Strong Hierarchically Porous Monoliths by Pulsed Current Processing of Zeolite Powder Assemblies

Binderless hierarchically porous monoliths have been produced from silicalite-1 and ZSM-5 zeolite powders by a rapid and facile powder processing method where the zeolite powders are assembled in a graphite die and subjected simultaneously to a compressive pressure and a pulsed current. Pulsed current processing (PCP) or, as it is commonly called, spark plasma sintering, enables rapid thermal processing of zeolite powder assemblies with heating and cooling rates at 100 °C/minute or more, which results in the formation of strong powder bodies without any addition of secondary binders. Nitrogen adsorption measurements show that it is possible to form strong zeolite monoliths by PCP that maintain between 85 and 95% of the surface area of the as-received silicalite-1 and ZSM-5 powders. Line-broadening analysis of X-ray powder diffraction data by the Rietveld method and high-resolution electron microscopy showed that the formation of strong interparticle bonds is associated with a local amorphization reaction at the interfacial contact points between the zeolite particles. The PCP-treated binderless ZSM-5 monoliths display a high selectivity in xylene isomer separation.