Bulut, BetulIsbilen, EmrahAtakul, HusnuTantekin-Ersolmaz, S. Birgul...
14页
查看更多>>摘要：NaX- and NaY-based adsorbents were used for desulfurization of Liquefied Petroleum Gas (LPG). Zeolites were modified by incorporation of Cu2+, Zn2+ and Cu2+-Zn2+ metal ions through liquid phase ion-exchange (LPIE) and characterized for their crystal structure, surface area, acidity, ion-exchange rate, and adsorption mechanism. Desulfurization experiments were carried out by static and dynamic methods using dimetyhl disulfide (DMDS) and thiophene (TP) dosed LPG containing 196 mg/L total sulfur as the feed. The sulfur removal performance of zeolites increased after modification and the adsorption capacities of the modified zeolites for DMDS and TP removal were found in the order of Cu > Cu-Zn > Zn for both NaX and NaY zeolites. The breakthrough DMDS adsorption capacities of modified zeolites were 14-37% and 16-45% higher than those of the original NaX and NaY zeolites, respectively. As for TP, modified NaX and NaY zeolites displayed 9-22% and 10-25% increase in breakthrough capacity compared to original zeolites, respectively. The modification did not cause any degradation in the zeolite crystal structure and the metal ions were successfully dispersed in zeolites. The incorporation of Cu2+ ions enhanced the Lewis acid sites of zeolites. The Cu-X and Cu-Y adsorbents binded DMDS by direct sulfur-metal (S-M) interaction while both direct S-M interaction and pi-complexation were effective in TP adsorption onto zeolites. The adsorption of DMDS and TP over Cu-X and Cu-Y followed pseudo-second-order kinetics and was best described by the Langmuir isotherm model. The best performing adsorbent, Cu-Y, is promising for industrial scale LPG desulfurization.
查看更多>>摘要：This study reports the preparation of highly porous, SBA-15-based monolithic materials with pore sizes spanning over four scales (micro-/meso-/small macro-/large macro-pores). Two approaches were explored. The first one involves the preparation of PMMA scaffolds obtained from chemically-bonded beads and their further infiltration using SBA-15 slurries with suitable viscosity; while the second one directly uses the same amount of PMMA beads dispersed within the slurries. Emphasis was given to the comparison of the textural, structural, and mechanical properties obtained following each approach. Then, application of a thermal consolidation step and its influence over the monoliths properties was investigated, with an optimum observed at 950 degrees C. The second method systematically allowed reaching higher mechanical resistances (86 vs 32 kPa at 950 degrees C) for comparable specific surface areas (274 vs 290 m(2)/g at 950 degrees C), however at the expense of smaller macropores and lower ordering in the monoliths.
查看更多>>摘要：The toluene methylation reaction via methanol is an important process to produce high-value para-xylene (PX), it has always been our goal to explore a catalyst with high activity and selectivity for PX. Cu+ is used to modify HZSM-5 (BAS/Cu+-HZSM-5) zeolite, and the microscopic reasons for the excellent catalytic performance to produce PX on BAS/Cu+-HZSM-5 are investigated according to the intrinsic reaction and molecular diffusion. The intrinsic activation energies of methanol dissociation and xylene formation on BAS/Cu+-HZSM-5 are obtained by the density functional theory (DFT). Calculations indicate that the energy required for methanol dissociation is 109.7 kJ mol(-1), which is lower than that on pure HZSM-5. In addition, PX, meta-xylene (MX) and ortho-xylene (OX) formed with little activation energies of 12.7, 11.8 and 14.2 kJ mol(-1), respectively. Therefore, the formation of these xylenes on BAS/Cu+-HZSM-5 has high activity and strong competition. On the other hand, the self-diffusion coefficients of three xylenes on BAS/Cu+-HZSM-5 are analyzed by molecular dynamics (MD) simulation. And the self-diffusion coefficient of PX is found to be much larger than that of MX and OX in all cases, which indicates that the channel characteristics of BAS/Cu+-HZSM-5 are beneficial to the diffusion and separation of PX. Therefore, it can be concluded that BAS/Cu+-HZSM-5 has better catalytic performance and high PX selectivity for the toluene methylation reaction via methanol.
查看更多>>摘要：In this work we present a synthesis strategy for the preparation of Sto center dot ber-type mesoporous particles functionalized with inorganic species. The procedure is based on a combination of the Atrane and the Sto center dot ber methods. Both as a source of silicon and of the incorporated heteroelements (Fe, Zn, Al, Ti) the corresponding atrane complexes are used as hydrolytic reagents. These complexes are easily formed by reaction with triethanolamine. Mesoporosity is achieved using surfactant micelles as templates. Obtaining uniform spherical particles is achieved by optimizing the amount of water-ethanol in the reaction medium. The particle sizes have been modulated by controlling simple parameters such as reaction time or temperature. The incorporation of inorganic species is on many occasions incompatible with the preservation of spherical morphology, resulting in heterogeneous particles in shape and size and even phase segregation for high functionalization degrees. The methodology that we propose makes it possible to achieve a high concentration of highly dispersed heteroelements (even at molecular level), maintaining, to a large extent, both sphericity and particle size homogeneity. The Si/M molar ratios achieved are significantly lower (greater functionalization) than those usually reported in the literature. The strategy is generalizable for the incorporation of a great variety of elements, and specially for first row transition elements.
查看更多>>摘要：This study reports a seeding-polymer-assisted method using inexpensive tetrapropylammonium bromide (TPABr) to synthesize titanium silicalite-1 (TS-1) ranging from supported embryonic (< 8 nm) to crystalline nano-/ micrometersized (asymptotic to 0.1-1.0 mu m) particles by kinetic regulation. The in situ grown embryonic TS-1 on the amorphous silica presents defective Ti(OH)(OSi)3, tetrahedral framework Ti ( "TiO4 "), and extraframework Ti ( "TiO6 ") species, while crystalline nano-/micro-metersized TS-1 particles exhibit either "TiO4 " or both "TiO4 " and "TiO6 " species and a smaller external surface area, S-ext. Turnover frequency (TOF) of TS-1 catalysts in the oxidation of dibenzothiophene (DBT) changes by an order of magnitude with the alteration of active Ti species. For instance, the TOF of supported embryonic TS-1 is 224.3 h(-1) while it is 32.6 h(-1 )for the micro-metersized particles due to differences in the active Ti species. However, the TOF of the different TS-1 samples with similar Ti active sites scales only in proportion to S-ext. The supported embryonic TS-1 on amorphous silica presents similar structural and chemical stability in comparison with crystalline nano-/micro-metersized TS-1 catalysts under water-free reaction conditions. Consequently, in situ prepared supported embryonic TS-1 combining improved accessibility (via increased external surface area) of different types of Ti species is a promising alternative for the conversion of bulky substrates.
查看更多>>摘要：The utility of the nonlinear diboronic acid 2, obtained from 3,7-dibromodibenzo[b,d]thiophene 5,5-dioxide 1, for the preparation of Covalent Organic Frameworks was investigated. Despite significant deviation of boronic groups in 2 from the colinear arrangement, a highly crystalline porous material DBSO-COF was obtained by dehydrative polycondensation with 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) using a solvothermal approach. Subsequent PXRD studies supported by periodic DFT modelling revealed the formation of the 2D honeycomb-type lattice with eclipsed stacking model. The antiparallel orientation of neighboured layers is strongly favoured owing to dipole-dipole and C-H center dot center dot center dot O interactions of sulfone moieties. This gives the net stabilization energy of 45 kJ mol(-1) per single sulfone motif, being primarily responsible for the effective formation of the ordered network and strongly contributing to its thermodynamic stability. The morphology was analyzed by SEM which revealed that the material forms uniform in size ca. 40 x 150 nm rod-like nano-crystallites. The Grand Canonical Monte Carlo (GCMC) simulation performed on a single nanoparticle of DBSO-COF allowed to reproduce the experimental isotherm. It also showed that N-2 molecules are mostly located close to the C-H bonds, while they are repulsed by sulfone groups. Apart from increasing the scope of useful boronic linkers beyond centrosymmetric structures, it was demonstrated that the presence of guest molecules in a porous network should be taken into account in order to obtain a more accurate prediction of porosity parameters.
查看更多>>摘要：High-performance amorphous silica-alumina (ASA) is an important acid material in the chemical industry. In this work, we successfully synthesized mesoporous ASA with enhanced specific surface area, Lewis acidity and total acidity by pH-swing method. The morphology and structure of ASA were systematically investigated. With the increase of SiO2 content from 20.1% to 67.0%, the morphology of ASA varied considerably from fibrous to granular, and the specific surface area decreased from 436 to 306 m(2) g(-1). Meanwhile, the gradual increase of surface silanol groups facilitated the formation of pseudo-bridged silanol groups and promoted the formation of Brunsted acid sites (BAS). Furthermore, the concentration of BAS was found to increase with increasing tetra- and penta-coordinated aluminum and decrease with increasing octa-coordinated aluminum. In addition, the acidity-activity relationship was also explored by applying the as-synthesized ASA samples directly to the cracking reaction of cumene. The results showed that the activity of ASA was proportional to the concentration of BAS. The pH-swing method can controllably synthesize ASA materials with different structures and acidity for petrochemical industry.
Monteiro, Arthur Felipe de FariasRibeiro, Stephany Larissa da SilvaSantos, Thiago Izidoro SilvaFonesca, Jose Daniel da Silva...
15页
查看更多>>摘要：A 2D Cu-based Metal-Organic Framework (MOF), namely copper-terephthalate (Cu(1,4-BDC)), was successfully synthesized by electrochemical method for effective methylene blue (MB) sorption from aqueous solutions. The composition, morphology, and the presence of functional groups in the obtained material were verified by Fourier Transform Infrared spectroscopy (FTIR), Powder X-Ray Diffraction (PXRD), Thermal (TGA), and Elemental (EA) analysis, as well as Scanning Electron Microscopy (SEM). The effect of electrochemical parameters applied in the synthesis protocol (i.e., a potentiometric or amperometric mode) on the resulting product composition was evaluated. The electric current value was determined as a variable controlling the type of crystal structure present in the obtained MOF. A structure with open channels CuBDC1 was favored under the current higher than 0.35 A conditions. In contrast, for the lower current values and upon the amperometric mode in the material, a CuBDC2 phase with DMF molecules occupying the grids of the layers was also present. The MB sorption studies were analyzed both with kinetic and equilibrium models. The obtained results showed the time evolution could be fitted with a pseudo-second-order model with the rate constant k(2) equal to 0.047 g mu mol(-1) h(-1). According to the Langmuir isotherm model, the maximum sorption capacity was determined as 76.63 mu mol g(-1). After MB sorption, the MOF material could be easily regenerated under mild conditions with good recyclability up to the four cycles (76.77%).
查看更多>>摘要：Activated alumina has a porous structure and large specific surface area. It is often used as a catalyst carrier for various reactions. Currently, solution-phase methods (sol-gel reactions) that cause environmental pollution and resource waste are often used to synthesise activated alumina. To overcome this disadvantage, in this study, an eco-friendly low-heat solid-phase precursor method was developed to prepare activated alumina with improved properties (phase stability and specific surface area). The difference between the activated alumina synthesised by this method and a sol-gel method was studied in terms of the specific surface area and high thermal stability. The results indicated that after 4 h of treatment at 1100 ?, pure activated alumina obtained by the low-heat solid-phase precursor method maintained the gamma-phase and had a specific surface area of 92 m(2)/g and pore volume of 0.68 cm(3)/g. On the other hand, pure activated alumina produced by the sol-gel method mainly consisted of the alpha-phase and had a specific surface area of only 21 m(2)/g and a low pore volume of 0.16 cm(3)/g. Upon doping with La and Ba, and heat-treating at 1100 C & nbsp;for 4 h, the specific surface areas of the activated alumina samples obtained by the low-heat solid-phase precursor method and sol-gel methods were 109 and 119 m(2)/g, respectively. When heated at high temperatures, the percentage loss of the specific surface area of the activated alumina synthesised by the low-heat solid-phase precursor method was lower than that of the sample obtained by the sol-gel method, indicating that it can inhibit the crystal-phase transformation of alumina at high temperatures.
NSTL
Elsevier