Solvent-free and Mesoporogen-free Synthesis of Mesoporous Aluminosilicate ZSM‑5 Zeolites with Superior Catalytic Properties in the Methanol-to-Olefins Reaction

Large crystalline particles of ZSM-5 zeolites (S-ZSM-5) have been successfully synthesized by adjusting crystallization time and Si/Al ratios in the starting solid mixtures in the absence of water solvent. Catalytic tests in the methanol-to-olefins (MTO) reaction show that these S-ZSM-5 zeolites obtained from the solvent-free route exhibit superior catalytic properties including excellent propylene selectivity and extraordinarily long life in the MTO reaction. Particularly, when the crystallization time is 30 h and the Si/Al ratio in the starting solid mixture is adjusted at 150 under the solvent-free conditions, the S-ZSM-5-30h-150 catalyst with the large particle sizes (10–20 μm) gives propylene selectivity as high as 50.0% and catalyst life as long as 9 h, which are much better than those (propylene selectivity at 38.9% and catalyst life of 3 h) of the conventional ZSM-5 zeolite with smaller crystals (ca. 5 μm) synthesized from the hydrothermal route. High-resolution TEM images of these S-ZSM-5 zeolites demonstrate that there is mesoporosity in the samples. More interestingly, these mesopore size distributions could be adjusted by the crystallization time during the solvent-free synthesis. Obviously, the presence of mesoporosity is very favorable for the mass transfer, and an appropriate Si/Al ratio in the zeolite framework could offer suitable acidic density for the catalytic conversion, which should be responsible for the superior catalytic properties in the MTO over the S-ZSM-5-30h-150 catalyst. The features of mesoporosity in the S-ZSM-5 crystals and sustainability for the solvent-free synthesis could be potentially important for wide applications of these S-ZSM-5 zeolites in the future

Strong Metal–Support Interactions Achieved by Hydroxide-to-Oxide Support Transformation for Preparation of Sinter-Resistant Gold Nanoparticle Catalysts

The strong metal–support interactions (SMSI) are well-known but crucial for preparation of supported metal nanoparticle catalysts, which generally occur by reduction and oxidation under harsh conditions. Here, we delineate the example of constructing SMSI without reduction and oxidation, where the key is to employ a hydroxide-to-oxide support transformation. The covering of Au nanoparticles by oxides, electronic interaction, and changes in CO adsorption tests of the catalyst are identical to those of the classic SMSI. Owing to the SMSI with oxide barriers on the Au nanoparticles, the supported Au catalysts are sintering-resistant at high temperatures, which benefit long-life reactions, outperforming the conventional supported catalysts

Hierarchical Sn-Beta Zeolite Catalyst for the Conversion of Sugars to Alkyl Lactates

Enhancing the yield of alkyl lactate from sugars is in great demand but challengeable to accomplish. Here we report a facile but efficient route to make this by employing a hierarchical and Sn-containing Beta zeolite (Sn-Beta-H). The hierarporosity in the Sn-Beta-H facilitates the conversion of sugars into important intermediates for producing alkyl lactate in the competition with undesirable side reactions, thus outperforming the conventional Sn-zeolite catalysts in yielding alkyl lactate from a wide scope of sugars. Particularly, the yield of alkyl lactate could reach as high as 72.1% from sucrose. Importantly, the Sn-Beta-H is stable and can be easily recycled for five times with constant catalytic performances

Solvent-Free Synthesis of Zeolites from Anhydrous Starting Raw Solids

Development of sustainable routes for synthesis of zeolites is very important because of wide applications of zeolites at large scale in the fields of catalysis, adsorption, and separation. Here we report a novel and generalized route for synthesis of zeolites in the presence of NH₄F from grinding the anhydrous starting solid materials and heating at 140–240 °C. Accordingly, zeolites of MFI, BEA*, EUO, and TON structures have been successfully synthesized. The presence of F^– drives the crystallization of these zeolites from amorphous phase. Compared with conventional hydrothermal synthesis, the synthesis in this work not only simplifies the synthesis process but also significantly enhances the zeolite yields. These features should be potentially of great importance for industrial production of zeolites at large scale in the future