Modulating the Interaction of NiSO4 and Nb2O5 Boosts the Dimerization of Propylene

Propylene dimerization is an attractive way to branch out the bulk chemicals to high-value-added fine chemicals. Based on the coordinatively unsaturated surface sites of nickel and solid acid sites for boosting highly selective dimerization of propylene, a series of NiSO4/Nb2O5 catalysts were synthesized by tuning the synergistic effect through adjusting the calcination temperatures. Under the conditions of 70 °C, 2.5 MPa, and LHSV = 3 h–1 in a fixed-bed reactor, the NiSO4/Nb2O5-400 catalyst exhibits the highest propylene conversion of ca. 89% with 75% selectivity to C6 products (mainly including 4-methyl-2-pentene and 3-hexene). A possible Cossee–Arlman pathway has been proposed for the dimerization of propylene. In the long-term stability testing, an induction period has been observed, which may be attributed to the coordination of propylene molecules to unsaturated Ni2+ cations generating some active nickel species. Subsequently, the NiSO4/Nb2O5-400 catalyst presents a stability up to 30 h. The interesting results inspired us to modulate the interaction of metal (salt) and acid sites to strengthen the selective dimerization of low-carbon olefins.