Bimetallic Zeolite Beta Beads with Hierarchical Porosity as Brønsted-Lewis Solid Acid Catalysts for the Synthesis of Methyl Lactate

Abstract

Bimetallic zeolite Beta in bead format and containing Al sites with Brønsted acid behavior and Sn, Zr or Hf sites with Lewis acid character, were prepared using a two-step synthetic route. First, zeolite Beta in the format of macroscopic beads (400 to 840 μm) with hierarchical porosity (micropores accessed through meso- and macropores in the range of 30 to 150 nm) were synthesized by hydrothermal crystallization in the presence of anion-exchange resin beads as hard template and further converted into their H-form. Next, the zeolite beads were partially dealuminated using different concentrations of HNO3 (i.e., 1.8 or 7.2 M), followed by grafting with one of the above-mentioned metals (Sn, Zr or Hf) to introduce Lewis acid sites. These bimetallic zeolites were tested as heterogeneous catalysts in the conversion of dihydroxyacetone (DHA) to methyl lactate (ML). The Sn-containing zeolite Beta beads treated by 1.8 M HNO3 and grafted with 27 mmol of SnCl4 (Sn-deAl-1.8-Beta-B) demonstrated the best catalytic activity among the prepared bimetallic zeolite beads, with 99% selectivity and 90% yield of ML after 6 h at 90 °C. This catalyst was also tested in combination with Au-Pd nanoparticles supported on functionalized carbon nanotubes (CNTs) as multifunctional catalytic system for the conversion of glycerol to ML, achieving 29% conversion of glycerol and 67% selectivity towards ML after 4.5 h at 140 °C under 30 bar air. The catalytic results were rationalized by means of a thorough characterization of the zeolitic beads with a combination of techniques (XRD, N2-physisorption, SEM, XRF, TEM, UV-vis spectroscopy and pyridine-FT-IR).

Hydrotalcites as Versatile Functional Materials for Renewable Feedstock Upgrading to Value-added Chemicals

“…The catalytic reaction is one of the several synthesis routes for biodiesel formation (Figure 8A), which is involved with the replacement of alkyl groups of vegetable oils with methyl or ethyl alcohol groups to produce biodiesel (alkyl esters) [150] . As stated above, glycerol is the main by-product of the esterification reaction [151] .…”

Intergrowth Zeolites, Synthesis, Characterization, and Catalysis

“…364 Similarly, bimetallic Beta zeolites containing Brønsted-Lewis solid acids have been used as multiphase catalysts for the conversion of dihydroxyacetone (DHA) to methyl lactate (ML) with a selectivity of 99% and yields of up to 90%. 368 Undoubtedly, Lewis and Brønsted acidity-integrated solid catalysts have powerful functions, while ensuring biomass conversion activity and resistance, the complex reaction steps and process flow are greatly simplified, which is of extraordinary significance in the integrated processing of the catalytic industry. significant increase in molecular access.…”

Synergistic Catalytic Effects of Alloys of Noble Metal Nanoparticles Supported on Two Different Supports: Crystalline Zeolite Sn-Beta and Carbon Nanotubes for Glycerol Conversion to Methyl Lactate

“…To expand the scope of active heterogeneous catalysts facilitating the one-pot conversion of glycerol to methyl lactate, our prior research focused on developing a new catalytic system to conduct this reaction. This system employed Au and Pd nanoparticles supported on carbon nanotubes, combined in a physical mixture with spherically shaped Sn-zeolite Beta [17]. The synthesis of Sn-Beta beads involved a hard-templating technique, enabling the creation of hierarchical porosity and shaped zeolite Sn-Beta, concurrently [29].…”

“…The synthesis of Sn-Beta beads involved a hard-templating technique, enabling the creation of hierarchical porosity and shaped zeolite Sn-Beta, concurrently [29]. However, this particular catalytic system exhibited only moderate activity in the targeted reaction, prompting the further exploration of new catalytic systems [17]. To advance the catalytic properties of the newly developed catalysts and maximize their efficacy in converting glycerol to methyl lactate, we investigated the influence of the particle size and dispersibility of zeolite Sn-Beta powder compared to spherically shaped Sn-Beta on the catalytic performance.…”