Zeolite based catalysts are used globally in large quantities across a wide range of applications including chemical production from both renewable and more traditional fossil feedstocks, automotive emissions reduction, gas separation and water treatment. They are able to serve such diverse applications as they are crystalline, microporous materials (pores less than 2 nm) that exhibit robust hydrothermal stability, allowing them to be used under demanding process conditions. Zeolites are naturally occurring minerals, but most that are industrially used are synthetically manufactured. New materials and compositions are demanded to optimize processes and serve new applications, and are often developed by trial and error methods guided by researcher experience since the crystallization process is at best partially understood. The inefficiency of this method makes the development of new materials a time-consuming, costly process. Therefore, the primary scientific objectives of this project were to investigate the synthesis of zeolites using advanced characterization techniques, and especially monitor heteroatom incorporation (the catalytic active site), with the ultimate goal to bring greater insight to the process so that more advanced materials can be engineered.
During this project we have investigated the full lifetime of zeolite catalysts from crystallization to deactivation using advanced characterization techniques including atom probe tomography (APT) and scanning transmission X-ray microscopy (STXM). APT is a type of 3-D microscopy that can produce atom-by-atom material reconstructions with sub-nanometer resolution, and STXM is able to produce spatially resolved (50 nm spot size) XANES (X-ray absorption near edge structure) maps of materials to learn more about the local environment of specific elements. Using these advanced characterization techniques, we have added insight to the underlying mechanisms of material crystallization, the distribution of active sites in materials and the deactivation of catalysts. Some of the notable catalysts that were investigated include SAPO-34, which is industrially used to convert methanol (sourced from both renewable and non-renewable feedstocks) into desirable commodity chemicals such as propylene and ethylene, as well as copper-exchanged zeolite SSZ-13 that is used to reduce NOX emissions in diesel vehicles. These applications are top priorities for the European Union within Horizon 2020 as they allow for increasing use of renewables as well as reducing air pollution.
