Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-1-specialthat Г s /f changed insignificantly at the catalyst poisoning. So poisoning results in the increaseof activation energy of rate constant k + . Noteworthy that this conclusion is true when thequantity of surface oxygen is low in comparison with the number of surface catalyst atoms.After three oxygen poisonings, this corresponds to the increase of its activation energy by 2,0-2,5 kcal/mol.According to the Temkin theory, the increase of activation energy of k + means that theeffect of oxygen sorption on the catalyst consists in the increase of activation energy ofnitrogen chemisorptions at a fixed heat of nitrogen chemisorption. So activation energy ofnitrogen adsorption rate depends not only on the heat of nitrogen chemisorption but also onthe quantity of oxygen on the catalyst. Earlier such conclusion was made on the base ofstudying of the effect of oxygen sorption on the catalyst of ammonia synthesis on the rate ofisotope exchange in molecular nitrogen and on the rate of nitrogen adsorption [3].This conclusion is in agreement with studies of Ertl et. all [4], in which a significantincrease (about 300 times at 430 K) of the rate of nitrogen adsorption on a Fe (100) singlecrystal surface after evaporation of potassium on it was observed [5]. It was concluded thatactivation energy of activated complex at nitrogen chemisorption reduced at the decrease ofwork function of electrons.Oxygen sorption on a properly reduced catalyst leads to re-oxidation of promoters and tothe increase of activation energy of nitrogen chemisorptions [6].Results of this study show that this conception can be applied for description of kineticsof ammonia synthesis at poisoning of promoted catalyst with oxygen-containing gases.References:1. Temkin M.I., Morozov N.M., Shapatina E.N. // Kinet. Katal., 1963, v.4, no. 2 p.260; no. 4, p.565.2. Kuchaev V.L., Shapatina E.N., Shub F.S., Temkin M.I. // Translated from Kinetika I Kataliz, 1991, v.32,no. 5, pp.1107.3. Boreskova E.G., Kuchaev V.L., Temkin M.I. // Kinet. Katal., 1984, v.25, no. 1 p.116.4. Ertl G., Weiss M., Lee S.B. // Chem. Phys. Letters. 1979. v.60. p.3915. Ertl G. // Catalysis Rev. 1980. v.21. no 2. p.201.6. Enikeev E.Kh., Krilova A.V. // Kinet. Katal., 1962, v.3, no. 1 p.139.30