Kinetic Study of Initiation adn Growth of Filamentous Carbon during Methane Carcking over Ni/alpha-Al_2O_3

摘要

The kinttics of filamentous carbon formation on promoted (Mg, Ca) and unpromoted Ni/alpha-Al_2O_3 was studied in an oscillating microbalanece reactor at a methoane partial pressure of 130 kPa, hydrogen partial pressures from 0 to 150 kPa, and temperaturesf rom 773 to 923 K. The presence of hydrogen and promoters influenced the induction and autoacceleration periods significantly. The apperent activation energy changed gradually form a negative to a positive pseudo constant value with carbon formation, and the change in apparent activation energy showed a strong hydrogen dependence. The rate-determining step during the filamentous carbon formation seems to change with carbon deposition. Possible causes are discussed based on the mechanism of filamentous carbon formation.