Isomorphous substitution of Mn(II), Ni(II) and Zn(II) in AlPO-31 molecularsieves and study of their catalytic performance

Isomorphously substituted molecular sieves, MAPO-31, NAPO-31 and ZAPO-31, w ere prepared under mild hydrothermal conditions from gels containing source s of aluminium, phosphorus, appropriate metal and dipropylamine (DPA), pres umably acting as a structure-directing template. They were characterized by XRD, FTIR, TGA, inductively coupled plasma (ICP), ESR, Brunauer, Emmett, T eller (BET) and diffusion reflectance spectroscopy (DRS) techniques. In the XRD, the peak at 2 theta = 16.7 degrees of the metal substituted AlPO-31 i s more intense than that of pure AlPO-31 suggesting preferential occupation of the plane corresponding to it as compared to other planes. The O-H stre tch in the IR spectra of the metal-substituted molecular sieves is blue-shi fted with respect to the parent AlPO-31 molecular sieves possibly due to me tal substitution. The g values obtained from the ESR spectra of MAPO-31 and NAPO-31 also substantiate framework substitution. Ethylation of toluene wa s carried out between 300 and 450 degrees C over the above catalysts as a m odel test reaction. The high toluene conversion over metal-substituted mole cular sieves proves the isomorphic substitution of metal ions in the AlPO-3 1 framework.