Journal
JOURNAL OF CATALYSIS
Volume 198, Issue 1, Pages 116-121Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1006/jcat.2000.3117
Keywords
selective oxidation; methane; formic acid; hydrogen-oxygen gas mixture; palladium; vanadium substitution; heteropoly compound
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The selective oxidation of methane catalyzed by heteropoly compounds having the formulas M(x)Cs(2.5)H(0.5-2x+y)PV(y)Mo(12-y)O(40) (M = pd(2+), Rh(2+), Ru(2+), Pt(2+), Mn(2+), Hg(2+), Fe(3+) Co(2+), Cu(2+); X = 0-3, y = 0-3) was investigated. It was demonstrated that addition of Pd and incorporation of V had a strong influence on oxidation with a H(2)-O(2) gas mixture and that Pd(0.08)Cs(2.5)H(0.34)PVMo(11)O(40) showed the highest yield of formic acid. The reaction proceeded at temperatures as low as 423-593 K. Moreover, the reaction rate reached 1.2 x 10(-4) mol h(-1) g(-1) at 573 K; this value is about 300 times higher than that with FePO(4) catalyst. Addition of steam promoted the production of formic acid, and the yield reached a maximum at a partial pressure of steam of 9.1 kPa. The coexistence of H(2) and O(2) was indispensable for the selective oxidation of methane. It is suggested that an active oxygen species is formed by the reaction of H(2) with O(2) catalyzed by Pd and acidic sites of supports. Pressure dependencies were expressed by -dP(CH4)/dt = kP(H2)(1.0)P(O2)(1.0)P(CH4)(1.0), and is consistent with the idea that the reaction of an active species formed from H(2) and O(2) with CH(4) is rate determining. (C) 2001 Academic Press.
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