Influence Of Metal Oxides Research Articles

ChemInform Abstract: The Influence of Metal Oxides on the Activity and Selectivity of Transition Metal Catalysts

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The influence of metal oxides on the activity and selectivity of transition metal catalysts

The catalytic activity and selectivity of transition metals are known to be affected by metal oxides deposited on their surface. Such deposits can result from the transfer of portions of the support during catalyst preparation or be introduced intentionally. The structure and composition of both monolayer and multilayer deposits of metal oxides on Rh and Pt are discussed and the effects of oxide composition and coverage on the rate of CO and CO 2 hydrogenation are examined. It is shown that the effectiveness of an oxide correlates with its Lewis acidity, and that the later property can be described by the Pauling electronegativity of the cations in the oxide. The effects of oxide deposits on other reactions are also reviewed.

Catalytic combustion of soot deposits from diesel engines

The catalytic combustion of diesel soot under the influence of metal oxides and metals has been studied. The catalytically active materials, dispersed on a carrier of γ-alumina, have been studied in order to simulate the conditions in a catalytic particulate trap. A mixture of soot and catalyst was placed in a flow reactor and a gas mixture containing 6% oxygen, 7% water and balance of nitrogen was led through it at a flow-rate of 90 l/h. The combustion rate was determined between 573 and 698 K. The results showed that V 2O 5 is the most active catalyst for the combustion of diesel soot whereas oxides of copper, manganese and chromium as well as the metals silver and platinum are active in the combustion of hydrocarbons that desorb from the diesel soot upon heating. Catalytically active materials sensitive to sulphur poisoning are deactivated immediately during the experiments as large amounts of SO 2 are released from the diesel soot when heated. The results indicate that V 2O 5 is not sensitive to sulphur poisoning. This study shows that a catalyst for the combustion of diesel soot should be based on V 2O 5.

Investigation of the influence of metal oxides on the thermal degradation of chlorine-containing polymers by thermogravimetry

The influence of oxides of zinc, magnesium, antimony and aluminium on the thermal degradations of polychloroprene, chlorinated polyethylene and epichlorhydrin homopolymer has been investigated. The investigations showed that these metal oxides can change the thermal stabilities and degradation processes of chlorine-containing polymers. A considerable acceleration of the dehydrochlorination of these polymers was found in the presence of zinc oxide.

The influence of metal oxides on crosslinking occurring in rubber modified by benzthiazole and dithiodimorpholine vulcanization accelerators

Model systems containing weakly crosslinked rubber chains modified by sulphur containing benzthiazole or morpholine accelerator fragments (pendants) have been used in an investigation of reactions occurring in these systems in the presence of activators. The nature of the pendants has a marked effect on the action of metal oxides at the stage examined, and this is associated with the formation of intermediate compounds of non-uniform stability.