Nature of Synergy between Brønsted and Lewis Acid Sites in Sn-Beta Zeolites for Polyoxymethylene Dimethyl Ethers Synthesis

Advancements and Challenges in the Synthesis of Oxymethylene Ethers (OMEs) as Sustainable Transportation Fuels

The urgent need for sustainable alternatives to fossil fuels in the transportation sector is driving research into novel energy carriers that can meet the high energy density requirements of heavy-duty vehicles without exacerbating the climate change. This concept article examines the synthesis, mechanisms, and challenges associated with oxymethylene ethers (OMEs), a promising class of synthetic fuels potentially derived from carbon dioxide and hydrogen. We highlight the importance of OMEs in the transition towards non-fossil energy sources due to their compatibility with the existing Diesel infrastructure and their cleaner combustion profile. The synthesis mechanisms, including the Schulz-Flory distribution and its implications for OME chain length specificity, and the role of various catalysts and starting materials are discussed in depth. Despite advancements in the field, significant challenges remain, such as overcoming the Schulz-Flory distribution, efficiently managing water as an undesirable byproduct, and improving the overall energy efficiency of the OME synthesis. Addressing these challenges is crucial for OMEs to become a viable alternative fuel, contributing to the reduction of greenhouse gas emissions and the transition to a sustainable energy future in the transportation sector.

Double Four Ring Units-Containing Zeolites: Synthesis, Structural Modification and Catalytic Applications

In zeolite frameworks, double four-ring (d4r) configurations are among the most frequent composite building units. The composition variations in d4r units greatly influence the energy and structural modifiability of the zeolitic framework. The introduction of germanium, with a larger ionic radius than silicon or aluminum, not only reduces the energy constraints of d4r in the nucleation and crystal growth of zeolites, but also opens a new window for constructing novel crystalline structures, especially with large or extra-large pores and channels. Ge-enriched d4r units endow germanosilicates with structure diversity readily for post treatments. Promising catalytic materials have been gradually developed and increasingly studied by direct synthesis or post-synthetic isomorphous substitution for Ge. This review focuses on the recent progress in the synthesis, modification, and catalytic application of d4r-containing zeolites, including germanosilicates, aluminosilicates, and silicates.

Defective acidic 2D COF-based catalysts for boosting the performance of polyoxymethylene diethyl ether synthesis under mild conditions

Polyoxymethylene diethyl ethers (PODEEn) are oxygenated fuel additives with high performance due to their advantageous fuel properties. PODEEn can alleviate carbon debt as the production can utilize bioethanol and biomass syngas. Heterogeneous solid acid catalysts are desirable for an efficient PODEEn synthesis. In this study, well-defined sulfonated phthalocyanine-containing polymers were prepared, and the physicochemical properties were analyzed, exhibiting a 2D π-π stacking structure with crystalline-amorphous mixed phases. Owing to the tuning defects of the COF framework by mixing polymerization, the accessibility of the network and the capacity of strong acid were improved for the polymeric catalyst, showing an excellent activity with trioxane (TOX) conversion of 89% and PODEE2-8 selectivity of 87% at 80 °C under atmospheric pressure.