Low-temperature oxidation of CO catalysed by Co3O4 nanorods

Abstract

Low-temperature oxidation of CO, perhaps the most extensively studied reaction in the history of heterogeneous catalysis, is becoming increasingly important in the context of cleaning air and lowering automotive emissions. Hopcalite catalysts (mixtures of manganese and copper oxides) were originally developed for purifying air in submarines, but they are not especially active at ambient temperatures and are also deactivated by the presence of moisture. Noble metal catalysts, on the other hand, are water tolerant but usually require temperatures above 100 degrees C for efficient operation. Gold exhibits high activity at low temperatures and superior stability under moisture, but only when deposited in nanoparticulate form on base transition-metal oxides. The development of active and stable catalysts without noble metals for low-temperature CO oxidation under an ambient atmosphere remains a significant challenge. Here we report that tricobalt tetraoxide nanorods not only catalyse CO oxidation at temperatures as low as -77 degrees C but also remain stable in a moist stream of normal feed gas. High-resolution transmission electron microscopy demonstrates that the Co(3)O(4) nanorods predominantly expose their {110} planes, favouring the presence of active Co(3+) species at the surface. Kinetic analyses reveal that the turnover frequency associated with individual Co(3+) sites on the nanorods is similar to that of the conventional nanoparticles of this material, indicating that the significantly higher reaction rate that we have obtained with a nanorod morphology is probably due to the surface richness of active Co(3+) sites. These results show the importance of morphology control in the preparation of base transition-metal oxides as highly efficient oxidation catalysts.

Self-healing catalysts: Co3O4 nanorods for Fischer–Tropsch synthesis

“…In contrast, the nanoparticles possess {111} and {001} facets where the only surface species is Co 2+ . 20 A similar effect of faceting has been observed for the electrocatalytic oxygen reduction in cobalt oxide nanocatalysts for DMFC. 21 This effect suggests that by carefully selecting the crystallographic planes of Co 3 O 4 exposed at the catalyst surface, the reduction of the catalyst could be promoted, effectively negating oxidation during FTS.…”

“…19 Another recent report illustrated significant enhancement of surface redox reactions on cobalt oxide nanorods, as compared with cobalt oxide nanoparticles. 20 Cobalt oxide nanorods exhibit {110} facets with both Co 2+ and Co 3+ exposed on the surface. In contrast, the nanoparticles possess {111} and {001} facets where the only surface species is Co 2+ .…”

“…The Co nanorods and nanoparticles studied were synthesized following literature, 20,27 and the general morphologies are shown in the transmission electron microscopy (TEM) images, Fig. 1 and 20,27 The synthesized Co nanoparticles exhibit particle sizes between 10 nm and 40 nm.…”

“…1 and 20,27 The synthesized Co nanoparticles exhibit particle sizes between 10 nm and 40 nm. The particle sizes of the nanorods and nanoparticles are comparable to the size range (10-210 nm) typically investigated for model FTS catalysts.…”

Catalysis on singly dispersed bimetallic sites

“…Reduction of nitric oxide with CO was used as a probing reaction. Co 3 O 4 nanorods were synthesized through a colloidal method [8][9][10] . Rh atoms were introduced to the surface of Co 3 O 4 nanorods through precipitation of Rh 3 þ in the format of Rh(OH) Z species (Fig.…”