METAL-SUPPORT EFFECTS ON THE ACTIVITY AND SELECTIVITY OF NI CATALYSTS IN CO-H2 SYNTHESIS REACTIONS

Titania-supported nickel catalysts exhibit unusual properties in COH2 reactions relative to conventional nickel catalysts. The activity of Ni TiO2 is significantly greater than that of Ni powder or Ni on SiO2, Al2O3, or graphite when compared on a per gram of catalyst basis or on the basis of specific activities determined from hydrogen chemisorption. In addition, the selectivity of Ni TiO2 relative to the other catalysts is shifted to higher molecular hydrocarbons which are paraffinic. The shift in selectivity is not accompanied by a suppression of the methanation activity, but results from an increase in the rates of chain growth reactions producing an overall increase in catalyst activity. Studies of on-stream deactivation and of the rates of Ni(CO)4 formation gave further evidence of the unusual properties of Ni TiO2. Whereas Ni Al2O3 deactivated with time on feed, Ni TiO2 showed little or no loss in activity, indicating a greater resistance to carbon deposition and/or metal sintering. With regard to Ni(CO)4 formation, Ni TiO2 exhibited rates of formation at least an order of magnitude less than Ni SiO2 catalysts. The evidence from catalytic and chemical studies and, to a lesser extent, chemisorption and XRD investigations is indicative of a unique metal-support interaction in the Ni TiO2 system. The nature of the interaction which so markedly modifies catalytic and chemical properties of metals is not yet well understood. © 1979.