Interrelationship of Cuprous Acetylide Cu₂C₂ Formation and Catalytic Performance in the Reppe Ethynylation of Formaldehyde

Abstract Cuprous acetylide (Cu 2 C 2 ) is widely accepted as the catalytically active species in the ethynylation of formaldehyde to produce industrially valuable 1,4‐butynediol (BYD). Although the Cu 2 C 2 formation could be shown under reaction conditions recently, no experimental investigations existed on its relation to catalysis. The present study reports for the first time in detail the direct correlation of catalytic activity in the ethynylation reaction with properties like dispersion and crystallinity of Cu 2 C 2 formed in situ on silica‐supported copper oxide‐based pre‐catalysts during activation. With implemented safety precautions, unequivocal qualitative characterizations of the explosive Cu 2 C 2 have been accomplished using Raman spectroscopy and X‐ray diffraction. Interrelationships of the active phase and catalysis of the Cu/Bi/SiO 2 pre‐catalysts could be concluded by varying copper loading (optimum 35 wt.%), bismuth promoter concentration (optimum 4 wt.%), and pre‐catalyst calcination procedure. The formation rate, amount, and dispersion of Cu 2 C 2 determine the reaction rate and yield of BYD, thus bridging the former gap between copper oxide pre‐catalysts and the actual active cuprous acetylide phase.