• Journal of the Korean Wood Science and Technology
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• v.37 no.4
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• pp.372-380
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• 2009

After supercritical water treatment of poplar wood meals (passed through 60 mesh) for 60s between 325 and $425^{\circ}C$ at the fixed pressure at $220{\pm}10atm$, some solid residues were present in the degradation products. They mainly consisted of chemically modified lignin and fibrous materials. Glucose and xylose were identified as main sugar components of fibrous materials, and the highest ratio of glucose/xylose was achieved at the highest reaction temperature. As reaction temperature was elevated, the portion of fibrous materials decreased in the solid residues, while lignin was further accumulated. The H : G : S ratio of lignin in solid residues was estimated by analytical pyrolysis. Irrespective of reaction temperatures, the H:G:S ratios were not significantly changed in the lignin in solid residues. Compared to poplar milled wood lignin (MWL), it was remarkable that H type monomers were further lowered, while portion of S type monomers increased. The amount of G type monomers were relative stable. In presence of HCl catalyst, lowering H type as well as enhancing S type was further distinguishable. According to the result of nitrobenzene oxidation (NBO), ca. 265 mg of vanillin and syringaldehyde was yielded from poplar MWL as main products. However, remarkably reduced amount of NBO products were determined from solid residues by raising operating temperature as well as by the addition of HCl catalyst. These results strongly indicate that $\beta$-O-4 linkage could be easily cleaved during supercritical water treatment, so that the lignins in the solid residues seem to be condensed phenol polymers, which are mainly formed by carbon-carbon linkages rather than $\beta$-O-4 linkage.

• Korean Journal of Materials Research
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• v.10 no.11
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• pp.778-783
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• 2000

Effects of the $Al_2$O$_3$surface protective layer, deposited on the SnO$_2$sensing layer by aerosol flame deposition (AFD) method, on the sensing properties of SnO$_2$thin film ags sensors were investigated.Effects of Pt doping to the $Al_2$O$_3$surface protective layer on the selectivity of CH$_4$ gas were also investigated. 0.3$\mu\textrm{m}$ thick SnO$_2$thin sensing layers on Pt electrodes were prepared by R.F. magnetron sputtering with R.F. power of 50 W, at working pressure of 4mTorr, and at 20$0^{\circ}C$ for 30 min. $Al_2$O$_3$surface protective layers on SnO$_2$layers were prepared by AFD using a diluted aluminum nitrade (Al(NO$_3$).9$H_2O$) solution. The sensitivity of CO gas in the SnO$_2$gas sensor with an $Al_2$O$_3$surface protective layer was significantly decreased. But that of CH$_4$gas remained almost same with pure SnO$_2$gas sensor. This result shows that the selectivity of CH$_4$gas is increased because of the $Al_2$O$_3$surface protective layer. In the case of SnO$_2$gas sensors with Pt-doped $Al_2$O$_3$surface protective layers, low sensing property to CO gas and high sensing property to CH$_4$were observed. This results in the increasing of selectivity of CH$_4$gas selectivity are discussed.

• Clean Technology
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• v.29 no.2
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• pp.126-134
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• 2023

Direct catalytic decomposition is a promising method for controlling the emission of nitrous oxide (N₂O) from the semiconductor and display industries. In this study, a γ-Al₂O₃ catalyst was developed to reduce N₂O emissions by a catalytic decomposition reaction. The γ-Al₂O₃ catalyst was prepared by an extrusion method using boehmite powder, and a N₂O decomposition test was performed using a catalyst reactor that was approximately 25.4 mm (1 in) in diameter packed with approximately 5 mm of catalysts. The N₂O decomposition tests were carried out with approximately 1% N₂O at 550 to 750 ℃, an ambient pressure, and a GHSV=1800-2000 h^-1. To confirm the N₂O decomposition properties and the effect of O₂ and steam on the N₂O decomposition, nitrogen, air, and air and steam were used as atmospheric gases. The catalytic decomposition tests showed that the 1% N₂O had almost completely disappeared at 700 ℃ in an N₂ atmosphere. However, air and steam decreased the conversion rate drastically. The long term stability test carried out under an N₂ atmosphere at 700 ℃ for 350 h showed that the N₂O conversion rate remained very stable, confirming no catalytic activity changes. From the results of the N₂O decomposition tests and long-term stability test, it is expected that the prepared γ-Al₂O₃ catalyst can be used to reduce N₂O emissions from several industries including the semiconductor, display, and nitric acid manufacturing industry.