Bimetallic Wiregauze Supported Pt-Ru Nanocatalysts for Hydrogen Mitigation.

Passive autocatalytic recombiner (PAR) is one of the most suitable devices for mitigation of hydrogen, generated in nuclear power plant under accidental conditions. For this purpose we report development of stainless steel wire gauze supported Pt-Ru nanoparticles as catalysts. Simultaneous electroless deposition has been employed for the synthesis of the catalysts. Pt-Ru based bimetallic catalysts were characterized for their rate of coating kinetics, noble metal loading, phase purity by XRD and surface morphology by SEM, TEM and elemental analysis by SIMS. Developed catalysts were found to be active for efficient recombination of hydrogen and oxygen in air as well as in presence of various prospective poisons like CO2, CH4, CO and relative humidity. Pt-Ru based bimetallic catalyst with 0.9% loading was found to be active for CO poisoning up to 400 ppm of CO.

The dual role of palladium in enhancing the photocatalytic activity of CdS dispersed on NaY-zeolite.

A stable photocatalyst, CdS dispersed on zeolite with Pd as both the dopant and the co-catalyst, has been developed. Enhancement of photocatalytic activity for hydrogen generation is observed for CdS when doped with palladium and dispersed on NaY-zeolite (CdPdS-Z). A further increase in the photocatalytic activity of CdPdS-Z is observed when palladium is added as a co-catalyst (Pd-CdPdS-Z). Cd0.95Pd0.05S-Z is synthesized via a facile soft chemical route and the Pd co-catalyst is loaded onto the composite using a wet impregnation method. This composite catalyst exists as two phases consisting of CdPdS and zeolite and CdPdS exists as a highly dispersed phase on zeolite as revealed by TEM studies. The Pd doped CdS-zeolite composite exhibits increased visible light absorption indicating the alteration of the band structure of CdS as a result of doping. Time resolved fluorescence studies reveal that the lifetime of the charge carriers is higher in the composites than in pure CdS. A detailed characterization using XRD, Raman and X-ray photoelectron spectroscopy indicates that Pd has substituted for Cd in the CdS lattice and Pd exists in the Pd(2+) oxidation state. Solid state MAS NMR studies indicate that an interaction exists between CdS (or CdPdS) and zeolite at the interface and Cd selectively interacts with Al of the zeolite framework. The photocatalytic activity of the Pd-CdPdS-Z catalyst remains unchanged with repeated cycles. Characterization of the used catalyst indicates that it is stable under the present experimental conditions. The enhanced photocatalytic activity of Pd-CdPdS-Z is attributed to the enhanced visible light absorption arising due to Pd doping and increased lifetime of the photogenerated charge carriers assisted by zeolite and the Pd co-catalyst. This study highlights the multiple roles played by palladium in enhancing the photocatalytic activity of the CdS-zeolite composite.

Mechanistic insight by in situ FTIR for the gas phase photo-oxidation of ethylene by V-doped titania and nano titania.

Vanadium-doped titania is found to be a better photocatalyst for gas phase photo-oxidation of ethylene than nano titania. In situ FTIR studies were undertaken to elucidate the mechanistic pathway for ethylene oxidation on these two catalyst surfaces. Vanadium doping leads to formation of more chemisorbed hydroxyl species, which makes it a better photocatalyst. The labile hydroxyls which were responsible for the reduction of V(5+) to V(4+) during the process of calcination were also ascertained. The ethylene decomposition occurs via formation of ethoxy groups, transformed to acetaldehyde or enolates, subsequently to acetates/formates, and then to CO(2). The enolates were more stabilized on the TiO(2) surface, leading to formation of formates along with the acetates. On vanadium-doped TiO(2), acetaldehyde was more stabilized than its enol tautomer, leading to the formation of labile acetic acid and acetates. The formation of the labile acetic acid, adsorbed acetates, and the adsorbed acetate -M salts led to easier oxidation of them to provide higher yield of CO(2). The higher positive charge density over Ti in Ti(0.95)V(0.05)O(2) with respect to nano TiO(2) makes the acetate (stronger nucleophile) a more stable intermediate on it.

A pulse-step model of accommodation dynamics.

Abrupt step changes in human ocular accommodation have been traditionally modeled using a continuous feedback control system supplied by a step-position control signal. However, recent behavioral data show that, while the velocity of the step response increases proportionally with response magnitude, the peak acceleration remains constant. This argues against a step input control signal and suggests the existence of a dual-mode control of accommodation: an initial fixed innervation component related to the constant acceleration followed by an innervation component that increases with response amplitude. Specifically, we proposed a pulse-step that provides a velocity-coded input to the system that is integrated to form two position-input signals, that when combined produce high velocity responses. The pulse height controls the acceleration; the pulse width controls the velocity and the step height controls the position of the accommodation response. The pulse-step model simulations were similar to empirical observations and illustrated an enhancement of the peak velocity of accommodation when compared to when the pulse component was removed from the model. The main functional advantage of the pulse is to overcome the high viscosity of the crystalline lens and achieve rapid step responses.