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

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_yAl_12-yO_19-δ, (A=Ba, La, Sr) to ensure controlled nanoparticle formation and to avoid uncontrolled Ni⁰ 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 CH₄, simultaneously higher hexaaluminate phase content obtained undoes catalytic stability, reasoned by Ni⁰ 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. Mission nickel part II: The influence of major parameters of Ni-hexaaluminates such as calcination temperature, Ni substitution degree and mirror plane cation (Ba, La and Sr) are investigated in this study. The achieved highly textural growth of Ni⁰ nanoparticles can be used to perform stably dry reforming of methane at elevated pressure.