Structure–Activity Relationships of Nickel–Hexaaluminates in Reforming Reactions Part II: Activity and Stability of Nanostructured Nickel–Hexaaluminate‐Based Catalysts in the Dry Reforming of Methane

Abstract

Abstract Ni–hexaaluminates exhibiting a high magnetoplumbite or β“‐alumina phase content (>80 wt %) and high specific surface areas (10–30 m 2 g −1 ) were investigated under dry reforming conditions. Ni content and choice of mirror plane cation are the key factors controlling the structure–property relationship in the dry reforming reaction of CH 4 . The Ni content is favorably kept below a threshold of y =0.25 in ANi y Al 12‐ y O 19− δ , (A=Ba, La, Sr) to ensure controlled nanoparticle formation and to avoid uncontrolled Ni 0 nanoparticle growth apart from the support. Sr,Ni and Ba,Ni–hexaaluminates promote high activity of the catalyst in the dry reforming reaction of CH 4 , but show fast deactivation if the Ni content is maladjusted in the hexaaluminate framework ( y ≥0.5). La,Ni–magnetoplumbites display much lower activity accompanied by fast deactivation. The use of very high calcination temperatures (1600 °C) resulting in low specific surface area is detrimental to the activity in the dry reforming of CH 4 , simultaneously higher hexaaluminate phase content obtained undoes catalytic stability, reasoned by Ni 0 nanoparticles produced after reduction cannot be stabilized over surface defects typically found on hexaaluminate platelets calcined at moderated temperatures (<1300 °C). As a result, larger metallic Ni ensembles are built up, selectivity to coke is increased and catalytic stability is compromised.