Thermochemical Properties of Synthesized Urea from Recovered Ammonia and Carbon Dioxide in Well-Ordered Nanospaces of Hollow Silica Spheres.

The present work investigated the thermochemical properties of urea synthesized in well-ordered nanospaces of porous hollow silica spheres' shells from recovered ammonia and carbon dioxide in aqueous solution. Thermochemical behaviors of the urea synthesized in well-ordered nanospaces of the hollow spheres' shells prepared with 1-dodeclyamine were analyzed from the results of thermogravimetric analysis (TGA) and differential thermal analysis (DTA), and endothermic peaks assigned as the phase transition and decomposition were observed at ca. 440 and 514 K, respectively, which were higher than those of pristine urea (405 and 408 K, respectively), probably because of the nanoconfinement effect. The decomposition behavior was also confirmed by the result of diffuse reflectance infrared Fourier transform (DRIFT) spectra of the samples treated at various temperatures up to 573 K, and the decomposition of urea synthesized in the well-ordered nanospaces of the hollow spheres' shells started at 468 K and completed up to 533 K.

Conversion of Recovered Ammonia and Carbon Dioxide into Urea in the Presence of Catalytically Active Copper Species in Nanospaces of Porous Silica Hollow Spheres.

The present study firstly reported porous silica hollow spheres as a host material for recovery of ammonia and carbon dioxide and conversion of the compounds into urea. These compounds were effectively introduced into the hollow spheres from an aqueous solution including ammonium and carbonate ions accompanied with catalytically active copper ions from the analyses of diffuse reflectance infrared Fourier transform (DRIFT) spectra and diffusion reflectance ultraviolet-visible and near-infrared (DR UV-vis-NIR) spectra. The ammonium and carbonate ions were converted into urea in the hollow spheres at 323 K under 0.5 MPa of argon atmosphere from the results of the DRIFT spectra. From the results of nitrogen sorption isotherms and X-ray photoelectron spectra (XPS) spectra, the amount of the generated urea depended on the amount of the introduced ammonium ions and the size distribution of the nanospaces in the hollow spheres. Urea was highly generated in the hollow spheres with a high amount of ammonium ions and well-ordered nanospaces from the reactants at high density.

Influence of the Water/Titanium Alkoxide Ratio on the Morphology and Catalytic Activity of Titania-Nickel Composite Particles for the Hydrolysis of Ammonia Borane.

This work reports the influence of the water/titanium alkoxide ratio during the preparation of titania-nickel composite particles on their morphology and catalytic activity toward the hydrolysis of ammonia borane. The titania-nickel composite particle catalysts were fabricated by using a sol-gel method, followed by an activation process in aqueous solution containing sodium borohydride and ammonia borane. From the scanning electron microscopy images and pore-size distributions calculated from nitrogen sorption data, the particle dispersion was significantly enhanced at ratios above 6000, and increased with increasing water/titanium alkoxide ratio. Stoichiometric amounts of hydrogen were evolved in the presence of all of the prepared titania-nickel composite particle catalysts. The particle dispersion influenced the hydrogen evolution rate from aqueous ammonia borane solution, and the samples with the most highly dispersed particles showed the highest hydrogen evolution rate. The most active catalyst showed an apparent activation energy comparable to that of other reported catalysts and high cycle ability for the hydrolysis of ammonia borane.

Development of Plasmonic Cu2O/Cu Composite Arrays as Visible- and Near-Infrared-Light-Driven Plasmonic Photocatalysts.

We describe efficient visible- and near-infrared (vis/NIR) light-driven photocatalytic properties of hybrids of Cu2O and plasmonic Cu arrays. The Cu2O/Cu arrays were prepared simply by allowing a Cu half-shell array to stand in an oxygen atmosphere for 3 h, which was prepared by depositing Cu on two-dimensional colloidal crystals with a diameter of 543 or 224 nm. The localized surface plasmon resonances (LSPRs) of the arrays were strongly excited at 866 and 626 nm, respectively, at which the imaginary part of the dielectric function of Cu is small. The rate of photodegradation of methyl orange was 27 and 84 times faster, respectively, than that with a Cu2O/nonplasmonic Cu plate. The photocatalytic activity was demonstrated to be dominated by Cu LSPR excitation. These results showed that the inexpensive Cu2O/Cu arrays can be excellent vis/NIR-light-driven photocatalysts based on the efficient excitation of Cu LSPR.

Porous Materials for Hydrolytic Dehydrogenation of Ammonia Borane.

Hydrogen storage is still one of the most significant issues hindering the development of a "hydrogen energy economy". Ammonia borane is notable for its high hydrogen densities. For the material, one of the main challenges is to release efficiently the maximum amount of the stored hydrogen. Hydrolysis reaction is a promising process by which hydrogen can be easily generated from this compound. High purity hydrogen from this compound can be evolved in the presence of solid acid or metal based catalyst. The reaction performance depends on the morphology and/or structure of these materials. In this review, we survey the research on nanostructured materials, especially porous materials for hydrogen generation from hydrolysis of ammonia borane.

Effect of Oxide Coating on Performance of Copper-Zinc Oxide-Based Catalyst for Methanol Synthesis via Hydrogenation of Carbon Dioxide.

The effect of oxide coating on the activity of a copper-zinc oxide-based catalyst for methanol synthesis via the hydrogenation of carbon dioxide was investigated. A commercial catalyst was coated with various oxides by a sol-gel method. The influence of the types of promoters used in the sol-gel reaction was investigated. Temperature-programmed reduction-thermogravimetric analysis revealed that the reduction peak assigned to the copper species in the oxide-coated catalysts prepared using ammonia shifts to lower temperatures than that of the pristine catalyst; in contrast, the reduction peak shifts to higher temperatures for the catalysts prepared using L(+)-arginine. These observations indicated that the copper species were weakly bonded with the oxide and were easily reduced by using ammonia. The catalysts prepared using ammonia show higher CO2 conversion than the catalysts prepared using L(+)-arginine. Among the catalysts prepared using ammonia, the silica-coated catalyst displayed a high activity at high temperatures, while the zirconia-coated catalyst and titania-coated catalyst had high activity at low temperatures. At high temperature the conversion over the silica-coated catalyst does not significantly change with reaction temperature, while the conversion over the zirconia-coated catalyst and titania-coated catalyst decreases with reaction time. From the results of FTIR, the durability depends on hydrophilicity of the oxides.

Bimetallic Au-Ni nanoparticles embedded in SiO2 nanospheres: synergetic catalysis in hydrolytic dehydrogenation of ammonia borane.

Gold-nickel nanoparticles (NPs) of 3-4 nm diameter embedded in silica nanospheres of around 15 nm have been prepared by using [Au(en)(2)Cl(3)] and [Ni(NH(3))(6)Cl(2)] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH(4)/NH(3)BH(3). Compared with monometallic Au@SiO(2) and Ni@SiO(2), the as-synthesized Au-Ni@SiO(2) catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H(2), the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs.