Isovalent Substitutions in Composite Catalysts Na/W/Mn/SiO 2

Isovalent analogues of the composite catalyst Na/W/Mn/SiO 2 prepared by solid-phase reactions, namely, Li/Na(Rb)/W/Mn/SiO 2 , Na(Li,Rb,Cs)/Mo/Mn/SiO 2 , Na/W/Re/SiO 2 , Na/W/Mn/GeO 2 , and a nonisovalent analogue Mg(Ca,Sr,Ba)/W/Mn/SiO 2 were studied by X-ray powder diffraction. The composites Li/Na/W/Mn/SiO 2 and Li/Rb/W/Mn/SiO 2 having an equimolar contents of alkali elements with nonadditive changes in SiO 2 matrix polymorphism and the formation of mixed tungstates show equally high product yields (23–24%) in oxidative coupling of methane (OCM), these yields being comparable to those observed for Na/W/Mn/SiO 2 . Substitutions of W by Mo, Mn by Re, and Si by Ge in the composite Na/W/Mn/SiO 2 , as well as substitutions of Na by Mg, Ca, Sr, and Ba, change the phase constitution of the composite and reduce its catalytic activity.