Rational Design of Catalytic and Hydrocarbon Trapping Materials to Meet Automotive Emissions Regulations

Rational Design of Catalytic and Hydrocarbon Trapping Materials to meet Automotive Emissions Regulations

As the emission legislation for vehicle pollutants is becoming more stringent worldwide due to increasing concerns of the impact of air pollution on both the environment and public health, much opportunity is created in the fields of catalysis and catalytic materials.  Several challenges for which I am particularly well-positioned to make important advancements include the following:  (i) Developing catalytic materials that are active for the oxidation of diesel at temperatures as low as 150 ^oC, (ii) Studying and understanding the function of hydrocarbon (HC) trapping materials, such as ion-exchanged zeolites with different metals, for both fundamental and applied purposes, (iii) Investigating the direct conversion of methane (natural gas) to ethanol, where ethanol blends (e.g. E85) are provided by most gas station in the US.  To-date, availability of direct conversion of methane to ethanol and higher alcohols is still limited.  Data such as these will lead to the development of catalysts and processes for more energy efficient vehicles and lower automotive exhaust emissions.

My Ph.D. thesis at the University of South Carolina focused on developing a fundamental understanding of the synthesis of dendrimer-stabilized nanoparticles in solution and on oxide supports.  Most researchers had focused on the final catalytic material, and left untouched the interactions of dendrimers with the metal ions in solution.  Our goal was to investigate the complexation between dendrimer templates and metal ions and increase the metal uptake by the dendrimers by varying the experimental conditions.  By doing so, I developed a new synthetic procedure towards the formation of dendrimer-stabilized Au/Rh nanoparticles and the subsequent synthesis of cost-effective supported metal catalysts.  The major novelty of this synthetic route is that pH control helps to regulate the size of Au/Rh nanoparticles formed, when a dendrimer route is used.  This project was funded by Toyota Motor Engineer and Manufacturing of North America, Inc. and I have participated in the design and writing of 3 annual proposals that were successfully funded.  Diverging from this project – in conjunction with Dr. Michael Amiridis and Dr. John Regalbuto, I also became interested in different synthetic routes of nearly uniform and highly dispersed nanoparticles on high surface area oxide supports.  To this end, I synthesized a series of Ag heterogeneous catalysts using the Strong Electrostatic Adsorption (SEA) technique, previously unexplored in the literature, in which the metal nanoscale size is manipulated by altering the experimental conditions. 

In my postdoctoral research in Oak Ridge National Laboratory, I developed a method to treat automobile exhausts for the regulated hydrocarbon (HC) emissions resulting from cold-starting engines.  The most effective solution is to employ suitable materials which can trap HCs temporarily, such as ZSM-5 and β-zeolites.  The silver exchanged ZSM-5 and β-zeolites, exhibited an increased propylene adsorption/desorption in the absence of both H₂O and CO₂.  Combination of synthesis and evaluation of such materials gives me tools to better elucidate fundamental understanding in the adsorption of HCs in the automotive exhaust emissions before they pass to the catalytic converter.  Recently I have initiated a project for the design of Pd based catalytic materials supported on a ZrO₂-SiO₂ mixed oxide support, aiming to enhanced low-temperature oxidation performance.  Under certain conditions, Pd/ZrO₂-SiO₂ outperformed a Pd/Pt commercial diesel oxidation catalyst.  The rigorous synthesis of catalytic materials was new for my research group in ORNL.  As a result, I now have experience in starting up an academic research lab including designing and constructing laboratory process equipment necessary for my research.

Apparently, catalytic materials with enhanced low-temperature oxidation performance are necessary, with significant attention being paid to their stability under harsh reaction environments, typical to automotive emissions control due to hydrothermal aging and poisoning.  Furthermore, HC porous trapping materials for the treatment of automobile exhausts resulting from cold-starting engines need to be developed, ensuring temporary retention of HCs until automotive emission control catalysts are lit off.  After resolving those issues, future work will build upon my expertise in catalyst synthesis and HC trapping materials to develop fundamental understanding of structure-activity relationships for the formation of useful materials that will provide a basis for lowering the automotive emissions.  Since this is an emerging field, I anticipate this type of studies to extent into the future and I seek to undertake them as a tenure track faculty.