On March 1st, news from the Science and Technology Bureau of Ordos City, Inner Mongolia, revealed that a joint effort by Professor Wei Fei's research group and Professor Qian Weizhong's research group from the Tsinghua University Ordos Laboratory has made significant strides. By employing the world's most advanced aberration-corrected electron microscopy technology, they observed the interaction between acid sites (Al-T sites) in zeolite channels and single thiophene molecules. Their findings have been successively published in the international academic journals "Science" and "Nature."
Investigating the imaging and conformation of organic small molecules within porous materials like zeolites at the single-molecule level is fundamental and crucial for a deep understanding of their phase transitions, adsorption, catalysis, and interaction processes. Imaging of organic small molecules at room temperature or higher has always been a challenging bottleneck in the field of electron microscopy.
Thiophene molecules, being smaller than benzene or pyridine molecules, can rotate freely within the channels of ZSM-5 zeolites (a type of zeolite). Their rotation speed is so fast that it is extremely difficult to capture and clearly observe with an electron beam. However, because thiophene molecules contain sulfur, they can form O-H-S hydrogen bonds with the zeolite channels, thus establishing stronger interactions with the zeolite than molecules like benzene, pyridine, or xylene. This bonding restricts the free rotation of thiophene molecules in the channels, allowing the molecules to present a plane configuration nearly perpendicular to the electron beam, thereby observable with the most advanced electron beam imaging technology. Moreover, the approximately 0.5-nanometer channels in ZSM-5 zeolites are not infinitely symmetrical circular sections. Different spatial steric hindrances at various Al-T sites result in different hydrogen bonding angles and probabilities with thiophene molecules, allowing for the analysis of thiophene molecules' subtle spatial configurations.
This research represents a breakthrough in zeolite electron microscopy imaging technology and a concrete manifestation of the complex interactions between zeolite channels and guest molecules. It provides a new direction for understanding the essence of catalysis and controlling product selectivity at the picometer level. This will effectively address common fundamental issues in the synthesis of olefins or aromatics from advanced coal chemical synthesis gas and in the production of green aviation fuel and green chemicals from CO2 hydrogenation.
