Siliceous self-pillared pentasil (SPP) zeolite with incorporated phosphorus groups in catalytic formation of butadiene by dehydra-decyclization of tetrahydrofuran: Study of catalyst stability by NMR and REDOR analysis

Siliceous self-pillared pentasil (SPP) zeolite catalysts with incorporated phosphorus groups were synthesized using four different percentages of P, obtaining a network of nanosheets in a house-of-cards arrangement. The catalysts were used in the dehydra-decyclization of tetrahydrofuran (THF) as biomass-derived molecule to obtain 1,3-butadiene. The presence and stability of phosphate (PO43-) and phosphite (PO33-) groups incorporated in the SPP zeolite framework was evidenced. The analysis of fresh and used catalysts by nuclear magnetic resonance (NMR) tests showed that 95% phosphorus in zeolite catalysts is present as orthophosphate groups and less than 5% as pyrophosphate or other polyphosphate groups. The P bonded to Si (Si-O-P, corresponding to orthophosphate groups), identified by 31 P-{29Si}- Rotational Echo Double Resonance (REDOR) -NMR analysis, are proposed as the active sites responsible for the dehydra-decyclization of THF to obtain 1,3-butadiene. The P-SPP zeolite catalyst with 0.2 ratio of precursors P and Si in the synthesis, presented the best performance.