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

Cuprous acetylide (Cu2C2) is widely accepted as the catalytically active species in the ethynylation of formaldehyde to produce industrially valuable 1,4‐butynediol (BYD). Although the Cu2C2 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 Cu2C2 formed in situ on silica‐supported copper oxide‐based pre‐catalysts during activation. With implemented safety precautions, unequivocal qualitative characterizations of the explosive Cu2C2 have been accomplished using Raman spectroscopy and X‐ray diffraction. Interrelationships of the active phase and catalysis of the Cu/Bi/SiO2 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 Cu2C2 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.