Browsing by Subject "Impregnation"

Now showing 1 - 4 of 4

Open Access
Conversion of wooden structures into porous SiC with shape memory synthesis
(2011) Dhiman, R.; Petrunin V.; Rana, K.; Morgen P.
Synthesis of structured silicon carbide materials can be accomplished using wooden materials as the carbon source, with various silicon impregnation techniques. We have explored the low cost synthesis of SiC by impregnation of carbon from wood with SiO gas at high temperatures, which largely retains the structure of the starting wood (shape memory synthesis). Suitably structured, porous SiC could prove to be an important type of catalyst support material. Shape memory synthesis (SMS) has earlier been tried on high surface area carbon materials. Here we have made an extensive study of SMS on carbon structures obtained from different types of wood. © 2011 Elsevier Ltd and Techna Group S.r.l.
Open Access
Identification, stability and reactivity of NOx adsorbed species on titania-supported manganese catalysts
(2001) Küçükkal, Mustafa U.
The needs of improved fuel economy, and lower emission of green-house gases such as CO2, is projected to increase the demand for diesel engines through the world. These engines operate at air/fuel ratio higher than stoichiometric (lean-burn conditions). This results in relatively low hydrocarbon/NOx ratio in the exhaust and an additional amount of reductant (typically about 2-3% of additional fuel) should be fed upstream of de-NOx catalyst. For this reason, it is important to study the interaction of NOx species produced upon adsorption of NO/O2 mixtures on the catalyst surface with long chain saturate hydrocarbons, which are typical for diesel fuel.In recent years many de-NOx lean-burn catalysts have been proposed among which supported metal oxides have been taken in consideration for their potential thermal stability and large composition variability. Subjects of this study are titania (anatase)-supported manganese catalysts, prepared by impregnation and ion-exchange from aqueous solutions of Mn2+ ions. TiO2 (anatase) is stable in SO2 containing atmosphere, typical for the exhaust gases in diesel engines. The identification of the NOx species formed during the adsorption of NO, NO/O2 mixtures and NO2 is performed by in situ FTIR Spectroscopy. the thermal stability and reactivity of the surface NOx forms towards n-decane is followed by application of the same technique. It is established that adsorption of NO on the support and manganese-containing catalysts is reactive and leads to linearly adsorbed NO and formation of anionic nitrosyl, NO− and NO3 − species. Contrary to the impregnated catalyst, the ion-exchanged catalyst does not contain NO− species coordinated to Ti4+ ions. This experimental fact is in agreement with the high dispersion of Mn3+ ions concluded from the CO adsorption experiments.The NO/O2 co-adsorption on the anatase and catalysts studied results in formation of NO3 − species differing in the mode of their coordination. Under these conditions no NO− species are detected. The surface nitrates formed on the manganesecontaining catalysts possess lower thermal stability than those on the pure support. This difference explains the higher reactivity of the former toward the n-decane. The nitrates formed upon NO/O2 co-adsorption on the manganese-containing catalysts are able to activate and oxidize the hydrocarbon at temperatures as low as 373 K. The latter process gives rise to adsorbed CO2, formic acid and isocyanate species. The NCO species is considered as an important intermediate in the formation of nitrogen. The extent of oxidation of n-decane is higher on the ion-exchanged catalyst. It is concluded that this catalyst can be promising in the selective catalytic reduction of NO by longer-chain saturated hydrocarbons.
Open Access
Synthesis and characterisation of mesoporous transition metal ion modified silica-zirconia and silica-sulfated zirconia materials towards NOx catalysis
(2006) Samarskaya, Olga
The purpose of this work is to design and investigate mesostructured material as a potential support for the reaction of the methane with surface NOx species. Several objectives have been pursued in achievement of the goals. The first objective is to develop a facile procedure for the synthesis of mesoporous silica-zirconia mixed oxide supports that are modified with the sulphate (SO4 2-), cobalt (Co2+) and palladium (Pd2+) ions. The support with requisite catalytic properties was obtained through the adjustment of the synthetic steps and optimisation of the composition. The second objective is to explore the effect of cobalt and zirconia loading in the reaction of the NOx species with methane over the Co-, Pd-, and Co-Pd-silica-sulfated zirconia (Si-SZr). A one-pot synthesis procedure has been developed to prepare the mesoporous silica-zirconia (Si-Zr), Si-SZr supports and the supermicroporous Co(II) incorporated Si-SZr catalysts with a wide range of zirconia loadings. Introduction of the Co(II) active sites by various post-synthesis methods leads to the modification of the surface, whereas the direct (co-precipitation) techniques have provided the modification of both surface and bulk of the supports. The palladium ions were introduced by the conventional impregnation methods onto the calcined solid materials. The detailed analysis of the materials has revealed that the silica and zirconia are well mixed in the framework, whereas the cobalt and sulfate ions are uniformly dispersed on the internal surface of the silica-zirconia supports. The materials prepared in this thesis possess sufficient stability, requisite catalytic properties, as well as good Bronsted and Lewis acidity. However, the high cobalt loading renders the catalytic performance of the Pd-Si-SZr catalysts. Among the investigated catalysts, the interaction of the NOx species with the CH4 takes place at the lowest temperature over the Co-, Pd-, Co-Pd-supported zirconia rich (Zr/Si = 28) Si-SZr catalysts.
Open Access
Synthesis, characterization, and wear and friction properties of variably structured SiC/Si elements made from wood by molten Si impregnation
(2012) Dhiman, R.; Rana, K.; Bengu, E.; Morgen P.
We have synthesized pre-shaped SiC/Si ceramic material elements from charcoal (obtained from wood) by impregnation with molten silicon, which takes place in a two-stage process. In the first process, a porous structure of connected micro-crystals of β-SiC is formed, while, in the second process, molten Si totally or partly infiltrates the remaining open regions. This process forms a dense material with cubic (β-)SiC crystallites, of which the majority is imbedded in amorphous Si. The synthesis of preshaped "sprocket" elements demonstrates that desired shapes of such a dense SiC/Si composite ceramic material can be achieved, thus suggesting new industrial applications. The structure and composition of numerous as-synthesized samples were characterized in detail by using a wide range of techniques. Wear and friction properties were also investigated, with polished samples. The properties found for the present samples are very promising for abrasive applications and for new generation brake systems. © 2011 Elsevier Ltd.