Monoliths with MFI zeolite layers prepared with the assistance of 3D printing: Characterization and performance in the gas phase isomerization of α-pinene

Three-dimensional (3D) printing represents a promising technology of solid catalysts/reactors preparation with almost unlimited architecture. A casting route applied in this work for preparation of catalysts with the assistance of a 3D-printed template using the high-resolution Digital Light Processing (DLP) technology renders a possibility to control at the micron-scale macroporosity of the monolithic catalysts, their shape and size, with a very small shrinkage occurring during thermal treatment. We have demonstrated that the monoliths prepared with the assistance of 3D printing templates could be readily functionalized by deposition of ZSM-5 type zeolite (MFI) layers. The one-step hydrothermal process of a preparation and deposition was developed to control the Si/Al ratio and thickness (20-50 mu m) of the zeolite layer. In all the cases, the phase composition (X-ray diffraction), porosity (low-temperature sorption of nitrogen), morphology and the Si/Al molar ratio in the layers (SEM/EDS), were studied. Moreover, the status of silicon and aluminium nuclei was followed by solid-state Si-29 and Al-27 MAS NMR, while the acidity of the zeolite layers was estimated using thermodesorption of ammonia. The catalytic performance of the monoliths was tested in the gas-phase isomerization of alpha-pinene. It was shown that the acidity and catalytic performance could be conveniently controlled by adjusting the Si/Al ratio in a starting gel. Over the sample with the lowest Si/Al ratio in MFI layer (Si/Al = 30), during 4 h on stream, the conversion of alpha-pinene changed between 97-79%, while the selectivity to limonene and camphene varied between 7-27 % and 31-39 %, respectively. Moreover, it was found that the monolithic catalyst can be regenerated by short treatment with air at 700 degrees C.