Catalytic activation of a non-noble intermetallic surface through nanostructuration under hydrogenation conditions revealed by atomistic thermodynamics

Abstract

The unique electronic and crystallographic structure of intermetallics is known to result in excellent catalytic performances for selected chemical reactions. Moreover, owing to the specific bonding network of these compounds, a high structural stability of their surfaces is generally assumed, even under reaction conditions. Transition metal (TM = Fe and Co) aluminides of the Al₁₃TM₄ stoichiometry have been previously demonstrated to exhibit high activities and selectivities in partial hydrogenation of alkynes and alkadienes. Focusing on the Al₁₃Co₄(100) surface as a model catalyst for butadiene hydrogenation, the hydrogen-rich reaction conditions are predicted – based on DFT calculations and atomistic thermodynamics – to modify the relatively flat surface structure identified under ultra-high vacuum, in the form of highly cohesive clusters emerging from the bulk lattice. Unlike the flat one, this termination presents favorable adsorption properties, able to make it catalytically active and fully selective to butenes. In addition, its contrasted catalytic behavior as compared to that of the reference Al₁₃Fe₄(010) surface – which is more active but less selective – is rationalized in terms of butadiene, butene and hydrogen co-adsorption properties. This work demonstrates that a realistic description of surface structures under reaction conditions is mandatory for designing new-generation catalysts based on the complex topology of intermetallic surfaces.