2994.     RUSSELL, W. W., AND TAYLOR, H. S.  Promoter Action of Thoria on Nickel Catalysts.  Jour. Phys. Chem., vol. 29, 1925, pp. 1325-1341; Chem. Abs., vol. 20, 1926, p. 325.

        Reaction CO₂+4H₂=CH₄+2H₂O is a surface reaction strongly affected by the adsorbing power of the catalyst surface for the reactant.  The activity of Ni alone as catalyst, either supported or unsupported, is greater the lower the temperature at which the Ni was reduced, presumably because the number of highly unsaturated Ni atoms per vol. of catalyst is greater the lower the temperature of reduction.  Heating a catalyst above the temperature at which it was reduced markedly reduces its activity, because the increase in the mobility of the atoms with temperatures brings about the coalescence of the unsaturated atoms with loss of effective adsorptive power.  The primary function of ThO₂ as promoter with supported Ni catalysts is to make possible the existence of a greater number of Ni atoms of a highly unsaturated character per unit of catalyst, through the creation of ThO₂-Ni interfaces.  With unsupported Ni catalysts, ThO₂ may function as promoter (a) by the creation of a more active surface through the above interface mechanism, (b) by an increase in the extent of surface, inasmuch as the promoter acts as a support, and (c) by a favorable alteration in the ratio in which the reacting substances, and possibly the products, are adsorbed.  The activation of Ni by Th may be so extensive that the speed of reduction of CO₂ by H₂ to CH₄ is increased 10-fold.  This may be due to the increase in surface area and the adsorption ability of this type of Ni catalyst.  The conclusions are based on the results of both adsorption and reaction-velocity measurements on samples of promoted and unpromoted, supported and unsupported Ni catalysts.