The effect of addition of a third component on the behaviour of the lithium doped magnesium catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane was studied with the use of promoted Li/MgO catalysts at temperatures of 600¿650°C. The addition of known promoters, cobalt and tin, gave a slight Increase In activity but a strong decrease in selectivity to ethylene under the conditions used. The addition of sodium improved the selectivity to ethylene and suppressed the formation of carbon monoxide. Using a feed of 12 vol% ethane and 6 vol% oxygen, the U/Na/MgO catalyst with 3.2wt% sodium showed a selectivity of 86 % to ethylene at 38 % conversion of ethane; the Li/MgO catalyst showed a selectivity of 80 % at similar conversions Thermal Investigations of the Li/Na/MgO catalyst showed that an eutectic melt of LINaCO3 is formed at 490°C; the existence of this molten phase is probably the cause of the Increased selectivity

The oxidative coupling of methane and the oxidative dehydrogenation of ethane over a niobium promoted lithium doped magnesium oxide catalyst

The promoting effect of niobium in a Li/MgO catalyst for the oxidative coupling of methane (OCM) and for the oxidative dehydrogenation of ethane (ODHE) has been studied in some detail. It has been found that a Li/Nb/MgO catalyst with 16 wt % niobium showed the highest activity for the C2 production in the OCM reaction; the activity at 600 °C was ten times that of the Li/MgO catalyst at the same temperature. The Li/Nb/MgO catalyst was also slightly more active for the ODHE reaction than was the Li/MgO catalyst. However, the Li/Nb/MgO catalyst produced considerably more carbon dioxide in the both reactions. Structural investigation of the catalyst showed that the addition of niobium to the Li/MgO catalyst increased the surface area and gave an increase in the lithium content of the calcined catalysts. Two niobium phases, LiNbO3 and Li3NbO4, were formed; it is shown that the first of these probably causes the increased activity. Ageing experiments showed that the activity of the catalyst was lost if the catalyst was used above 720 °C, the melting point of the lithium carbonate phase. The catalyst showed a decrease of surface area after ageing and a sharp decrease of the amount of the two niobium phases. The addition of carbon dioxide to the feed could not prevent the deactivation of the Li/Nb/MgO catalyst

The oxidative coupling of methane and the oxidative dehydrogenation of ethane over a niobium promoted lithium doped magnesium oxide catalyst

The promoting effect of niobium in a Li/MgO catalyst for the oxidative coupling of methane (OCM) and for the oxidative dehydrogenation of ethane (ODHE) has been studied in some detail. It has been found that a Li/Nb/MgO catalyst with 16 wt % niobium showed the highest activity for the C2 production in the OCM reaction; the activity at 600 °C was ten times that of the Li/MgO catalyst at the same temperature. The Li/Nb/MgO catalyst was also slightly more active for the ODHE reaction than was the Li/MgO catalyst. However, the Li/Nb/MgO catalyst produced considerably more carbon dioxide in the both reactions. Structural investigation of the catalyst showed that the addition of niobium to the Li/MgO catalyst increased the surface area and gave an increase in the lithium content of the calcined catalysts. Two niobium phases, LiNbO3 and Li3NbO4, were formed; it is shown that the first of these probably causes the increased activity. Ageing experiments showed that the activity of the catalyst was lost if the catalyst was used above 720 °C, the melting point of the lithium carbonate phase. The catalyst showed a decrease of surface area after ageing and a sharp decrease of the amount of the two niobium phases. The addition of carbon dioxide to the feed could not prevent the deactivation of the Li/Nb/MgO catalyst

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Document(en) uit de collectie Chemische Procestechnologie.DelftChemTechApplied Science

The effect of addition of a third component on the behaviour of the lithium doped magnesium catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane was studied with the use of promoted Li/MgO catalysts at temperatures of 600¿650°C. The addition of known promoters, cobalt and tin, gave a slight Increase In activity but a strong decrease in selectivity to ethylene under the conditions used. The addition of sodium improved the selectivity to ethylene and suppressed the formation of carbon monoxide. Using a feed of 12 vol% ethane and 6 vol% oxygen, the U/Na/MgO catalyst with 3.2wt% sodium showed a selectivity of 86 % to ethylene at 38 % conversion of ethane; the Li/MgO catalyst showed a selectivity of 80 % at similar conversions Thermal Investigations of the Li/Na/MgO catalyst showed that an eutectic melt of LINaCO3 is formed at 490°C; the existence of this molten phase is probably the cause of the Increased selectivity

The kinetic and mechanistic aspects of the oxidative dehydrogenation of ethane over Li/Na/MgO catalysts

Kinetic and mechanistic aspects of the oxidative dehydrogenation of ethane catalysed by Li/MgO and Li/Na/MgO have been investigated. Initial rate measurements at 600°C; revealed that the Li/MgO catalyst produced C2H4, CO2, CO and H2 by parallel reactions whereas the sodium-promoted catalyst produced only C2H4 and CO2, again by parallel reactions. Experiments were also carried out in which water and carbon dioxide were added to the feed, these being designed to study the mechanism of hydrogen production. The results indicate that the hydrogen and carbon monoxide are unlikely to have been produced by steam reforming or carbon dioxide reforming of ethane or by the water-gas shift reaction; they are possibly formed directly from the ethane via surface ethoxy species