Improving the hydrothermal stability of zeolite Y by La3+ cation exchange as a catalyst for the aqueous-phase hydrogenation of levulinic acid

Abstract

La³⁺ cation exchange is shown to improve the hydrothermal stability and catalytic activity of bifunctional zeolite Pt/Y catalysts in the aqueous-phase hydrogenation of levulinic acid (LA) with formic acid (FA) as hydrogen source. La³⁺ cation exchange of zeolite Y (n_Si/n_Al = 16) was conducted both in aqueous solution and in the solid state. The hydrothermal stability of La³⁺-containing zeolite Y probed by exposure to the reaction mixture (0.2 mol L⁻¹ LA, 0.6 mol L⁻¹ FA) at 473 K under autogenous pressure for 24 h improves with increasing La content. The material exhibiting the highest La content (0.5 mmol g⁻¹) is the most stable with a preservation of 25% of the initial specific micropore volume after the hydrothermal treatment, whereas unmodified zeolite Y completely loses its microporosity. A new procedure using DRIFTS is a useful supplementary tool for quantifying the framework degradation of Y-type zeolites after hydrothermal treatment. Bifunctional Pt/Y catalysts after La³⁺ cation exchange are more active than the parent Y-zeolite for the hydrogenation of LA to γ-valerolactone (GVL), with significant enhancements in LA conversion, i.e., 94% vs. 42%, and GVL yield, i.e., 72% vs. 34%., after 24 h.