Cation effects in the oxidative coupling of methane on phosphate catalysts

The conversion of methane and the selectivities to the various products have been measured at 700 and 775 °C on a variety of phosphates of La(III), Zr(IV), V(V), Cr(III), Mn(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Al(III), B(III), Pb(II), Bi(III) and Sm(III) in the presence and absence of carbon tetrachloride. The conversions reach as high as 30 and 49% at 700 and 775 °C, respectively, with methane and oxygen at partial pressures of 200 and 25 Torr, respectively. The highest C₂₊ selectivities (61 and 82%, respectively) were obtained for lead(II) phosphate at 700 and 775 °C, respectively. In general the conversions and C₂₊ selectivities are enhanced on addition of carbon tetrachloride (1.1 Torr) to the feedstream, although there are notable exceptions. Significantly high selectivities to formaldehyde are observed with a number of the catalysts, in particular 32% with boron(III)phosphate.