The effect of metal additives on the thermal stability of an alumina support pellet was investigated to obtain the basic information of the deterioration of catalysts for automotive emission control.
The alumina support was impregnated with aqueous solutions of various metal salts to deposit metals of 1-4wt% of the support, dried at 105°C in air, and then calcined at 1, 000°C in air for 24 hours in an electric furnace.
Physical properties, such as pore distribution, specific surface area, crush strength, attrition loss and X-ray powder diffraction, were measured.
It was ascertained from the results that the desirable physical properties, such as high surface area, adequate pore structure, high attrition resistance, etc., of all heat treated supports were remarkably inferior to those of the fresh support, due to sintering accompanied by the phase transformation of γ-alumina to intermediates or α-alumina, and that the decrease in the surface area was proportional to the increase of the loss in attrition. It was further recognized that the metals promoting the thermal deterioration of the alumina support were Fe, Ti, Cr, B, Zn, etc., and the metals retarding the deterioration were Na, K, Mg, Ca, Ba, Ni, Th, etc.