Detailed quantitative XAF investigation revealed single-atom Pt interacting with partly reduced CuOα (α<1) as favourable local structure for acetylene semihydrogenation

This study is an addendum to our earlier communication (CEJ, 2024. 479: p. 147496) wherein we compared the structure–activity-relationships of ZSM-5 supported oxalate ligand functionalized platinum alloyed with copper (PtCuOx/Z) or cobalt (PtCoOx/Z) catalysts in semihydrogenation of acetylene (SHA). Herein we provide additional quantitative findings from extended X-ray absorption fine structure spectroscopy (EXAFS) to support the superior ethylene yield (YC2H4) of 87.6 % over (PtCuOx/Z) compared to 62.9 % over PtCoOx/Z at 200°C when acetylene conversion (XC2H2) was highest over both catalysts. X-ray absorption near-edge spectroscopy (XANES) and EXAFS spectra under the SHA showed that besides the Pt-O and Pt-M (M=Co or Cu) bonds that represent oxidized and Pt-metal alloyed particles, respectively, there is an additional Pt-O-M bond wherein O in the partly reduced cobalt and copper oxides is pushing Pt atoms further apart to form Pt-CoO (Pt-O-Co) and Pt-CuOα (α<1) (Pt-O-Cu) local atomic structures. Under the SHA reaction, while the Pt-Co alloy contribution showed a coordination number (CN) of 4.35 which is higher than the 2.21 CN for Pt-Cu alloy, the CN of the Pt-O-CuOα (α < 1) bond (7.45) is 6.48 times higher than the CN of Pt-CoO (1.15). Furthermore, there was no Cu-Cu metal coordination in the PtCuOx/Z under the SHA reaction. These factors combined favor the YC2H4 over PtCuOx/Z. In contrast, the PtCoOx/Z catalyst showed the presence of isolated Pt and significant Co-Co metal CN of 4.45 which in combination promoted C2H4 hydrogenation leading to a lower YC2H4 due to an increase in undesired C2H6 selectivity. This result provides new opportunities for further investigation of Pt in the chemistry of SHA.