Double effect of La as a promoter for Ni/Al2O3 cordierite monoliths in the oxydehydrogenation of ethane (ODE)

Abstract

In the present work different amounts of lanthanum were added to Ni/Al2O3 cordierite monoliths with the objective to enhance the catalytic performance of the un-promoted structured catalyst in the oxidative dehydrogenation of ethane (ODE). The impact of the amount of promoter on the catalytic performance of the structured catalysts is discussed through the use of different characterization techniques: LRS, FTIR, Py-TPD, TPR, XPS and SEM-EDX. The incorporation of La was found to increase ethane conversion by an increase in the reducibility of Ni species, with a drop in the ethylene selectivity. Despite this drop, at constant reaction temperature the olefin selectivity maintained a constant value with the increase of ethane conversion, generating a beneficial effect in these catalysts. The presence of La generated: i) a new type of Ni2+ species due to Ni-La-O interactions and ii) La-Al-O species, which moderated the Ni-Al ones promoting the drop of the ethylene selectivity. Both species also modify the total acidity and reduce the strong acid sites, preventing ethylene oxidation. Thus, as the ethylene production increases, its selectivity remains invariant. An optimal La/Ni ratio was found around 0.08, which generated appropriate interactions among the active species, boosting the ethylene yield at 400 °C by 2.7 times from 4.9% (un-promoted structured catalyst, Ni-M) to 13.4% (NiLa-M, La/Ni: 0.08).