Size-Controlled Synthesis and Microstructure Investigation of Co₃O₄ Nanoparticles for Low-Temperature CO Oxidation

Abstract

Noble-metal-free functional oxides are active catalysts for CO oxidation at low temperatures. Spinel-type cobalt oxide (Co 3 O 4 ) nanoparticles can be easily synthesized by impregnation of activated carbon with concentrated cobalt nitrate and successive carbon burn off. Mean size and particle size distribution can be tuned by adding small amounts of silica to the carbon precursor, as witnessed by whole powder pattern modeling of the X-ray powder diffraction data. The catalytic tests performed after silica removal show a significant influence of the mean domain size and of size distribution on the CO oxidation activity of the individual Co 3 O 4 specimens, whereas defects play a less important role in the present case.

Nanocast Mixed Ni–Co–Mn Oxides with Controlled Surface and Pore Structure for Electrochemical Oxygen Evolution Reaction

“…They reveal two characteristic peaks centered around 855.0–855.2 and 872.6–873.1 eV, assigned to the Ni 2p 3/2 and Ni 2p 1/2 spin–orbit levels, respectively, which are attributed to Ni 2+ species. , The spectra are similar to the spectrum of Ni­(OH) 2 , which might indicate the existence of surface OH groups originating from the conditions used for the removal of the template, as already mentioned above. Spectra of the Co 2p core level present two clear spin–orbit doublets assigned to Co 2p 3/2 and Co 2p 1/2 (Figure b), correlating with previous data in the literature. ,− The shakeup peaks of Co 2p can be used for identification of the oxidation state of cobalt. Increasing the calcination temperature changes the Co 2+ /Co 3+ surface ratio of the Ni x Co y Mn z O 4 samples.…”

“…Increasing the calcination temperature changes the Co 2+ /Co 3+ surface ratio of the Ni x Co y Mn z O 4 samples. For the material calcined at 300 °C, both Co 2+ and Co 3+ species are present on the surface with a slightly increased amount of Co 2+ as compared to the reference spinel Co 3 O 4 . , These results correlate with the assumption that calcination at 300 °C might have led to the formation of a mixture of Co-rich spinel phases, e.g., Co 3 O 4 , NiCo 2 O 4 , and so on, where Co has an oxidation state 3+. Ni x Co y Mn z O 4 calcined at 500 °C show less surface Co 3+ species compared to Ni x Co y Mn z O 4 -300, making Co 2+ species predominant.…”

Synthesis-Structure-Activity Relationships in Co3O4 Catalyzed CO Oxidation

“…It should be noted that in this analysis η is changing mainly as a function of grain size and particle size and that other structural variables, such as the pre-calcination phase, are constant. Moreover, neither particle size nor grain size independently showed a significant correlation with catalytic activity, which is in contrast to other reports that have suggested that smaller particles favor activity due to their greater number of low coordination atoms (Dangwal Pandey et al, 2012 ; Mankidy et al, 2014 ). Here, by directly comparing those two effects, it is evident that the consolidation of grain boundaries is significantly more important than the particle size alone.…”

“…An example of one such system are cobalt oxide nanoparticles. The properties of cobalt oxide nanomaterials, such as phase, morphology, and crystal faceting are known to affect properties such as active site density and redox properties which are important for catalyst reactivity in various oxidation and hydrogenation reactions, but the accessibility of these features through nanoparticle synthesis is poorly established (Jiang and Dai, 2010 ; Dangwal Pandey et al, 2012 ; Wang et al, 2012 ; Bai et al, 2013 ; Pang et al, 2013 ; Li and Shen, 2014 ; Iablokov et al, 2015 ; Ahn et al, 2016 ; Hu et al, 2016 ).…”

Ultra-Low-Temperature CO Oxidation Activity of Octahedral Site Cobalt Species in Co3O4 Based Catalysts: Unravelling the Origin of the Unique Catalytic Property

“…Supported Au nanocluster catalysts have shown excellent activity below 0 °C. − However, a cheaper alternative for this reaction is highly desirable. Some metal oxides, especially Co 3 O 4 , are also known to be active for CO oxidation at ambient temperature. − CO oxidation below even −50 °C over Co 3 O 4 has been intensively studied, and varying activities (in terms of T 50 ) have been reported depending on physical properties and reaction conditions. ,,,− The activity in Co 3 O 4 is significantly enhanced by doping with various metal substituents like Fe, Bi, In, etc., although these metals have hardly any role in the redox reaction itself. − These few metal doped Co 3 O 4 catalysts have shown T 100 for CO oxidation at nearly −100 °C.…”