ON THE INHOMOGENEITY OF LOW NICKEL LOADING METHANATION CATALYST

Temperature-programmed reduction (TPR) and continuous stepwise reducti on-methanation (CSRM) have been used to identify and separate the acti ve phases of Ni/Al2O3 catalyst. It is found that there are four hydrog en consumption peaks representing four nickel species on Al2O3; the pe ak temperatures for three of them are below 673 K when the reduction t emperature does not exceed to 973 K. For the methanation of both CO an d CO2, three distinct active phases are discovered, the activation tem peratures of which coincide with the peak temperatures of the first th ree TPR peaks, respectively. This indicates that different oxidized ni ckel species exist on Al2O3 prior to reduction and form different acti ve phases for the methanation of both CO and CO2 after reduction. The methanation activities on each phase for both CO and CO2 in terms of C H4 yield or initial methanation temperature and turnover number differ significantly, Each phase also exhibits different activity for CO and CO2 methanation. It is suggested that the mechanism of methanation fo r CO or CO2 on different phases may vary, and that the mechanism for C O and CO2 on the same phase may also vary. CSRM is convenient for sepa rating different active phases for the methanation of both CO and CO2 on Ni/Al2O3 catalyst. (C) 1997 Academic Press.