,制得的复合颜料具有最好的呈色性能(L^*=53.68,a^*=7.58,b^*=-62.89)。同时,引入不同的金属元素,可实现对复合颜料颜色的调控,引入Ca²⁺后,所制备的Co_xCa_1-xAl₂O₄复合颜料偏红相,而引入Zn²⁺后,所制备的Co_xZn_1-xAl₂O₄复合颜料偏绿相。通过相关表征,提出了复合颜料的呈色机理,在颜料制备过程中,引入与Co²⁺离子半径接近的Mg²⁺或Zn²⁺,Mg²⁺或Zn²⁺可进入CoAl₂O₄的四面体配位中,部分替代Co²⁺,形成MgAl₂O₄-CoAl₂O₄或ZnAl₂O₄-CoAl₂O₄的固溶体,而引入离子半径较大的Ca²⁺,形成CaAl₂O₄和CoAl₂O₄的均相混合物。最后,将制得复合颜料应用到有机硅耐热涂料中,可以明显提高有机硅涂料的热稳定性。     

焙烧-水化络合法脱除镁废渣中钙杂质的研究

以含钙镁废渣为原料,采用高温焙烧-EDTA络合法脱除其中的钙杂质制备高纯氧化镁,探究了焙烧温度与时间、EDTA溶液浓度、络合温度、液固质量比与水化时间对钙杂质脱除效果的影响。利用X射线衍射(XRD)、X射线光电子能谱(XPS)等方法对样品结构进行表征。结果表明,镁废渣中钙、镁分别以碳酸钙(CaCO₃)和碱式碳酸镁[4MgCO₃·Mg(OH)₂·4H₂O]形式存在,经过高温焙烧过程分别分解为氧化钙(CaO)和氧化镁(MgO)。热力学计算表明,体系中钙、镁离子与EDTA的络合能力存在较大差异,EDTA与钙离子络合能力强,与镁离子络合能力极弱,络合作用促进CaO溶解,使钙离子进入液相,MgO停留在固相,实现钙、镁分离。在800℃、0.5 h、c(EDTA)=0.01 mol/L、液固质量比为80∶1、常温水化时间为2.0 h时,钙脱除率达到98.78%,产物经105℃烘干8.0 h,MgO纯度大于99.00%。     

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.     

Low-Silica Glasses Based on Calcium Aluminates

An exploratory study of the effects of compositional variation on glass formation in low-silica aluminate compositions revealed that CaO is essential for glass formation at ordinary quenching rates. Other oxides, such as Li₂O, MgO, BaO, ZnO, Na₂O, K₂O, BeO, B₂O₃, and PbO, can be present in the glass in limited amounts (in some cases up to 30 mol%). A necessary, but insufficient, condition for easy glass formation is that the ratio of oxygen ions to network-forming cations (assumed to be Si⁴⁺ and Al³⁺) be ∼2.5. The glass-forming compositions were also characterized by liquidus temperatures below ∼1500°C (2732°F). Young's modulus ranged from 13.0 to 17.8×10⁶ psi. Glasses containing network-modifying cations with high field strengths generally had the higher moduli. Strength (420,000 to 650,000 psi in 0.3-mil fibers), static fatigue, viscosity, annealing, and surface tension were studied to a limited extent for the composition (in mol%) 30Al₂O₃-4SiO₂-60CaO-6MgO.     

Grain Growth of the Lime and Periclase Phases in a Synthetic Doloma

Simultaneous grain growth of the lime (CaO) and periclase (MgO) phases was studied in a synthetic, hydroxide-derived doloma over the temperature range 1400° to 1700°C. The grain growth kinetic exponents were 5 and 6 and the activation energies 333±45 and 437±47 kJ/mol for the CaO and MgO phases, respectively. The large kinetic exponents are attributed to the topological restraints of the two phases on the growth of one another. The parameters suggest that the grain growth of the CaO may be governed by Ca²⁺ diffusion within the CaO phase for it is the continuous phase in the microstructure. In most instances for grain growth of the MgO phase, the Mg²⁺ must diffuse through the lime phase, and this process is believed to be limited by movement of associated defects involving Mg²⁺ within the CaO structure.     

Efficient MgO-doped CaO sorbent pellets for high temperature CO2 capture

Novel MgO-doped CaO sorbent pellets were prepared by gel-casting and wet impregnation. The effect of Na⁺ and MgO on the structure and CO₂ adsorption performance of CaO sorbent pellets was elucidated. MgO-doped CaO sorbent pellets with the diameter range of 0.5-1.5 mm exhibited an excellent capacity for CO₂ adsorption and adsorption rate due to the homogeneous dispersion of MgO in the sorbent pellets and its effects on the physical structure of sorbents. The results show that MgO can effectively inhibit the sintering of CaO and retain the adsorption capacity of sorbents during multiple adsorption-desorption cycles. The presence of mesopores and macropores resulted in appreciable change of volume from CaO (16.7 cm³∙mol⁻¹) to CaCO₃ (36.9 cm³∙mol⁻¹) over repeated operation cycles. Ca2Mg1 sorbent pellets exhibited favorable CO₂ capture capacity (9.49 mmol∙g⁻¹), average adsorption rate (0.32 mmol∙g⁻¹∙min⁻¹) and conversion rate of CaO (74.83%) after 30 cycles.     

Origin and Growth Kinetics of Platelike Abnormal Grains in Liquid-Phase-Sintered Alumina

The grain-growth behavior of Al₂O₃ compacts with small contents (≤10 wt%) of various liquid-forming dopants was studied. Equiaxed and/or elongated grains were observed for the following dopants: MgO, CaO, SiO₂, or CaO + TiO₂. The platelike grains, defined as the abnormal grains larger than 100 μm with an aspect ratio ≥5 and with flat boundaries along the long axis, were observed when the boundaries were wet with the liquid phase and the codoping satisfied two conditions of size and valence. These dopings were Na₂O + SiO₂, CaO + SiO₂, SrO + SiO₂, or BaO + SiO₂. However, an addition of MgO to the Al₂O₃ doped with CaO + SiO₂ resulted in the change of grain shape from platelike to equiaxial. Equiaxed grains were also observed for the MgO + SiO₂ doping, indicating that two conditions were necessary but not sufficient to develop the platelike grains. The fast growth rate of the platelike grains was explained by an increased interfacial reaction rate due to the codopants. AT the same time the codopants made the basal plane, which appeared as the flat boundaries, the lowest energy plane. The appearance of the platelike grains was favored in compacts with a small grain size and with a narrow size distribution at the onset of abnormal grain growth. Accordingly, the use of starting powders with a small particle size and narrow size distribution, smaller amounts of dopings, and high sintering temperature resulted in an increased number of the platelike grains.     

Cation distribution between cristobalite, tridymite, and coexisting glass phase in used silica bricks

The chemical composition of cristobalite, tridymite, glass, and accessory phases of different zones of used silica bricks taken from the roof of a glass tank was studied with a high resolution microprobe. Tridymite and cristobalite contain as impurities TiO₂ (≤ 0.36 wt%), Al₂O₃ (≤ 0.37 wt%), and Na₂O (≤ 0.27 wt%). Main constituents of the glass phase coexisting with crystalline silica are: SiO₂ (74 to 60 wt%), TiO₂ (0.4 to 9 wt%), Al₂O₃ (1 to 5 wt%), Fe₂O₃ (0.3 to 3 wt%), CaO (5 to 20 wt%), and Na₂O (8 to 17 wt%). Temperature curves within the bricks during operation of the glass tank have been estimated using direct temperature measurement at the hot front of the bricks, and the transition temperatures of cristobalite to tridymite ( 1450°C), and of - to β-wollastonite ( 1200°C). Microchemical data and supposed temperatures were correlated with the Nernst distribution law. The applicability of the Nernst law shows that local equilibrium conditions were reached during the use of the bricks; they have been preserved during cooling of bricks. The results of the Nernst law cation distribution imply that structural saturation with Al₂O₃, TiO₂, and Na₂O was not reached in the investigated composition range. Al³⁺ is believed to substitute Si⁴⁺ at tetrahedral lattice sites. Al³⁺ substitution is favoured with decreasing temperature in relation to the Al₂O₃ content in the glass phase. Al³⁺ → Si⁴⁺ substitution produces charge deficiency, which is compensated by interstitial entry of Na⁺ into structural channels and voids of tridymite and cristobalite. Ti⁴⁺ incorporation into the cristobalite and tridymite structures is favoured at higher temperatures with respect to the TiO₂ content of the glass phase. The close reciprocal dependence between Al³⁺ and Ti⁴⁺ in silica may indicate that Ti⁴⁺ is tetrahedrally incorporated as well.     

Approach by zeta-potential measurement on the surface change of hydrating C3S

The adsorption of Ca²⁺ on C₃S surface and the formation of C-S-H in the induction period of C₃S hydration were investigated by measuring zeta-potential, heat evolution change and by analyzing dissolved ions. Within 20 minutes, the dissolution of Ca²⁺ and silicate ions and the adsorption of Ca²⁺ on the surface of C₃S were alternately repeated. In the induction period (20 50 minutes), Ca²⁺ was adsorbed fairly strongly on C₃S surface giving positive zeta-potentials and the dissolution stopped for a time. In the hydration between 60 and 140 minutes, the C-S-H gel proceeded to crystallize and Ca²⁺ began to dissolve again, giving negative zeta-potentials by Si-O⁻. After 140 minutes, the second evolution was caused by the crystallization of C-S-H and Ca(OH)₂.     

Reactor and in situ FTIR studies of Pt/BaO/Al2O3 and Pd/BaO/Al2O3 NOx storage and reduction (NSR) catalysts

The reduction of NO under cyclic “lean”/“rich” conditions was examined over two model 1 wt.% Pt/20 wt.% BaO/Al₂O₃ and 1 wt.% Pd/20 wt.% BaO/Al₂O₃ NO_x storage reduction (NSR) catalysts. At temperatures between 250 and 350 °C, the Pd/BaO/Al₂O₃ catalyst exhibits higher overall NO_x reduction activity. Limited amounts of N₂O were formed over both catalysts. Identical cyclic studies conducted with non-BaO-containing 1 wt.% Pt/Al₂O₃ and Pd/Al₂O₃ catalysts demonstrate that under these conditions Pd exhibits a higher activity for the oxidation of both propylene and NO. Furthermore, in situ FTIR studies conducted under identical conditions suggest the formation of higher amounts of surface nitrite species on Pd/BaO/Al₂O₃. The IR results indicate that this species is substantially more active towards reaction with propylene. Moreover, its formation and reduction appear to represent the main pathway for the storage and reduction of NO under the conditions examined. Consequently, the higher activity of Pd can be attributed to its higher oxidation activity, leading both to a higher storage capacity (i.e., higher concentration of surface nitrites under “lean” conditions) and a higher reduction activity (i.e., higher concentration of partially oxidized active propylene species under “rich” conditions). The performance of Pt and Pd is nearly identical at temperatures above 375 °C.     

Reduction of Eu3+ to Eu2+ in Aluminoborosilicate Glasses Prepared in Air

Eu₂O₃-doped aluminoborosilicate glasses were prepared in air at high temperature. Luminescence measurements were used to investigate a valence change from Eu³⁺ to Eu²⁺ ions in the aluminoborosilicate glasses. The results showed that the doped Eu³⁺ ions were partially reduced to Eu²⁺ in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=CaO, SrO, BaO, Li₂O) glasses, but not in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=Na₂O, K₂O) glasses. The changes of Eu reduction with different RO components were discussed with the variation of optical basicity of RO and with different valency of R cations. The effects of co-doping BaO and ZnO in aluminoborosilicate glasses on Eu reduction were also investigated and discussed.     

Ca2+对序批式生物反应器活性污泥性能的影响

二价阳离子能够中和活性污泥表面负电荷,影响微生物活性和生物絮凝性能。本文采用序批式生物反应器（SBR）考察Ca²⁺对污泥活性和污泥絮体表面性质的影响,利用红外光谱和三维荧光光谱分析胞外聚合物（EPS）组分和结构的变化,揭示Ca²⁺与污泥疏水性和zeta电位之间的联系,明确Ca²⁺在生物絮凝中的作用。结果表明：在进水COD、TN和NH₄⁺-N分别为420mg/L、40mg/L和35mg/L的条件下,当Ca²⁺浓度达到160mg/L时,COD、NH₄⁺-N和TN去除率最高（分别为96.7%、90.02%和73.2%）,DHA活性和耗氧呼吸速率（OUR）达到最大,分别为124mgTF/L和3.1mg/（min·L）。Ca²⁺促进了污泥微生物EPS的生成,增大了EPS中蛋白质含量。Ca²⁺与EPS表面带负电的官能团形成架桥,吸附桥联的Ca²⁺中和EPS表面的负电荷,减少了污泥表面负电荷之间的静电斥力,使污泥絮体保持稳定;同时增大了污泥表面的疏水性,改善了污泥的絮凝性和沉降性。     

Effect of Additives on the Hydration Resistance of Materials Synthesized from the Magnesia–Calcia System

The effect of a variety of doping additives on the hydration resistance of calcined materials in the MgO–CaO system was investigated. Samples were prepared from lightly calcined flotation magnesite that was mixed with dolomite, as well as from analytically pure CaO and MgO; then, the samples were doped with additives that contained cations with various valences (monvalent to tetravalent). Both the hydration rate and the powdering rate were measured. The important role of the higher-valence cations in improving the hydration resistance of the MgO–CaO materials was revealed. This behavior is believed to be due to the formation of vacancies in solid solutions of CaO or MgO with higher-valence cations. The Ti⁴⁺ cation forms a solid solution with CaO, which reduces the Ca²⁺ concentration and leads to the improved hydration resistance of calcined materials from the MgO–CaO system.     

Zinc doping effect on the optical bands of cr3 in LiNbO3: Zn, Cr crystals

The optical absorption and luminescence of Cr³⁺ ions in ZnO doped LiNbO₃:Cr³⁺ crystals have been studied. It has been found that ZnO produces the same effect as that observed in MgO co-doped samples: A strong reduction in the Cr³⁺ concentration together with a shift in the ⁴A₂ → ⁴T₁ vibronic transition to lower energy. As in the case of MgO co-doped samples a new Cr³⁺ centre is formed in ZnO co-doped samples.     

Characterization of Pd-based FCC CO/NOx control additives by in situ FTIR and extended X-ray absorption fine structure spectroscopies

Pdⁿ⁺/Ceⁿ⁺/Na⁺/γ-Al₂O₃-type materials used as FCC additives for CO/NO_x control were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and in situ FTIR. The EXAFS data indicate that in freshly prepared samples palladium is present in the form of highly dispersed PdO species. Reduction with H₂ at 500 °C leads to the formation of small Pd clusters incorporating on average approximately six to eight metal atoms at a Pd−Pd bond distance of 2.76 Å. All components of these materials can interact with NO and promote the formation of nitrate/nitrite species, essentially “trapping” NO_x species on the catalyst surface. However, the Na⁺ species dominate the surface chemistry and readily form sodium nitrates with a characteristic IR band at 1370–1385 cm⁻¹. Finally, hydroxyls from the support are also actively participating in the formation of HNO_x type compounds with characteristic stretching vibrations in the 3500–3572 cm⁻¹ region.     

Influence of exchanged cations (Na, Cs, Sr and Ba) on xylene permeation through ZSM-5/SS tubular membranes

Na-ZSM-5 membranes were synthesized by secondary growth on the outer surface of stainless steel porous tubes. The membranes were ion-exchanged with Cs⁺, Ba²⁺ and Sr²⁺ to investigate their effect upon the separation of p-xylene from m-xylene and o-xylene. The permeation through the membranes was measured between 150 and 400 °C using each xylene isomer separately and a ternary mixture. All the membranes were selective to p-xylene in the temperature range studied. N₂ and xylene permeation measurements together with SEM observations were used to determine whether or not cracks and/or pinholes developed after exposure to the xylene isomers at high temperature (400 °C). Neither pore blockage nor extra-zeolitic pores developed after the ion exchange procedure and subsequent calcination. Furthermore, duplicate synthesized membranes of each cation form had similar separation factors and permeances. The duplicate values differ much less than the measurement error. The p-xylene permeation flux decreased in the order: Na-ZSM-5 > Ba-ZSM-5 > Sr-ZSM-5  Cs-ZSM-5 while the permeation flux of the m- and o-xylene decreased in the order Na-ZSM-5 > Sr-ZSM-5 > Ba-ZSM-5 > Cs-ZSM-5. The membrane that exhibited the best performance was Ba-ZSM-5, with a maximum p/o separation factor of 8.4 and a p-xylene permeance of 0.54 × 10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹ at 400 °C.     

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.