Effect of transition metal on the hydrogen storage properties of Mg–Al alloy

Mg–Al alloys were prepared via sintering combined with ball milling, and the effect of a transition metal (TM = Ti, V, Ni) on the hydrogen storage properties of these alloys was investigated; the alloys were characterized via X-ray diffraction, pressure composition isotherms, and differential scanning calorimetry. The results showed that the alloys were mainly composed of Mg and the Mg₁₇Al₁₂ phase, and the cell volume of these phases decreased after the addition of TM (TM = Ti, V, Ni), which is attributed to the improved hydrogenation kinetics of Mg–Al alloy. Moreover, the hydrogenation/dehydrogenation temperature of the Mg–Al alloy decreased with the addition of TM (TM = Ti, V, Ni). Ti, Ni, and V acted as a catalyst, thereby lowering the reaction barrier for dehydrogenation and promoting the reversible hydrogenation reaction of the Mg–Al alloy. The onset temperature of dehydrogenation of the Mg–Al–V alloy was ~244 °C, which was 66 °C lower than that of the Mg–Al alloy (~310 °C). And the apparent activation energy of the Mg–Al–V alloy was 80.1 kJ mol^?1, where it was 34.6 kJ mol^?1 lower than that of Mg–Al alloy.     

纳米晶镁铝水滑石制备机理及抗毒性研究

以尿素为沉淀剂制备纳米晶镁铝水滑石,考察不同镁铝比制备的纳米晶镁铝水滑石催化剂对大豆油酯交换的影响以及催化剂的抗水抗酸性和使用寿命,并探讨纳米晶镁铝水滑石的合成机理.随镁铝摩尔比增加,酯交换反应所需时间减少,当m(Mg2 ):m(Al3 )=3:1时,转化率高达94.2%;当m(Mg2 ):m(Al3 )=4:1时,使用寿命最长,可重复使用5次.纳米晶镁铝水滑石具有较强抗水抗酸性,故在进行酯交换反应中无须脱水脱酸.     

Modification of FAU zeolite as an active heterogeneous catalyst for biodiesel production and theoretical considerations for kinetic modeling

In this work, a high purity FAU-type zeolite catalyst was prepared from shale rock and modified as a heterogeneous efficient catalyst for biodiesel production from sunflower oil. The characterization properties for both of the prepared catalysts were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), Brunauer–Emmett–Teller (BET), and Fourier-transform infrared spectroscopy (FTIR). The incipient wetness impregnation method was adopted for loading the catalyst with three base precursors: NaOH, KOH, and Ca(OH)3. Different factors affecting transesterification reaction onto modified Na-K-Ca-FAU zeolite were investigated such as; temperature (35, 45, 55, and 65 °C), catalyst concentrations (2, 3,4, 5, and 6 wt%) and the molar ratio of methanol to sunflower oil (3:1, 6:1, 9:1 and 12:1). The optimum conditions of transesterification reactions were obtained for reaction time (4 h) and agitation rate (700 rpm) in a batch reactor at 65 °C reaction temperature, 5% catalyst concentration, and a 9:1 M ratio of methanol to oil. The experimental results showed that the conversion of triglyceride in sunflower oil to fatty acid methyl ester (FIME) increased from 48.62 to 91.6% when the FAU zeolite was loaded with 15 wt% of the three bases. The properties of the produced biodiesel were evaluated within the standard performance ASTM D-6751. This study shows that the three base precursors (i.e., NaOH, KOH, and Ca(OH)3) were successfully loaded onto support FAU zeolite and functioned as excellent catalysts for biodiesel production. Theoretical considerations for kinetic modeling in the heterogeneous transesterification reaction were investigated using MATLAB programming. The experimental and theoretical considerations for kinetic modeling were fitted well.     

Catalytic characterization of bi-functional catalysts derived from Pd-Mg-Al layered double hydroxides

Hydrotalcite like precursors containing Pd^II-Mg^II-Al^III with varying molar ratios, (Pd + Mg)/Al ≈ 3 and Mg/Pd ≈ 750 to 35, were prepared by coprecipitation of metal nitrates at constant pH. Characterization of samples as synthesized and their calcined products by elemental analyses, powder XRD, TG-DTA, FT-IR spectroscopy, TPR and N₂ physisorption indicated a well crystalline hydrotalcite like structure with incorporation of Pd²⁺ in the brucite layers. Thermal decomposition of hydrotalcite precursors at intermediate temperatures led to amorphous mixed oxides, Pd/MgAl(O), which on reduction yielded bi-functional catalyst, Pd°/MgAl(O). The resultant catalysts with acid, base and hydrogenating sites, were highly active and selective for one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen. The results showed an optimal balance between acid-base and metallic sites were required to increase the selectivity of MIBK and stability of the catalysts.     

Mg/Al水滑石对腐殖酸的去除性能研究

采用共沉淀法制备了 Mg/Al 水滑石,并在不同温度下煅烧。探究了煅烧温度、材料投加量、pH 值、腐殖酸初始浓度对水滑石去除腐殖酸的影响。结果表明,当金属物质的量比为3的 Mg/Al 水滑石投加量为0.5 g/L, pH 值为8.5,温度为25℃时,水滑石对10 mg/L 的腐殖酸的去除率能达到96.64%,此时,水滑石的饱和吸附量为19.33 mg/g。Mg/Al 水滑石经3次再生后,对腐殖酸的去除率仍然高达95%以上,表明 Mg/Al 水滑石的可重用性好。     

MgAl-LDH吸附甲基橙性能研究

在水热反应温度为180℃,反应溶液pH值=9～10,反应时间为4h,反应总物质浓度为0.1mol/L的实验条件下,探索Mg/Al的摩尔比对MgAl-LDH吸附甲基橙性能的影响,并考察了材料再生后的吸附性能。研究结果表明,Mg/Al摩尔比为2.5∶1时的MgAl-LDH吸附甲基橙性能最优;在最佳吸附条件下,MgAl-LDH对甲基橙吸附量高达83.33mg/g;并对吸附材料循环利用焙烧温度进行探讨,可再生循环焙烧温度在400℃达到最佳,循环使用3次吸附性能保持良好。此外,对Mg/Al-LDH及其各个温度焙烧产物进行TG-DTA和SEM表征,显示其片状构型及对甲基橙进行的离子交换吸附和表面静电吸附作用。     

Selectivity engineering in hydroxyalkoxylation of phenol by ethylene carbonate using calcined hydrotalcite

The high consumption of mono-ethylene glycol phenyl ether in various sectors requires clean and green synthesis. Herein, we report an efficient, selective and green route of hydroxylation using calcined hydrotalcite (CHT) for the preparation of mono-ethylene glycol phenyl ether. Various types of solid base catalysts were prepared and well characterized by TGA–DSC, FTIR, XRD, CO₂-TPD, NH₃-TPD, SEM and BET surface area. The catalyst CHT (3:1) possesses very high activity for hydroxyalkoxylation of phenol and ethylene glycol with 96% conversion at 180 °C in 2 h with catalyst loading of 0.03 g cm^?3. The insight of reaction reveals that it is kinetically controlled with second-order reaction and follows power law model. The apparent activation energy for the reaction is 21.3 kcal mol^?1. The catalyst is highly reusable and shows green chemistry prospective and gives excellent results up to four runs.     

超细镁铝复合阻燃剂的制备与表征

采用化学共沉淀的方法,在相同的工艺条件下,固定Mg2+的浓度,通过改变Al3+的量,分别制备Mg与Al的物质的量比为5∶1、4∶1、3∶1、2∶1、1∶1的复合粉体和单一的氢氧化镁与氢氧化铝,通过X射线衍射、透射电镜、热重-差热分析、氮气吸附测定比表面积、堆密度等手段对合成样品进行表征。结果表明,合成样品为类水滑石结构Mg6Al2(OH)18.4.5H2O为主的混合物,呈现卷曲片状的形貌;Mg与Al的物质的量比为4∶1时制备的粉体为Mg(OH)2和Mg6Al2(OH)18.4.5H2O的混合物,分散性好,分解温度高,是一种优良的阻燃剂。     

Synthesis and sulfate ion-exchange properties of a hydrotalcite-like compound intercalated by chloride ions

To reduce the generation of hydrogen sulfide gas from sulfate ions, we synthesized a layered double hydroxide hydrotalcite-like compound intercalated with chloride ions in the interlayer (HT-Cl) using a coprecipitation reaction. The resultant HT-Cl material had a Mg/Al molar ratio of approximately 2, and the molar fraction of the chloride ions on the intercalated anion layer of the HT was 0.90. A higher molar fraction of chloride ions can be inserted into the interlayers of the HT by increasing the initial concentration ratio of chloride ions to aluminum ions [Cl(-)](0)/[Al(3+)](0) in the solution. Approximately 98% of the sulfate ions in the solution were removed within 10 min after adding 1.12 times the stoichiometric quantity of synthesized HT-Cl, which contained a Mg/Al molar ratio of 2 equal to a solution containing a 12 mM calcium sulfate solution.     

ZnO impregnated MgAl(O) catalyst with improved properties for biodiesel production: The influence of synthesis method on stability and reusability

ABSTRACT

A magnesium-aluminum layered double hydroxide was synthesized with co-precipitation method and zinc salt was impregnated on it. The final product was calcined and used as a catalyst in the transesterification reaction to produce biodiesel from waste cooking oil. Both MgAl hydrotalcite and Zn impregnated compound (Zn/MgAl(O)) were characterized using X-Ray Diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) techniques. High surface area and nanometric pore size of Zn/MgAl(O) was determined using Bruneure-Emmett-Teller N₂ physisorption technique. Another fully co-precipitated ZnMgAl mixed oxide was synthesized by and compared with Zn impregnated product in the transesterification reaction. The reactions were performed at 65°C using 9:1 methanol to oil ratio for 3?h. The biodiesel yields were measured by gas chromatography (GC). Leaching amounts of surface active components of as-synthesized mixed metal oxides were determined by EDS and ICP analysis of used catalyst. Zn impregnated catalyst showed 78.45% conversion of the fatty acid to methyl esters and just 1.16% leaching of Zn was observed, that is much lower than the diminishing in the co-precipitated compound. Finally, the reaction and leaching proofs and the effect of synthesis method on the firmness of catalyst were discussed.     

Deformation mechanism of aluminum–magnesium alloys at elevated temperatures

The study concentrates on the formulation of a reliable constitutive equation for plastic forming of Al–Mg-based alloys above 400 °C and at strain rates above 10^?3 s^?1. The deformation mechanisms of two coarse-grained Al–Mg alloys, also known as AA5182, with grain sizes 21 and 37 μm were investigated. They exhibited optimum extension at 10^?2 s^?1 and at T equal to 425 °C and above 475 °C, respectively, with uniform elongation above 300 %. The strain-rate sensitivity and the stress exponent were equal to 0.25 and 4, respectively, suggesting that the deformation is controlled by the solute drag of gliding dislocations whereas dislocation climb occurs also in grains whose orientation renders them hard. Grain boundary sliding may contribute to a small extent in the deformation process. The threshold stress was found to be small and the activation energy lies between 144 and 136 kJ mol^?1, i.e., that of Al self-diffusion and Mg diffusion in Al. It is concluded that coarse-grained materials may well fulfill the industrial requirements of forming and within this scope, the use of the low purity coarse-grained Al–Mg-based alloys of the AA5182 type would constitute the next step in the course for further cost reduction.     

Optical transmittance enhancement and bandgap widening of ZnO:Al powders by W codoping

(Al, W)-codoped ZnO powders with a constant molar ratio of Zn:Al (99:1) and various molar ratios of W:Al (0–0.02) were synthesized by a sol–gel process and characterized by X-ray diffraction, field emission scanning electron microscopy, and UV–vis and luminescent spectrophotometry. The experiments indicated that the powders illustrated increased c-orientation and a decreased average particle size with increasing W content. The W doping also resulted in the enhancement of transmittance in the UV–vis light range and the widening of the bandgap. Optimal efficiency appeared at molar ratio of W:Al = 0.01. Moreover, the W doping led to the formation of a new emission center and the enhancement of the emissions in range of visible light.     

掺杂镧的固体碱MgO/SBA-15催化大豆油制备生物柴油

采用浸渍法制备了掺杂镧的固体碱MgO/SBA-15催化剂,将其用于大豆油酯交换制备生物柴油的反应。XRD表征结果显示,活性组分在载体SiO2骨架中高度分散。考察了不同镧镁物质的量比、焙烧温度和催化剂用量等因素对催化剂性能的影响,发现镧的引入有利于催化剂与反应物的接触,从而提高催化剂的活性;镧和镁物质的量之比为0.5∶1,催化剂焙烧温度700℃,焙烧时间3h,催化剂质量分数为3%,反应时间3h时,生物柴油的产率达到95%以上。     

Metallothermic reduction of zinc sulfide induced by ball milling

Stoichiometric mixtures of ZnS + Al and ZnS + Mg were milled for different times in a planetary ball mill. The XRD traces of the as-milled samples showed the presence of zinc, MgZn₂, and MgS after 30-min milling in the ZnS–Mg system. The traces of MgZn₂ disappeared after 1-h milling and the reduction reaction seemed to have been completed after 5-h milling. The ZnS–Al system was somewhat different with only slight reduction to zinc after 1 h and ZnS peaks still present after 10 h of milling. Isothermal heating under argon atmosphere of 3-h-milled samples showed the presence of hexagonal ZnAl₂S₄ and mixtures of MgS and Zn_0.68Mg_0.32S in the ZnS–Al and ZnS–Mg systems, respectively. These results show that the reaction in the ZnS–Al system progressed gradually during milling. The decrease in the crystallite size of reactants materials (especially ZnS) during milling operation led to decrease in the formation temperature of hexagonal ZnAl₂S₄ phase and decrease in the transformation temperature of sphalerite (ZnS) to hexagonal wurtzite.     

Thermal and electrical conductivity of binary magnesium alloys

Thermal conductivity is a key parameter for thermal design and management of the electronic components in their passive cooling processes. In this work, thermal and electrical conductivities of six groups of binary Mg alloys (Mg–Al, Mg–Zn, Mg–Sn, Mg–Zr, Mg–Mn, and Mg–Ca) in as-cast, as-solution, and annealed states were measured and the corresponding microstructures were observed. In both as-cast and as-solution states, thermal/electrical conductivities of the six groups of Mg alloys decreased with composition. Effects of solution treatment and annealing on thermal/electrical conductivities of the as-cast samples were also investigated and discussed. Moreover, the specific thermal/electrical resistivity (thermal/electrical resistivity increment of the alloy derived from one atom addition) of the solute elements for Mg alloys was drawn as follows, Zn < Al < Ca < Sn < Mn < Zr. Atomic volume difference of the solute elements with Mg atom (ΔV/V _Mg), valency, and configuration of extra-nuclear electron of the solute were believed as the main reasons for the differences.     

Greenhouse gases mitigation by CO<Subscript>2</Subscript> reforming of methane to hydrogen-rich syngas using praseodymium oxide supported cobalt catalyst

This study focuses on the potential of hydrogen-rich syngas production by CO₂ reforming of methane over Co/Pr₂O₃ catalyst. The Co/Pr₂O₃ catalyst was synthesized via wet-impregnation method and characterized for physicochemical properties by TGA, XRD, BET, H₂-TPR, FESEM, EDX, and FTIR. The CO₂ reforming of methane over the as-synthesized catalyst was studied in a tubular stainless steel fixed-bed reactor at feed ratio ranged 0.1–1.0, temperature ranged 923–1023 K, and gas hourly space velocity (GHSV) of 30,000 h^?1 under atmospheric pressure condition. The catalyst activity studies showed that the increase in the reaction temperature from 923 to 1023 K and feed ratio from 0.1 to 1.0 resulted in a corresponding increase in the reactant’s conversion and the product’s yields. At 1023 K and feed ratio of 1.0, the activity of the Co/Pr₂O₃ catalyst climaxed with CH₄ and CO₂ conversions of 41.49 and 42.36 %. Moreover, the catalyst activity at 1023 K and feed ratio of 1.0 resulted in the production of H₂ and CO yields of 40.7 and 40.90 %, respectively. The syngas produced was estimated to have H₂:CO ratio of 0.995, making it suitable as chemical building blocks for the production of oxygenated fuel and other value-added chemicals. The used Co/Pr₂O₃ catalyst which was characterized by TPO, XRD, and SEM-EDX show some evidence of carbon formation and deposition on its surface.     

Facile synthesis of layered sodium disilicates as efficient and recoverable nanocatalysts for biodiesel production from rapeseed oil

In this study, α, β and δ phases of layered sodium disilicates were synthesized and used as heterogeneous catalysts for transesterification of rapeseed oil with methanol to methyl esters (biodiesel). The catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) technique, Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption-desorption, and thermogravimetric analysis (TGA-DTA). δ-Na₂Si₂O₅ showed better catalytic efficiency than the other two phases of sodium disilicate, and showed excellent activity at the optimized conditions. The transesterification conditions, such as the catalyst dosage, molar ratio of methanol to oil, reaction temperature and reaction time were investigated. The results revealed that with a catalyst loading of 4?wt%, methanol to oil ratio of 30:1, reaction temperature of 65?°C and reaction time of 3?h, conversion of biodiesel reached 97.8%.     

Parameters affecting oleochemical production from waste bleaching earth via alcoholysis

The edible oil industry is one of the largest industries in the world. In the edible oil refining process, large amounts of waste are discarded every day. Evaluation of these wastes is vital for environmental issues. Most of this waste is due to the bleaching process in which bleaching earths are largely used. Due to its high adsorption capacity, bleaching earth adsorbs oil nearly 40% of its weight. In order to evaluate this waste for oleochemical production, alcoholysis reactions were investigated. Parameters affecting the reaction, such as catalyst type and amount, alcohol type, alcohol:oil molar ratio and temperature, were investigated. The reactions were conducted in the presence of different catalysts such as NaOH, NaOCH₃ and homogeneous alkali polymeric gel catalyst (HAPJEK) and performed at a temperature range of 60–78°C and in the presence of a catalyst (1–2% based on oil weight) at alcohol:oil molar ratios of 5:1–7:1. Based on optimisation by response surface methodology (RSM), the critical synthesis conditions for 210 min reaction time with a maximum of 85.8% methyl ester content were determined as temperature: 68.4°C, catalyst amount 1.5% based on oil weight and methanol/oil molar ratio: 6.4.     

Liquid–liquid equilibrium (LLE) study for six-component transesterification system

Transesterification of oils/triglycerides (TGs) with alcohol in the presence of catalyst has been the most commonly used process to produce biodiesel. Major limiting factors of conventional biodiesel transesterification process are phase separation and product purification. Precise and correct knowledge of the phase equilibrium behaviour is crucial for future industrial biodiesel reaction, separation and purification processes. For this purpose, it is important to consider the phase equilibrium behaviour in order to thoroughly understand the entire transesterification system for biodiesel production, which consists of six components. This work is to discuss on the liquid–liquid equilibrium (LLE) data of six-component system which involves TG, palm biodiesel (FAME), methanol (MeOH), glycerine (GLY), diglyceride (DG) and monoglyceride (MG). The phase equilibrium data of this system were determined experimentally through transesterification of crude palm oil (CPO). The experimental LLE data have been transposed into a pseudo-ternary diagram as TG–DG–MG + MeOH–GLY + FAME for better visualisation and understanding of the six-component system. Results showed that the transesterification of TG to FAME has formed a two-phase system where CPO-rich phase and MeOH-rich phase co-existed during the reaction. Due to immiscibility of CPO and MeOH, as well as the miscibility of FAME and MeOH, the LLE data suggested that at specific reaction operating condition, the reacted product (FAME) could be continuously removed by separating the MeOH phase from the CPO phase. This favours the forward transesterification reaction and eventually enhances the reaction efficiency to produce an oil-free FAME.     

CuNi/Al hydrotalcites synthesized in presence of microwave irradiation

To enhance the electronic properties of nanoparticles, functional clusters are usually supported on metal oxides as alumina. Copper and nickel clusters supported on magnesia or alumina are promising materials to catalyze the decomposition of methane to produce hydrogen. A mixed support of alumina and magnesia can be proposed in the form of a hydrotalcite. In this work, the synthesis of hydrotalcites containing Cu, Ni, Mg and Al in the presence of microwave irradiation is studied. Cu/Al hydrotalcite which is hardly synthesized through conventional methods was easily prepared in the presence of microwaves.