The reduction of nitric oxide with hydrocarbons in an oxidizing atmosphere over metal oxide catalysts.

摘要

As automotive catalytic convertors could experience temperatures greater than 1073 K, a practical catalyst for NO reduction under oxidizing conditions must have both high activity and durability. These requirements may be met by a metal oxide catalyst as metal oxides can be prepared in a hydrothermally stable form. The lean reduction of NO with C{dollar}rmsb3Hsb6{dollar} over Cu-ZrO{dollar}rmsb2, Ga/Alsb2Osb3{dollar}, Cu-Ga/{dollar}rm Alsb2Osb3{dollar}, and Ag/Al{dollar}rmsb2Osb3{dollar} was examined in this thesis.; CO TPR, EPR, XPS, XRD, and steady-state reaction studies of Cu-ZrO{dollar}sb2{dollar} and Cu-Ga/Al{dollar}rmsb2Osb3{dollar} indicated that as the Cu dispersion decreased, the % competitiveness at T{dollar}rmsb{lcub}max{rcub}{dollar} decreased, while the reactivity of the lattice oxygen increased. The low % competitiveness of poorly dispersed Cu catalysts was suggested to result from the reaction of the hydrocarbon with the highly reactive lattice oxygen.; Steady-state reaction studies and pulse experiments over Cu-ZrO{dollar}sb2{dollar} dispelled previous suggestions that gas phase NO{dollar}sb2{dollar} was a necessary intermediate and indicated that NO{dollar}sb2{dollar} was rapidly reduced to NO in the presence of hydrocarbon. A reaction scheme was proposed in which adsorbed NO{dollar}sb2{dollar} reacts with adsorbed hydrocarbon to form a N-containing hydrocarbon intermediate. Further reaction of this intermediate with NO generates N{dollar}sb2{dollar}. In situ IR spectroscopy indicated that cyanide and isocyanate may be the surface intermediates responsible for N{dollar}sb2{dollar} formation.; The NO conversions to N{dollar}sb2{dollar} were high over 2 wt.% Ag/Al{dollar}rmsb2Osb3{dollar} which contained well dispersed Ag ions but low over 6 wt.% Ag/Al{dollar}rmsb2Osb3{dollar} which contained poorly dispersed Ag ions. Based on H{dollar}sb2{dollar} TPR and XRD the different extents of dispersion was suggested to result in the catalysts having different oxidation states under reaction conditions; the 2 wt.% Ag/Al{dollar}rmsb2Osb3{dollar} was believed to contain Ag{dollar}sp{lcub}1+{rcub}{dollar} while the 6 wt.% Ag/Al{dollar}rmsb2Osb3{dollar} was thought to contain a large number of Ag{dollar}sp0{dollar} particles. The presence of Ag{dollar}sp0{dollar} was suggested to result in a high rate of C{dollar}rmsb3Hsb6{dollar} combustion at the expense of N{dollar}sb2{dollar} formation.; A synergistic effect was observed over a mixture of Ag/Al{dollar}rmsb2Osb3{dollar} and Al{dollar}rmsb2Osb3{dollar} and was attributed to the transfer of a very short-lived reaction intermediate from Al{dollar}rmsb2Osb3 to Ag/Alsb2Osb3{dollar} or visa versa.