Maria Gomez, JoseMontes, IgnacioDiez, EduardoRodriguez, Araceli...
11页
查看更多>>摘要：Synthesis of Low Silica X zeolite (LSX) with hierarchical porosity was achieved. The low silicon/aluminum ratio of this zeolite allowed to increase the number of active sites, as cationic positions (>25%) respect to the previous mesoporous X zeolite. Mesoporosity was induced by using sodium dodecylbenzene sulfonate (SDBS) during the synthesis. A dissolution time of 24 h for SDBS improved the zeolite crystallinity, maintaining the FAU characteristic framework, with a silicon/aluminum molar ratio near the unity (<1.1), limit of the Lowenstein' rule. The surfactant removal at 773 K promoted the development of a wider pore size distribution. The heating rate highly determined the pore size distribution, resulting in a bimodal distribution (maxima at 80 angstrom and 290 angstrom) at low heating rate (1.3 K/min) and a unimodal distribution, with a maximum at 230 angstrom, at higher heating rate (8 K/min). The analysis by Transmission Electronic Microscopy (TEM) showed the mesoporous cavities in the zeolite nanoparticles. These cavities were generated by the SDBS spherical micelles removal. Mesopomus Low Silica X zeolite (MLSX) showed higher catalytic activity than the same zeolite without mesoporosity in the deoxygenation of oleic acid. The conversion reached a constant value around 100% with higher yield toward C-9-C-18 hydrocarbons, representative fraction of sustainable aviation fuel (SAF). Therefore, this new mesoporous low silica X zeolite (MLSX) has a significant potential use as catalyst in the processing of bulky molecules.
查看更多>>摘要：The potential of hierarchically porous carbons is drastically limited by their intrinsic fragility, tedious preparation, high cost, and poor processability. Here we develop a novel solvent-induced phase separation technique for fast and continuous preparation of hierarchically macro-/microporous carbon beads (MMCBs). The asprepared MMCBs show spherical shape with millimeter size, which give the carbons many value-added physical properties such as regular geometry, good mechanical properties, low dust, and good flowability. The MMCBs have a high BET surface area of 1099 m2 g-1, and percolating macroporous superstructure with axialoriented macrovoid channel and sponge-like bicontinuous network issued from solvent-induced macrophase separation and microphase separation, respectively. In addition, the MMCBs have a high nitrogen doing of 4-5 wt% originated from their nitrogen-rich polyacrylonitrile precursor. The MMCBs could directly sever as the metal-free carbon catalysts for room-temperature oxidation of NO to NO2 with over 80% conversion, and the urea-loaded MMCBs could use for selective catalytic reduction of NO to N2 with long-time NOx removal. This convenient synthesis to porous carbons with the engineered morphology and percolating macropores has great potential in practical applications where both rapid mass transport and high surface areas are required.
查看更多>>摘要：A molecular template (tetrapmpylammonium hydroxide, TPAOH) and a phosphorus-containing template (tetrabutylphosphonium hydroxide, TBPOH or tetrabutylphosphonium bromide, TBPBr) were used as dual templates to prepare the mesopomus ZSM-5 zeolites. The physicochemical properties of the as-prepared ZSM-5 catalysts were characterized by means of XRD, N-2 adsorption, NH3-TPD, FT-IR spectra of adsorbed pyridine,Al- 27 MAS NMR, etc., and their performances for the catalytic cracking of the n-octane to light olefins were investigated. The results indicated that the acidity of ZSM-5, especially the concentration of strong Bronsted acid sites (SBAS) can be finely modulated by tuning the molar ratio of TPA(+)/TBP+. The charge-compensation effect of TBP+ and the phosphorus species played critical roles in regulating the SBAS concentrations of ZSM-5. Consequently, the as-prepared ZSM-5 catalysts with suitable strong Bronsted acid sites density was favorable for enhancing the selectivity to light olefins. At the temperature of 600 degrees C, the selectivity of propene and light olefins over MFI-9/2.5 catalyst were achieved 34.7% and 70.4%, which were higher than those over conventional ZSM-5 by 2.4% and 5.1%, respectively. Selectivity to C2(=)similar to C4(=) light olefins was found to be decreased with increasing the concentration of strong Bronsted acid sites due to the reduction of SBAS which inhibited the hydrogen transfer reaction. This work will provide insights and new platforms for the design of high-efficiency zeolite catalysts for important industrial reactions.
查看更多>>摘要：A nanoarchitectural approach for synthesis of highly crystalline zeolites based on natural aluminosilicate nanotubes with adjustable silica to alumina ratio has been developed. A double template technique was proposed for synthesis of zeolite microcrystals with geometric morphology defined by the initial aluminosilicate nanotubes (halloysite). Remarkable and unique zeolite microcrystal shapes (submicron spheres, pompon-like systems and coffin-shaped prisms) possessing different internal structures (sodalite, analcime, mordenite, mordenite framework inverted) were obtained from halloysite by hydrothermal method. Halloysite Si/Al adjustments (acid etching, addition of extra silica or alumina) significantly affected crystalline structure and morphology of the obtained materials, while changing organic templates did not have a considerable effect.
查看更多>>摘要：Inspired by the fascinating merits of hydrogen-bonded frameworks (HOFs) materials such as large surface area, simple preparation and regeneration, and excellent water stability etc., a HOF (PFC-1) was prepared and applied to remove the two organic dyes rhodamine B (RhB) and methyl orange (MO) from wastewater. PFC-1 showed an excellent removal ability towards these two dyes, with a maximum adsorption capacity of 317 mg/g for RhB and 252 mg/g for MO at 298.15K. Both of the adsorption processes can be well fitted with the Langmuir isotherm model and pseudo-second-order kinetic model. Characterization techniques such as PXRD, XPS, and FTIR complemented with DFT calculations were employed to investigate the adsorption mechanisms for RhB and MO. The influence of the pH on the dyes removal was also investigated. The above results indicated that electrostatic attraction, hydrogen bonding and pi-pi interactions were mainly responsible for the adsorption of RhB onto PFC-1, while van der Waals force largely contributed to the adsorption of MO. Moreover, the calculation of thermodynamic functions suggested that the adsorption of PFC-1 towards RhB was an endothermic process whereas the adsorption for MO was an exothermic process, respectively. Last but not least, PFC-1 could maintain a high removal performance towards RhB and MO even after five cycles, proving its good recyclability and sustainability. Overall, this novel adsorbent has provided new application possibilities of HOFs and suggested their great potential in the area of environmental remediation.
查看更多>>摘要：Heteroatom metal-zeolite, with heteroatom metal (oxide) dispersed in the zeolite framework, enables the reactions typically catalyzed by bulk metal oxide counterpart but with maximized the atomic utilization. However, the distribution of heteroatoms in the framework is strongly influenced by the preparation method. In this work, Ti-Beta zeolites were postsynthesized using the recrystallization (Ti-Beta-Re) and solid-state ion-exchange (Ti-Beta-SSIE) methods. Characterizations showed that more Ti species were incorporated in the tetrahedral framework site of Ti-Beta-Re to form Lewis acid sites than in that of Ti-Beta-SSIE. In addition, intra-crystallite mesopores were developed in Ti-Beta-Re due to partial dissolution of BEA framework during alkaline etching and subsequent recrystallization of the etched framework. These zeolites were then tested for ketonization of biomass derived propionic acid at 350 degrees C and atmospheric pressure. The turnover frequency of ketonization was found to be 25% higher on Ti-Beta-Re (0.25 min(-1)) than on Ti-Beta-SSIE (0.20 min(-1)), whereas the apparent activation energy of 80 kJ/mol on Ti-Beta-Re is lower than 95 kJ/mol on Ti-Beta-SSIE. Moreover, the selectivity of 3-pentanone kept > 95% on Ti-Beta-Re while it dropped to similar to 63% on Ti-Beta-SSIE with increase of reaction time at a space time of 2 h. This work demonstrated that the tetrahedrally coordinated Ti species are the active sites and the presence of intra-crystallite mesopores facilitates selective ketonization of carboxylic acids.
查看更多>>摘要：Solution foaming technique was adopted to fabricate polyamide-610 (PA610) foams, in which anhydrous formic acid and sodium carbonate were selected as the acid/base for performing neutralization reaction to in situ produce CO2 working as foaming agent. The major affecting parameters were investigated to adjust the cellular structure and diameter distribution, such as controlling the polyamide concentration, the sodium carbonate concentration and mixing rate (the rate to add carbonate solution into polyamide-610 solution) to tune the generation rate of CO2. The best foaming parameters were determined as 16 wt% PA concentration and 7 wt% sodium carbonate concentration, while the mixing rate was 1 mL/min. The resulting foams were subjected to diverse characterizations. SEM micrographs show that the foams have hierarchical open cell structures. The foaming process has effects on crystallization of the foams, further affecting foams' thermal performance. The adsorption capacities of the foams towards bisphenol A (BPA) were tested, and the maximum adsorption quantity can be up to 94.84 mg/g. The adsorption isotherm fits better with Freundlich isotherm, indicating multilayer adsorption of the foams towards BPA. The adsorption kinetic follows the pseudo-second order model. After 3 adsorption-desorption cycles, the foams still have medium adsorption level towards BPA.
查看更多>>摘要：The measurement of diffusivity within porous solids is vital for the characterization of materials, especially in heterogeneous catalysis and separation processes. Numerous methods have been developed to measure gas-phase diffusivities within materials. However, establishing correlations between the diffusivities and the properties of a material is challenging. Herein, we report a method for obtaining trends in gas-phase diffusivity of N-2 at 77 K within three different sets of mesoporous materials, disordered, ordered silica, and carbons-based materials. Synthesis procedures are reproducible and controlled precisely to achieve monodisperse particle size and defined pore size distributions. A standard physisorption device, Micromeritics 3Flex, is used to obtain the required transient data. These two aspects offer a suitable database of materials to identify trends and reduce the challenges associated with obtaining experimental data. A simplified model is fitted over the transient data with MATLAB to obtain empirical diffusivities used for trend analysis. The trends are based on a constant Dt, an ensemble value representing various diffusion processes occurring during a transient uptake process. The analysis identifies several correlations between the diffusivity and properties of materials, such as type of pore structure, pore size, and the chemical nature of the material. Based on the principles reported, this study can be extended to other adsorptive molecules or different temperatures. The possibility of using standard sorption instrumentation will allow a broader user community to employ the reported methodology.
查看更多>>摘要：Two-dimensional (2D) zeolite nanosheets open exciting opportunities for the application in catalysis and separations. Exfoliation of layered zeolite shows a promising way for the preparation of 2D zeolite nanosheets. Herein, non-swollen MCM-22P with ordered layer spacing was successfully exfoliated to dispersible MWW nanosheets. Firstly, a wet-oxidization method, i.e., heating in a mixture of H2SO4 and H2O2 (called piranha solution) was adopted to remove the template of pyridine (PI) from as-synthesized MCM-22P zeolite. IR, TG, XRD, N-2 adsorption confirmed that the wet-oxidization could efficiently remove PI from MCM-22P zeolite while preserving the MWW crystal structure. Exfoliation of the detemplated MCM-22P zeolite was successfully achieved by an ultrasonic treatment in water. After purification by sedimentation, 2D MWW zeolite nanosheets dispersed in aqueous solution were obtained. The monolayer MWW nanosheets with high purity are confirmed by SEM and TEM observations. The wet oxidation followed by the sonication method provides an alternative way for the exfoliation of layered zeolite to dispersed nanosheets.
NSTL
Elsevier