AN APPARENT ENSEMBLE EFFECT IN THE OXIDATIVE COUPLING OF METHANE ON HYDROXYAPATITES WITH INCORPORATED LEAD

The introduction of small quantities of lead into calcium hydroxyapati te catalysts produces marked increases in the selectivity to C-2+ hydr ocarbons, while the conversion of methane remains relatively constant. Small surface concentrations of lead are sufficient to achieve C-2+ s electivities of 80 and 90%, with oxygen and nitrous oxide, respectivel y, in contrast with 18 and 46%, respectively, obtained in the absence of lead. Since surface concentration of lead species sufficient to sta bilize pairs of methyl radicals in dose proximity to each other would be expected to facilitate the formation of C-2 hydrocarbons, an ensemb le effect appears to be extant.