Preparation of active Cs2HPW12O40 catalyst with the ‘core–shell’ secondary structure by a self-organizing process

• Ageing the mixture of HPW and Cs3PW, Cs2HPW salt with core–shell structure, is formed.
• The core–shell structure of Cs2HPW salt is impossible to obtain by standard method.
• Protons in core–shell structure are more accessible than those in solid solution.
• Cs2HPW salt with core–shell structure is more active than that with solid solution.

By mixing and ageing of the powdered H3PW12O40 acid and the Cs3PW12O40 salt, at the molar ratio of 1:2, the Cs2HPW12O40 salt with a unique ‘core–shell’ secondary structure is being formed. The self-organizing process proceeds in a solid state at ambient temperature and its rate depends on the humidity of air atmosphere. The formation of new secondary structure of the Cs2HPW12O40 salt was proved by number of techniques (XRD, DRIFT, DSC/TG and N2-sorption). Its properties were compared with those of the Cs2HPW12O40 salt prepared by the standard method, with the ‘solid solution’ secondary structure. The characterization techniques evidenced the substantial differences between various structures of the Cs2HPW12O40 salt. The microcalorimetric method showed that the process of ammonia sorption on the Cs2HPW12O40 salt with the new structure is quite similar to that on the K2HPW12O40 salt with well-known ‘core–shell’ structure. The catalytic activity of the Cs2HPW12O40 samples with different secondary structure was compared in the dehydration of ethanol and in the transformation of m-xylene. It turn out that the Cs2HPW12O40 salt with the ‘core–shell’ structure exhibited significantly higher catalytic activity than the same salt with the ‘solid solution’ structure and was also more active than the Cs2.5H0.5PW12O40 salt. It can be suggested that in the ‘core–shell’ structure of the Cs2HPW12O40 salt the protons are easily accessible for the reactants.

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