SnO2-based solid solutions for CH4 deep oxidation: Quantifying the lattice capacity of SnO2 using an X-ray diffraction extrapolation method

A series of SnO 2 -based catalysts modified by Mn, Zr, Ti and Pb oxides with a Sn/M (M = Mn, Zr, Ti and Pb) molar ratio of 9/1 were prepared by a co-precipitation method and used for CH 4 and CO oxidation . The Mn 3+ , Zr 4+ , Ti 4+ and Pb 4+ cations are incorporated into the lattice of tetragonal rutile SnO 2 to form a solid solution structure. As a consequence, the surface area and thermal stability of the catalysts are improved. Moreover, the oxygen species of the modified catalysts become easier to be reduced. Therefore, the oxidation activity over the catalysts was improved, except for the one modified by Pb oxide. Manganese oxide demonstrates the best promotional effects for SnO 2 . Using an X-ray diffraction extrapolation method, the lattice capacity of SnO 2 for Mn 2 O 3 was 0.135 g Mn 2 O 3 /g SnO 2 , which indicates that to form stable solid solution, only 21% Sn 4+ cations in the lattice can be maximally replaced by Mn 3+ . If the amount of Mn 3+ cations is over the capacity, Mn 2 O 3 will be formed, which is not favorable for the activity of the catalysts. The Sn rich samples with only Sn-Mn solid solution phase show higher activity than the ones with excess Mn 2 O 3 species.