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).

Biomethane can be isolated from biogas through selective CO₂ adsorption. Faujasite-type zeolites are promising adsorbents for CO₂ separation due to their high CO₂ adsorption capacity. While commonly inert binder materials are used to shape zeolite powders into the desired macroscopic format for application in an adsorption column, here we report the synthesis of Faujasite beads without the use of a binder and their application as CO₂-adsorbents. Three types of binderless Faujasite beads (d = 0.4–0.8 mm) were synthesized using an anion-exchange resin hard template. All the prepared beads consisted mostly of small Faujasite crystals, as demonstrated by characterization with XRD and SEM, which are interconnected through a network of meso- and macropores (10–100 nm), yielding a hierarchically porous structure, as shown by N₂ physisorption and SEM. The zeolitic beads showed high CO₂ adsorption capacity (up to 4.3 mmol g⁻¹ at 1 bar and 3.7 mmol g⁻¹ at 0.4 bar) and CO₂/CH₄ selectivity (up to 19 at the partial pressures mimicking biogas, i.e., 0.4 bar CO₂ and 0.6 bar CH₄). Additionally, the synthesized beads have a stronger interaction with CO₂ than the commercial zeolite powder (enthalpy of adsorption −45 kJ mol⁻¹ compared to −37 kJ mol⁻¹). Therefore, they are also suitable for CO₂ adsorption from gas streams in which the CO₂ concentration is relatively low, such as flue gas.