Effects of cobalt loading on the properties of alumina-supported cobalt oxide

Synthesis of Mesoporous γ-Alumina-Supported Co-Based Catalysts and Their Catalytic Performance for Chemoselective Reduction of Nitroarenes

“…These results demonstrated that the diffraction peaks for spinel phases of the x Co 3 O 4 /γ-MA materials in the XRD patterns of Figure were predominantly due to the Co–Al spinels instead of bulklike Co 3 O 4 crystallites. It was observed that when the Co content was increased to 20 wt % in the gels, the H 2 consumption in the temperature region of 500–770 °C could be clearly deconvoluted into two curves peaked at ∼570 and ∼675 °C, respectively, in agreement with the analyses of TPR profiles on alumina-supported Co oxides in the previous literature. − Such a large difference of these two reduction temperatures (>100 °C) could not be caused by the two-step reduction of Co 3+ ions (Co 3+ → Co 2+ → Co 0 ) but seemed to arise from the individual reduction of surface Co 3+ ions and Co 3+ –Al 3+ oxide crystallites, respectively . Generally, the starting reduction temperatures for all types of the Co species shifted to lower reduction temperatures, and the ratios of low-temperature H 2 consumptions to high-temperature ones clearly increased with raising the Co content in the gels.…”

“…It was clear that compared to those of the 20Co 3 O 4 /γ-MA sample, the total peak areas of H 2 consumptions associated with Co 3 O 4 crystallites, surface Co 3+ ions, and Co 3+ –Al 3+ oxide crystallites exhibited an obvious increase, whereas the one due to the Co δ Al (8/3–2/3δ) O 4 spinel had a significant decline. It should be noted that TPR peak locations of supported Co oxide species showed a high complexity due to the interaction between Co species and support, which have a close relation with the nature of support, preparation method, particle size, Co content, calcination conditions, and reduction gas composition; therefore, several interpretations for the Co oxide species supported on alumina in the published literature have still been ambiguous and even sometimes contradictory to date. − …”

Reoxidation and Deactivation of Supported Cobalt Fischer−Tropsch Catalysts

“…The TPR traces indicate that the oxides formed during H 2 O/He treatment (curve b in Figure ) are different from the oxides present in the fresh (calcined) catalyst (curve a). The origin of the TPR peaks observed for the calcined catalyst has been discussed in several previous papers. − Briefly, low-temperature peaks (500−700 K) are usually assigned to reduction of large, crystalline Co 3 O 4 particles, whereas the high-temperature peak (800−1000 K) is attributed to highly dispersed amorphous cobalt oxides, interacting strongly with the alumina support. In the presence of metal promoters like Pt or Re, the reduction temperature of this phase is shifted to lower temperatures. , Cobalt aluminate spinel, formed by diffusion of cobalt ions into the alumina lattice, requires even higher reduction temperatures, usually between 1100 and 1200 K. (The 518 K peak shown in curve a is caused by reductive decomposition of residual nitrates on the catalyst 11,13,16 ).…”

“…In the unreduced state, the cobalt/alumina system is known to contain several cobalt oxide phases, each having different characteristics with respect to dispersion, extent of interaction with the support, and ease of reduction. − The TPR of the H 2 O/He-treated catalyst suggests that some changes in the distribution of these phases are occurring during the H 2 O/He treatment. The virtually unchanged position of the low-temperature peak (615 vs 628 K for the unreduced catalyst) seems to indicate no major changes in the properties of the large, crystalline Co 3 O 4 particles.…”

X-ray Absorption Spectroscopic Studies at the Cobalt K-Edge on a Reduced Al2O3-Supported Rhenium-Promoted Cobalt Fischer−Tropsch Catalyst

“…The synthesis of hydrocarbons is an important stage in converting natural gas to petrochemicals. This is exemplified by the Fischer−Tropsch process in which linear high-molecular-weight aliphatic hydrocarbons are synthesized by catalytically hydrogenating carbon monoxide using alumina-supported cobalt as the catalyst. − The paper by Holmen et al contains a comprehensive review of the recent literature concerning this system and its variations.…”