Modulation effects of Cu modification and ligands (oxalate and borohydride) functionalization on Pt d-band center, upper d-band edge, and alloyed PtCe support acidity on semihydrogenation of acetylene

Decreased in Pt particle sizes shifted the Pt catalyst d -band centre downward of Fermi level leading to formation of ethylene, while large Pt particles shifted d -band centre upward toward Fermi level leading to ethane formation. The modulating effects of Cu modification and oxalate or borohydride ligands functionalization on the structure, catalyst d -band center ( ε d ), upper d -band edge ( ε u ), and acetylene partial hydrogenation of expediently synthesized Ce alloyed Pt supported catalysts were investigated. Firstly, a 5 wt% Pt alloyed Ce was synthesized via flame spray pyrolysis. The PtCe sample was further supported on zeolite Y, ZY, (PtCe/ZY) and copper modified ZY (PtCe/Cu-ZY). Furthermore, the PtCe was supported on two other oxalate and borohydride ligands functionalized copper modified ZY (PtCe/CuX-ZY and PtCe/CuB-ZY, respectively). The high-angle annular darkfield scanning transmission electron microscopy (HAADF/STEM) data showed a reduction in the PtO average particle size from 2.65 nm in PtCeO 2 to average 1.73, 0.64, and 0.30 nm in PtCe/Cu-ZY, PtCe/CuX-ZY, and PtCe/CuB-ZY, which was corroborated by the electron energy-loss spectroscopy (EELS) results wherein nonhomogeneous mixing of elements was seen with segregated Pt clusters in the non-functionalized samples. Conversely, both PtCe/CuX-ZY and PtCe/CuB-ZY samples showed near-perfect homogeneity with no distinct Pt signals. The measured ε u values for PtCe, PtCe/Cu-ZY, PtCe/CuX-ZY, and PtCe/CuB-ZY are +1.85, +0.40, −0.15, and −0.19 eV, respectively. The positive values indicated strong metal-adsorbate bonding typical of large Pt sizes while the negative values indicated weak metal-adsorbate bonding due to highly downsized Pt sizes. The ethylene yield ( Y C2H4 ) over the PtCe sample showed depletion as the reaction temperature increased, while it reflected maxima at 120 °C with 55.3% Y C2H4 over PtCe/ZY. The maxima shifted to 180 °C with enhanced Y C2H4 of 71.4% in PtCe/Cu-ZY. On the contrary, both PtCe/CuX-ZY and PtCe/CuB-ZY exhibited a monotonous increase in Y C2H4 up to the maximum C 2 H 2 conversion with Y C2H4 of 81.9% and 92.1% at 180 and 160 °C, respectively. These results showed that both the Cu modification and ligands functionalization were highly invaluable to enhance the properties and activities of the semihydrogenation of acetylene (SHA) catalysts.