Capping with multivalent surfactants for zeolite nanocrystal synthesis

Multiammonium surfactants exhibited a remarkable capping effect for zeolite synthesis in the forms of nanoparticles, nanorods, and nanosponges in cases where common monovalent surfactants failed. A nanorod-shaped mordenite zeolite synthesized in this manner showed significantly enhanced catalytic lifetimes in acid-catalyzed cumene synthesis reactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.128301sciescopu

Experimental study on the propulsion performance of a partially submerged propeller

The present study concerns an open water performance of a partially submerged propeller. To investigate the free surface effects on the propulsion performance, the force and moment were measured, and the ventilation phenomena were visualized with respect to submergence ratios and advance coefficients. The thrust loss in heavy load conditions due to ventilation at the suction side of the propeller blade was observed. The extent of the ring-shaped ventilation phenomena increased as the advance coefficients decreased, resulting in thrust loss. Using the underwater camera and the fast Fourier transform results of the thrust, the ventilation phenomena were classified into five types. Also, the shaft excitation force of the propeller was analyzed. The shaft-bearing load was approximately 100% greater than the propeller weight in the ballast draft condition. A larger load was applied to the shaft due to the movement of the thrust eccentricity near the free surface

Rare-earth-platinum alloy nanoparticles in mesoporous zeolite for catalysis

Platinum is a much used catalyst that, in petrochemical processes, is often alloyed with other metals to improve catalytic activity, selectivity and longevity1-5. Such catalysts are usually prepared in the form of metallic nanoparticles supported on porous solids, and their production involves reducing metal precursor compounds under a H-2 flow at high temperatures(6). The method works well when using easily reducible late transition metals, but Pt alloy formation with rare-earth elements through the H-2 reduction route is almost impossible owing to the low chemical potential of rare-earth element oxides(6). Here we use as support a mesoporous zeolite that has pore walls with surface framework defects (called `silanol nests') and show that the zeolite enables alloy formation between Pt and rare-earth elements. We find that the silanol nests enable the rare-earth elements to exist as single atomic species with a substantially higher chemical potential compared with that of the bulk oxide, making it possible for them to diffuse onto Pt. High-resolution transmission electron microscopy and hydrogen chemisorption measurements indicate that the resultant bimetallic nanoparticles supported on the mesoporous zeolite are intermetallic compounds, which we find to be stable, highly active and selective catalysts for the propane dehydrogenation reaction. When used with late transition metals, the same preparation strategy produces Pt alloy catalysts that incorporate an unusually large amount of the second metal and, in the case of the PtCo alloy, show high catalytic activity and selectivity in the preferential oxidation of carbon monoxide in H-2.11Nsciescopu

Random-graft polymer-directed synthesis of inorganic mesostructures with ultrathin frameworks

A widely employed route for synthesizing mesostructured materials is the use of surfactant micelles or amphiphilic block copolymers as structure-directing agents. A versatile synthesis method is described for mesostructured materials composed of ultrathin inorganic frameworks using amorphous linear-chain polymers functionalized with a random distribution of side groups that can participate in inorganic crystallization. Tight binding of the side groups with inorganic species enforces strain in the polymer backbones, limiting the crystallization to the ultrathin micellar scale. This method is demonstrated for a variety of materials, such as hierarchically nanoporous zeolites, their aluminophosphate analogue, TiO2 nanosheets of sub-nanometer thickness, and mesoporous TiO2, SnO2, and ZrO2. This polymer-directed synthesis is expected to widen our accessibility to unexplored mesostructured materials in a simple and mass-producible manner. In the right direction: Mesostructured inorganic materials, such as zeolite nanosponge, TiO2 nanosheets, and nanosponges of TiO2, SnO2, and ZrO2 were synthesized using amorphous polymers as the structure-directing agent. Many of these materials possessed quite uniform mesopores. Some of them even exhibited small-angle X-ray diffraction. The structure-directing mechanism is also presented. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.124241sciescopu

Continuous-wave THz generation from ingaas-based photomixers pumped by a tunable dual-wavelength DFB laser

Continuous-wave (CW) THz generation from InGaAs based photomixers has been demonstrated by using a tunable dual-wavelength 3-section DFB laser diode as the optical beat source. The wavelength of each lasing mode can be tuned by adjusting currents in micro-heaters which are fabricated on the top of the each DFB section. The CW THz frequency emitted from the InGaAs photomixers is continuously tuned from 0.16 to 0.49 THz