Effect of potassium content in the activity of K-promoted Ni/Al2O3 catalysts for the dry reforming of methane

In this paper the effect of the potassium content in the structure and properties of the Ni active phase and in the activity and selectivity of the NiK/Al2O3 catalysts for dry reforming of methane has been studied. The following characterization techniques were used: SEM, TEM, temperature programmed reduction (TPR-H-2) and reaction (TPR-CH4), temperature programmed oxidation (TPO) and XAFS. The reforming of methane with CO2 was carried out at 973 K using 0.18 g of catalyst and a mixture CH4:CO2 (50:50, 60 ml/min, space velocity of 22,500 h(-1)). Catalytic tests for 6 and 24 h have been developed. TPR-H-2 and XAFS results reveal that potassium does not modify the arrangement of Ni atoms although facilitates the reduction of nickel species by H-2 due to the modification of the interaction between metallic species and the alumina support. The activity data indicate that the addition of a low amount of potassium (0.2 wt.% K2O) allows to obtain a catalyst with an acceptably high activity (over 63% methane conversion, close to thermodynamic equilibrium) and very low coke deposition (below 30 mg C/g cat. during 6 h reaction). Independently of the amount of potassium, the catalytic activity remains almost constant during at least 24 h. (c) 2005 Elsevier B.V. All rights reserved.