Reduction Of Cobalt Species Research Articles

Influence of synthesis conditions of Co/SiC and TiC-SiC catalyst on H2 production from NH3

Developments in suitable catalytic design (including novel and low-cost supports and active metal) gain the perspective of ammonia as ‘hydrogen carrier’ for the decarbonization of the energy sector. Herein, this study provides valuable insight into the utilization of different cobalt loadings (1.5–10 wt%) and cobalt precursors (nitrate, citrate, acetate and chloride) on SiC and TiC-SiC-based supports for hydrogen production from ammonia decomposition. The reduction degree, particle size and surface area were found to determine the catalytic activity. Hence, 2.5 wt% and 5 wt% of Co led to an optimal particle size and amount of active sites on TiC-SiC and SiC supports, respectively. The choice of a suitable cobalt precursor had a clear effect on the reduction of cobalt species. A higher reduction degree with an enhanced ammonia conversion resulted from the nitrate precursor, whereas a lower catalytic performance was obtained when cobalt chloride was used in both supports. On the other hand, the in-situ ammonia pre-treatment was found to be an efficient alternative for activating the cobalt catalysts in both supports. Among the different investigated catalyst formulations, the highest activity was achieved when a nitrate precursor and both in-situ H2/Ar or NH3/Ar pre-treatments were used to prepare the TiC-SiC-based catalyst. The 2.5Co-N/TiC-SiC catalyst reached a specific activity of 0.11 molH2 molCo-1 s-1 with an ammonia conversion higher than 80 % at 450 ºC.

Selective oxidation of cyclohexane over Co-APO-5: Effects of solvent and modification method on the catalytic performance

A series of Co-APO-5 molecular sieves were prepared and used as the catalysts in the selective oxidation of cyclohexane; the effects of solvent and modification method on the catalytic performance of Co-APO-5 were investigated. The results illustrated that polar solvents containing π-bonds are favorable for the oxidation reaction and the conversion of cyclohexane increases with the increase of solvent polarity. The introduction of Si and F leads to a decrease of the tetrahedral cobalt content in the Co-APO-5 framework. However, introducing F can improve the crystallinity of Co-APO-5, whereas adding Si may promote the oxidation and reduction of cobalt species and then enhance the catalytic activity in oxidation. In general, the activity of Co-APO-5 catalysts is related to the content of tetrahedral cobalt in the framework, suggesting that the framework Co(II) is probably the catalytically active species for the oxidation of cyclohexane.

In-situ X-ray absorption spectroscopy analysis of capacity fade in nanoscale-LiCoO2

The local structure of nanoscale (∼10–40 nm) LiCoO2 is monitored during electrochemical cycling utilizing in-situ X-ray absorption spectroscopy (XAS). The high surface area of the LiCoO2 nanoparticles not only enhances capacity fade, but also provides a large signal from the particle surface relative to the bulk. Changes in the nanoscale LiCoO2 metal-oxide bond lengths, structural disorder, and chemical state are tracked during cycling by adapting the delta mu (Δμ) technique in complement with comprehensive extended X-ray absorption fine structure (EXAFS) modeling. For the first time, we use a Δμ EXAFS method, and by comparison of the difference EXAFS spectra, extrapolate significant coordination changes and reduction of cobalt species with cycling. This combined approach suggests Li–Co site exchange at the surface of the nanoscale LiCoO2 as a likely factor in the capacity fade and irreversible losses in practical, microscale LiCoO2.

Studies on Cobalt-Based Catalyst to Synthesize Heavy Hydrocarbons

With incipient impregnation method, cobalt-based catalysts were prepared. The effects of the ZrO2 modification of support and the addition of the second metal Ru on heavy hydrocarbon synthesis were investigated in a fixed-bed reactor. The results revealed that, in cobalt-based catalysts modified with ZrO2, cobalt species were presented in the form of Co3O4, Zr species were highly dispersed or amorphous on the surface of the catalysts. ZrO2 addition also increased the desorption amount of CO, which was correlative with the degree of reduction of cobalt species. When the catalysts modified with ZrO2, the strong interaction between Co species and γ-Al2O3 support was replaced by a weak interaction between Co species and ZrO2. The ZrO2 modification increased the amount of easily reducible Co species. It is noteworthy that addition of a small quantity of Ru promoted the reduction of cobalt species, which led to the reduction temperature decreasing. For the 15w%Co0.4w%Ru4.3w%ZrO2/γ-Al2O3, at a reaction condition as feed gas ratio n(H2):n(CO)=2.0, 483K, 1.5MPa and 800h-1, the conversion of CO was 76.98 %, the selectivity of C5+ 88.36 %, the chain growth probability 0.86, and as to 15.0%Co0.4%Ru/γ-Al2O3, the conversion of CO was 67.15%, the selectivity of C5+ 84.41% and the chain growth probability 0.84.

Pore Size Effects in Fischer Tropsch Synthesis over Cobalt-Supported Mesoporous Silicas

Pore size effects on Fischer Tropsch reaction rates and selectivities over cobalt catalysts were studied at atmospheric pressure using periodic (SBA-15 and MCM-41) and commercial mesoporous silicas as catalytic supports. The catalysts were characterized by nitrogen adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and oxygen titration. Fischer Tropsch reaction rates were found much higher on cobalt catalysts with the pore diameter exceeding 30 Å than on the narrow pore catalysts. A larger diameter of catalyst pores also led to significantly higher C5+ selectivities. The catalytic effects were interpreted in terms of different cobalt particle size and reducibility in the wide pore and narrow pore silicas. XRD and XPS showed that the size of supported cobalt species strongly depended on the pore size, increasing with increases in catalyst pore diameter. TGA and oxygen titration indicated higher extent of overall reduction of cobalt species in wide pore supports. Lower reducibility of small cobalt particles is likely to be one of the reasons responsible for the lower Fischer Tropsch reaction rates and higher methane selectivities on narrow pore cobalt catalysts.