For wider social implementation of hydrogen energy, efficient hydrogen storage persists as a key issue. Although lithium hydride has quite a high class of hydrogen storage capacity (12.7 wt%), its practical application is hindered by high-temperature conditions (>900 °C) for hydrogen release. A major reason that high temperatures are necessary for hydrogen release from this material is that the formation of metallic lithium by transferring an electron from hydride (H−) to lithium cation (Li+) is thermodynamically unfavorable. Several reports have described that hydrogen release temperatures can be decreased using additives which might avoid metallic lithium formation. Those works inspired us to develop strategies to find suitable additives for facile hydrogen release from lithium hydride. These strategies are illustrated herein. Successful examples employing carbonaceous materials of graphite and fullerene as well as conjugated hydrocarbon macromolecules as additives are described with detailed hydrogen storage and release properties and reaction mechanisms.
Titania (TiO2) is widely investigated in relation to the environmental remediation and the production of clean energy resources. In the design of TiO2-based powder and thin film type of photocatalysts, surface modification, utilization of nanospace, and control of chemical composition, shape and structure at the nanoscale lead to improve the photocatalytic performance with additional functions. Unique activity and functionality is enable to be realized by these techniques, which is different from conventional systems. This review article mainly describes our recent research results on the design of TiO2-based powder and thin film photocatalysts. The advanced functions of inorganic-organic hybrid TiO2-based photocatalyst, composite photocatalyst of meso- and macroporous silica and TiO2, and TiO2-based thin film photocatalyst for surface coatings of materials are briefly summarized.
Development of heterogeneous catalysts which can achieve both high activity and high selectivity requires establishment of sophisticated and uniform active sites on the surface of solid materials, but formation of uniform active sites is difficult in heterogeneous catalysts because of the nonuniformity of heterogeneous catalysts. Selective hydrogenation of the carbonyl group of unsaturated carbonyl compounds is particularly difficult because hydrogenation of the olefin group is thermodynamically and kinetically preferable to that of the carbonyl groups. Therefore, various heterogeneous catalyst systems have been developed to achieve high selectivity. Recently developed effective heterogeneous catalysts for the selective hydrogenation of unsaturated carbonyl compounds such as unsaturated aldehydes and unsaturated ketones to the corresponding unsaturated alcohols using H2 as a reducing agent are reviewed. Model reactions include liquid-phase selective hydrogenation of crotonaldehyde and liquid-phase selective hydrogenation of benzylideneacetone using a batch reactor, and gas-phase selective hydrogenation of crotonaldehyde with a fixed-bed reactor. Particularly, this review mainly covers metal oxide- or metal cation-modified noble metal catalysts.
Hydrogen production by photocatalytic water splitting under sunlight is one of the most promising approaches to addressing present day energy and environmental issues. For this reason, the research and development of systems for this purpose has recently accelerated on a worldwide basis. This review summarizes developments in the field of photocatalytic water splitting under visible light, especially systems using particulate photocatalysts. Focusing on visible-light-responsive photocatalyst materials, both one-step and two-step excitation systems are examined, as well as recently reported photocatalyst sheet systems in which particulate photocatalysts are fixed on a conductive plate. Some topics related to reactor designs incorporating UV-responsive model photocatalysts are also addressed. Finally, this review describes a demonstration of water splitting under actual sunlight using a 1 m × 1 m prototype reactor that exhibits a solar to hydrogen conversion efficiency of approximately 0.4 %.
Emulsion flooding is a promising technique for enhanced recovery of the residual oil that cannot be recovered through waterflooding processes. Visual micromodels are powerful tools for examining the mechanisms of oil recovery from porous media at the pore level. A glass micromodel was used to investigate the effects of polymer and different industrial nanomaterials on emulsion viscosity, stability and recovery factor of crude oil. The used micromodel has uniform pore throats and grains. Experiments showed that injection of nanoparticle-stabilized water-in-oil emulsions is an effective enhanced oil recovery method. Ultimate oil recovery was greater using nanoparticle-stabilized emulsion/water than water/nanoparticle-stabilized emulsion/water, and the efficiency of nanoparticle-stabilized emulsion/polymer/water also achieved greater recovery. Image analysis showed that the ultimate recovery factor was increased from 33.99 % using water flooding to 63.28 % using nanoparticle-stabilized emulsion/polymer/water flooding. The results of this study are helpful for the mechanistic understanding of enhanced oil recovery projects.
Heavy fuel oils usually have high sulfur content and most of the sulfur compounds have bulky thiophenic structures which resist desulfurization. Oxidation of these sulfur compounds to sulfones weakens the C–S bonds and sulfur can be removed as SO2 by thermolysis. This study investigated oxidative desulfurization of heavy vacuum gas oil (2.81 wt% S). Oxidation was achieved with hydrogen peroxide and formic acid. Then, the oxidized feed underwent thermolysis at 355-410 °C for 0.5-3 h to identify the maximum desulfurization with minimum feed conversion to light products. The effects of parameters such as time and temperature were studied. Temperature had significant effects in comparison to other parameters. Desulfurization of 65 % with 6 wt% conversion of feedstock to light products was achieved under the optimum conditions.