ENHANCEMENT OF THE CATALYTIC ACTIVITY OF VPO AMMOXIDATION CATALYSTS BY USE OF VANADYL(IV) ORTHOPHOSPHATE PRECURSOR COMPOUNDS

(VO)(3)(PO4)(2). 7H(2)O and (VO)(3)(PO4)(2). 9H(2)O vanadyl(rv) orthop hosphate hydrates (V/P = 1.5) used as precursor compounds were transfo rmed into highly active ammoxidation catalysts during different pretre atment procedures. These structural transformations have been investig ated in the presence of ammonia-containing gases or under nitrogen, le ading into materials that contain crystalline (NH4)(2)(VO)(3)(P2O7)(2) (V/P = 0.75) and (VO)(2)P2O7 (V/P = 1) specimens, respectively, as we ll as an additional X-ray-amorphous phase of partially crystalline van adium oxides. These vanadium oxides represent the molar vanadium exces s of the original precursor material in comparison to the defined vana dium amount of the crystalline proportion of the transformation produc t. Both components of these solids are tightly grown together to form microdomains. The solids generated this way were characterized by XRD, EDX, FTIR spectroscopy, P-31 MAS NMR spectroscopy XPS and chemical an alyses and used as catalysts in the ammoxidation of toluene to benzoni trile. The results of the heterogeneous catalytic ammoxidation on the orthophosphate derived catalysts were compared with those runs obtaine d by the application of pure, as-synthesized (NH4)(2)(VO)(3)(P2O7)(2), similar transformation products derived from VOHPO4. 0.5H(2)O precurs or (V/P=1) and pure (VO)(2)P2O7. Owing to the existence of mixed-valen t vanadium oxides in increased portions of the orthophosphate derived catalysts, these solids reveal a significant enhancement of the toluen e conversion rate at almost equal high nitrile selectivities in compar ison to usual VPO catalysts.