Synthesis, Physicochemical Characterization, and Catalytic Evaluation of Fe³⁺-Containing SSZ-70 Zeolite

Whereas one-dimensional, 10-membered ring zeolites are typically used for hydroisomerization, Fe3+-containing SSZ-70 (Fe-SSZ-70) shows remarkable isomerization selectivity for a zeolite containing 12- and partially blocked 14-membered rings, in addition to 10-membered rings. Fe-SSZ-70 was compared to Al3+-containing SSZ-70 (Al-SSZ-70) in constraint index and n-decane hydrocracking tests. Fe-SSZ-70 exhibited a 74% total isomer yield (64% yield of monobranched isomers and 10% cracking yield) at 85% conversion compared to 49% total isomer yield (41% yield of monobranched isomers and 36% cracking yield) for Al-SSZ-70 at the same conversion. The selectivity to isomerization is attributed to the weaker acid strength of Fe-SSZ-70 over Al-SSZ-70. Fe-SSZ-70 was directly synthesized with Fe3+ isomorphously substituted in tetrahedral positions. The coordination environment of the Fe3+ was characterized using Mössbauer, electron paramagnetic resonance, and diffuse reflectance UV-vis spectroscopies. The physicochemical properties were further probed with inductively coupled plasma atomic emission spectroscopy, temperature-programmed desorption of isopropylamine, and nitrogen adsorption-desorption. The Fe3+ was tetrahedrally coordinated in the as-made materials and became partially octahedrally coordinated upon calcination; enough Fe3+ remained in the framework after calcination for Fe-SSZ-70 to remain catalytically active.