Synthesis and stability evaluation of hierarchical silicoaluminophosphates with different structural frameworks in the methanol to olefins process

Silicoaluminophosphates (SAPOs) with different pore structures were synthesized through the implementation of polyethylene glycol (PEG) as a mesopores impregnation agent. Using PEGs with different molecular weights (MWs) and concentrations in the synthesis precursor, several samples were synthesized and characterized. Applying a PEG capping agent to the precursors led to the formation of tuned mesopores within the microporous matrix of the SAPO. The effects of the PEG molecular weight and PEG/Al molar ratio were investigated to maximize the efficiency of the catalyst in the methanol-to-olefin (MTO) process. Using PEG with a MW of 6000 resulted in the formation of both Zeolite Rho and chabazite structural frameworks (i.e., DNL-6 and SAPO-34). Pure SAPO-34 samples were successfully prepared using PEG with a MW of 4000. Our results showed that the PEG concentrations affect the porosity and acidity of the synthesized materials. Furthermore, the SAPO-34 sample synthesized with PEG (MW of 4000) and a PEG/Al molar ratio of 0.0125 showed a superior catalytic stability in the MTO reaction owing to the tuned bi-modal porosity and tailored acidity pattern. Finally, through reactivation experiments, it was found that the catalyst is stable even after several regeneration cycles.     

Sonoprecipitation dispersion of ZnO nanoparticles over graphene oxide used in photocatalytic degradation of methylene blue in aqueous solution: Influence of irradiation time and power

In this paper, ZnO/Graphene Oxide (ZnO/GO) is synthesized via ultrasound assisted precipitation method and the effect of power and ultrasound time irradiation is studied on photocatalyst properties. The synthesized samples are used for methylene blue (MB) degradation as an organic water pollutant. Physicochemical properties of the samples are investigated by XRD, FESEM, EDX, BET-BJH, FTIR and DRS techniques. Moreover, pH_pzc of the sample with the best performance is calculated to study the effect of acidity on the photocatalyst efficiency in photocatalytic process. Ultrasound has a positive effect on photocatalyst performance that is because of its effect on distribution of particles and semiconductor band gap, but it has no effect on photostability of the nanocomposite. Sonication has modified distribution of particles by enhancing the active sites for oxidation process. Making structural gaps by ultrasound irradiation increases available surface area which has a similar effect on photocatalyst performance. Graphene oxide as electron collector and transporter prevents electron-hole recombination and it can be an acceptable reason for enhancement at photocatalyst performance. Finally, some of operational parameters such as pH, photocatalyst loading and dye concentration are investigated.     

CO oxidation over sonochemically synthesized Pd–Cu/Al2O3 nanocatalyst used in hydrogen purification: Effect of Pd loading and ultrasound irradiation time

The bimetallic Pd–Cu nanocatalysts with different Pd loadings and ultrasonic irradiation times were sonochemically synthesized and their activities toward CO oxidation were investigated. XRD, FESEM, TEM, BET, FTIR and TG-DTG techniques were employed in nanocatalysts characterization. XRD data confirmed formation of CuAl₂O₄ spinel with an average crystallite size of 4.9 nm. FESEM images revealed more uniform pattern and also fewer agglomerations were observed by increasing ultrasonic irradiation time. In agreement with FESEM result, TEM images depicted nanoparticles and uniform dispersion of active phase over alumina. BET surface analysis showed that increasing the Pd loading has no significant effect on surface area; whereas by increasing irradiation time the surface area increases slightly. Catalytic performance tests of synthesized samples showed that Pd(1.5%)–Cu(20%)/Al₂O₃ with 95 min ultrasonic irradiation time had the best activity over the course of reaction. In addition, increasing CO at feed composition revealed that among synthesized nanocatalysts with 0.5%, 1% and 1.5% of Pd, synthesized sample with 1.5% of Pd had the best low-temperature activity.     

负载于HZSM-5上的CuO-ZnO-Al2O3纳米粒子：尿素－硝酸盐燃烧合成和理化表征

用尿素-硝酸盐燃烧法制备了一系列的负载于HZSM-5上的CuO-ZnO-Al2O3纳米复合材料(CZA/HZSM-5)。研究了燃料与氧化物的比率对所合成的复合材料的理化性质的影响。用TGA/DTG,FTIR和XRD等研究了尿素-硝酸盐凝胶的热分解和煅烧粉体的相演变过程。FESEM结果表明在燃烧过程中燃料的用量对CZA/HZSM-5的性质有重大影响。CuO和ZnO的晶粒首先随尿素量的增加而增大,然后随尿素量的增加而减小。CuO和ZnO的相对结晶度随燃料量的增加表现为非单调趋势。随着燃料与硝酸盐的比率的增加,CZA/HZSM-5不仅形貌变得超细和均一,而且表面孔隙率也显著增加。FTIR结果表明HZSM-5的结构甚至在负载了CuO-ZnO-Al2O3纳米粒子后也未被破坏,而且在CuO和ZnO与HZSM-5之间还有表面的键合。TGA/DTG结果指出燃烧合成法是一种由若干过程组合起来的方法,例如前驱体的热分解和前驱体间的放热反应等。另外,提出了CuO-ZnO-Al2O3负载在HZSM-5上的生成机理。     

Catalytic cracking of polyethylene over nanocrystalline HZSM-5: Catalyst deactivation and regeneration study

In this work, catalytic cracking of low density polyethylene (LDPE) over nanocrystalline HZSM-5 zeolite in a batch reactor at 340 °C was carried out with the aim of study both the catalyst resistance to deactivation and the catalyst regeneration process. For looking into the catalyst deactivation, consecutive polyethylene cracking experiments were carried out. Subsequently, the same reactions has been also performed but by regenerating the zeolite after each experiment by promoting coke combustion at 550 °C under air flow. Zeolites used were two samples of nanocrystalline HZSM-5 with very different textural properties (sample A, with most of its surface corresponding to zeolitic micropores and sample B with a considerable amount of external surface, mesopores and super-micropores) in order to study the effect of their textural properties in the deactivation and regeneration experiments. Although conversion and activity values reached over both samples are quite high taking into account the mild conditions used, sample B shows a very much higher initial activity than A due to its improved textural properties. In both samples two different deactivation mechanisms occur: a reversible deactivation by coke deposition removable by the regeneration procedure, and an irreversible or permanent deactivation by other factors. Deactivation of sample B occurs faster due to the higher amount of coke deposited on this material. However, the improved textural properties of this catalyst supposes an advantage for the regeneration process, since coke deposited either on the external surface or on the super-micropores and mesopores, makes easier the regeneration procedure.     

Hydrothermal-assisted sol–gel synthesis of Cd-doped TiO2 nanophotocatalyst for removal of acid orange from wastewater

Journal of Sol-Gel Science and Technology - This research is based on synthesis of titania (TiO2) nanophotocatalyst followed by cadmium (Cd) doping to activate the photocatalyst in visible part of...     

Ultrasound assisted co-precipitation of nanostructured CuO–ZnO–Al2O3 over HZSM-5: Effect of precursor and irradiation power on nanocatalyst properties and catalytic performance for direct syngas to DME

Nanostructured CuO–ZnO–Al₂O₃/HZSM-5 was synthesized from nitrate and acetate precursors using ultrasound assisted co-precipitation method under different irradiation powers. The CuO–ZnO–Al₂O₃/HZSM-5 nanocatalysts were characterized using XRD, FESEM, BET, FTIR and EDX Dot-mapping analyses. The results indicated precursor type and irradiation power have significant influences on phase structure, morphology, surface area and functional groups. It was observed that the acetate formulated CuO–ZnO–Al₂O₃/HZSM-5 nanocatalyst have smaller CuO crystals with better dispersion and stronger interaction between components in comparison to nitrate based nanocatalysts. Ultrasound assisted co-precipitation synthesis method resulted in nanocatalyst with more uniform morphology compared to conventional method and increasing irradiation power yields smaller particles with better dispersion and higher surface area. Additionally the crystallinity of CuO is lower at high irradiation powers leading to stronger interaction between metal oxides. The nanocatalysts performance were tested at 200–300 °C, 10–40 bar and space velocity of 18,000–36,000 cm³/g h with the inlet gas composition of H₂/CO = 2/1 in a stainless steel autoclave reactor. The acetate based nanocatalysts irradiated with higher levels of power exhibited better reactivity in terms of CO conversion and DME yield. While there is an optimal temperature for CO conversion and DME yield in direct synthesis of DME, CO conversion and DME yield both increase with the pressure increase. Furthermore ultrasound assisted co-precipitation method yields more stable CuO–ZnO–Al₂O₃/HZSM-5 nanocatalyst while conventional precipitated nanocatalyst lost their activity ca. 18% and 58% in terms of CO conversion and DME yield respectively in 24 h time on stream test.     

Compatibilization of immiscible poly(lactic acid)/poly(ε-caprolactone) blend through electron-beam irradiation with the addition of a compatibilizing agent

The aim of this study was to compatibilize immiscible poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend by using electron-beam radiation method with the addition of a compatibilizing agent. Glycidyl methacrylate (GMA) was chosen as the compatibilizing agent, in the expectation that the GMA plays a role as a monomeric compatibilizer and a reactive agent at the interface between the PLA and the PCL phases. Compatibilization process has been investigated through the melt mixing of the PLA/PCL and the GMA by using a twin-screw extruder and the exposure of the PLA/PCL/GMA mixture to electron-beam radiation at room temperature. The melt mixing process was performed to locate the GMA at the interface, thereby expecting a finer morphology due to the GMA as the monomeric plasticizer. The exposure process was carried out to induce definite interfacial adhesion at the interface through electron-beam initiated cross-copolymerization by the medium of the GMA as the reactive agent. To investigate the results of this compatibilization strategy, the morphological, mechanical, and rheological properties of the blend were analyzed. The morphological study clearly showed the reduced particle size of dispersed PCL domains and significantly improved interfacial adhesion by the electron-beam irradiation with the addition of the GMA. The stress–strain curves of the blends irradiated at less than 20 kGy showed the typical characteristics of ductile materials. The tensile properties of the blend were strongly affected by the dose of irradiation.     

Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

Magnesium oxide nanocrystallites exhibit certain abnormal characteristics when compared to those of other wide band gap oxide semiconductors in the sense they are most prone to water absorption and formation of a hydroxide layer on the surface. The problem can be rectified by heating and pure nanocrystallites can be synthesized with controllable sizes. Inevitably the defect properties are distinctly divided between two stages, the one with the hydroxide layer (region I) and the other after the removal of the layer by annealing (region II). The lattice parameters, the optical band gap and even the positron annihilation characteristics are conspicuous by their distinct behavior in the two stages of the surface configurations of nanoparticles. While region I was specific with the formation of positronium-hydrogen complexes that drastically altered the defect-specific positron lifetimes, pick-off annihilation of orthopositronium atoms marked region II. The vacancy clusters within the nanocrystallites also trapped positrons. They agglomerated due to the effect of the higher temperatures and resulted in the growth of the nanocrystallites. The coincidence Doppler broadening spectroscopic measurements supported these findings and all the more indicated the trapping of positrons additionally into the neutral divacancies and negatively charged trivacancies. This is apart from the Mg²⁺ monovacancies which acted as the dominant trapping centers for positrons.     

Ultrasound-assisted rapid hydrothermal design of efficient nanostructured MFI-Type aluminosilicate catalyst for methanol to propylene reaction

The influence of ultrasound-assisted rapid hydrothermal synthesis of aluminosilicate ZSM-5 catalysts was examined in this work. A series of MFI-type nanostructured materials with sonochemical approach and conventional heating were synthesized and evaluated for conversion of methanol to propylene reaction. The prepared samples were tested by characterization analyses such as XRD, FESEM, BET-BJH, FTIR, TPD-NH₃ and TG/DTG. The obtained results confirmed that ultrasound treatment enhanced the nucleation process and crystal growth for ZSM-5 sample synthesized at moderate temperature of 250 °C. Therefore, it was found the formation of pure MFI zeolite with high crystallinity and improved textural, structural and acidic properties for ZSM-5(UH-250) sample compared with the other zeolites. This observation was attributed to the relationship between the perfect crystallization mechanism and catalytic properties, which led to producing an efficient MFI zeolite toward the optimal catalytic performance. In this manner, the methanol conversion and products selectivity of prepared materials were carried out in MTP reaction at 460 °C and atmospheric pressure. The ZSM-5(UH-250) zeolite with slower deactivation regime exhibited the constant level of methanol conversion (84%) and high propylene selectivity (78%) after 2100 min time on stream. Moreover, the synthesis pathway for MFI zeolite at moderate temperature and also deactivation mechanism of improved sample were proposed.