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 (nSi/nAl = 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.
Highlights
Lanthanum cation exchange, conducted both in liquid phase and in solid state, has been extensively studied and applied for improving the hydrothermal stability of zeolite Y (Y) in uid catalytic cracking (FCC), typically operated in the gas phase at moderate to high temperatures, e.g., 573–1073 K.1–4 An important advantage of La3+ cation exchange is the high preservation of both the crystalline structure and textural properties of zeolite Y a er ion exchange either in the aqueous phase[5,6,7,8,9,10,11] or in the solid state.[7]
Independent of the ion exchange procedure, La3+ cations were successfully incorporated into zeolite Y, which was demonstrated by the bulk La content determined by EDX analysis (Table 1, Fig. S1 and S2†)
The stabilization effect is proportional with the La3+ cation exchange degree irrespective of the ion exchange procedure applied
Summary
Lanthanum cation exchange, conducted both in liquid phase (mostly water) and in solid state, has been extensively studied and applied for improving the hydrothermal stability of zeolite Y (Y) in uid catalytic cracking (FCC), typically operated in the gas phase at moderate to high temperatures, e.g., 573–1073 K.1–4 An important advantage of La3+ cation exchange is the high preservation of both the crystalline structure and textural properties of zeolite Y a er ion exchange either in the aqueous phase[5,6,7,8,9,10,11] or in the solid state.[7]. An important advantage of La3+ cation exchange is the high preservation of both the crystalline structure and textural properties of zeolite Y a er ion exchange either in the aqueous phase[5,6,7,8,9,10,11] or in the solid state.[7] The incorporation of La3+ cations into zeolite Y has been proven to increase its stability in FCC This retards undesired dealumination during catalyst regeneration, which is facilitated under the typical regeneration conditions, i.e., at 973 K in the presence of steam generated through coke combustion.[12,13] In addition, La3+ cation exchange of faujasitic zeolites was reported to enhance the catalytic activity for acid-catalyzed reactions, e.g., isomerization, hydroisomerization and cracking, owing to the presence of “super acid sites” arising from the interaction between Si–OH–Al and La3+ cations in their vicinity.[14,15,16] Most studies, deal with gas-phase applications of La3+ cation-exchanged zeolite Y, while its hydrothermal stability in liquid water at elevated. A new procedure using diffuse re ectance infrared Fourier transformation spectroscopy (DRIFTS) was examined as a supplementary tool for quantifying the deterioration degree of the zeolite Y framework a er exposure to APP-related conditions
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