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“The “quasi-liquid phase” behavior: Based on the following findings, Misono and others proposed a quasi-liquid phase reaction model for heteropolyacids: (1) When examining the relationship between the water content, surface area, and catalytic activity of heteropolyacids, it was found that when hydrated heteropolyacids were ground in a mortar, the crystalline water would escape; after some time, they would absorb moisture again and turn into an aqueous solution. (2) According to IR measurements, the structure of the heteropolyanion is not affected by the crystalline water or counterions. However, when the amount of crystalline water and counterions changes, the XRD patterns of the heteropolyacids change significantly. This led to the conclusion that the primary structure is stable while the secondary structure is prone to change. (3) IR spectroscopy measurements of heteropolyacids that had absorbed pyridine showed the appearance of vibration absorption peaks characteristic of pyridinium ions. By comparing the absorption intensities of pyridine and the heteropolyanion, it was determined that the number of pyridine molecules corresponded to the number of protons in the entire solid phase, indicating the formation of (HPy)3PMo12O40. These facts serve as direct evidence for the establishment of the quasi-liquid phase model. (4) Micropore analysis showed that pyridine is absorbed not on the inner surfaces of the micropores but rather within the gaps between the heteropolyanions. As pyridine is absorbed, the volume of the heteropolyacid lattice increases. Misono et al. argue that since nitrogen-containing basic molecules and water molecules can easily enter and exit the bulk phase of heteropolyacids, it is natural for the catalytic reaction to take place within the bulk phase as well. Along with this absorption, the heteropoly compounds transform from a rigid solid to a soft structure similar to a concentrated solution. The diffusion of reaction molecules within the solid phase, along with the rearrangement of anions, causes the reaction to proceed in a manner similar to that in solution. Thus, Misono proposed a \"quasi-liquid phase\" reaction model for heteropoly acids at the American Chemical Society Catalysis Symposium in 1979. Heteropoly acid catalysts do not possess \"quasi-liquid\" properties in all cases; whether a \"quasi-liquid\" state is formed depends on the composition of the heteropoly compound (especially the counterion), as well as the properties of the reacting molecules and the reaction conditions. Generally, Group A salts of heteropolyacids tend to form a \"quasi-liquid phase\"; Group B salts have large cation radii and surface areas, which result in a rigid secondary structure and make it difficult for them to form a \"quasi-liquid phase\". Polar or basic molecules, as well as molecules with small sizes, are easily absorbed into the bulk phase, thereby forming a \"quasi-liquid phase\". Absorption tests on molecules with different polarities show that what determines the absorption rate is primarily basicity (or polarity), followed by the size of the molecule. The number of absorbed molecules is proportional to the number of protons; for example, the numbers 3, 6, 9, etc., of polar molecules absorbed in tungstic acid 122 indicate that the absorbed molecules have formed stable secondary structures in the bulk phase. Reference: Research Progress on Heteropoly Acids and Their Supported Catalysts – Wang Guoliang, Li Shuben, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences (Lanzhou, Gansu Province 731000); Liu Jinlong, Luoyang Petrochemical Engineering Company (Luoyang, Henan Province 471003)