Decomposition of nitrous oxide over the catalysts derived from hydrotalcite-like compounds

Catalytic decomposition of nitrous oxide into nitrogen and oxygen has been carried out on ‘in situ' thermally calcined hydrotalcites of general formula M(II)–M(III)-CHT where M(II)=Mg, Co, Ni, Cu or Zn and M(III)=Al, Fe or Cr having different M(II)/M(III) atomic ratios. The reaction was performed in a recirculatory static reactor at 50 Torr (133.3 Pa) initial pressure of N₂O in the temperature range 423–773 K. Among the catalysts screened, Ni and Co containing catalysts with Al as the trivalent cation showed good activity (even at 423 K) wherein 50% and 100% conversion was achieved at 463 K and 523 K, respectively. Results on effect of composition for Co–Al system indicated that the activity increased with increase in the active metal ion concentration (Co²⁺), with closer dependence on the surface concentration (as determined by XPS). The observed activity pattern is explained on the basis of redox property and electronic effects. These materials were further evaluated under flow conditions (at Air Products and Chemicals, USA) simulating the industrial process streams (10% N₂O, 2% H₂O, 2% O₂ and balance N₂ and GHSV=18,500). Among the non-precious metal ions investigated, cobalt-based catalysts offered comparable activity similar to metal-exchanged zeolites for removing N₂O from combustion and Nylon-6,6 processes.     

Synthesis,characterization, and SO2 removal capacity of MnMgAlFe mixed oxides derived from hydrotalcite-like compounds

Fe (III), Mn (II)-substituted Mg–Al hydrotalcite-like compounds were prepared by co-precipitation method and MnMgAlFe mixed oxides derived from hydrotalcite-like compounds (calcination at 1023 K for 4 h) were tested for SO₂ removal under the conditions similar to those of FCC units. XRD, IR, TG/DTA and N₂ adsorption analysis were performed to investigate the physicochemical and textural properties of the samples. The results showed that all samples exhibited good dispersion of metal oxides in the matrix. The SO₂ adsorption–reduction tests showed that on the basis of MgAl adsorbent, addition of a certain amount manganese and iron could enhance the the SO₂ removal capacity and adsorption rates of catalysts in FCC units and the sample that contains 5% Fe and 10% Mn showed the best effect. Further analysis suggested that Fe and Mn could cooperatively promote the oxidation of SO₂ to SO₃ that is easier to be chemisorbed by catalysts and Fe simultaneously played a role as reducing promoter which is essential for reusability of the catalysts.     

Engineering investigation for the size effect of graphene oxide derived from graphene nanoplatelets in polyurethane composites

In this study, commercial polyurethane (PU) and graphene nanoplatelets (GnP) and their derivative graphene oxide (GO) were used to fabricate PU composites. The size effect of fillers on mechanical properties and anti-corrosion performance of as-prepared composites was thoroughly investigated. It was found that GO was more uniformly dispersed in the PU matrix than GnP due to its compatibility with PU. Furthermore, GO led to the higher mechanical properties and anti-corrosion performance than PU/GnP composites, and the properties were strongly dependant on the size of the GO. Specifically, incorporating large sized GO (GO-M25) in 0.5 wt% indicated the highest average synergetic tensile modulus up to 53% from the neat PU and the lowest corrosion rate of 0.001 MPY (1 MPY = 0.547 g · m⁻² · d⁻¹). This phenomenon was attributed to the fact that the larger size of GO is not only uniformly dispersed within the PU matrix but also enables interaction between PU and GO. Conversely, PU composites incorporated with the small sized GO (GO-C750) did not show elastic behaviour from 0.1 to 0.5 wt% of the filler. This is due to the fact that the high surface area and hydrophilic functionalities of GO-C750 resulted in hard-segment content reduction in PU. This research can help in the design of a PU coating that is physically improved and that has a superior anti-corrosive capacity, particularly for pipelines in the oil-sands transportation industry.     

以类水滑石为前驱体制备的复合氧化物同时吸附烟道气中SO2和NO研究

采用共沉淀法制备NiMgAlO、CuMgAlO、ZnMgAlO和FeMgAlO类水滑石复合氧化物，并用于常压下同时氧化吸附模拟烟道气中的SO2和NO。模拟烟道气中SO₂的摩尔分数为1%, NO的摩尔分数为0.2%，O₂以及He作为载气。研究结果表明，这四种催化剂对烟道气中的SO₂和NO具有良好的同时氧化吸附效果。比较四种催化剂的吸附效果发现，NiMgAlO和CuMgAlO要优于ZnMgAlO和FeMgAlO，且NiMgAlO对SO₂和NO的吸附效果最佳。     

Zn/Al类水滑石及其插层材料的光催化性能

以氨水为共沉淀剂,采用低温共沉淀法合成了不同摩尔比的Zn/Al类水滑石,并通过离子交换法在层板间引入磷钨酸根离子,经焙烧后得到具有光催化性能的催化材料,研究插层前后类水滑石焙烧产物对甲基橙等染料的光催化降解性能。结果表明,CZn-Al-r催化剂具有优良的光催化降解有机染料的性能,通过调整催化剂前驱体中金属元素的比例,甲基橙和亚甲基蓝的降解率可在2 h内接近100%。而经磷钨酸插层后,IZnAl-2的光催化降解速率较CZnAl-2有所下降。     

水滑石材料再水合性能的研究

采用共沉淀法制备了碳酸根型和硝酸根型镁铝水滑石材料,同时制备了2种类型的钡掺杂水滑石,研究了以上4种水滑石材料焙烧后混合氧化物的再水合性能以及钡离子存在对水滑石再水合性能的影响,发现硝酸根型水滑石较碳酸根型水滑石难重构,并对重构能力的区别进行了探讨;钡掺杂的硝酸根型水滑石实际引入的钡很少,表现出和硝酸根型水滑石相同的衍射峰,但材料的再水合性能降低。     

超细水滑石类化合物的制备

介绍了共沉淀法、成核/晶化隔离法、溶胶-凝胶法、微波照射法、超声波共沉淀法及分散剂介入法等制备超细水滑石类化合物的方法,其中,成核/晶化隔离法、溶胶-凝胶法、微波照射法合成的水滑石化合物粒径都可以达到纳米级。超声波共沉淀法对水滑石粒径的减小较为显著,中值粒径从普通共沉淀的8.06μm减小到超声辐射下的0.53μm;分散剂的分散作用也很大程度上阻止了颗粒的凝聚,中值粒径从0.53μm减小到0.32μm。     

镍镁铝三元水滑石类化合物的合成和表征

采用恒定pH值法合成了NiMgAl-HTLcs三元类水滑石化合物,利用X射线衍射、差热分析对合成物进行了表征.讨论了pH值、原料配比、焙烧温度对合成水滑石结构的影响.结果表明在体系pH值8～9,n(Mg+Ni)n(Al)=1～3、n(Mg)n(Ni)=8～16条件下采用恒定pH值法可得到晶相单一的NiMgAl-HTLcs,焙烧温度高于500℃水滑石结构完全破坏,生成NiO、MgO和Al2O3复合氧化物.     

纳米铜-镁-铝类水滑石的制备与表征

采用恒定pH低过饱和共沉淀法制备纳米铜-镁-铝类水滑石,采用单因素试验得出最佳反应工艺条件。在超声波反应器中反应,恒定pH=7.5~9.0,n(铜+镁)/n(铝)=2.0~4.0,n(铜)/n(镁)=0.25~1.0的条件下,采用冷冻干燥法可得到晶相单一的铜-镁-铝类水滑石,且制得的产物晶面生长的有序程度高,结晶度好。采用X射线衍射(XRD)、红外光谱(FT-IR)和扫描电镜(SEM)对其进行表征,大多数分子粒度为纳米级尺寸,粒径为50 nm左右。     

B4C/metal boride composites derived from B4C/metal oxide mixtures

This study examines the reactions occurring from room temperature to 2180 °C during the heating under argon of mixtures of B₄C and metal oxides, as well as the properties of the ceramic composites prepared by these reactions. The cations of the oxides investigated, belonged to the transition metal and to the lanthanide groups. The mixtures underwent solid-state reactions in the range between 1100 and 1900 °C. These reactions resulted in composites in which the metal borides and B₄C are the majority phases. The boron carbide/metal boride(s) mixtures resulted from these reactions exhibited a sintering aptitude significantly higher than that of pure boron carbide. The improvement in the sintering aptitude was proportional to the oxide content present in the initial mixture, up to an upper limit. B₄C/boride(s)-type composites, exhibiting bulk densities ≥97% TD, could be prepared for certain compositions by pressureless heating at 2180 °C. The ceramic parts prepared under these conditions are characterized by strength and hardness values similar to those determined for pure boron carbide.     

水滑石类复合氧化物催化生物柴油制备的研究

生物柴油是一种环境友好的新型燃料,是近年来新型能源开发的一个热点。水滑石类复合氧化物是一种理想的固体催化剂,它具有相互连通的大孔隙、适度的酸碱位浓度和疏水表面,催化活性强,易于与产品分离,回收利用率高。对水滑石类化合物催化制备生物柴油进行了概述,并对前景进行了展望。     

以类水滑石为前驱体制备Ru基CH_4-CO_2重整催化剂

以类水滑石为前驱体,采用共沉淀法制备了不同Ru含量的xRu/Mg(Al)O催化剂(x=1,2,4),采用XRD、H2-TPR和CO脉冲吸附等表征催化剂结构和Ru金属分散度,并评价Ru含量对CH4-CO2重整反应活性与稳定性的影响。XRD与CO脉冲吸附结果表明,Ru含量增加时,还原后Ru金属颗粒的表面活性位数目增加,但分散度降低,Ru金属的粒径增大。活性测试结果表明,Ru质量分数为2%时,催化剂活性最高。Ru质量分数为1%时,催化剂具有较好的稳定性,归属于高分散Ru金属颗粒与Mg(Al)O载体之间的强相互作用。     

Sintering behaviors and properties of porous ceramics derived from artificially cultured diatom frustules

Bimodal porous ceramics with high strength have been fabricated by conventional powder metallurgy utilizing artificially cultured diatom frustules (DFs). The effect of sintering temperature on thermal behaviors, phase transition, and pore structures features of DFs-based porous ceramics is investigated between 800 and 1200°C. The phase evolution of DFs powders is investigated with thermal analysis (DIL and DSC-TG). Phase transition behaviors analyzed with XRD, Raman, and FT-IR spectra confirm the transformation of quartz into cristobalite phases occurs under 1050°C. Sintering under 950°C could bind DFs powders tightly into high strength porous ceramics while maintain the multilayer pore structures simultaneously, having porosity of 56.4%, compressive strength of 15.0 MPa and surface area of 50.9 m²/g, respectively. Slit-shaped microstructures and mesopores (2-50 nm) are observed in DFs-based porous ceramics sintered under 1050°C. Collapse and blockage of pore structures as well as partial fusion of DFs particles happened at the temperature of 1100°C, indicating the presence of diminished multilayers and particle agglomeration.     

类水滑石化合物的制备及应用

水滑石类化合物是一类具有特殊层状结构的阴离子粘土材料,具有碱性、离子交换性以及"结构记忆效应",近年来备受人们的广泛关注。本文综述了HTLcs的制备方法及其在催化、离子交换、吸附、医药以及功能材料方面的应用。     

Biogas reforming over La-NiMgAl catalysts derived from hydrotalcite-like structure: Influence of calcination temperature

Hydrotalcite-like compound with general formula [M(II)_1 − xM(III)_x(OH)₂]^x+(Aⁿ⁻_x/n) ^· mH₂O, where Aⁿ⁻ is the compensation anion, has been used as precursor of active catalysts for biogas reforming. This precursor was calcined at six different temperatures between 250 and 750 °C and the resulting catalysts were tested in order to evaluate the influence of the calcination temperature on the catalytic activity and stability. XRD characterization showed that from 250 °C the hydrotalcite structure is no longer detected, leading to Mg(Ni,Al)O solid solutions, where no peaks related to lanthanum appear. An increase on the calcination temperature increased the grain size and cell parameter value. 50 h-catalytic tests were carried out at 700 °C, CH₄:CO₂ molar ratio of 1:1 and a mass/feed alimentation ratio (W/F) of 0.4 mg min cm^− 3. Used catalysts were characterized by temperature programmed oxidation (TPO), scanning electron microscopy (SEM) and Raman spectroscopy in order to obtain information about coke deposition. Catalytic tests highlighted the great influence of calcination temperature over catalytic activity and stability, having found that, as a general trend, calcination temperatures below 750 °C decrease both the stability and catalytic activity, with the exception of the catalyst calcined at 550 °C, where a higher activity was achieved but with a comparatively low stability.     

Hierarchical MnNiCo ternary metal oxide/graphene nanoplatelets composites as high rated electrode material for supercapacitors

For achieving a higher supercapacitor performance, electrode material with high surface area and conductivity such as graphene, graphene nanoplatelets (GNP), and carbon nanotubes along with Transition Metal oxides (TMO) can be used. Herein, the composite of graphene nanoplatelets with ternary metal oxide of manganese, nickel, and cobalt (MNC) is synthesized through a facile cost-effective hydrothermal process and its compositional, morphological, and electrochemical properties are investigated. As-synthesized MNC-GNP composite showed excellent electrochemical properties owing to the high porosity offered by graphene nanoplatelets and synergistic effects produced by individual components of the composite. For comparative studies, ternary oxide MNC was prepared by the same hydrothermal route. The cubic structure of the MNC-GNP composite is confirmed by X-ray diffraction (XRD). Scanning Electron Microscope (SEM) showed distinct hierarchical dendritic structures which showed an increase in density by the addition of graphene nanoplatelets. Electrochemical testing revealed that MNC-GNP exhibited an enhanced specific capacity of 605 mAh g^-1 which is higher compared to MNC which exhibited 243 mAh g^-1 at a current density of 2 mV s^-1. GCD also depicted an increased charge-discharge time in the case of MNC-GNP as compared to its counterpart. MNC-GNP has also shown charge stability up to 99.5 % of capacity retention up to 1000 cycles. Hence, synthesized composite shows to be an effective electrode material for supercapacitors owing to enhanced electrochemical properties.     

Zn, Al, Rh-mixed oxides derived from hydrotalcite-like compound and their catalytic properties for N2O decomposition

The catalytic decomposition of nitrous oxide was studied over Zn, Al, Rh-mixed oxides derived from hydrotalcite-like compounds (HTlc) as a precursor. The study showed that, when the Zn/Al atomic ratio was 3, the rate of ZnAlRh-HTlc for N₂O decomposition increased with Rh loading up to 1.4 wt% (4.55 × 10⁴ μmol g⁻¹ h⁻¹ at 400°C), and levels off with further increase in Rh loading. Analogous behavior was found in the presence of NO₂ and water. In the presence of 0.5% water, the activity decreased with decreasing Zn/Al ratio, whereas the activity for N₂O decomposition in the presence of 0.1% NO₂ reached a maximum when the Zn/Al ratio was 3. The observed catalytic activities were comparable to those of the reported catalysts in the presence of NO₂ and water.     

Electrolyte materials for solid oxide fuel cells derived from metal complexes: Gadolinia-doped ceria

Gadolinia doped ceria (GDC) powders with different gadolinium contents were successfully prepared by the thermal decomposition of ceria complexes. All the calcined powder samples were found to be ceria-based solid-solutions having a fluorite-type structure. The powders were cold-isostatically pressed and sintered in air at 1500 °C for 5 h to attain a sintered density of about 90% of its theoretical value. The electrical conductivity of the GDC pellets in air was studied as a function of temperature in the 225–700 °C range, by using two-probe electrochemical impedance spectroscopy measurements. The highest total conductivity (σ_600 °C = 0.025 S/cm) was found for the Ce_0.85Gd_0.15O_1.925 composition.     

Preparation of porous carbon nanofibers derived from graphene oxide/polyacrylonitrile composites as electrochemical electrode materials

Porous carbon nanofibers (CNFs) derived from graphene oxide (GO) were prepared from the carbonization of electrospun polyacrylonitrile nanofibers with up to 15 wt.% GO at 1200 °C, followed by a low-temperature activation. The activated CNFs with reduced GOs (r-GO) revealed a specific surface area and adsorption capacity of 631 m²/g and 191.2 F/g, respectively, which are significantly higher than those of pure CNFs (16 m²/g and 3.1 F/g). It is believed that rough interfaces between r-GO and CNFs introduce oxygen pathways during activation, help to produce large amounts of all types of pores compared to pure activated CNFs.