Ruthenium-containing small-pore zeolites for shape-selective catalysis

Ruthenium-containing small-pore zeolites with the framework types LTA, KFI, MER and RHO were prepared by addition of ruthenium(III) chloride to the gel of the hydrothermal zeolite synthesis in the absence of organic templates. This synthesis strategy was described earlier for the large- and medium-pore zeolites Ru/Na-X (FAU) and Ru/Na-ZSM-5 (MFI), respectively. The majority of the ruthenium species in the modified small-pore zeolites has a diameter in the order of 1 nm or less and is located inside the pores of the frameworks. These species are available for shape-selective catalytic conversions as demonstrated by the competitive hydrogenation of 1-hexene and 2,4,4-trimethyl-1-pentene. This test reaction allows to differentiate between ruthenium particles within the zeolite pores and those on the external crystal surface. Consequently, LTA-type zeolites with intrazeolitic ruthenium species could be synthesized with ruthenium loadings of up to 4.0 wt.%. A further increase of the ruthenium content to 8.0 wt.% resulted in a significant fraction of the ruthenium (oxide) clusters on the external crystal surface. Ruthenium species on the outer crystal surface also exist after the hydrothermal zeolite synthesis. These can, however, be removed by ion exchange with an aqueous calcium nitrate solution.