CHARACTERIZATION OF NI ON LA MODIFIED AL2O3 CATALYSTS DURING CO2 REFORMING OF METHANE

0.15 wt% Ni/x wt% Ln/Al2O3 (x=0, 1.7, 8.5, Ln=rare earth mixture) cata lysts have been tested for life time stability (60-600 h) during CO2 r eforming of methane in a fluidized bed reactor at 800 degrees C and 1 atm with CH4:CO2:N-2=2:2:1. The catalyst with 1.7% Ln is more active a nd stable than the unpromoted catalyst and the catalyst with 8.5% Ln. Samples of the catalysts were taken out after different times on strea m and characterized using magnetic measurements and Transmission Elect ron Microscopy (TEM). The characterization results showed that even af ter prereduction at 1000 degrees C (5% H-2/He, 2 h), Ni is continuousl y reduced during testing of the Ln-containing catalysts. This effect i s more pronounced at higher Ln loadings (8.5% vs. 1.7% Ln). An increas e in Ni particle size during testing was also observed. The results in dicate that Ni sintering is initially a major reason for deactivation, while coking becomes increasingly important with longer times on stre am (i.e., >60 h). The catalyst with 1.7% Ln has a higher initial Ni di spersion than the catalyst with 0% Ln. The higher activity of the prom oted vs. unpromoted catalyst cannot be fully explained by this differe nce. However, the activity difference between the catalyst promoted wi th 1.7% or 8.5% Ln may be explained by a lower reduction of Ni for the 8.5% Ln-promoted catalyst. (C) 1997 Elsevier Science B.V.