Comparative study of structure-catalytic activity relationship for Ni–Cr–Al–O and Cu–Ni–Cr–Al–O spinel oxide solid solutions

Abstract

A spinel solid solution expressed by a composition formula of Cu x Ni 1¹x Al 1.8 Cr 0.2 O 4 (0¯x¯0.2) was studied focusing on the role of Cu species in the catalytic activity toward NO reduction under a simulated three-way catalysis condition. X-ray Rietveld analysis revealed that Cu and Cr prefer to occupy the tetrahedral site and the octahedral site, respectively, whereas Ni and Al are distributed across both sites. Although NiAl 1.8 Cr 0.2 O 4 (x = 0) showed negligible catalytic activity for NO reduction, the partial replacement of Ni by Cu significantly enhanced the activity, achieving the highest activity at x = 0.05 not only for NO reduction but also for CO and C 3 H 6 oxidation. Based on the infrared spectra and pulsed reaction experiments, it was concluded that the monovalent Cu site in the tetrahedral site plays a key role in CO chemisorption, oxygen vacancy formation, and subsequent NO reduction via the Marsvan Krevelen mechanism.

Cr–Fe–Ni–Cu Quaternary Nanostructure as a Substitute for Precious Metals in Automotive Three-Way Catalysts

“…Part of the added Cr may be incorporated into the NiFe 2 O 4 moiety to form a multinary oxide phase. According to our previous study, 12 , 45 the incorporation of Cr into spinel oxides such as in Cu 0.05 Ni 0.95 Al y Cr 2– y O 4 effectively improves the activity for C 3 H 6 –O 2 reactions.…”

Heat- and corrosion-resistant catalytic materials for environmental and energy applications

“…22)26) The second example is a bulk solid solution based on multicomponent spinel-type oxides whose composition is expressed by Cu 0.05 Ni 0.95 Al 1.8 Cr 0.2 O 4 . 27), 28) This quaternary oxide exhibited an NO reduction activity under practical TWC condition in the presence of H 2 O (²5 %) even after thermal aging at 900°C. By contrast, most conventional binary and/or ternary spinel oxides lose the NO reduction activity in the presence of water vapor and/or after high-temperature aging.…”