Relation between the ctalytic activity of binary compounds of group II metals with nonmetals and the positions of the elements in Mendeleev's periodic system Communication 2: Catalytic decomposition of isopryopyk alcohol over oxides of group IIB metals

Abstract

1. A study was made of the catalytic activity and selectivity of oxides of Group IIB metals - BeO, MgO, ZnO, CdO, and HgO- in the decomposition of isopropyl alcohol in a flow system at atmospheric pressure in the temperature range 190–454°. 2. Over MgO, ZnO, CdO, and HgO under the conditions studied, the predominant reaction is the dehydrogenation of isopropyl alcohol. Over BeO dehydrogenation and dehydration proceed to about the same extent.In all cases rise in temperature results in an increase in the extent of dehydration, i.e. the activation energy for dehydration is higher than that for dehydrogenation. 3. Variations in the method of preparing the oxides greatly affect their catalytic properties - activity and activation energies for dehydration and dehydrogenation - and also their specific surfaces.However, these changes do not obscure the differences due to the position of oxide-forming element in the periodic system. The concept “specific catalytic activity" is not applicable to the characterization of the relation between the catalytic activity of an element and the position of this element in the periodic system. 4. Impurities originating during the preparation of the catalyst or introduced artifically (e.g. S04 2−) substantially affect its activity and the direction of the process. 5. When the catalytic properties of oxides of Group II metals are considered in relation to the positions of the metals in the periodic system it is found that catalytic activity increases with increase in the atomic weight of the metal. There is a simultaneous increase in the extent of dehydrogenation of the alcohol, and the activation energies for dehydration and dehydrogenation fall. 6. When the decomposition of the alcohol takes place in the adsorption layer at low surface coverage (2–8%), the course of the reaction may be different. Over ZnO under these conditions, dehydration predominates over dehydrogenation. 7. It is suggested that there is a relationship between the course of the decomposition of isopropyl alcohol and the electronic and acid-base properties of the catalyst.