Characterization of nickel catalysts on RHA-Al2O3 composite oxides prepared by ion exchange

RHA-Al2O3 composite oxide supports were prepared by impregnation of rice husk ash with an aluminum sulfate solution. These were then used to prepare supported nickel catalysts by the ion exchange method. The supports and catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analyzer (TGA), temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) of hydrogen and n-butylamine. In addition, the BET surface area was also determined by nitrogen adsorption method. These results show that nickel compound with a layer structure was formed after the drying step. The decomposition temperature of nickel compound to nickel oxide started above 773 K. The interaction between the nickel oxide and the support was strong for smaller nickel oxide crystallites. Furthermore, the nickel crystallites were finely distributed on the support even at high loading, as revealed by EDS-mapping tests. The BET surface area of the unreduced catalysts decreased with the nickel loading up to 2.44 wt.% and then increased with further deposits. The average size of nickel crystallites increased with nickel loading. The acidity of catalysts increased with nickel loading up to 11.1 wt.%. Further deposition could not markedly increase the acidity of the catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.