Controlling the reaction pathways of C10 aromatics transalkylation with 2-methylnaphthalene over shape-selective La2O3–SiO2–Pt–HBeta with lamellar crystals

Abstract

A zeolite catalyst, 2.0 wt%La₂O₃–SiO₂(IV)–0.1 wt%Pt–HBeta, with lamellar crystals was applied in the transalkylation of C₁₀ aromatics with 2-methylnaphthalene (2-MN) for the synthesis of 2,6-dimethylnaphthalene (2,6-DMN) under an H₂ atmosphere. The reaction pathways were accurately controlled by the precise cooperation among six aspects: (1) the synergy of excellent molecule diffusibility of the lamellar crystals with an appropriate shape selectivity at the pore openings narrowed by silicon deposition, capable internal acidity, and reactive participation of the surface active hydrogen species likely formed based on both metal Pt and Lewis acid sites resulted in remarkably enhanced transalkylation reactivity. (2) The teamwork of the inactive external surface covered by silicon and the space-limitation effect and properly assembled reactive sites (metal-Pt and acid) in the channels effectively avoided the naphthalene-ring loss. (3) The methylnaphthalene dealkylation and 2-MN isomerization were significantly weakened due to the reduced internal acidity resulting from La₂O₃ modification, selectively eliminating some strong acid sites. (4) The generation of multi-alkylnaphthalenes was greatly avoided, which was attributed to the space limitation and reasonable acid strength in the pores and shorter retention time of the diffusion reaction of lower alkylnaphthalenes in the lamellar crystals. (5) The pore-mouth shape-selectivity obviously enhanced the 2,6-DMN proportion in dimethylnaphthalenes (DMNs). (6) The strong capabilities of the modified lamellar crystals for resisting and accommodating coke with a reasonable catalytic hydrogenation and a providential internal acid strength ensured their excellent catalytic stability. As a result, a 2-MN conversion of >56.9%, a high DMN selectivity of >88.3%, and an enhanced 2,6-DMN yield of >19.3% were obtained during a 280 h on-stream reaction.