Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-11(1) [V 5+ O 2– V 5+ ] +CH 4 → 2V 4+ + products chain generation(2) V 4+ + N 2 O → [V 5+ O – ] + N 2(3) V 4+ + О 2 ⇔ [V 5+ O 2– ](3a) [V 5+ O 2– ] + V 4+ → 2 [V 5+ O – ] chain propagation (steps 2-4)(4) [V 5+ O – ] +CH 4 → V 4+ + products(5) [V 5+ O – ] + V 4+ → [V 5+ O 2– V 5+ ] chain terminationFor such mechanism, an inversion of the reaction rate position becomes possible(Fig. 2b). The reaction rate simulation was made using the realistic values of the preexponentialfactors [6]: k 1,o = 10 12 , cm 3 /(mole⋅s); k 2,o = 10 11 , cm 3 /(mole⋅s); k 3,o = 10 12 ,сm 3 /(mole⋅s); k -3,o = 5⋅10 13 , s –1 ; k 3a,o = 10 14 , s –1 ; k 4,o = 10 12 , s –1 ; k 5,o = 10 10 , s –1 ; activationparameters: (E i /R, K): E 1 /R = 20000; E 2 /R = 0; E 3 /R = 0; E -3 /R = 30000; E 3a /R = 15000;E 4 /R = 10000; E 5 /R = 5000; and concentrations: [R] = [N 2 O] = 2[O 2 ] = 1.25⋅10 –5 , mole/сm 3(30 vol.% at 1 atm).Fig2a. Experimental dataFig2b. Simulated data00-1Log(TOF)-2-3O2N2O-1Log(TOF)-2-3N2OO2-40,001 0,0011 0,0012 0,0013 0,0014 0,00151/T-40,001 0,0011 0,0012 0,0013 0,0014 0,00151/TSimulated data are in a qualitative accordance with experimental data. It can be also notedthat participation of both O – anion-radicals and O 2– ions in the reaction of partial methaneoxidation with N 2 O over MoO 3 /SiO 2 is assumed in [7]. Besides, the mechanism, proposed in[7], is, in fact, the surface chain mechanism like mechanism analyzed in the present work.Obtained results allow to make conclusion that N 2 O as an oxidant is more appropriate forlow-temperature oxidation reactions proceeding on easy reducible oxide catalysts.References1. Panov G.I. Abstracts of the VI Conference on Mechanisms of Catalytic Reactions, Moscow, 2002, P.11.2. Chen S.I., Wilcox D. Ind.Eng.Chem.Res., 32 (1993) 584; 33 (1994) 832.3. Zhen K.J., Khan M.M., Mak C.H., Lewis K.B., Somorjai G.A., J.Catal. 94 (1985) 501.4. Ilchenko N.I., Hanke W., Raevskaya L.N., Golodets G.I., Ohlmann G. React.Kinet.Catal.Lett. 41 (1990)147.5. Kazansky V.B. In: Problems of chemical kinetics of elementary chemical reactions. Nauka, Moscow, 1973,P.131-139.6. Krylov O.V., Kyslyuk M.U., Schub B.R., et al. Kinetics and Catalysis, 13 (1972) 598.7. Liu H.-F., Lin R.-S., Liew K.Y., Johnson R.E., Lunsford J.H., J.Am.Chem.Soc. 106 (1984) 4117.47