Preparation of nanostructured diphosphate Na2CaP2O7. Avoiding of any acid catalysts. The prepared catalyst is reusable and eco-friendly. The method is easy and contains simple experimental procedure.

A powerful, magnetic, supported, acid catalyst, NiFe 2 O 4 @SiO 2 -H 3 PW 12 O 40 , was prepared by chemical support of Keggin (H 3 PW 12 O 40 ) heteropolyacid (HPA) on silica-coated NiFe 2 O 4 magnetic nanoparticles. XRD, TEM, SEM, VSM, and FTIR confirmed that the keggin HPA is well dispersed on the surface of silica-coated NiFe 2 O 4 magnetic nanoparticles. The magnetically recoverable catalyst could be easily recycled at least six times without significant loss of catalytic activity. After full characterization, its catalytic activity was investigated in the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3-c]pyrazole derivatives. Graphical Abstract (1) Novel silica-coated magnetic NiFe 2 O 4 nanoparticles-supported H 3 PW 12 O 40 was fabricated and characterized. (2) Recyclability of the catalyst. (3) Avoiding use of corrosive acid catalysts. (4) Green chemistry.