抄録
The characteristics of active center and sintering mechanism of a supported metal catalyst were investigated using the palladium silica-alumina prepared by the cation exchange method which has an ideal mechanical structure. Data on catalytic activity were obtained from benzene hydrogenation reaction. The palladium surface area and crystal lattice imperfection were determined by electron microscope and X-ray diffraction. The following results were obtained.
(1) The rise of calcination temperature in air brought the decrease of the activity and the increase of size of supported palladium particles leaving the lattice imperfection unchanged. This result indicates that the deactivation during calcination step is caused by the quantitative sintering resulting in reduction of the palladium surface area (number of active site decreases).
(2) Both activity and lattice imperfection of the supported palladium crystal decreased with the elevation of reduction temperature, but the size of palladium particle remained constant. The deactivation during reduction step was explained to be caused by the qualitative sintering where lattice imperfection (strong active center) annealed.
(3) Addition of either Al3+, La3+ or Th4+ as a promoter to the supported palladium catalyst was found to be effective for the prevention of the deactivation caused by quantitative sintering. Addition of Li+ or Ba2+, however, showed no effect. These results indicate that trivalent and quadrivalent metal cations are the excellent promoters on the stabilization of active surface.
