Hydrocarbon Storage Simulation in Rhodium Software and Validation via Reactor Testing
Minnie Lahoti, Southwest Research Institute
Zeolites are widely used in NOX-SCR catalysts and as hydrocarbon (HC) traps to meet stringent emission regulations. In diesel cars, zeolite-based HC traps can be used to assist Diesel Oxidation Catalysts (DOCs) during the cold-start period, when the exhaust gas temperatures are below light off temperature of the DOC (200 – 300 °C). Once light off temperature is reached, HCs desorb and are oxidized by the DOC. However, it is very challenging to meet all the requirements simultaneously, due in part to the wide variety of HC mixtures that can be present in exhaust, as well the presence of various inhibitors (such as lube-oil related poisons). These factors can cause changes in diffusive and chemical properties of the zeolite that are not yet well understood. Additionally, the HC trapping process is largely a physical process dictated by a match between the size of the HC molecule and the size of the Zeolite pores. However, SwRI has the capability to find solutions to these challenges using the in-house developed simulation software called RhodiumTM.
RhodiumTM software, developed by Dr. Jonathan Bohmann, is SwRI’s internally developed molecular docking simulation program. It accounts for detailed molecule-surface interactions and molecule-molecule interactions. Rhodium performs unbiased, traceable docking simulations by utilizing the entire structure of a molecule, which can be derived from common virtual compound libraries, without the need for pre-selecting, and thus biasing, any particular docking site. With the integration of new super computing capabilities, seven to ten million compounds a day can be processed and screened. During this screening, automatically generated structure alerts for optimal binding interactions are produced which, for complicated systems, can reveal unexpected mechanisms. Finally, and most importantly, Rhodium has a well-established track record for producing highly accurate predictions. As an example, on a CPRIT funded project after screening 50,000 compounds for EBOV inhibitors, 50 were down selected by use of the Rhodium software and, among those, 40 where proven later to be active hits.
The objective of the project is to explore the kinetic modeling capabilities of Rhodium to predict the performance of zeolite catalysts in adsorption and desorption of hydrocarbons. The second part of the project is to washcoat catalyst cores with the best zeolite candidates and conduct hydrocarbon storage testing via USGR® system and compare performance results with Rhodium simulations. In this way, it is hoped that the Rhodium tool can be confirmed as a valid tool for use in developing zeolites for this, and other exhaust applications.