In this paper, Co3O4/CoO nanoparticles prepared from solid state thermal decomposition of [Co(NH3)5Cl]Cl2/PVA composite at 600oC for 1 h. Co3O4/CoO nanoparticles was characterized by Fourier transformed infra-red spectroscopy (FT-IR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM). XRD results show that nanoparticles contain mixture of CoO and Co3O4. TEM results show that the crystalline size of nanoparticles is in 50 – 500 nm.

Cobalt nanocrystals were prepared by precipitation method using cobalt nitrate precursor in the presence of 1) Oxalic acid, 2) KOH, and thus oxidized to grow on varying temperatures. The morphology and crystallite size of cobalt oxide (Co3O4) nanocrystalline were characterized by SEM and XRD patterns.The SEM images of initial powder showed nanorods and second one showed nanoparticles.The XRD patterns studies of these nanopowders indicated a cubic polycrystalline structure for both samples. Purity of polycrystalline powders were investigated by IR spectroscopy. The radius of nanorods of first sample was calculated to be 40 nm approximately by scherrer formula. The particle size of second sample calculated by scherrer equation, and the average particle size become 16.5 nm at 573 K calcinating temperature.

The objective of this research is to model and optimize the effective operation parameters of catalytic oxidation of carbon monoxide (CO) using 15 wt. % cobalt-cerium oxide with weight ratio of cobalt to cerium=1. 5 supported by multiwalled carbon nanotubes by response surface method. Therefore, 30 sets of experiments were employed to evaluate the influence of the four independent variables including temperature, gas hourly space velocity, O2 concentration, and CO concentration in 5 levels (-2,-1, 0, +1, +2). The experimental design results showed that there is a quadratic model as a functional relationship between CO conversion (response variable) and four independent variables. The data from response surface method explored that CO conversion was highly affected by temperature and O2 concentration. The optimum amounts of the effective parameters for 100% conversion of CO were followed as: temperature= 200 ° C, CO concentration =780 ppm, O2 concentration =5. 25 vol. %, and Gas hourly space velocity= 10000 h-1. Analysis of variance with R2 value of 0. 9994 showed a satisfactory correlation between the experimental data and predicted values for conversion of carbon monoxide.

Cobalt oxide is a candidate material for thermochemical heat storage via reversible reduction and re-oxidation reactions. In this research, the relationship between Gibb’ s free energy (Δ G) with reaction temperature (T) and oxygen partial pressure (PO2) and the relationship between equilibrium temperature (Te) and PO2 were investigated theoretically. It was found that an increase in reduction temperature decreases the reduction Δ G. Also, increasing PO2 increases the Te and reduces Δ G. In addition, isothermal reduction kinetics of Co3O4-5wt% Al2O3 (CA) and Co3O4-5wt% Y2O3 (CY) were investigated at various temperatures (1040-1130° C) by thermogravimetric analysis. Results showed that the CA sample desorbs more oxygen than the CY sample in similar conditions. A model-free method was used to calculate the reduction activation energies. It was found that activation energy required for reduction of CA and CY samples, depending on conversion fraction (α ), is in the range of 40-65 kcal/ mol and 25-50 kcal/mol, respectively. Furthermore, results showed that the reduction activation energy of CA and CY samples decreased and increased as the conversion fraction (α ) increased, respectively. The difference in the performance of alumina and yttria additions on the reduction of cobalt oxide was attributed to their ionic radii difference, the ability to create new compounds with different decomposition temperatures, and their different effect on the sintering of cobalt oxide particles.

The effect of Al2O3 (1-10 wt %) and Y2O3 (1-10 wt %) additions on thermochemical heat storage properties of Co3O4/CoO system was investigated by thermogravimetry, XRD, and SEM analyses. Results showed that the addition of Al2O3 to Co3O4 at constant 8 h mechanical activation improved the redox cycle stability and increased oxygen sorption value and rate. It was found that oxygen sorption and their rate decreased with increasing the alumina content to more than 8 wt %. The formation of the spinel phase and an increase in its amount by increasing the alumina content led to a decrease in the oxygen sorption capacity. SEM studies showed that Al2O3 prevented the sintering and particle growth of cobalt oxide particles during reduction and re-oxidation processes. In addition, results showed that the addition of Y2O3 in all ranges to Co3O4 improved the redox cycle stability of cobalt oxide; however, it significantly decreased the oxygen sorption in the Co3O4/CoO system. XRD patterns of a sample containing 10 wt % yttria before the redox process indicated the presence of only Co3O4 phase; however, after three redox cycles, other phases including CoO and Y2O3 appeared.