Speaker
Description
CO2 reduction should minimize hydrogen use while co-producing base chemicals. Plasma pyrolysis generates black carbon along with ethylene and acetylene1. Due to operational hazards, concentrated acetylene must be selectively hydrogenated into valuable ethylene. Pd-based catalysts are commonly used for this reaction. However, the surface and subsurface dynamics of active catalysts during acetylene hydrogenation are not yet fully understood. A rational design approach involves using 2-D Laterally Condensed Catalysts (LCCs), which features a nonreactive functional interface between a thin metal layer (3 nm Pd, Pd-Au), a buffer layer (20 nm SiO2), and a reactive interface exposed to the feed gas. These interfaces can be examined using operando spectro-microscopy. Pd-Au LCCs were employed to investigate catalyst multidimensional development during acetylene hydrogenation. DFT calculations show that higher selectivity towards semi-hydrogenation can be achieved by introducing C or Au to the Pd LCC. The heteroelement modifies the adsorption energies of acetylene and ethylene, favoring ethylene desorption before full hydrogenation occurs. Au not only mimics atomic carbon in Pd LCC, affecting Pd local electronic properties but also temporarily introduces mesoscopic geometric effects by influencing the distribution of Pd atoms at the surface as well as the concentration of Pd:C and Pd:H species in the subsurface. In the absence of Au, more carbon diffuses into the Pd (XPS), corroborated by the presence of a carbon interlayer beneath the spent Pd LCC (TEM). Prolonged operation (>20 h) paradoxically showed that the superior initial selectivity of Pd-Au LCC catalysts diminishes over time due to significant Pd segregation to the surface (TEM). On the macroscopic scale, less surface carbon blockage was observed (Raman). Additionally, Au in Pd LCC mitigated catalyst agglomeration. Single-phase bulk catalysts with varying Pd-to-Au atomic ratios were also studied as reference catalysts.
Reference
1 Gladisch, H. Acetylen‐herstellung im elektrischen lichtbogen. Chem. Ing. Tech. 41, 204-208, (1969).
