Hydrothermal Fabrication and Catalytic Properties of La_1-<i>x</i>Sr_<i>x</i>M_1-<i>y</i>Fe_<i>y</i>O₃ (M = Mn, Co) That Are Highly Active for the Removal of Toluene

Abstract

A series of La(1-x)Sr(x)M(1-y)Fe(y)O(3) (M = Mn, Co; x = 0, 0.4; y = 0.1, 1.0) perovskite-type oxide catalysts have been fabricated via a strategy of citric acid complexation coupled with hydrothermal treatment. The materials are characterized by a number of analytical techniques. The oxidation of toluene is used as a probe reaction for the evaluation of catalytic performance. It is found that both La(0.6)Sr(0.4)FeO(3) and LaFeO(3) exhibit high activities. The partial substitution of manganese and cobalt with iron can significantly improve the catalytic performance of La(0.6)Sr(0.4)MnO(3) and La(0.6)Sr(0.4)CoO(3). At toluene/O(2) molar ratio = 1/200 and space velocity = 20,000 h(-1), the catalytic activity decreases in the sequence of La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) > La(0.6)Sr(0.4)FeO(3) > La(0.6)Sr(0.4)Mn(0.9)Fe(0.1)O(3) > LaFeO(3) > La(0.6)Sr(0.4)CoO(3) > La(0.6)Sr(0.4)MnO(3). Compared to the Fe-free counterparts, the La(0.6)Sr(0.4)Mn(0.9)Fe(0.1)O(3) and La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) catalysts are, respectively, 50 and 85 degrees C lower with regard to the temperature required for complete toluene oxidation. Toluene can be completely oxidized at 245 degrees C over La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3). The excellent catalytic performance of La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) can be attributed to the presence of (i) Fe(3+)-O-Fe(4+) couples, (ii) a transition of electronic structure, and (iii) a trace amount of Co(3)O(4).