Versatile phosphorus-structure-directing agent for direct preparation of novel metallosilicate zeolites with IFW-topology

Abstract

[EN] To fabricate a novel metallosilicate zeolite with a tridirectional pore system of 8- and 10-ring channels, direct incorporation of B, Al and Ga into small and medium pore ITQ-52 zeolite with the IFW-type topology was carried out using a phosphorus-containing organic structure-directing agent (P-OSDA, 1,4-butanediylbis[tris(dimethylamino)]phosphonium hydroxide). The solids were characterized by XRD, FT-IR, 11B, 27Al, 31P and 71Ga MAS NMR spectroscopy before and after post-synthesis treatments and steaming. It was found that the P-species derived from OSDA were decomposed by heat treatments, forming extra-framework phosphates that remain in the cavities of the zeolite. The presence of P-species not only stabilized the Al or Ga located in framework positions which adopted a reversible octahedral configuration but also decreased the acid strength of the zeolites. The catalytic performance of the Al- and Ga-containing ITQ-52 zeolites in the MTO reaction was investigated. We have found that the presence of P in ITQ-52 enhanced the catalytic life time, and that the optimum P content for the samples with Si/Al = 120 and Si/Ga = 135 were found to be P/Al = 0.17 and P/Ga = 0.14, respectively, showing a propene selectivity higher than 35%.