Abstract: A novel central hole-expansion phenomenon is identified, in which the cation-exchange resin is pyrolyzed in a mixed atmosphere of nitrogen and oxygen at 400‍–‍500°C. In this reaction, the reaction path is predictable and always starts from the center of the resin particle to form a central hole, then continues and expands around the hole, finally forming a uniformly distributed hole group; the particle surface remains intact. Analysis shows that this formation mode is due to the different reaction paths of sulfonic groups between the surface and interior of the particle, caused by the temperature difference. On the surface, transformation reactions happen at high temperatures (410‍–‍500°C) to form stable organic sulfur structures, while decomposition occurs inside the particle at a relatively low temperature (<410 °C) and promotes complete pyrolysis of the copolymer matrix to form holes.

Key words: Non-catalytic gas-solid reaction; Cation-exchange resin; Pyrolysis; Central-hole expansion; Temperature difference; Transformation

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