Promoting tin into the framework of β zeolite via stabilizing Sn species and its catalytic performance for the conversion of ethyl levulinate to γ-valerolactone

Tin-containing β zeolite exhibits excellent catalytic performance in various biomass conversions to high-value chemicals due to its strong Lewis (L) acidity produced by framework Sn4+ sites. However, it is difficult to incorporate Sn species into the framework of β zeolite due to that the ionic radius of Sn (0.69 Å) is larger than that of Si (0.40 Å). Herein, organic additives with carbonyl, hydroxyl, aldehyde or amine groups were used to stabilize Sn species in the gel and framework Sn4+ in the zeolite. Among all additives, acetone (AC) has the best stabilizing effect on Sn species. The stabilization effect between AC and Sn4+ sites was observed by FT-IR. The characterization results indicate that more tin species were incorporated into β framework and the L acid density increased due to the complexation between carbonyl group and Sn species. Compared to Sn-β-3d synthesized without additive, the L acid density of Sn-β-AC-3d increased by ∼50% (from 21 μmol g−1 to 34 μmol g−1). For the conversion of ethyl levulinate to γ-valerolactone, the reaction reached equilibrium faster over Sn-β-AC-3d than over Sn-β-3d at the investigated reaction temperatures. A yield of 98% was obtained over Sn-β-AC-3d at 110 °C. Besides, Sn-β-AC-3d exhibited good stability and reusability.