Gasification reaction of a lignite char catalysed by Cr, Mn, Fe, Co, Ni, Cu and Zn in dry and wet air

A Spanish lignite was demineralized and pyrolysed in N 2 atmosphere at 1133 K. On the resulting char, metals from Cr to Zn were deposited from nitrates dissolved in ethanol. The behaviour of these supported catalysts in the reaction with dry and wet air was studied by thermogravimetry in the temperature range 733–773 K. To determine the reactivity per unit catalyst surface site, the dispersion of the metals or metal oxides was measured by X-ray diffraction. The dispersion values found were low; the turnover frequencies (TOF) showed that Cu and Cr (probably in the form of Cr 2O 3) are the best catalysts in this reaction when using either dry or wet air. Apparent activation energies were also obtained in the temperature range used; the Arrhenius plot for the copper-char sample shows that in this case the reaction may be diffusion-limited, although there is considerable increase in reactivity close to Tammann's temperature for copper (678 K). Oxygen chemisorption by Cr 2O 3 may justify an oxygen transfer mechanism.