Nicole Wilde

Highly efficient nano-sized TS-1 with micro-/ mesoporosity from desilication and recrystallization for the epoxidation of biodiesel with H2O2†

The epoxidation of the unsaturated fatty acid methyl esters (FAME) in biodiesel with H2O2 was investigated at 323 K in the liquid phase over microporous nano-sized TS-1 as well as micro-/mesoporous nano-sized TS-1. Nano-sized TS-1 with stacked morphology exhibits a catalytic activity per number of Ti sites up to 30% higher than a conventional, industrial TS-1 catalyst. Mesoporosity was successfully introduced by a desilication-recrystallization approach. Desilication by alkaline treatment in the presence of the structure-directing agent tetrapropylammonium cation (TPA+) or NaOH leads to the generation of undefined mesopores (10–40 nm), probably accompanied by an increase of the surface hydrophilicity. Consequently, the alkaline-treated materials show a two times lower catalytic activity in the epoxidation of biodiesel than the purely microporous parent material. The surfactant-assisted recrystallization of the alkaline-treated materials results in more uniform and smaller mesopores (3–10 nm). In the epoxidation, the recrystallized materials are remarkably more active with respect to both the purely microporous parent and alkaline-treated materials reaching a FAME conversion of 65% with an epoxide selectivity of 82%.

Accessibility enhancement of TS-1-based catalysts for improving the epoxidation of plant oil-derived substrates

TS-1-based catalysts with different textural features, namely layered TS-1, pillared TS-1, and Ti-pillared TS-1 as well as mesoporous TS-1, were investigated in the liquid-phase epoxidation of methyl oleate as a model compound for plant oil-derived substrates with hydrogen peroxide at 50 °C. While over the TS-1-based catalysts, except Ti-pillared TS-1, an epoxide selectivity of up to 93% is achieved, layered and pillared TS-1 are the most active (the amounts of methyl oleate converted after 5 h per number of Ti-sites are 4.64 mol mol−1 and 4.68 mol mol−1) with an efficiency for H2O2 conversion to the epoxide of 27%. Mesoporous TS-1 and conventional microporous TS-1 exhibit a similar activity (3.64 mol mol−1vs. 3.37 mol mol−1), whereas the mesoporous catalyst most efficiently utilizes H2O2 (39% efficiency). The lowest catalytic activity (0.82 mol mol−1), epoxide selectivity as well as H2O2 efficiency are observed over Ti-MCM-36, possessing mainly octahedrally coordinated Ti-sites. The results demonstrate the importance of accessibility of Ti-sites at external crystal surfaces within layered and pillared TS-1, significantly increasing the epoxidation activity with respect to the number of Ti-atoms present in the catalysts.

Silylated Zeolites With Enhanced Hydrothermal Stability for the Aqueous-Phase Hydrogenation of Levulinic Acid to γ-Valerolactone

A systematic silylation approach using mono-, di-, and trichlorosilanes with different alkyl chain lengths was employed to enhance the hydrothermal stability of zeolite Y. DRIFT spectra of the silylated zeolites indicate that the attachment of the silanes takes place at surface silanol groups. Regarding hydrothermal stability under aqueous-phase processing (APP) conditions, i.e., pH ≈ 2, 473 K and autogenous pressure, the selective silylation of the zeolite surface using monochlorosilanes has no considerable influence. By using trichlorosilanes, the hydrothermal stability of zeolite Y can be improved significantly as proven by a stability test in an aqueous solution of 0.2 M levulinic acid (LA) and 0.6 M formic acid (FA) at 473 K. However, the silylation with trichlorosilanes results in a significant loss of total specific pore volume and total specific surface area, e.g., 0.35 cm3 g−1 and 507 m2 g−1 for the silylated zeolite Y functionalized with n-octadecyltrichlorosilane compared to 0.51 cm3 g−1 and 788 m2 g−1 for the parent zeolite Y. The hydrogenation of LA to γ-valerolactone (GVL) was conducted over 3 wt.-% Pt on zeolite Y (3PtY) silylated with either n-octadecyltrichlorosilane or methyltrichlorosilane using different reducing agents, e.g., FA or H2. While in the stability test an enhanced hydrothermal stability was found for zeolite Y silylated with n-octadecyltrichlorosilane, its stability in the hydrogenation of LA was far less pronounced. Only by applying an excess amount of methyltrichlorosilane, i.e., 10 mmol per 1 g of zeolite Y, presumably resulting in a high degree of polymerization among the silanes, a recognizable improvement of the stability of the 3 PtY catalyst could be achieved. Nonetheless, the pore blockage found for zeolite Y silylated with an excess amount of methyltrichlorosilane was reflected in a drastically lower GVL yield at 493 K using FA as reducing agent, i.e., 12 vs. 34% for 3PtY after 24 h.

Influence of the preparation method of sulfated zirconia nanoparticles for levulinic acid esterification

Zirconia nanomaterials were prepared by hydrothermal synthesis with or without template and were modified by post synthesis method with sulfate groups. The materials were thoroughly characterized by X-ray powder diffraction, TEM, N2 physisorption, FTIR spectroscopy of adsorbed pyridine TG analysis and XPS spectroscopy. The catalytic performance of nanosized ZrO2 catalysts and their sulfated modifications was studied in levulinic acid esterification with ethanol. The sulfate group’s dispersion was predetermined by the use of template during the mesoporous zirconia synthesis. A relation between sulfate groups leaching and the applied synthesis conditions (with or without template) of the zirconia nanoparticles was found. Sulfated materials showed significantly higher activity compared to non-sulfated ones. Furthermore, it has been found that the presence of template during the mesoporous ZrO2 nanoparticles preparation influences significantly the zirconia phase and catalytic performance in levulinic acid esterification.