A novel microwave-assisted methanol-to-hydrocarbons process with a structured ZSM-5/SiC foam catalyst: Proof-of-concept and environmental impacts

Process Intensification at the Nanoscale: Embedding SiC in Zeolites for Energy-Efficient Catalysis

Microwave-absorbent materials are typically blended with low-absorption solids to improve local heating efficiency in catalytic systems. However, the mixing method has a crucial effect on the additive's heating efficiency. We report here how by embedding silicon carbide (SiC) nanoparticles in ferrierite (FER) zeolite crystals during their synthesis (FER@SiC), a 2.2-fold increase in the catalytic activity for mesitylene and benzyl alcohol alkylation was achieved compared to a physical mixture of FER and SiC nanoparticles (FER/SiC). While the properties of the zeolite in the FER@SiC hybrid and SiC-free FER zeolites are almost identical, we observed a significant increase in catalytic activity under microwave heating when SiC is present within FER crystals. This enhancement is not mirrored by the physical mixture, highlighting the importance of the SiC addition method and the intimate contact between the additive and catalytic phases for effective microwave heating. Actually, FER@SiC achieves the same conversion with 40% less energy, offering insights into designing more efficient zeolite-based catalysts for sustainable chemistry.

Advanced Catalysts for the Chemical Recycling of Plastic Waste

Plastic products bring convenience to various aspects of the daily lives due to their lightweight, durability and versatility, but the massive accumulation of post-consumer plastic waste is posing significant environmental challenges. Catalytic methods can effectively convert plastic waste into value-added feedstocks, with catalysts playing an important role in regulating the yield and selectivity of products. This review explores the latest advancements in advanced catalysts applied in thermal catalysis, microwave-assisted catalysis, photocatalysis, electrocatalysis, and enzymatic catalysis reaction systems for the chemical recycling of plastic waste into valuable feedstocks. Specifically, the pathways and mechanisms involved in the plastics recycling process are analyzed and presented, and the strengths and weaknesses of various catalysts employed across different reaction systems are described. In addition, the structure-function relationship of these catalysts is discussed. Herein, it is provided insights into the design of novel catalysts applied for the chemical recycling of plastic waste and outline challenges and future opportunities in terms of developing advanced catalysts to tackle the "white pollution" crisis.

The Oxygenate-Mediated Conversion of COx to Hydrocarbons─On the Role of Zeolites in Tandem Catalysis

Decentralized chemical plants close to circular carbon sources will play an important role in shaping the postfossil society. This scenario calls for carbon technologies which valorize CO2 and CO with renewable H2 and utilize process intensification approaches. The single-reactor tandem reaction approach to convert COx to hydrocarbons via oxygenate intermediates offers clear benefits in terms of improved thermodynamics and energy efficiency. Simultaneously, challenges and complexity in terms of catalyst material and mechanism, reactor, and process gaps have to be addressed. While the separate processes, namely methanol synthesis and methanol to hydrocarbons, are commercialized and extensively discussed, this review focuses on the zeolite/zeotype function in the oxygenate-mediated conversion of COx to hydrocarbons. Use of shape-selective zeolite/zeotype catalysts enables the selective production of fuel components as well as key intermediates for the chemical industry, such as BTX, gasoline, light olefins, and C3+ alkanes. In contrast to the separate processes which use methanol as a platform, this review examines the potential of methanol, dimethyl ether, and ketene as possible oxygenate intermediates in separate chapters. We explore the connection between literature on the individual reactions for converting oxygenates and the tandem reaction, so as to identify transferable knowledge from the individual processes which could drive progress in the intensification of the tandem process. This encompasses a multiscale approach, from molecule (mechanism, oxygenate molecule), to catalyst, to reactor configuration, and finally to process level. Finally, we present our perspectives on related emerging technologies, outstanding challenges, and potential directions for future research.