Construction of a copper-bismuth catalyst featuring Bi-N4 sites and synergistic Bi clusters derived from TCPP(Bi)@HKUST-1 for enhanced formaldehyde to butynediol

Abstract

The construction of functional catalysts that efficiently catalyze in a reducing atmosphere is considered rather challenging. In this study, the catalysts bridged by Bi-N₄ between copper and bismuth species were prepared. Herein, Bi-N₄ and bismuth cluster sites were incorporated into porous carbon–nitrogen networks along with copper nanoparticles (Bi_SAC&Clu-Cu-NC). For the synthesis, metalloporphyrin-modified HKUST-1 (TCPP(Bi)@HKUST-1) was employed as a precursor. Additionally, metalloporphyrin functioned as a capping agent during catalyst preparation, thereby enhancing the dispersion of Bi species after calcination. Notably, the Bi_SAC&Clu-Cu-NC catalyst demonstrated 93.8 % selectivity towards 1,4-butynediol over 20 h at a Bi loading of 0.6 wt% in a reducing atmosphere of acetylene and formaldehyde. Furthermore, a mechanistic model is proposed that elucidates the observed synergistic catalytic behavior based on experimental characterization and DFT calculations. This proposed model is termed “Nanoparticles with Cluster and Single Metal Sites”(NCS mechanism). The retention of the Bi cluster structure within the material matrix plays a pivotal role in enhancing the adsorption and activation of formaldehyde. Interfacial effects between different copper species favour the activation of the reaction substrate acetylene. Additionally, the Bi-N₄ structure can function as a crucial conduit, facilitating electron transfer between Cu and Bi elements and consequently lowering the activation energy barrier for key reaction intermediates.