Performance of Nanosponge and Nanosheet Al- and Ga-MFI Zeolites in Catalytic Pyrolysis of Biomass and Plastics

MFI zeolitic materials in the form of nanosponges (nSP) and nanosheets (nSH) have been synthesized incorporating Al and Ga into the framework. Characterization of the samples by Ar adsorption–desorption and FTIR/pyridine indicates that they present remarkable differences in terms of accessibility (external/mesopore surface area) and acidity (ratio between the concentration of Brønsted and Lewis acid sites). These materials have been investigated as catalysts in the pyrolysis of low-density polyethylene (LDPE) and lignocellulose (oak wood). In spite of very different reaction conditions and operation modes, some common results have been observed when comparing the catalytic performance of the Al- and Ga-MFI samples in both reactions. Nanosponge zeolites show superior cracking and deoxygenation activity during the catalytic conversion of LDPE and oak wood, respectively. On the other hand, Ga-containing materials favor the occurrence of dehydrogenation reactions due to their relatively high content of Lewis acid sites followed by the enhanced production of aromatic hydrocarbons. Overall, the Ga-MFI-nSP sample exhibits remarkable catalytic properties due to a suitable combination of accessibility and acid properties, the latter arising from the Ga incorporation into the zeolite framework.