Preparation, characterization and application of zirconium phosphate nanoparticles and its cation (Cu2+ and Zn2+) ion exchanged in organic
In this thesis, we first prepared zirconium phosphate (ZP) nanoparticles as an effective, eco-friendly and recyclable solid acid catalyst. Polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) were used as the organic matrix which were the dispersing agents and acted as a template for the nanoparticles. It seems H-bonds between ZP and PVA or PVP along polymer chains lead to a better dispersion of in situ formed ZP. Pure ZP nanoparticles with hexagonal shape were obtained after calcination of PVA/ZPor PVP/ZP. The catalysts were characterized by several physico-chemical techniques such as BET, EDX, ICP-OES, XRD, FT-IR, SEM and TEM. The Py-FTIR and TPD-NH3 analysis suggest the presence of a reasonable amount of Brønsted acid sites.
The acidic properties of zirconium phosphate nanoparticles were studied in some organic reactions such as Friedel-Crafts alkylation of phenol with cyclohexanol (which produced 2-cyclohexylphenol (2-CP), 4-cyclohexylphenol (4-CP) and 2,4-dicyclohexylphenol (2,4-DCP)) and tert-butanol (which produced 2-tert-butylphenol (2-TBP), 4-tert-butylphenol (2-TBP) and 2,4-ditert-butylphenol (2,4-DTBP)) under solvent-free conditions. Also, it was used for protection of hydroxyl and carbonyl groups. The catalyst showed excellent catalytic activity towards O-acetylation of substituted phenols and aliphatic alcohols with acetic anhydride (AA) under solvent-free conditions. Also, it showed excellent activity for the protection of aldehydes with AA at room temperature.
In the next part, zirconium phosphate nanoparticles were used for 14-aryl-14H-dibenzo[a,j]xanthenes using the condensation of β-naphthol with aryl aldehydes under solvent-free conditions. Morover, this catalyst was used for 3,4-dihydropyrimidin-2(1H)-ones (Biginelli reaction) with excellent yields and short reaction times. The steric and electronic factors associated with the substrates were influenced the reaction conditions of these multicomponent reactions. At the end of each reaction, the catalyst was recovered easily from the reaction mixture, regenerated and reused several times without significant loss in its catalytic activity.
In the next part of our study, copper zirconium phosphate (ZPCu) and zinc zirconium phosphate (ZPZn) were prepared as heterogeneous catalysts as well. The H+ of the P–OH being the exchangeable site and can be exchanged for other ions with proper enlargement of the interlayer distance. These catalysts were characterized by BET, EDX, ICP-OES, XRD, SEM and TEM. It was shown that the interlayer distance increased from 7.5 to 8.0 Å and 9.6 Å for ZPCu and ZPZn, respectively. The crystallinity went down after Cu2+ / Zn2+ were intercalated into the zirconium phsophate layers. ZpCu and ZPZn were used in oxidation and acylation of alcohols under solvet-free conditions. These catalysts can be recovered and reused for several times without a significant loss in their activity.