Microwave Synthesis of LTL Zeolites with Tunable Size and Morphology: An Optimal Support for Metal‐Catalyzed Hydrogen Production from Biogas Reforming Processes

Abstract

Here, a method is described for the synthesis of Linde type L (LTL) zeolite under microwave-assisted hydrothermal conditions, and its behavior as a support for heterogeneously catalyzed hydrogen production is detailed. Microwave heating reduces the reaction time and improves the quality of the LTL zeolite crystals in comparison to those obtained using conventional ovens. The size and morphology of zeolite can be fi nely modulated by the composition of the gel and reaction conditions (heating rate, static/dynamic conditions, aging, reaction time, etc). The physicochemical properties of the synthesized LTL zeolites make them appropriate catalyst supports for reforming reactions in which high hydrogen production yields are desired. Therefore, rhodium-and nickel-based bimetallic catalysts are prepared in order to be tested by dry and oxidative biogas reforming processes at 800 °C and atmospheric pressure for hydrogen production. For all the catalysts tested, except for the sodium-exchanged disc-shaped zeolite, hydrogen yields close to the predicted by the equilibrium conversion are reached.

Supramolecular Organization in Confined Nanospaces

“…In this way, one can obtain guest-host composites with remarkable organization patterns, up to endto-end sequenced chains of chromophores. [29,36,40] Other advantages are the facile synthesis of zeolite crystals with tailorable aspect-ratio [648][649][650] and the selective functionalization of their external surfaces, either at the base (channel entrances) or at the coat region. [616] These features allow to obtain zeolite crystals self-assembled via coordinative linkers, [651] arranged in close-packed monolayers, [652] integrated with devices, [61,653] and even connected with living systems such as bacteria, [654] which can then be targeted and killed by red-light irradiation.…”

Photoactive Nanomaterials Inspired by Nature: LTL Zeolite Doped with Laser Dyes as Artificial Light Harvesting Systems

“…Further details of the synthesis and characterization of the crystals can be found elsewhere [43]. In particular, in the herein reported work, disc-shaped zeolites (average thickness of 200 nm and average diameter around 1 μm) were used as hosts for the antennae, whereas barrels (length around 2 mm) were used for the measurements of stopcock localization under the fluorescence microscope.…”

Linde Type L Zeolite: A Privileged Porous Support to Develop Photoactive and Catalytic Nanomaterials

“…To this aim and, starting from a fixed gel composition optimized for each kind of zeolite, we focused on modifying the reaction conditions and gel pre-treatment for a fine-tuning of the size and morphology of the crystals. For all types of zeolites the microwave-assisted heating reduced the synthesis times up to 90% (days to hours) compared to the one afforded by conventional ovens [19,23]. Moreover, the precise control of the temperature and the homogeneous heating during the nucleation process in the microwave oven are reflected in a narrower size distribution of the particles and higher degree of crystallinity.…”

“…Afterward, the gel is heated (at reaction temperatures usually higher than 100°C) in a sealed high-pressure polytetrafluoroethylene (PTFE) vessel for a certain time period (optimal for each kind of zeolite). The size and morphology of the crystals can be modulated by changing the source of reactants, composition of the gel (alkalinity, water content, SiO 2 /Al 2 O 3, among others) reaction time, temperature, and aging time of the gel [23]. To this aim and, starting from a fixed gel composition optimized for each kind of zeolite, we focused on modifying the reaction conditions and gel pre-treatment for a fine-tuning of the size and morphology of the crystals.…”

“…The small size of these zeolites (15-50 nm) is suitable to allocate guests deep inside the pores thanks to the favored diffusion within the pores [23]. Furthermore, its large external surface makes them optimal supports for adsorption processes, e.g., adsorption of metal particles for catalytic processes [12].…”