PNNL

Abstract

Zeolites are highly crystalline and porous materials possessing a well-defined one- to three-dimensional pore structure. Zeolites play a major role in the petrochemical industry, exploitation of non-conventional petroleum resources and nonpetroleum resources like gas and coal. Recently, zeolite has been researched heavily in the valorization of biomass for renewable fuel and chemical generation. It has been reported widely that zeolite deactivation can occur via two main mechanisms. The first one is leaching of alumina from the unit structure of the zeolite in the presence of steam; this mechanism causes the irreversible deactivation. The second mechanism is the formation of coke during the transformation of organic compounds in the pores and/or the outer surface and the poisoning of the active sites and/or blocking of the pores. The catalyst deactivation from this mode can be regenerated by burning the catalyst under oxidative conditions. Repeated thermal treatment for spent catalyst regeneration is also shown to cause permanent modification of the zeolite structure. So identifying the nature and the location of the coking material and changes in Al distribution in catalyst after catalytic reactions becomes imperative. Recently, a relatively new technique called atom probe tomography (APT) has been increasingly used to perform 3D quantitative analysis of element distribution with sub-nanometer scale spatial resolution and high mass sensitivity up to the few ppm level of concentration of elements in materials. In the study we used a multimodal approach including C K-edge x-ray absorption along with 13C cross polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR) and APT to investigate element distribution within a HZSM-5 as-synthesized condition and after ethanol conversion reaction.