Effect of Fluorine and Chlorine on the Resistivity to Coke Formation of Nickel-Alumina Catalysts

摘要

Resistance to coke formation during n-hexane cracking over nickel-alumina catalysts promoted with loading of 0.5,2 and 4% F, and 2,4 and 10% Cl was studied in a fixed bed reactor at 633K and atmospheric pressure. Fresh and spent catalysts were analyzed by temperature-programmed desorption (TPD), temperature-programmed hydrogenation of the carbon deposit (TPH), and chemical analysis of carbon. The ordering of the unpromoted and fluorine-promoted nickel catalysts by their formation rate of carbon deposit is Ni > Ni-0.5F > Ni-4F > Ni-2F catalyst. The ordering of the unpromoted and chlorine promoted nickel catalysts by their formation rate of carbon deposit is Ni > Ni-10Cl > Ni-4Cl > Ni-2Cl catalyst. These ordering are found to be in accordance with the ordering of these catalysts by the peak temperature of their hydrogen TPD spectra. Except for Ni-2F catalyst, the reaction order with respect to the carbon deposit of the other unpromoted and promoted nickel-alumina catalysts were obtained to be 1. However, that of Ni-2F catalyst was zero.