Electron spin resonance and optical spectroscopy of tubular aluminophosphate materials containing framework vanadium

A series of aluminophosphate materials without (UHM-1) and with variable amounts of vanadium (VUHM-1) have been synthesized in the presence of a cationic surfactant cetyltrimethylammonium chloride and an organic base tetramethylammonium hydroxide. Powder X-ray diffraction and electron probe microanalysis show that both UHM-1 and VUHM-1 with V/Al ratios up to 0.05 possess disordered arrays of tubular channels which mimic the hexagonal MCM-41 structure. The overall P/Al ratio is about half of the initial unity ratio in the gel mixture, especially for VUHM-1. This indicates incomplete condensation of phosphorus oxide and a non-ideal aluminophosphate framework; this seems associated with poorer thermal stability than microporous aluminophosphate and mesoporous aluminosilicate MCM-41. Electron spin resonance and diffuse reflectance ultraviolet-visible spectroscopies reveal that in as-synthesized VUHM-1 the vanadium exists as monoatomically dispersed square pyramidal VO2+ ions and as tetrahedral V5+ ions which are consistent with a framework location for the vanadium. (C) 1998 Elsevier Science B.V.