EFFECT OF ALKALI AND ALKALINE-EARTH METALS ON THE RESISTIVITY TO COKE FORMATION AND SINTERING OF NICKEL ALUMINA CATALYSTS

Resistivity to coke formation and nickel sintering has been investigated over nickel-alumina catalysts with promoters such as Li, Na, K, Mg, or Ca, respectively. Studies were carried out by performing catalytic cracking of n-hexane in a fixed bed reactor at 773 K and atmospheric pressure. The characterizations of fresh and spend catalysts were analyzed by an X-ray diffractometer (XRD), temperature-programmed reduction (TPR), temperature-programmed depostion (TPD), temperature-programmed hydrogenation of the carbon deposit (TPH), and chemical analysis of carbon. The result shows that the resistivity to nickel sintering of promoted nickel-alumina catalyst is improved significantly. The promoter K is found to help in decreasing the coking rate of nickel catalysts. The ordering of promoted nickel catalysts by the temperature of the high-temperature peak of their TPH spectra is in accordance with that by the coking rate of these catalysts, which is Ni-Mgã Ni-Caã Ni-Liã Ni-Naã Ni-K catalyst. © 1990, American Chemical Society. All rights reserved.