Fe-Ni bimetallic atomic catalysts supported on ZIF-8 derived carbon for C3H6-SCR of NO: Catalytic performance and reaction mechanism

Abstract

N-doped hollow carbon derived from ZIF-8 was utilized as a carrier to prepare the atomically dispersed Fe-Ni bimetallic catalysts, i.e., (Fe, Ni)/NC. The reactivity of C3H6-SCR was evaluated. The strong synergistic interactions between Fe and Ni promoted the activity of C3H6-SCR at low temperatures under different oxygen conditions (0–6 % O2). The NO conversion increased from 74.5 % to 93 % in the 150–300 °C and the N2 selectivity was about 95.5 %. The dual-atom catalysts were characterized by SEM, EELS, XRD, XPS, FTIR, and N2 adsorption/desorption, as well as the AC-HAADF-STEM, XANES, EXAFS, and Wavelet Transform data, etc. Results showed that (Fe, Ni)/NC catalyst showed the rhombic dodecahedral and displayed type IV isotherms with prominent H4 hysteresis loop, suggesting the loading of Fe and Ni atoms on the carbon matrix resulted in the coexistence of micropores and mesopores. Bimetallic active sites can enhance catalytic activity. As reflected by the Fe K-edge EXAFS spectra with k2-weighted Fourier-transform (FT) in R-space, the coordination of active sites Fe-N and Fe-Ni appeared at 1.50 Å and 2.3 Å, respectively. Similarly, the Ni-N and Ni-Fe coordination were found to be positioned at 1.4 Å and 2.3 Å, respectively. The XANES and EXAFS data further confirmed that the (Fe, Ni)/NC catalysts existed in the unique bimetallic active site of the N3-Fe-Ni-N3. In situ DRIFTS showed O2 could promote the production of nitrate and CxHyOz substances, e.g., acetaldehyde and acetate, at Fe-Ni sites or surface defective oxygen sites. Nitrate and acetate species are the main active substances of C3H6-SCR.