Tuning zeolite properties for highly efficient synthesis of propylene from methanol

Series of nanosized ZSM-5 samples is synthesized at 170 °C, 150 °C, 120 °C and 100 °C. Experimental data show that the decrease of crystallization temperature leads to significant changes in zeolite properties. Crystals synthesized at 100 °C exhibit many framework defects with lower acid sites density, strength and larger external surface area. The selectivity to light olefins and the propylene-to-ethylene ratio increases as the crystallization temperature decreases. Propylene-to-ethylene ratio above 6 with the highest selectivity to propylene of 53 % is obtained over ZSM-5 catalyst prepared at 100 °C. Stability of the nanosized zeolite in MTO is also improved compared to industrial sample with similar Si/Al ratio. This catalytic performance is a result of the decrease in the acid sites density, strength and the crystals’ size, providing shorter diffusion path and larger external surface area. The presence of structural defects and different external surface are of the crystals has been shown to play an important role in the MTO catalyst performance

Time-resolved dissolution elucidates the mechanism of zeolite MFI crystallization

Zeolite crystal growth mechanisms are not fully elucidated owing to their complexity wherein the formation of a particular zeolite can occur by more than one crystallization pathway. Here, we have conducted time-resolved dissolution experiments of MFI-type zeolite crystals in ammonium fluoride medium where detailed structural analysis allowed us to extrapolate and elucidate the possible mechanism of nucleation and crystal growth. A combination of electron and scanning probe microscopy shows that dissolution initiates preferentially at lattice defects and progressively removes defect zones to reveal a mosaic structure of crystalline domains within each zeolite crystal. This mosaic architecture evolves during the growth process, reflecting the changing conditions of zeolite formation that can be retroactively assessed during zeolite crystal dissolution. Moreover, a more general implication of this study is the establishment that dissolution can be used successfully as an ex situ technique to uncover details about crystal growth features inaccessible by other methods

New method to find corner and tangent vertices in sketches using parametric cubic curves approximation

Some recent approaches have been presented as simple and highly accurate corner finders in the sketches including curves, which is useful to support natural human-computer interaction, but these in most cases do not consider tangent vertices (smooth points between two geometric entities, present in engineering models), what implies an important drawback in the field of design. In this article we present a robust approach based on the approximation to parametric cubic curves of the stroke for further radius function calculation in order to detect corner and tangent vertices. We have called our approach Tangent and Corner Vertices Detection (TCVD), and it works in the following way. First, corner vertices are obtained as minimum radius peaks in the discrete radius function, where radius is obtained from differences. Second, approximated piecewise parametric curves on the stroke are obtained and the analytic radius function is calculated. Then, curves are obtained from stretches of the stroke that have a small radius. Finally, the tangent vertices are found between straight lines and curves or between curves, where no corner vertices are previously located. The radius function to obtain curves is calculated from approximated piecewise curves, which is much more noise free than discrete radius calculation. Several tests have been carried out to compare our approach to that of the current best benchmarked, and the obtained results show that our approach achieves a significant accuracy even better finding corner vertices, and moreover, tangent vertices are detected with an Accuracy near to 92% and a False Positive Rate near to 2%.Spanish Ministry of Science and Education and the FEDER Funds, through CUESKETCH (Ref. DPI2007-66755-C02-01) and HYMAS projects (Ref. DPI2010-19457) partially supported this work.Albert Gil, FE.; García Fernández-Pacheco, D.; Aleixos Borrás, MN. (2013). New method to find corner and tangent vertices in sketches using parametric cubic curves approximation. Pattern Recognition. 46(5):1433-1448. https://doi.org/10.1016/j.patcog.2012.11.006S1433144846

Mesoporous zeolites by fluoride etching

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Spontaneous galvanic deposition of nanoporous Pd on microfibrous-structured Al-fibers for CO oxidative coupling to dimethyl oxalate

International audienceNanoporous palladium (np-Pd) is deposited spontaneously on microfibrous-structured Al-fibers (np-Pd/Al-fiber catalyst) via the galvanic replacement between Pd2+ and aluminium metal (2 Al + 3 Pd2+ → 2 Al3+ + 3 Pd). The np-Pd/Al-fiber catalyst combines the high activity and good stability of the np-Pd with the excellent heat conductivity and large permeability of the microfibrous-structured Al-fibers. The np-Pd/Al-fiber catalyst shows four times higher intrinsic activity (i.e., turnover frequency) than the conventional Pd/α-Al2O3 catalyst. The unique nanoporous palladium with interpenetrating network of nanoligaments is responsible for the improved activity in the CO oxidative coupling to dimethyl oxalate (2 CH3ONO + 2 CO → 2 NO + CH3OCOCOOCH3)

Low-temperature synthesis of α-alumina nanosheets on microfibrous-structured Al-fibers for Pd-catalyzed CO oxidative coupling to dimethyl oxalate

International audienceWe reported the low-temperature synthesis of -Al2O3 nanosheets on the microfibrous-structured Alfibers at 800 º C. The boehmite (AlOOH) nanosheets were initially formed on the Al-fibers through in situ endogenous growth. Then the AlOOH/Al-fibers was transformed to the -Al2O3/Al-fibers composite at 800 º C by a single heating step. The low-temperature phase transformation was tentatively attributed to the Al metal in the AlOOH/Al-fibers. Palladium was then dispersed on the -Al2O3/Alfibers composite, and the resulting Pd/-Al2O3/Al-fibers catalyst was examined in the strongly exothermic CO oxidative coupling to dimethyl oxalate (DMO) reaction. High CO conversion of 58 % and DMO selectivity of 95 % were obtained and maintained for at least 150 h using a feedgas of CH3ONO / CO / N2 (1 / 1.4 / 7.6, mole) at 150 º C with a gas hourly space velocity of 20000 mL g 1 h 1. Computational fluid dynamics calculations and experimental results indicated that the Pd/-Al2O3/Al-fibers catalyst remarkably decreased the hot-spot temperature of catalyst bed due to its enhanced thermal conductivity

Intra-crystalline mesoporous ZSM-5 zeolite by grinding synthesis method

International audienceZSM-5 zeolite with intra-crystalline mesopores was synthesized via grinding synthesis method (GSM). It was found that the formation of the mesopores in the ZSM-5 crystals is due to the difference between the speed of crystallization and dissolution processes occurring during the GSM synthesis. The alkalinity of the precursor gels tailored the formation of the mesoporous structure and the crystal size of the ZSM-5 zeolite. The most regular mesopores in the ZSM-5 crystals were formed under grinding synthesis of the precursor gel with a defined concentration of alkali cations (Na2O/SiO2=0.113). The size of the mesopores in the ZSM-5 crystals varied from 2 3nm to 25nm, while the size of the individual ZSM-5 crystallites is in the range of 50-300nm which depend mainly on the amount of NaOH in the precursor gel

NUMERICAL ANALYSIS AND EXPERIMENTAL STUDY ON THE RACK OF MASSAGE CHAIR

Aiming at the people’s requests of comfort and functions,a rack of massage chair was designed. Numerical analysis was done based on the three-dimensional model. Kinematic simulation was run on the virtual prototype model based on the ADAMS software,the functions was verified and the theoretical basis was supported for the choose of the electric putter.Finite element analysis was done on the key components of the structure under the environment of ANSYS Workbench,the strength and stiffness were checked. Experimental study was done after the prototypes were made. The research results indicate that the rack can meet the function requests of zero gravity and zero against the wall. The strength and stiffness of the structure can meet the requests of the testing standard. The experimental results consistent with the numerical analysis results. That verifies the validity of numerical analysis. The research results also offer important basis for the later structure optimization

THE STRUCTURAL DESIGN OF BOSS CHAIR FOOTREST AND IT’S STUDYING ABOUT MECHANICAL PROPERTY

According to customers’ needs,Based on ergonomics principle,a Boss Chair footrest was designed. Using Adams software to take kinematics simulation,which has verified the movement characteristics of the organization. Based on finite element analysis AWE environment on the organization,To check the strength and stiffness of the structure. On the basis of the physical prototype,to take mechanical properties test. It turned out that the footrest meet requirements of ergonomics size and movement stability,static strength,fatigue strength and stiffness of the structure conform to the BIFMA test standard. The testing results coincided with the finite element analysis