Abstract
Nickel phosphate catalysts were prepared by precipitation from aqueous solutions of Ni(NO/sub 3/)/sub 2/ and (NH/sub 4/)/sub 3/PO/sub 4/ and calcination at 400/sup 0/-900/sup 0/C for three hours. Paper chromatography showed a maximum content of long-chain polyphosphates in catalysts calcined at 500/sup 0/C; higher calcining temperatures resulted in increasing decomposition of polyphosphates to pyro- and orthophosphates. The maximum activity for propylene isopropanol dehydration to propylene at 250/sup 0/-350/sup 0/C occurred at 500/sup 0/C calcining temperature; the active sites are apparently weak Lewis acid sites formed on nickel ions by conversion of Ni-O-P to P-O-P bonds. The maximum activity for isopropanol dehydrogenation to acetone at 350/sup 0/ or 400/sup 0/C occurred at 700/sup 0/C calcining temperature, which coincided with the maximum content of strong Lewis acid sites as detected by adsorbed IR spectroscopy of adsorbed pyridine; this reaction probably involves both Lewis acid and adjacent basic sites, probably oxygen atoms bound to nickel. No free radical or Broensted acid sites were observed by ESR and IR spectroscopy. The results are relevant to the mechanism of activity of calcium nickel phosphate catalysts for dehydrogenation of butenes to butadiene or pentenes to isoprene.
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