Ph.D. Defense| Nawaf M. Alghamdi


Oxidation Kinetics over Rh/Al2O3 in a Stagnation-Flow Reactor

Nawaf Alghamdi, Ph.D. Candidate supervised by Prof. Mani Sarathy

Date: Thursday, February 16, 2023

Time: 5 - 6 PM

Location: Building 9, Level 2, Lecture Hall 1, Room 2322 



Transportation is responsible for 25% of the global CO2 emissions, with gasoline and diesel light-duty vehicles being responsible for nearly half the transportation sector energy use. The reduction of CO2 emissions from transportation is an enormous challenge. While electrification is on the horizon, around 70% of the world’s vehicles are expected to be non-electric by 2050. One pragmatic way of tackling the CO2 challenge is to optimize the systems employed in the over 1 billion vehicles on the road today. In this dissertation, we tackle the issue of reducing the transportation CO2 emissions from experimental and simulation points of view. This entails building a stagnation-flow reactor, which reduces the problem to one dimensional and helps attain accurate kinetic data and employing the state-of-the-art catalytic microkinetic modeling techniques.

Gasoline vehicles utilize three-way catalyst systems, where CO, NO and unburned hydrocarbons are simultaneously converted to CO2, N2 and H2O. These systems are based on platinum (Pt), rhodium (Rh) and palladium (Pd) catalysts. Rh is the most expensive metal and is estimated to only be 0.0002 ppm of the Earth's crust. Therefore, it is important to understand the detailed chemistry on Rh to better utilize it. We start by thoroughly characterizing a commercial 5 wt. % Rh/Al2O3 catalyst via N2-physisorption, ICP-OES, XRD, H2-TPR, H2--chemisorption, STEM, and EELS.

Additionally, the current microkinetic mechanisms for CO oxidation to CO2 over Rh/Al2O3 are limited to high temperature and cannot predict low temperature behavior, which is relevant to engine cold-start conditions. We attained an improved understanding of CO oxidation by performing experiments at low-temperature in the stagnation-flow reactor. This includes the effect of temperature, pressure, inlet composition, and flow rate.

Then, we generated a microkinetic mechanism that is DFT-parametrized and captures the CO oxidation behavior at low and high temperature. The mechanism is versatile and accurately predicts the observed behavior at vastly different conditions. We examined the detailed chemistry by performing sensitivity analysis at different compositions. We also examined the surface coverage and explained the surface behavior based on thermodynamics.

Lastly, we tested the oxidation of dimethyl ether, a potential alternative fuel for diesel engines, at low temperature in the stagnation-flow reactor. In addition to testing total oxidation conditions, we examined partial oxidation conditions where we isolated the oxidation zone from the reforming zone. This is of relevance to after-treatment of DME-powered engines. We report intrinsic activation energy values, which have not been previously reported for this catalyst system.

Overall, the work advances our knowledge of current and alternative transportation systems. It paves the way for accurate modeling of these catalytic process as well as rational design for cheaper and more effective catalysts.


Nawaf is a PhD candidate in chemical engineering in Professor Mani Sarathy's group. He joined CCRC in 2017 as a master's student then started his PhD in 2019. Prior to joining CCRC, he earned his bachelor's in chemical engineering from the University of Wisconsin-Madison as part of the KGSP program. In CCRC, he was the president of the Student Advisory Committee (2020 and 2021), the CCRC Student Mentor (spring and summer of 2019), and the CCRC best volunteer of 2021.


Event Quick Information

16 Feb, 2023
05:00 PM - 06:00 PM
Building 9, Level 2, Lecture Hall 1, Room 2322