he characteristic study,by means of in-situ IR spectroscopy, of chemisorbed species on the Ni-catalysts for the partial oxidation of methane(POM)to syngas demonstrated the existence of CH_x(a)and H_xCO(a)adspecies on...he characteristic study,by means of in-situ IR spectroscopy, of chemisorbed species on the Ni-catalysts for the partial oxidation of methane(POM)to syngas demonstrated the existence of CH_x(a)and H_xCO(a)adspecies on the functioning Ni-catalysts, Several designed experimental investigations on the reactivities of methane with CO_2 and with O_2,respectively,over the Ni-catalysts, and of CO_2 with the prereduced Ni-catalyst,ats well as of the deposited carbon with CO_2 and with O_2,respectlvely,liave been carried out and the reLqults were unfavorable to the two-step mechanistic interpretation proposed for the POM reaction. By means of tlie BOC-MP Approach,energetics of a set of elementary reactions,which may be involved in the POM process,on the clean(111)surface of Ni,Fe,Cu and Pd, re- spectively,has been studied.The result;of the experiments and the calculation of the present work favor the direct catalytic dissociation-plus-surface oxidation-plus-further debdrogenation mechanism as the dominant pathway making major contribution to the POM reaction.展开更多
ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the ...ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the interaction ofthese dioxygen adspecies with CH_4 and with CH_3 · (radical) from gas pliase liasbeen investigated. The results indicate that both oxides tend to forni less cliargedadspecies of dioxygen, with the flat-lying adsorption on (110) surface most favor-able energetically. All these cliemisorbed dioxygen species are capable of interactingeffectively with CH_4 and Abstract ing one hydrogen atom from the CH_4 molecule andtheir tendencies to reassociate with CH_3 · , which would easily lead to deep oxida-tion of the fragments of hydrocarbons, are enhanced with inereasing negativecliarges on them. In comparison with Na_2O, K_2O has a little stronger tendency tostabilize less charged dioxygen adspecies; this has a close relation with the knownexperimental fact that K￣+ showed better promoting effect than Na￣+ in improvingC_2-selectivity in methane oxidative coupling (MOC ).展开更多
文摘he characteristic study,by means of in-situ IR spectroscopy, of chemisorbed species on the Ni-catalysts for the partial oxidation of methane(POM)to syngas demonstrated the existence of CH_x(a)and H_xCO(a)adspecies on the functioning Ni-catalysts, Several designed experimental investigations on the reactivities of methane with CO_2 and with O_2,respectively,over the Ni-catalysts, and of CO_2 with the prereduced Ni-catalyst,ats well as of the deposited carbon with CO_2 and with O_2,respectlvely,liave been carried out and the reLqults were unfavorable to the two-step mechanistic interpretation proposed for the POM reaction. By means of tlie BOC-MP Approach,energetics of a set of elementary reactions,which may be involved in the POM process,on the clean(111)surface of Ni,Fe,Cu and Pd, re- spectively,has been studied.The result;of the experiments and the calculation of the present work favor the direct catalytic dissociation-plus-surface oxidation-plus-further debdrogenation mechanism as the dominant pathway making major contribution to the POM reaction.
文摘ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the interaction ofthese dioxygen adspecies with CH_4 and with CH_3 · (radical) from gas pliase liasbeen investigated. The results indicate that both oxides tend to forni less cliargedadspecies of dioxygen, with the flat-lying adsorption on (110) surface most favor-able energetically. All these cliemisorbed dioxygen species are capable of interactingeffectively with CH_4 and Abstract ing one hydrogen atom from the CH_4 molecule andtheir tendencies to reassociate with CH_3 · , which would easily lead to deep oxida-tion of the fragments of hydrocarbons, are enhanced with inereasing negativecliarges on them. In comparison with Na_2O, K_2O has a little stronger tendency tostabilize less charged dioxygen adspecies; this has a close relation with the knownexperimental fact that K￣+ showed better promoting effect than Na￣+ in improvingC_2-selectivity in methane oxidative coupling (MOC ).
