Methanol decomposition to synthesis gas over supported Pd catalysts prepared from synthetic anionic clays

Supported Pd or Rh catalysts were prepared by the solid-phase crystallizati on method starting from hydrotalcite anionic clay minerals based on [Mg6Al2 (OH)(16)CO32-]. 4H(2)O as the precursors. The precursors were prepared by a coprecipitation method from the raw materials containing Pd2+ and various trivalent metal ions which can replace each site of Mg2+ and Al3+ in the hy drotalcite. Rh3+ was also used for preparing the catalyst as comparison. Th e precursors were then thermally decomposed and reduced to form supported P d or Rh catalysts and used for the methanol decomposition to synthesis gas. Among the precursors tested, use of Mg-Cr hydrotalcite containing Pd2+ res ulted in the formation of efficient Pd supported catalysts for the producti on of synthesis gas by selective decomposition of methanol at low temperatu re. Although Pd2+ cannot well replace the Mg2+ site in the hydrotalcite, th e Pd supported catalyst (Pd/Mg-Cr) prepared by the solid-phase crystallizat ion method formed highly dispersed Pd metal particles and showed much highe r activity than that prepared by the conventional impregnation method. When the precursor was prepared under mild conditions, more fine particles of P d metal were formed over the catalyst, resulting in high activity. It is li kely that the high activity may be due to the highly dispersed and stable P d metal particles assisted by the role of Cr as the co-catalyst.