Shape-Dependence of Pd Nanocrystal Carburization during Acetylene Hydrogenation

Abstract

This interdisciplinary work combines the use of shape-and size-defined Pd nanocrystals (cubes of 10 and 18 nm, and octahedra of 37 nm) with in situ techniques and DFT calculations to unravel the dynamic phenomena with respect to Pd reconstruction taking place during acetylene hydrogenation. Notably, it was found that the reacting Pd surface evolved at a different pace depending on the shape of the Pd nanocrystals, due to their specific propensity to form carbides under reaction conditions. Indeed, Pd cubes (Pd(100)) reacted with acetylene to form a PdC 0.13 phase at a rate roughly 6-fold higher than that of octahedra (Pd(111)), resulting in nanocrystals with different degrees of carburization. DFT calculations revealed changes in the electronic and geometric properties of the Pd nanocrystals imposed by the progressive addition of carbon in its lattice.

Importance of surface carbide formation on the activity and selectivity of Pd surfaces in the selective hydrogenation of acetylene

“…Since the reaction energy of C 2 H 2 decomposition to produce 2C + 2H are more negative on Pd(100) than Pd(111), it can be concluded that the overall reaction barrier of carbon atom production should be lower over Pd(100). These results are in good agreement with the experimental results reported very recently, that acetylene reacts much faster with Pd(100) to form Pd carbide than with Pd(111) surface [40].…”

Preparation and structure-property relationships of supported trimetallic PdAuAg catalysts for the selective hydrogenation of acetylene

“…The negative shift of the reflection peak indicates that C is incorporated into Pd atoms, which induces lattice expansion. The lattice expansion (lattice parameter, a) is in proportion to the fraction of guest atoms (x = C/Pd), as expressed by the following equation [71]: a = a 0 + 0.69x (Å). Therefore, the x value of the m-PdAuAg 2 catalyst is 0.028, approximately double that of the cPdAuAg 2 catalyst.…”

Composition of the Green Oil in Hydrogenation of Acetylene over a Commercial Pd‐Ag/Al2O3 Catalyst

“…The most widely adopted process for acetylene removal is selective hydrogenation over supported Pd‐based catalysts 1, 2. In addition to its great industrial significance, this reaction has been frequently used as a model reaction for theoretical investigation 3–7, e.g., rational design of heterogeneous catalysts 8–10, testing new in situ characterization methods 11–16 etc.…”