Various porous materials with unique functions can be obtained through sol-gel synthesis. In many cases the performance of such materials can be significantly improved by controlling the morphology of them. Recently, we found that sol-gel derived materials can be molded into the form of monolithic microhoneycombs by freezing their parent hydrogel unidirectionally. In this process, the ice crystals which are formed within the hydrogel during freezing act as the template. The sizes of the monolith channels, the traces of the ice crystals, are in the micrometer range, therefore can be considered as macropores. The walls which form the channels have thicknesses around 1 μm, and have developed nanopores within them. Therefore, such monoliths are equipped with a unique hierarchical pore system in which short nanopores are directly connected to straight macropores. Due to this unique structure, such monoliths do not cause severe pressure drops when fluids are passed through them, even though the lengths of the diffusion paths within them are extremely short. This method can be applied to various hydrogels, either organic or inorganic, therefore monoliths having a wide variety of functions along with this unique structure can be easily obtained. This method can also be used to assemble fine particles into the form of a monolithic microhoneycomb by using a proper hydrogel as the binder.
Evaporation of fuel gas from the fuel tank of a gasoline vehicle into the atmosphere is strictly controlled by regulations because the gas includes materials highly toxic to human health. Therefore, vehicles are equipped with an evaporative loss control device, of which one of the major parts is a carbon canister filled with activated carbon. Evaporation of fuel gas into the air can be prevented by adsorption/retention in the activated carbon during parking and by desorption/combustion during driving. This paper presents the use of Computational Fluid Dynamics (CFD) for the numerical evaluation of n-butane adsorption, desorption, and diffusion in the carbon canister. Such transient phenomena require huge calculation times even using high-end computing resources. Therefore, a unique method was used for the solution of some equations, allowing convergence in very short time. These equations demonstrated good correlation between experiments and simulation of breakthrough performance of the carbon canister.
Non-thermal plasma assisted methane reforming is reviewed. Plasma catalysis is one of the innovative next generation green technologies that may meet the needs for energy and materials conservation as well as environmental protection. Non-thermal plasma uniquely generates reactive species independently of reaction temperature, and these species are used to initiate chemical reactions at unexpectedly lower temperatures than normal thermochemical reactions. Non-thermal plasma thus broadens the operation window of existing chemical conversion processes, and ultimately allows modification of the process parameters to minimize energy and material consumption. The general aspects of plasma assisted fuel reforming including arc plasma to non-thermal plasma are described. We specifically focus on dielectric barrier discharge (DBD) as one of the viable non-thermal plasma sources for practical fuel reforming. Two contrasting approaches of DBD-oriented plasma catalysis of methane are introduced: (1) Low temperature (300-500°C) methane steam reforming using a plasma-catalyst hybrid reactor, and (2) Room temperature direct methane conversion to methanol using a microplasma reactor. The practical background and unique characteristics of each application such as the plasma-catalyst synergistic effect and highly non-equilibrium product distribution are explained.
Physical and chemical properties of supercritical water were investigated by first principles molecular dynamics (FPMD). Hydrogen bonds are present in supercritical water, but do not form a network, resulting in formation of various sizes of clusters. FPMD confirmed that Beckmann rearrangement reaction of cyclohexanone oxime to ε-caprolactam occurs via a hydronium ion in the supercritical water at 670 K and 0.7 g/cm3, not due to the high temperature but to the low density. The hydronium ion is not completely solvated by three water molecules because of the low density of the supercritical water, resulting in high reactivity. No Beckmann rearrangement reaction takes place even at 670 K and normal water density of 1 g/cm3, since the hydronium ion is stabilized by complete solvation.
Dye-sensitized solar cells (DSCs) are photoelectrochemical cells consisting of mesoporous TiO2 electrodes sensitized with organic dyes such as ruthenium dyes, Pt counter-electrodes, and I−/I3− redox electrolytes. Increasing the durability and power conversion efficiency of DSCs are critical goals that will have to be met before DSCs can be put on the market on a large scale. For increasing durability, we have developed new gel-type polymeric solid electrolytes (PSEs) based on poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) to reduce leakage of the electrolyte solution, which is one of the main factors of poor DSC durability. The use of PSEs, however, is almost always accompanied by a decrease in the short-circuit current density (Jsc). We then studied the electrochemical properties of two different kinds of DSCs to determine why the conversion efficiency is lower in PSE-based DSCs than in liquid electrolyte-based DSCs. The diffusion coefficient of I3− and the cell-gap (the distance between the surface of the transparent conducting oxide substrate for the TiO2 electrode and that of the Pt counter-electrode) of DSCs were eventually understood to be key factors affecting the Jsc. This indicates that the design of the DSC structure is quite important for achieving higher conversion efficiency in a PSE-based DSC. Further, with the aim of increasing the power conversion efficiency, we have developed ultrahigh-aspect-ratio TiO2 nanotubes (TNTs), made by anodic oxidation of Ti metals in an extremely dilute perchloric acid solution, to establish good carrier pathways. Unlike TiO2 nanoparticles (NPs), TNTs of suitable dimensions serve as efficient light scatterers while also providing large surface areas for charge separation. We have succeeded in enhancing the power conversion efficiency of a DSC using a TiO2 electrode with a new bilayer structure, which consists of a light-scattering TNT layer formed upon a light-absorbing NP layer. We also found a promising application for TNTs formed on Ti substrates, i.e. their use in the fabrication of flexible, back-side illuminated DSCs. In this review we present our recent research on DSCs fabricated with PVDF-HFP-type PSEs and ultrahigh-aspect-ratio TNTs.
Nanoporous (np; 5-50 nm in pore diameter) Al2O3 was investigated as a matrix for a fluid catalytic cracking (FCC) catalyst as either a binder or a catalytic site using model compounds as feedstock to achieve not only high activity, but also less coking. The binder characteristics of np Al2O3 matrix were expected to increase the mechanical strength and hydrothermal resistance of the catalyst, because np Al2O3 from unimodal and non-aggregated boehmite sols has better mechanical strength than np Al2O3 from aggregated boehmite gels and can protect the zeolite component from hydrothermal degradation during catalyst regeneration more than np SiO2. Application of np Al2O3 with controlled crystallite and pore sizes as an active matrix for catalytic cracking resulted in less coking, which indicated that np Al2O3 has an important role as a pre-cracking agent. A np Al2O3 matrix with a pore size diameter of ca. 11-15 nm was found to be optimum for a catalytic cracking catalyst.
Amorphous silica–aluminas were prepared by the sol-gel method using carboxylic acids, malic acid (MA), succinic acid and citric acid, and the reactivity for catalytic cracking was investigated. When the ratio of MA/TEOS (tetraethoxysilane) increased, surface area, pore volume and pore diameter increased and mesopores were formed. The maximum total conversions of n-dodecane were around 30% with the single amorphous silica–alumina. In contrast, the total conversion reached 91% with the single beta-zeolite. To investigate the reactivity of amorphous silica–alumina as a matrix, mixed catalysts consisting of zeolite, amorphous silica–alumina and binder (alumina sol) were prepared. The product distribution changed compared with the single zeolite or silica–alumina, and comparable activity to that of zeolite was obtained although the mixed catalysts included only 1/4 of zeolite. Mixed catalysts using amorphous silica–alumina with mesopores (MA122-5) exhibited higher ratio of multi-branched to single-branched products in the gasoline fraction (C5-C11) than single zeolite. The effect of the addition of 1-dodecene and 1-methylnaphthalene was also investigated.
This research has been conducted to investigate the impact of chemical properties of gasoline on engine-out emissions, especially for the emissions of nitrogen oxides (NOx), through engine experiments using fifteen types of gasoline (model fuels) and the engine combustion analysis. Numerical simulations have also been conducted on the formation of nitrogen monoxide (NO) using the extended Zeldovich mechanism for a detailed analysis of the impacts of fuel properties on emissions, which including the analysis performed from the fundamental viewpoint of the formation mechanism of NO. The research reveals that concentrations of engine-out NOx emissions significantly vary by the type of fuels, which can be organized by two parameters: a parameter represented by adiabatic flame temperature and a parameter indicating the 50% combustion point which is determined from the experiment results. And the results of the numerical simulations indicate that these parameters are determined to represent the factor of thermodynamic characteristics of fuels and that of the changes in combustion duration caused by fuels, respectively, so that the numerical simulations serve to support the validity of the experiment results.
For the sustainable development of our society, much attention has been paid to biorefinery, where renewable lignocellulosic biomass is converted valuable chemicals and/or fuels. Alkakaline pretreatment before the enzymatic saccharification of the lignocellulosic biomass has been examined for a long time but further improvement is required to obtain a high yield of sugars. We have tried to improve the sugar yield using two different type lignocelluloses such as herbaceous napiergrass leaves and woody kudzu stalks. The trials to improve the sugar yields from the alkaline pretreated these lignocelluloses have been examined by supplementary subjecting to visible light illumination in the presence of Si. The yield of reducing sugars from herbaceous napiergrass leaves was improved from 60.3 to 86.7% by using the complemental illumination with Si after the enzymatic saccharification for 24 h. In the case of kudzu stalks, that was improved from 57.4 to 88.6% with the same treatment.
Ethanol production from lignocellulosic biomass requires pretreatment methods to increase the efficiency of enzymatic saccharification and so establish the whole process as economically viable. Hydrothermal and/or wet disk milling is a mechanochemical process that operates under wet conditions, so the process water might increase the energy consumption of the distillation process. Application of a dehydration process to the mechanochemical pretreatment process of the bioethanol production system has been proposed for process energy saving and cost reduction. However, the dehydration process has problems with the loss of sugars eluted in the liquid phase during the hydrothermal process. This study describes the incorporation of a dehydration process into the mechanochemical pretreatment of the bioethanol production system. Introduction of the dehydration process resulted in 9-17% reduction of production cost and 43-57% reduction of process energy.
The upgrading of a fast pyrolysis bio-oil was studied with different catalysts in a small batch reactor. The catalysts were reduced Ni/SiO2, Co/SiO2, Pt/SiO2, Pd/SiO2 and sulfided CoMo/Al2O3 catalysts. The experiments were carried out at H2 pressure 1-5 MPa, and temperature range of 300-350°C. Reduced Co/SiO2 catalyst showed the highest activity and highest aromatics selectivity for deoxygenation of guaiacol because this catalyst showed high activity for direct deoxygenation (DDO) of phenol giving mostly benzene.