Boosting Selective Propylene Tetramerization over NiSO4/γ-Al2O3 via Reverse Overloading Etching

Selective propylene tetramerization under mild conditions remains a major challenge because of broad carbon-number distributions and limited control over chain growth. In this work, a NiSO4/γ-Al2O3 catalyst was constructed using an overloading-etching strategy, in which water-washing selectively removed weakly bound NiSO4 aggregates while preserving the fraction strongly interacting with the support. The resulting 7.8%-NiSO4/γ-Al2O3-w catalyst achieved nearly complete propylene conversion and a C12 selectivity of 42.5% under 70 °C, 2.5 MPa, and a WHSV of 1 gC3/(gcat.·h), as well as long-term stability within a 140 h test. Structural characterization demonstrated that the water-washing treatment suppressed NiSO4 crystallization, re-exposed surface-accessible active species, increased the density of weak acid sites, and promoted the “C6 + C6” bimolecular coupling pathway. This work provides an effective route to improve tetramer selectivity in propylene oligomerization through postsynthesis reconstruction of surface NiSO4 species and offers useful insight into the structure-pathway relationship of supported nickel catalysts.