Gas Adsorption on Graphite Surfaces

In this review, the adsorption of non-polar and polar molecules on highly graphitized carbon black (GCB) which has a very homogeneous flat carbon surface is introduced along with the adsorption isotherms and the isosteric heats. There are two different adsorption mechanisms; (1) molecular layering adsorption on carbon surface, and (2) molecular clustering on very strong sites such as functional groups whose affinity is much greater than that of the carbon surface. Since the difference between the mechanisms give the difference to the uptake of isotherms and the isosteric heats, each example of gas adsorption is shown and the details of the mechanisms are explained. For simple gases, e.g. argon, nitrogen, and krypton adsorption proceeds by molecular layering on the carbon surface. Particularly, in adsorption at temperatures below the bulk triple point, the stepwise adsorption isotherm, type VI according to IUPAC classification, is observed due to the layering adsorption mechanism. On the other hands, for polar gas especially water molecules adsorb by clustering on the functional groups of GCB due to the hydrogen bonding, but do not adsorb on the carbon surface. The polar molecules weaker in polarity than water, e.g. methanol, and ammonia, adsorb by both layering and clustering mechanisms on GCB (called spill-over phenomenon)

ディップコーティングホウ ニヨル カシコウ オウトウ ヒカリショクバイ ハクマク ノ ソウセイ ト ソノ ヒカリブンカイ トクセイ ヒョウカ

The visible light responsive TiO2 thin film photocatalysts were prepared by applying a dip-coating process, for which the coating solution was prepared using titanium tetraisopropoxide as a source material and different organic solvents. The nitrogen was doped to the obtained TiO2 thin film during the calcination process as an agent for visible light response. The surface morphology was analyzed by AFM and FE-SEM. Nitrogen state in the lattice and crystalline stricture were measured by XPS and XRD, respectively. Photocatalytic decomposition activity of methylene blue on the films was also measured under visible light irradiation using the light emitting diodes

Temperature dependence of water cluster on functionalized graphite

Our recent experimental study of water adsorption in micro-mesoporous carbons at 263 K and 298 K show an unusual temperature dependence of adsorbed density with higher loading at 298 K at the same reduced pressure. The difference is in the filling of mesopore at 298 K and its absence at 263 K, and it was conjectured to the growth of water clusters on the functional groups in the confined space of mesopores in which the water clusters at 298 K are sufficiently large to induce the subsequent filling. Since the growth of these clusters and their coalescence is the prerequisite for filling, the filling is absent at 263 K simply because of the smaller size of the clusters, preventing them from coalescence and hence, no filling. In a quest to understand the effects of temperature on water adsorption in micro-mesoporous carbon, we used molecular dynamic simulation to reveal the mechanism of water adsorption around functional groups from 263 K to 328 K to clarify the growth of the water cluster as a function of temperature. The results clearly show that the water cluster is larger at 298 K compared to 263 K, confirming the conjecture from our previous works

Hydrogen Permeability of Palladium Membrane for Steam-Reforming of Bio-Ethanol

A Palladium membrane was prepared by electro-less plating method on porous stainless steel. The catalytic hydrogen production by steam-reforming of biomass-derived ethanol (bio-ethanol) using a Pd membrane was analyzed by comparing it with those for the reaction using reagent ethanol (the reference sample). And the hydrogen permeability of the palladium membrane was investigated using the same palladium membrane (H2/He selectivity = 249, at ΔP = 0.10 MPa, 873 K). As a result, for bio-ethanol, deposited carbon had a negative influence on the hydrogen-permeability of the palladium membrane and hydrogen purity. The sulfur content in the bio-ethanol may have promoted carbon deposition. By using a palladium membrane, it was confirmed that H2 yield (%) was increased. It can be attributed that methane was converted from ethanol and produced more hydrogen by steam reforming, due to the in situ removal of hydrogen from the reaction location

IR SPECTROSCOPIC ANALYSIS OF THERMAL BEHAVIOR OF ADSORBED WATER ON Y-TYPE ZEOLITE

In this study, we measured the IR spectra of water adsorbed at a differential temperature under constant pressure. Our purpose is to present a simple estimation method for the recycled temperature condition of water adsorbents. For a NaY zeolite, the IR integrated intensity of the bending vibration band of adsorbed water was increased with a decrease of temperature. The IR spectra were measured from 230℃ to 30℃ for several ion-exchanged Y-type zeolites. On the other hand, the adsorption isotherms of water on these zeolites were measured at 30℃. The result of this work is that the best correlation between the IR integrated intensity and the amount of adsorbed water was found for some of the zeolites. We concluded that the obtained correlation equation could easily estimate the amount of water desorbed between arbitrary temperatures

On the resolution of constant isosteric heat of propylene adsorptionon graphite in the sub-monolayer coverage region

An early experimental study by Bezus, Dreving and Kiselev [1] on the adsorption of propylene on Spheron-6 carbon black (graphitized at ∼3000C) reported a plot of constant isosteric heat versus loading in the sub-monolayer region. This contrasts with their report of a linear increase in isosteric heat for propane, a similar molecule to propylene. In this paper, we report extensive Grand Canonical Monte Carlo (GCMC) simulations and a high-resolution experimental study of propylene adsorption on Carbopack F, a highly graphitized thermal carbon black, over the same temperature range studied by Bezus et al. From this combined simulation and experimental study we conclude that propylene also shows a linear increase in the isosteric heat versus loading in the sub-monolayer region, indicating that the linear increase in the fluid-fluid interaction in this region more than compensates for the decrease in the solid-fluid interaction that results from the change in orientation of the adsorbate molecules. Our study contradicts the propylene results of Bezus et al., and careful inspection of their isotherm in the sub-monolayer region shows that it does not follow Henry’s law. This calls into question their argument that π-π interactions between propylene molecules are an explanation for the constant heat

Scanning curves of water adsorption on graphitized thermal carbon black and ordered mesoporous carbon

Adsorption isotherms of water on porous carbons generally show large hysteresis loops whose origin is believed to be different from simple gases adsorption in mesoporous solids. In this paper, we discussed in details the behavior of water adsorption isotherms and their descending scanning curves for two carbons of different topologies, a highly graphitized thermal carbon black, Carbopack F, and a highly ordered mesoporous carbon, Hex. For both solids, very large hysteresis loops are observed, but their behaviors are different. For Carbopack F, the loop extends over a very wide range of pressure and the loop is larger when the descending is started from a higher loading; while for Hex, the hysteresis loop shows distinct steps, the number of which depends on the loading where the descending starts. By carefully analyzing the scanning curves from different loadings, we established the mechanism of water adsorption in Hex as a sequence of three steps: (1) water molecules adsorb on functional groups located at the junctions between adjacent basal planes of graphene layers, (2) growth of water clusters around the functional groups, and (3) bridging of adjacent clusters to form larger clusters, followed by a complete filling of mesopores

A GCMC simulation and experimental study of krypton adsorption/desorption hysteresis on a graphite surface

Adsorption isotherms and isosteric heats of krypton on a highly graphitized carbon black, Carbopack F, have been studied with a combination of Monte Carlo simulation and high-resolution experiments at 77 K and 87 K. Our investigation sheds light on the microscopic origin of the experimentally observed, horizontal hysteresis loop in the first layer, and the vertical hysteresis-loop in the second layer, and is found to be in agreement with our recent Monte Carlo simulation study (Diao et al., 2015). From detailed analysis of the adsorption isotherm, the latter is attributed to the compression of an imperfect solid-like state in the first layer, to form a hexagonally packed, solid-like state, immediately following the first order condensation of the second layer. To ensure that capillary condensation in the confined spaces between microcrystallites of Carbopack F does not interfere with these hysteresis loops, we carried out simulations of krypton adsorption in the confined space of a wedge-shaped pore that mimics the interstices between particles. These simulations show that, up to the third layer, any such interference is negligible

On the resolution of constant isosteric heat of propylene adsorption on graphite in the sub-monolayer coverage region

An early experimental study by Bezus, Dreving and Kiselev [1] on the adsorption of propylene on Spheron-6 carbon black (graphitized at ∼3000C) reported a plot of constant isosteric heat versus loading in the sub-monolayer region. This contrasts with their report of a linear increase in isosteric heat for propane, a similar molecule to propylene. In this paper, we report extensive Grand Canonical Monte Carlo (GCMC) simulations and a high-resolution experimental study of propylene adsorption on Carbopack F, a highly graphitized thermal carbon black, over the same temperature range studied by Bezus et al. From this combined simulation and experimental study we conclude that propylene also shows a linear increase in the isosteric heat versus loading in the sub-monolayer region, indicating that the linear increase in the fluid-fluid interaction in this region more than compensates for the decrease in the solid-fluid interaction that results from the change in orientation of the adsorbate molecules. Our study contradicts the propylene results of Bezus et al., and careful inspection of their isotherm in the sub-monolayer region shows that it does not follow Henry's law. This calls into question their argument that π-π interactions between propylene molecules are an explanation for the constant heat

Application of Si/SiC ceramic filters as support for structural palladium catalysts for the reductive decomposition of aqueous nitrite

A Si/SiC ceramic filter was used to support a structural palladium catalyst in a continuous fixed-bed flow reactor during a reductive decomposition of nitrite. A previous report described the use of non-porous alumina spheres coated with Pd/C, a carbon monolith impregnated with Pd or a structural catalyst consisting of a polyurethane sponge skeleton impregnated with Pd resulted either in negligible activity or a complete stoppage of the flow by increasing the pressure drop in the flow system. The use of a Si/SiC filter impregnated with palladium, however, overcame the demerits and resulted in an 11% conversion of nitrite in 60 min. The use of a Si/SiC filter coated with a char intermediate followed by impregnation with Pd (Pd/C/Si/SiC) resulted in a structural catalyst that enhanced the activity to yield a 33% conversion of nitrite in 60 min. When five Pd/C/Si/SiC structural catalysts were used, however, the complete decomposition was achieved in the same amount of time. Although improvement was previously observed by using an alumina intermediate, use of the char intermediate resulted in a new factor for activity improvement. The characterization results show that it was the affinity between aqueous nitrite and the intermediate rather than palladium dispersion that contributed the most to the improvement of activity