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MgO
Cat&G-s Today, 13 (1992) 579-530 Elsevier Science Publiebers B.V., Amsterdam
579
XXCHANGR ISOTOPEKINEPICSANUACTIVATION MXCHANISMS OF EL’XANX ANDOXYGEN ON TIE OXIDE CATALYSTSOF OXIUATIVE COUPLINGOF XXrHANX Sm203Mgo and Nd203”rero A.A.Shestova,
v.s.Musykantova,
Yu.P.Tyulenlnb snd A.A.Xadushinb
‘Institute of Catalysis of Siberian Branch of USSR Academy of Sciences, pr.Acad.Lavrentieva, 5, 630090, NovosIbirBk, USSR bInBtitute of Chemical Physics of USSR Acadenry of Sciences, xosygin str. ) 4, 117334, XOBCOW, USSR The supported rare earth OXideS are the perspective catalysts of the OXidatiVe coupling of methane to C.@ydrOCBrbOnB 11-33. The present work contains the results of Studies of isotopic exchange of the reaction components - CH4, 02 (initial BubBtsIKeB) and C2H4 (one of the main selective oxidation product) - on S~03/Mg0 and Nd203/MgC (active component contents were 1 and 10% weight) and MgO (support). !Che stable isotopes of oxygen (180) and hydrogen (2H) were ueed. Isotopic exchange ~86 performed in static system connected with ma~8and spectrometer and computer for treatment of mass-spectra calculations of exchange parameters. The interval of pressures investigated WaB 10~150 Pa; the temperatures ranges were 700+950 X (exchange Of 021, 850+1000 (CH4) and 300~600 (C2H4). Mechanisms of exchange between twoatomic molecule O2 and Bu??faCeoxygen atOmB (0) in general are ClaBBified intO thrBB types 14-61, which are connected with three types of dissociative adsorption 171: 1) 220, 2) 20 + (0) and 3) 2(O), where 20 denotes the active surface form of oxygen. The use of the exact isotope-kinetic equations to studied catalysts showed the dominant contribution of the 2-nd exchange type and SW411 contribution of the 3-rd type (5-10X). The important result is the similarity of samples studied in respect to oxygen exchsnge, while these samples have a great differences in respect to oxldatlve coupling. The samples have the 6ame oxygen order of
1992 - Elsevier Science Publishers
B.V.
580
exchange (the I-st) end close values of activation energy (“95kJ). Thus the bond Strength of oxygen with surface of oxides is not essential factor of selectivity in oxidative coupling .(in contrary with complete oxidation). The homoexchsnge (the redistribution of the deuterohydrocarbon molecules) of fouratomic (in respect of atoms H) molecules (CH4 and C2H4) csn proceed through four types of mechanisms depending on atomicitles of surface Intermediate species 181: 1) 4H, 2) 2H + H2, 3) H + H3 and 4) 2H2. It was shown theoreticaly 18,91 the kinetic equations of homoexchange for methane and ethene have the same general form. The use of these equations to obtained experimental data on the isotopic molecules redistribution kinetics proves the third type of mechanism is dominated, i.e. the main Intermediate surface species in the homoexchange of both CH4 and C2H4 contain three atoms of h@rogen. All samples studied have the same order (the I-st) and close values of the activation energy (“95 kJ) in respect to methane homoexchange. Investigated samples are much more active in ethene exchange than In methane exchange. The presence of methane was found to effect on oxygen activation: a small addition CR4 essentially decreased oxygen exchange rate. It could be explained that the active surface forms of oxygen are binding by dissociative methane adsorption: CH4tZOtZ = ZCH3t ZOH . The reversible performance of this reaction realizes the methane homoexchange. It was found the addition of oxygen increased metane exchange rates on the supported rare earth oxides. 1 K.Otsuka, K.Jinno, A.Morikawa, J. Catal., 100 (1986) 353 2 V.R.Choudhary, S.T.Chaudhary, A.M.Rajput, V.H.Rsne, J. Chem. Soc.Chem.Com., (1989) No 9, 555 O.V.Krylov, Proc. 3 M.Yu.Sinev, Yu.P.Tyuleni.n, A.A.Kadushin, Mechanisms, p.93, 5th All-Union Conf. Catalytic Reaction Xoskva, 1990 4 K.Klier, J.Novakova, P.Jiru, J. Catal., 2 (1963) 479 5 V.S.J&zykentov, V.V.Popovski, G.K.Roreskov, Kinet. Katal., 5 (1964) 624 137 6 G.K.Roreskov, V.S.Musykantov, Ann.N.Y.Acad.Sci,213(1973) 7 V.S.Musykantov, React. Klnet. Catal. Lett., 35(1987) 437 8 V.S.Musyksntov, A.A.Shestov, ibid, 32 (1986) 307 9 V.S.Musyksntov, Ibid, 14 (1980) 311
579
XXCHANGR ISOTOPEKINEPICSANUACTIVATION MXCHANISMS OF EL’XANX ANDOXYGEN ON TIE OXIDE CATALYSTSOF OXIUATIVE COUPLINGOF XXrHANX Sm203Mgo and Nd203”rero A.A.Shestova,
v.s.Musykantova,
Yu.P.Tyulenlnb snd A.A.Xadushinb
‘Institute of Catalysis of Siberian Branch of USSR Academy of Sciences, pr.Acad.Lavrentieva, 5, 630090, NovosIbirBk, USSR bInBtitute of Chemical Physics of USSR Acadenry of Sciences, xosygin str. ) 4, 117334, XOBCOW, USSR The supported rare earth OXideS are the perspective catalysts of the OXidatiVe coupling of methane to C.@ydrOCBrbOnB 11-33. The present work contains the results of Studies of isotopic exchange of the reaction components - CH4, 02 (initial BubBtsIKeB) and C2H4 (one of the main selective oxidation product) - on S~03/Mg0 and Nd203/MgC (active component contents were 1 and 10% weight) and MgO (support). !Che stable isotopes of oxygen (180) and hydrogen (2H) were ueed. Isotopic exchange ~86 performed in static system connected with ma~8and spectrometer and computer for treatment of mass-spectra calculations of exchange parameters. The interval of pressures investigated WaB 10~150 Pa; the temperatures ranges were 700+950 X (exchange Of 021, 850+1000 (CH4) and 300~600 (C2H4). Mechanisms of exchange between twoatomic molecule O2 and Bu??faCeoxygen atOmB (0) in general are ClaBBified intO thrBB types 14-61, which are connected with three types of dissociative adsorption 171: 1) 220, 2) 20 + (0) and 3) 2(O), where 20 denotes the active surface form of oxygen. The use of the exact isotope-kinetic equations to studied catalysts showed the dominant contribution of the 2-nd exchange type and SW411 contribution of the 3-rd type (5-10X). The important result is the similarity of samples studied in respect to oxygen exchsnge, while these samples have a great differences in respect to oxldatlve coupling. The samples have the 6ame oxygen order of
1992 - Elsevier Science Publishers
B.V.
580
exchange (the I-st) end close values of activation energy (“95kJ). Thus the bond Strength of oxygen with surface of oxides is not essential factor of selectivity in oxidative coupling .(in contrary with complete oxidation). The homoexchsnge (the redistribution of the deuterohydrocarbon molecules) of fouratomic (in respect of atoms H) molecules (CH4 and C2H4) csn proceed through four types of mechanisms depending on atomicitles of surface Intermediate species 181: 1) 4H, 2) 2H + H2, 3) H + H3 and 4) 2H2. It was shown theoreticaly 18,91 the kinetic equations of homoexchange for methane and ethene have the same general form. The use of these equations to obtained experimental data on the isotopic molecules redistribution kinetics proves the third type of mechanism is dominated, i.e. the main Intermediate surface species in the homoexchange of both CH4 and C2H4 contain three atoms of h@rogen. All samples studied have the same order (the I-st) and close values of the activation energy (“95 kJ) in respect to methane homoexchange. Investigated samples are much more active in ethene exchange than In methane exchange. The presence of methane was found to effect on oxygen activation: a small addition CR4 essentially decreased oxygen exchange rate. It could be explained that the active surface forms of oxygen are binding by dissociative methane adsorption: CH4tZOtZ = ZCH3t ZOH . The reversible performance of this reaction realizes the methane homoexchange. It was found the addition of oxygen increased metane exchange rates on the supported rare earth oxides. 1 K.Otsuka, K.Jinno, A.Morikawa, J. Catal., 100 (1986) 353 2 V.R.Choudhary, S.T.Chaudhary, A.M.Rajput, V.H.Rsne, J. Chem. Soc.Chem.Com., (1989) No 9, 555 O.V.Krylov, Proc. 3 M.Yu.Sinev, Yu.P.Tyuleni.n, A.A.Kadushin, Mechanisms, p.93, 5th All-Union Conf. Catalytic Reaction Xoskva, 1990 4 K.Klier, J.Novakova, P.Jiru, J. Catal., 2 (1963) 479 5 V.S.J&zykentov, V.V.Popovski, G.K.Roreskov, Kinet. Katal., 5 (1964) 624 137 6 G.K.Roreskov, V.S.Musykantov, Ann.N.Y.Acad.Sci,213(1973) 7 V.S.Musykantov, React. Klnet. Catal. Lett., 35(1987) 437 8 V.S.Musyksntov, A.A.Shestov, ibid, 32 (1986) 307 9 V.S.Musyksntov, Ibid, 14 (1980) 311