SnO2-TiO2 solid solution catalyst for simultaneous reduction of SO2 and NO by COII.: Physicochemical properties of the catalyst

The physicochemical properties of the Sno(2)-TiO2 solid solution catalyst have studied by XRD, XPS, CO-TPD, HN3-TPD, SO2-TPD and IR spectroscopy. Different ratios of SnO2 to TiO2 can form continuous solid solution which has rutile crystal structure. The particle size of the solid solution is smaller than that of pure TiO2 or pure SnO2. The change of the surface area of the SnO2-TiO2 solid solution with the SnO2 or TiO2 content is a volcano shape curve. The function of SnO2 in the solid solution is to prevent its surface area from decreasing during the phase change of TiO2 from anatase to rutile, and the function of TiO2 is to form a structure frame to ensure large surface area. SnO2 tends to enrich on the surface of the solid solution. The content of oxygen on the solid solution surface is higher than that on the pure SnO2 surface but lower than that on the pure TiO2 surface. The adsorbed oxygen on the surface of SnO2, TiO2 or SnO2-TiO2 and crystal lattice oxygen on the surface of them can be reduced by CO, but only about 0.001 % of the crystal lattice oxygen can be reduced to form oxygen anion vacancy. TiO2 increases the amount of the surface crystal lattice oxygen. The surface of TiO2 is non-acidic, the surface of SnO2 and SnO2-TiO2 is weakly acidic. The SnO2-TiO2 solid solution reduced by CO has a large number of strong basic centers as a result of the synergism between TiO2 and SnO2. These chemical properties of the SnO2-TiO2 solid solution are all favorable for the SO2 + CO, NO + CO and SO2 + NO + CO redox reactions.