Catalytic benzene hydroxylation over copper-substituted aluminophosphate molecular sieves (CuAPO-11)

Copper-substituted aluminophosphate molecular sieves (CuAPO-11, AEL topology) containing various copper fractions, which have been synthesized by hydrothermal crystallization, were characterized using several physicochemical techniques, such as XRD, SEM, FTIR, ²⁷Al and ³¹P MAS NMR, etc. In combination of early reported characterization results, the isomorphous substitution of copper in the framework of the parent AlPO₄-11 was further confirmed. For example, FTIR spectroscopy provides clear evidence of copper incorporation into the framework of the AEL structure due to the occurrence of a new absorption band around 1050 cm^-1 as compared with the pure AlPO₄-11, which may be tentatively attributed to some stretching vibration related to the lattice oxygen-coordinated copper species. The selective oxidation activity of CuAPO-11 was evaluated using liquid phase-H₂O₂ hydroxylation of benzene as a probe reaction and compared with another redox analog CuAPO-5 (AFI topology). The catalytic test results suggest that comparable benzene conversion over these copper-containing materials was associated with the framework-incorporated copper atoms whereas different product distributions were governed by the structure type, viz. AEL or AFI topology.