Papers by Keyword: Mesoporous

Abstract: The meso-porous TiO₂ and Sm-doped meso-porous TiO₂ were synthesized by a sol-gel method. Polyethylene glycol, with different added content, was added as a structure-directing agent. The prepared meso-porous TiO₂ was characterized by nitrogen adsorption, X-ray diffraction and ultraviolet-visible diffuse reflectance spectroscopy, and the photocatalytic performance was evaluated by the decomposition of methyl orange. The results revealed that PEG plays a key role in creating porous structure during the heat-treatment. The photocatalytic performance of TiO₂ is improved by adding proper content PEG, and Sm-doping can further promote the photocatalytic performance.

Abstract: Five different types of silica catalyst (SBA-15, SBA-15-PO₃H₂, and three different Si/Al ratio of commercial zeolites (30, 80 and 280) were used to study the transformation of methanol to hydrocarbon (MTH). The aim of this study was to investigate the effect of pore diameter and acidity in the structure of silica catalysts on the process performances in terms of methanol conversion and hydrocarbon selectivity. The mesoporous silica catalysts were prepared by co-condensation method. The catalysts samples were characterized by GC-MS, XRD, BET, and NH₃-TPD techniques. The catalytic performance of synthesized and commercial catalysts for MTH process was evaluated using a homemade fixed bed reactor at temperature (300°C). It was found that the liquid hydrocarbon product provided by zeolite catalysts is aromatic hydrocarbons-rich. High Si/Al zeolites with larger pore size lead to higher selectivity and yield to paraffins (C1-C7). In contrast to commercial zeolite catalyst, SBA-15 and its modification with phosphorus species showed no conversion under studied condition. These results indicate that both pore diameter and acidity influence the product distribution in methanol to hydrocarbon process.

Abstract: The high interest in the synthesis of mesoporous catalyst demands that novel materials are developed with simple methods capable of improving process yields. In this work, a novel heterogeneous mesoporous catalyst support has been synthesized using mesoporous SBA-15 loaded with mixed bimetal oxides of CeO₂ and MgO. Formation of the SBA-15 was actuated in air at room temperature (25°C) and in oven conditions at 100°C after which cerium nitrate and magnesium nitrate precursors were then impregnated into the SBA-15 framework and calcined at 550°C for each of the air and oven crystallization processes. XRD peak patterns confirmed SBA-15 formation and dispersion of nanocrystallites of CeO₂ and MgO within the porous framework of SBA-15. Both the air and oven dried processes produced mesoporous MgO-CeO₂/SBA-15 catalysts with isotherms that exhibit typical H1 type hysteresis confirming that they possess open-ended cylindrical mesopores. The structural data extracted gave average pore size, pore volume and surface area values in the ranges of 3-5.2 nm, 0.600-2.500 cc/g and 400-500 m²/g respectively which is ideal for several industrial applications.

Abstract: Fe-SBA-15 materials with different Fe content have been prepared using tetraethyl orthosilicate (TEOS) and iron nitrate (Fe (NO₃)_3·H₂O as precursors and Pluronic P123 as structure directing agent through evaporation-induced self-assembly (EISA) method. The materials were characterized by nitrogen sorption, powder X-ray diffraction and TEM. All the Fe-SBA-15 samples appeared ordered 2D hexagonal mesostructure. The BET surface area and pore diameter were about 500 m²/g and 4 nm respectively. In the reaction of phenol hydroxylation to dihydroxybenzenes, the Fe-SBA-15 materials showed good catalytic activity, giving 20.2% of phenol conversion, 58.2% of selectivity for o-dihydroxy benzene and 41.8% of selectivity for p-dihydroxy benzene. After five cycles, the product yield was 25.2%, while selectivities of o-dihydroxy benzene and p-dihydroxy benzene were 58.2% and 41.8%, respectively. All these findings indicated the potential of Fe-SBA-15-10 could be used as a cost-effective, environment-friendly catalyst.

Abstract: A series of hierarchical HZSM-5 catalysts were synthesized by alkaline (denoted as HZSM-5-At) and/or alkaline-acid (denoted as HZSM-5-At-acid) treatments, and they as catalyst pairs were employed for the synthesis of glycerol and ammonia toward pyridine bases in a series-connected two-stage reactor. The characterization was analysed by means of N₂-physorption and NH₃-TPD techniques. The catalytic evaluation showed that the lower Si/Al ratio (Si/Al = 25 before treatment) in catalyst pairs (HZSM-5-At + ZnO/HZSM-5-At-acid) possessed the highest total yield of pyridine bases among all the catalyst pairs, but the suitable Si/Al ratio in alkaline-treated ZSM-5 (Si/Al = 38 before treatment) in the first stage of reactor and ZnO/HZSM-5-At-acid (Si/Al = 25 before treatment) in the second stage of reactor had the stronger stability relative to other catalyst pairs. The characterization revealed that the amount of acid sites play a vital role in the formation of pyridine bases whereas the appearance of mesoporous structure and the declined concentration of acid sites were main reasons for promoting the stability.

Abstract: We present a direct soft templating method to synthesise mesoporous tin dioxide network that maintains a porous structure after calcination at 400 °C and 500 °C and has a relatively high BET surface area of 220 and 100 m² g^-1, respectively. TEM, BET and XRD results confirm that both crystal and pore sizes increase as a result of increasing the temperatures during the calcination step. This method is highly reproducible.

Abstract: Titanium dioxide (TiO₂) thin films were prepared by means of electrochemical anodisation or anodic spark deposition (ASD) from thin and flat metallic titanium (Ti) films pre-deposited on high quality quartz substrates by electron beam evaporation. AFM analysis indicates the formation of uniform mesoporous layers and a definite increase about 50% of the film thickness upon anodisation and about 90% upon annealing. Anodised mesoporous TiO₂ films have been characterized by Raman spectroscopy, which indicates the presence of well-defined peaks related to anatase structure. Phase transformation from anatase to rutile was observed after annealing at temperatures up to 900°C for 3h.

Abstract: The mesoporous CeO₂ were prepared via a surfactant-assisted method of nanoparticle assembly, CTAB was used as surfactant. The mesoporous CeO₂ were used as the supports for preparing xAu/CeO₂ catalysts by the chemical reduction method, and the catalytic activities of the total oxidation of propane were studied. The prepared catalysts were characterized by XRD, TEM and N₂ adsorption techniques. The content of Au can affect the catalytic properties of the xAu/CeO₂ catalysts. 4Au/CeO₂ exhibited the highest catalytic activity in propane complete oxidation with the T₁₀₀ of 420 °C.

Abstract: In this research, several precursors were chosen to solve the drawbacks of using toxic and expensive chemicals in the synthesis of fibrous mesoporous silica particle via self-assembly process in microemulsion system. The synthesis of this emerging material normally is realized by using toxic cetylpyridinium bromide (CPB) as common structure directing agent in conjunction with combined cyclohexane and n-pentanol as expensive solvent and co-solvent, respectively. Less toxic cetyltrimethylammonium bromide (CTAB) can be the replacement for CPB but the use of this surfactant may drastically reduce the surface area of the resulting product. Herein, we report that the use of CTAB with combined toluene and n-butanol as affordable solvents can be used to synthesize fibrous mesoporous silica particle with high surface area. The material was well characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), N₂ adsorption/ desorption, X-ray difraction (XRD)and thermal gravimetry (TG). This material might be applied in potential applications such as catalysis, drug delivery and adsorption. Moreover, it can be used as a hard-template for fabricating another novel fibrous materials.

Abstract: Aluminium is found to play a key role in the process of forming a mechanically stable and highly porous and granular structure of 4H silicon carbide. The material is prepared by a high temperature reaction of the elemental constituents. The reactions are carried out under different background atmospheres, including nitrogen. Ternary carbides containing Al, Si and N, are formed in the process, and are believed to be responsible for the final outcome of the process, at the highest reaction temperatures, in the form of pure, well-connected grains of 4H-SiC forming a strong and rigid structure with high porosity. The Al containing compounds function as structural promoters for the 4H polytype recrystallization. This is expected - and partly shown - to take place through substitution with 4H-SiC and evaporation of all other constituents during the high temperature sintering step. When extruded into honeycomb structures prior to the sintering process this pure mesoporous SiC final product turns out to be ideal for a combined diesel particulate filter with support for catalysts in the pores.