Syngas production over La0.9NiyAl11.95-yO19-δ catalysts during C14-alkane partial oxidation: Effects of sulfur and polycyclic aromatic hydrocarbons

Abstract

Partial oxidation studies were conducted over a series of Ni-substituted lanthanum hexaaluminate catalysts, La0.9NiyAl11.95-yO19-δ (y = 1.0, 0.8, 0.4 and 0.2) to evaluate the effect of higher alkane, sulfur and polycyclic aromatic hydrocarbons using tetradecane (n-C14), dibenzothiophene (DBT) and 1-methylnapthalene (1-MN) as model reaction compounds. XRD showed the Ni-substituted lanthanum hexaaluminate catalysts to have magnetoplumbite structure. Lattice parameters along the a,b-axis are shown to increase systematically with increasing Ni substitution. The unit cell is also shown to increase systematically with Ni substitution providing clear evidence of Ni2+ substitution for Al3+ in the lanthanum hexaaluminate lattice. Catalytic activity and product yields were evaluated by temperature programmed surface reaction (TPSR) using n-C14 partial oxidation as a probe reaction. Between 750 and 900 °C, H2 and CO yields are shown to increase with increasing Ni surface sites while aromatic and olefin yields are shown to decrease. Step response experiments were performed to show the effect of 0.1 wt% 1-MN addition on catalytic activity and performance. As expected, at lower Ni substitution, thermal chemistry predominates suggesting fewer available active Ni sites. At the conditions tested, the site blocking effect is shown to be reversible at all levels of Ni substitution. Similar catalytic behaviors are observed with step response experiments to 50 ppm w/w dibenzothiophene (DBT) where site blocking is shown to produce a concomitantly greater effect on catalytic performance and active site occlusion with catalysts that have less active sites. The step response to DBT is also observed to be reversible. Post analysis of the used catalysts shows that coke deposition is greater on the catalysts with lower Ni substitution.