Abstract
The composition, structural evolution and the related property variations of mixed cesium/ammonium acidic salts of heteropolyacids were investigated in detail by tracking and analyzing the initial precipitates, evaporation residues and the calcined products in their preparation process. Results show that V cannot completely enter the heteropolyanions in the initial precipitates when the Cs+ added amount is low, and the increase in Cs+ adding amount improves the substitution of V for Mo in the heteropolyanions. Both the initial precipitates and the evaporation residues are mixtures of cesium and ammonium salts of heteropolyacids before calcination. Thermal treatment causes the decomposition of the ammonium salts and the formation of single-phase solid solutions from mechanical mixtures. The calcined products of the initial precipitates and the evaporation residues vary greatly in textural properties. The determinants of the catalytic performance for the oxidation of methacrolein to methacrylic acid are acidity and specific surface area of the compounds. The increase in specific surface area mainly improves the conversion of methacrolein, but not the selectivity of methacrylic acid. Insufficient acidity caused by high Cs+ content in the compounds is responsible for the low selectivity.
Highlights
IntroductionIt is well known that the structure of Keggin-type Heteropoly compounds (HPCs) can be subdivided into the primary, secondary and tertiary structure [11]
It was supposed that the heteropolyanion was [PMo11 VO40 ]4− and the counterions were H+ and NH4 +, that is the initial Heteropoly compounds (HPCs) were probably a mixture of H4 PMo11 VO40 and its ammonium salt
After CsNO3 was added to the slurry, it reacted with H4 PMo11 VO40, generating insoluble cesium salt
Summary
It is well known that the structure of Keggin-type HPCs can be subdivided into the primary, secondary and tertiary structure [11]. I.e., the heteropolyanion, such as [PMo12 O40 ]3− , the central phosphorus atom is located at the center of a PO4 tetrahedron, which is surrounded by twelve MoO6 octahedra. The three-dimensional arrangement of heteropolyanions and counterions, perhaps including water of crystallization and some additional molecules, is called the secondary structure. There are important relationships between the catalytic function and the primary or the secondary structure of HPCs. It has been reported that V can partially substitute for Mo in the heteropolyanions and improve the catalytic property for selective oxidation reactions [12,13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
