High-efficiency transalkylation of C10 aromatics with 2-methylnaphthalene over shape-selective SiO2-Cu-HMOR with nanoneedle crystals

Abstract

Here, a nanoneedle HMOR zeolite modified by loading 2.5 wt% Cu and subsequently by SiO₂ deposition with four cycles was designed as a catalyst for the transalkylation of C₁₀ aromatics with 2-methylnaphthalene (2-MN) for synthesizing 2,6-dimethylnaphthalene (2,6-DMN) in a H₂ atmosphere. Firstly, a remarkably improved transalkylation reactivity for dimethylnaphthalene generation (catalyzed by protonic acid sites) was achieved depending on two key factors: (1) a probable concerted catalysis of the internal metal-Cu and acid sites under a H₂ atmosphere; (2) the high-efficiency diffusion of the molecules into/out the shorter and shape-selective micropores of modified nanoneedle crystals. Secondly, the side-reactions resulting in multi-alkylnaphthalene formation and naphthalene-ring loss were effectively suppressed, and the greatly enhanced selectivities of 2,6-DMN and β,β-dimethylnaphthalenes were also obtained. It is due to the combined effects of the elimination of external reactive sites, the interspace limitation inside channels, and the product shape-selectivity at the reasonably narrowed pore-openings. Furthermore, the catalyst also exhibited good catalytic stability attributed to its strong capabilities of resisting coke deposition depending on reasonable hydrogenation catalyzed by metal Cu sites and high-efficiency molecule diffusion of short channels, and accommodating considerable coke on its nanoneedle crystals. As a result, a 2-MN conversion of >73.78%, a dimethylnaphthalene selectivity of >85.98%, and a 2,6-DMN yield of >19.56% were obtained during a 180 h on-stream reaction.