THERMAL-STABILITY OF ALKALI-METALS DEPOSITED ON OXIDE SUPPORTS AND THEIR INFLUENCE ON THE SURFACE-AREA OF THE SUPPORT

Different alkali metal-promoted supports were prepared by impregnating SiO2, Al2O3, Cr2O3 and MgO with solutions of lithium, sodium or potassium nitrate or carbonate. They were calcined under an air flow at 773, 1023 and 1173 K in order to measure the thermal stability of the alkali metal and the modifications of the surface area of the support. It was found that the deposited alkali metals are fairly stable on Cr2O3 or Al2O3 and slightly less so on SiO2. With MgO, an important loss of alkali metal was observed with calcination temperatures >773 K. This effect, increasing from lithium to potassium, was attributed to a reaction with the walls of the reactor.