Hydrothermal synthesis of Sr–Ce–Sn–Mn–O mixed oxidic/stannate pyrochlore and its catalytic performance for NO reduction

Mixed oxides and pyrochlore-type materials based on the Sr, Ce, Sn, and Mn elements have been prepared by hydrothermal method using a mixture of nitrate salts at 200 °C for 40 h under N2 atmosphere. Two groups of solids were synthesized: (i) (SrxCe1−x)2Sn2O7±δ (0.345 ≤ x ≤ 0.365) and (ii) (SrxCe1−x)2(SnyMn1−y)2O7±δ (0.345 ≤ x ≤ 0.365, 0.385 ≤ y ≤ 0.395). The structure of the solids were studied by X-ray diffraction and the main crystal phases determined were SnO2, (SrCe)2Sn2O7 and a trace amount of CeO2 in group (i) and only SnO2 and CeO2 were detected in group (ii). The mixed oxides/stannate pyrochlore have been tested as catalyst for NO reduction with hydrocarbons (CH4, C2H4, and C3H6) in the presence of O2. The CeO2 containing stannate Sr2xCe2−2xSn2O7±δ pyrochlore coexist with SnO2 (group (i)) was found to be the best for NO + C3H6 reaction giving very high N2 production at 350 °C in the presence of O2 and water vapor. SnO2 as well as CeO2 alone were also synthesized by the hydrothermal method and their NO reduction properties have been compared with those of the groups (i) and (ii).