Studies on Carbon Deposition in CO2Reforming of CH4over Nickel–Magnesia Solid Solution Catalysts

Carbon formation behavior under CH₄-CO₂reaction and through CH₄decomposition and CO disproportionation was investigated over Ni_0.03Mg_0.97O solid solution, supported Ni/MgO, and NiO-Al₂O₃catalysts by means of thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Ni_0.03Mg_0.97O showed high resistance to carbon formation in CO₂reforming of methane and the selectivity to carbon formation was much lower than two other catalysts. It is suggested that CO₂plays an important role in the inhibition of carbon formation on Ni_0.03Mg_0.97O through the activation of CO₂at the interface between small nickel particles and the support surface.     

Coarsening in liquid-phase-sintered α-SiC

Liquid-phase-sintered (LPS) SiC ceramics represent a new class of microstructurally toughened structural materials. In order to understand better the microstructural evolution in these ceramics, the coarsening kinetics in LPS α-SiC, containing a yttrium aluminum garnet (YAG) based liquid phase, was studied. It was confirmed that the coarsening occurs primarily by solution-reprecipitation (Ostwald ripening). Most importantly, the SiC grains were found to be faceted in nature, and the coarsening rate was found to be independent of the vol.% liquid in the system or the average diffusion path length. Based on these observations it is inferred that interface-reaction controls the solution-reprecipitation coarsening in LPS SiC.     

Two-dimensional graphitic carbon nitride for membrane separation

Recent years, membrane separation technology has attracted significant research attention because of the efficient and environmentally friendly operation. The selection of suitable materials to improve the membrane selectivity, permeability and other properties has become a topic of vital research relevance. Two-dimensional (2D) materials, a novel family of multifunctional materials, are widely used in membrane separation due to their unique structure and properties. In this respect, as a novel 2D material, graphitic carbon nitride (g-C₃N₄) have found specific attention in membrane separation. This study reviews the application of carbon nitride in gas separation membranes, pervaporation membranes, nanofiltration membranes, reverse osmosis membranes, ion exchange membranes and catalytic membranes, along with describing the separation mechanisms.     

Selective catalytic reduction of nitric oxide with ammonia on copper (II) ion-exchanged offretite

Copper K-offretite catalysts prepared by ion exchange were characterized by XRD, H₂-TPR and evaluated in the selective catalytic reduction of NO (NO-SCR) by ammonia. Despite several successive exchanges, the quantity of copper introduced remains low and the exchange ratio does not exceed 50%. The NO conversion profiles have a sigmoid curve shape. Full NO conversion in N₂ is reached above 340 °C at a volume space velocity of 332,000 h⁻¹. N₂O formation at low temperature is due to the presence of small oxide particles generated by the successive copper exchanges during the preparation. The presence of K ions “blocks” the cancrinite access to copper ions and maintains the deNO_x efficiency over the whole range of temperature.     

Cellular automata computations and secret key cryptography

In this paper, cellular automata (CAs) are used to design a symmetric key cryptography system based on Vernam cipher. CAs are applied to generate a pseudo-random numbers sequence (PNS) which is used during the encryption process. The quality of PNSs highly depends on the set of applied CA rules. Rules of radius r=1 and 2 for nonuniform one-dimensional CAs have been considered. A new set of rules has been discovered using an evolutionary technique called cellular programming. This set provides very high quality encryption, and the system is very resistant to attempts of breaking the cryptography key.     

Solvothermal synthesis of nanocrystalline KTaO3: Effect of solvent dielectric constant

A set of KTaO₃ nanopowders has been prepared at T = 180 °C using various aliphatic alcohols and water as solvents. Pronounced connection between the solvent type and potassium tantalate structures was found. Structural X-ray, TEM and Raman scattering experiments have shown that the solvent dielectric constant ? is an important critical parameter. At ? ～ 24 the cubic perovskite-type phase was formed. Mixed perovskite and pyrochlore phases were formed at larger values of ?. Only pure pyrochlore phase is realized when ? ～ 80. Pyrochlore-free perovskite-structure nanopowder phase formation with the particle size of ～18 and 28 nm was achieved when ethanol and isopropanol solvents were used. Under annealing the coherent domain size decreased down to 6 and 18 nm respectively, since the amorphous phase crystallized. Crystallinity of both as-prepared and annealed powder is the best when isopropanol solvent is used.     

Nanoporous copper fabricated from Zr65Cu17.5Fe10Al7.5 amorphous alloy and its electrocatalytic oxidation performance

A series of bi-continuous and uniform nanoporous structures were fabricated successfully through chemical dealloying from quaternary Zr₆₅Cu_17.5Fe₁₀Al_7.5 amorphous ribbons in hydrofluoric acid (HF) solutions under a free corrosion condition. Nanoporous structures obtained from dealloying amorphous ribbons for 5 h in 0.02 M,0.035 M and 0.05 M HF solutions have mean pore sizes of 30–40 nm. A three-dimensional bi-continuous nanoporous copper (NPC) structure formed on Zr₆₅Cu_17.5Fe₁₀Al_7.5 ribbon alloys has pore sizes of 44.91 nm,52.60 nm and 57.37 nm, respectively, after immersion in 0.02 M HF solution for 15 h, 20 h, and 25 h. It shows that the pore size of NPC structure increases with increasing the dealloying time. The cyclic voltammetry (CV) results reveal that all NPC structures have the obvious electrocatalytic ability to the oxidation of (CH₂OH)₂ solution, compared with the initial amorphous ribbon without oxidation peak on CV curve. Zr-Cu-Fe-Al amorphous alloys can be new candidates for fabricating NPC structures.     

MOF作模板制备多孔Au/CuxO催化剂及其CO氧化性能

采用MOF材料作模板,通过在Cu-BTC材料表面预先负载贵金属Au再热解的方法,成功制备了具有正八面体结构的新型多孔Au/Cu_xO负载型催化剂。通过降低热解环境中的O₂浓度,调节氧化时间,实现了Au/Cu-BTC氧化产物组分的调节,分别制得了Au/Cu₂O、Au/Cu₂O-CuO、Au/CuO复合催化材料。将其用于CO催化氧化,发现所有Au/Cu_xO催化剂都表现出比Cu-BTC和Au/Cu-BTC更优异的催化性能,其中由于拥有较高的比表面积、Cu₂O含量以及更好的Au的分散性,Au/Cu₂O的CO氧化活性最佳,180℃即能实现CO的完全转化。