Catalytic enhancement of graphite - CO2 reaction by in situ reduced chromium and nickel from their oxides Cr2O3 and NiO over the temperature range 850-1100°C

Abstract

The kinetics of the CO2 gasification of carbon catalysed by Cr and Ni reduced in situ from their corresponding oxides Cr2O3 and NiO within the temperature range 850-1100°C are reported. Experiments were carried out under a carbon dioxide atmosphere and the isothermal weight loss of the samples was determined as a function of time. The experimental data were interpreted using the grain model in conjunction with a technique involving effectiveness factor proposed by Roberts and Satterfield. Single porous disks made of carbon (graphite)-Cr2O3 and carbon (graphite)-NiO mixtures were employed in a thermogravimetric arrangement. The effect of temperature and reactant gas flow rate on the rate constant for the chemical reaction, which is described according to Langmuir-Hinshelwood kinetics, were determined. It was found that Cr and Ni freshly reduced from their oxides acted as a fairly strong catalyst for the solution-loss reaction, especially at lower temperatures and the catalytic activities were ranked in the order Ni > Cr > Fe. The catalytic effects of these metals were observed to be dependent quite markedly on their history and the method of sample preparation. For the uncatalysed process, the activation energy for the Boudouard reaction was found to be 82·0 kcal mole-1, a value fairly close to that in the literature. For the Cr and Ni catalysed processes, the activation energy values are 10·2 kcal mole-1 and 7·8 kcal mole-1, respectively.