Nano ZSM-5 type ferrisilicates as novel catalysts for ethylbenzene dehydrogenation in the presence of N2O

Nanosized ZSM-5 type ferrisilicates were successfully prepared using hydrothermal process. Several parameters including gel initiative compositions (Na⁺ or K⁺ alkali system), SiO₂/Fe₂O₃ molar ratios and hydrothermal temperature were systematically investigated. The samples were characterized by XRD, TEM, SEM-EDS, BET surface area and ICP techniques. It was found that surface areas and the total pore volume increase with increasing in the SiO₂/Fe₂O₃ molar ratio at Na-FZ ferrisilicates. The catalytic performance of the synthesized catalysts was evaluated in ethylbenzene dehydrogenation to styrene in the presence of N₂O or steam at temperatures ranging from 400 °C to 660 °C under atmospheric pressure. The effects of gel initiative compositions, SiO₂/Fe₂O₃ molar ratio as well as the hydrothermal synthesis temperature on the catalytic performance of these catalysts have been addressed. It was shown that styrene yield significantly influenced by altering in the SiO₂/Fe₂O₃ ratio but was not greatly influenced by changes in hydrothermal synthesis temperatures. The comparison between performance of potassium and sodium containing catalysts was shown that the one with potassium has higher yield and selectivity toward styrene production at an optimum temperature of 610 °C.     

Effect of alloying contents and processing factors on the microstructure and homogenization of Si alloyed Cr–Mo sintered steels

Fe–Si alloys are of significant commercial and academic interests, due to the large diversity of their physical properties. In practice, alloy powders are unsuitable because of their hardness, poor compactibility and resulting excessive tool wear. Therefore the powder mixture route is suitable as alloying technique. The properties of the Fe–Si sintered materials depend strongly on the influence of the element Si and content of it, which influence mainly the compactibility and the sintering behaviour as well as sintering parameters such as the optimum temperature. In this study, Cr–Mo prealloyed steel powders with different Si contents were prepared by powder mixture route. Mixed powders compacted under pressing pressure of 600 MPa, and then sintered at 1120 and 1250 °C. It was found out that in Si alloyed Cr–Mo steels sintered at higher temperatures such as 1250 °C, an intermediate liquid phase appeared and caused extreme shrinkage and distortion, but strongly accelerated sintering and had a beneficial effect also on homogenization.     

The effect of ultrasonic irradiation on the structure,morphology and photocatalytic performance of ZnO nanoparticles by sol-gel method

In this research, the effect of ultrasonic irradiation power (0, 75, 150 and 200 W) and time (0, 5, 15 and 20 min) on the structure, morphology and photocatalytic activity of zinc oxide nanoparticles synthesized by sol-gel method was investigated. Crystallographic structures and the morphologies of the resultant powders were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns showed that ZnO samples were crystallized in their pure phase. The purity of samples was increased by increasing the ultrasonic irradiation power and time. Not only did ultrasonic irradiation unify both the structure and the morphology, but also it reduced the size and prohibited particles from aggregation. The optical behavior of the samples was studied by UV–vis spectroscopy. Photocatalytic activity of particles was measured by degradation of methyl orange under radiation of ultraviolet light. Ultrasound nanoparticles represented higher degradation compared to non-ultrasound ones.     

Vapour pressure osmometry determination of water activity of binary and ternary aqueous (polymer + polymer) solutions

Precise water activity measurements at T = 308.15 K were carried out on several binary (water + polymer) and ternary {water + polymer (1) + polymer (2)} systems using the vapour pressure osmometry (VPO) technique. Polymers were polyethylene glycol 400 (PEG400), polyethylene glycol 6000 (PEG6000), polypropylene glycol 400 (PPG400), polyvinylpyrrolidone (PVP) and dextran (DEX). The water activity results obtained were used to calculate the vapour pressure of solutions as a function of concentration and the segment-based local composition models, NRTL and Wilson, were used to correlate the experimental water activity values. It was found that, for the polymer concentration range studied here, the values of the water activity obtained for the binary (water + polymer) solutions decrease in the order DEX > PVP > PEG6000 > PPG400 > PEG400. Furthermore, water activities of solutions of each polymer in the aqueous solutions of (5, 10, 15 and 20)% (w/w) other polymers investigated were also measured at T = 308.15 K. The ability of polymer (1) in decreasing the water activity of binary {water + polymer (2)} solutions was discussed on the basis of the (polymer + water) and {polymer (1) + polymer (2)} interactions.     

Dry reforming of greenhouse gases CH4/CO2 over MgO-promoted Ni–Co/Al2O3–ZrO2 nanocatalyst: effect of MgO addition via sol–gel method on catalytic properties and hydrogen yield

Sol–gel method was employed to prepare Ni–Co/Al₂O₃–MgO–ZrO₂ nanocatalyst with various loadings of MgO (5, 10 and 25 wt%) for dry reforming of methane. The physiochemical properties of nanocatalysts were characterized by XRD, field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), BET and fourier transform infrared spectroscopy (FTIR) analysis. Evaluation of catalytic performance was conducted in atmospheric pressure, stoichiometric feed ratio, GHSV of 24 l/g_cat h and temperature range from 550 to 850 °C. XRD patterns represented that as MgO content increases, the amorphous behavior slightly intensifies and also dispersion of active phase improves which probably caused by strong metal–support interaction. Furthermore, FESEM analysis confirmed that all of prepared samples are nano scale. EDX results besides verifying the declared claim about the dispersion of samples proved the presence and detected the position of the various elements. In addition, based on the FESEM analysis, narrow particle size distribution, uniform morphology and dispersion without agglomeration were found for Ni–Co/Al₂O₃–MgO–ZrO₂ with 25 wt% MgO. Moreover, smallest average particle size 11.6 nm (close to the critical size for Ni–Co catalyst to avoid carbon formation) was obtained for this nanocatalyst. Also, according to the BET analysis, MgO rich nanocatalyst represented the higher surface area than the other ones. Based on the excellent characterizations, Ni–Co/Al₂O₃–MgO–ZrO₂ with 25 wt% MgO exhibited the best products yield through all of the investigated temperature e.g. H₂ = 96.9 % and CO = 97.1 % at 850 °C. Furthermore, this nanocatalyst demonstrated the stable yield with H₂/CO close to unit during 1,440 min stability test.     

Unstable Fracture Behavior of Rubber Toughened Poly(Styrene-co-Acrylonitrile)

A linear elastic fracture mechanics (LEFM) approach was used to study fracture characteristics of ABS materials. The effects of crack (ligament) length and rubber content on the microscopic deformations taking place at the front of crack tip and in the bulk of the specimens were investigated. The results of fractography studies showed that, in addition to rubber content, the microscopic deformations are influenced by crack length. For some materials this manifests itself as a change in macroscopic response. The ligament length dependent behavior was increased for the samples with higher rubber contents. The results also showed that, although the elastic behavior with unstable crack growth is the dominant micromechanism of deformation, stable crack propagation still occurred in some compositions. All the fracture parameters, including fracture toughness, fracture energy, plastic zone size, and crack tip opening, increased with rubber content. The changes in microscopic and, as a consequence, in the macroscopic deformation behavior of a given specimen with ligament length were attributed to changes in yield stress of the sample and maximum stress on the ligament.     

Fabrication of ZiF-8 metal organic framework (MOFs)-based CuO-ZnO photocatalyst with enhanced solar-light-driven property for degradation of organic dyes

In this research, novel CuO-ZnO/ZiF-8 metal–organic frameworks (MOFs) photocatalyst with different mass percentages of ZiF-8 were prepared for water purification applications under visible light. The precipitation method was used to synthesize CuO-ZnO/ZiF-8 photocatalysts. Some techniques, including XRD, FESEM, EDX, BET-BJH, FTIR, DRS, and pH_pzc, were performed to determine the structural, chemical, and optical properties of the prepared samples. DRS analysis represented that CuO-ZnO/ZiF-8(20) had narrower band gap energy compared to CuO-ZnO and ZiF-8. Also, BET-BJH analysis results showed that CuO-ZnO had a low surface area that impeded the absorption of pollutant molecules. In contrast, the CuO-ZnO/ZiF-8(20) sample, due to the presence of ZiF-8, had a high specific surface area which enabled higher pollutant adsorption on the photocatalyst surface.Moreover, the synthesized samples were evaluated for the solar-light-driven removal of different organic dyes, such as Acid Orange 7, Methylene blue, and Malachite green. The tremendously enhanced photocatalytic activity under the simulated solar light with 98.1% removal of AO7 was observed over CuO-ZnO/ZiF-8(20) sample. Then, the effect of initial solution pH as an essential factor on photocatalytic activity was investigated. Finally, the reaction mechanism of AO7 degradation over CuO-ZnO/ZiF-8(20) was proposed.     

Hydrothermal synthesis and physicochemical characterization of CuO/ZnO/Al2O3 nanopowder. Part I: Effect of crystallization time

A hydrothermal method was successfully used for synthesis of CuO/ZnO/Al₂O₃ (CZA) nanopowder with atomic ratio of 6:3:1. The effect of crystallization time (3, 6, 9, and 12 h) on physicochemical properties of nanopowder was investigated. Nanopowders were characterized using XRD, FESEM, EDX, FTIR, TG, and BET techniques. The XRD patterns confirmed metal oxides formation and their good crystallinity with average crystallite size of 20 nm as obtained by the Scherrer equation. Relative crystallinity was shown to increase with increasing crystallization time. In agreement with XRD results, FESEM images also illustrated nanosized particles. EDX mapping indicated homogenous dispersion of elements. BET specific surface area analysis showed acceptable surface area for CZA nanopowder. FTIR spectroscopy confirmed metal oxides formation during hydrothermal and calcination processing. TG results illustrated high thermal stability of the synthesized nanopowders. TG-DTG and FTIR analyses were used to propose a reaction mechanism for nanopowder formation during processing. Physicochemical characterization showed optimal crystallization time to be 6 h.