THE ROLE OF SODIUM PROMOTER IN IMPROVING THE PROPERTIES OF CALCIUM-OXIDE CATALYSTS FOR THE OXIDATIVE COUPLING OF METHANE

The sodium promoter increases the specific activity of the calcium oxi de catalyst surface in the oxidative methane coupling, but not to the same extent for various reaction prod acts. There exists an optimum of the sodium promoter amount, at which the degree of methane conversion and the specific activity of a surface unit of the catalyst as well a s the selectivity of hydrocarbon C-2+ formation reach their maximal va lues. Apart from the creation of new specific active sites described i n the literature, the presence of the sodium promoter in the calcium o xide catalyst hinders its carbonation and facilitates tile removal of carbon dioxide from its surface, thus enabling a quicker regeneration of sites, on which active oxygen can be chemisorbed. Improvement of th e selectivity of the promoted catalysts is a result of a greater incre ase in the rate of C-2+ hydrocarbons formation than of the rate of car bon oxides formation, as well as elimination and blocking of low-coord inated sites of the catalysts surface.