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

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%.

Automated summary

A novel metallosilicate zeolite with a tridirectional pore system of 8- and 10-ring channels was successfully fabricated by direct incorporation of B, Al and Ga into ITQ-52 zeolite using a phosphorus-containing organic structure-directing agent. The presence of phosphorus species stabilized the framework positions of Al or Ga and decreased the acidity of the zeolites, ultimately enhancing the catalytic performance in the MTO reaction. The addition of P in ITQ-52 improved the catalytic lifetime and the propene selectivity of the samples.