Methane is an abundant hydrocarbon that is the primary component of natural gas as well as produced by livestock. Methane emission negatively impacts the environment and is responsible for around 30% of the recent rise in global temperature [1]. Fortunately, the abundance of methane and its chemical composition make it an ideal feedstock for catalytic conversion [2]. With the aid of catalysis (chemically facilitated molecular conversions), methane can be used to produce more valuable chemicals and fuels such as ethane while minimizing the environmental impact of methane emissions [3, 4].
While catalytic conversion of methane is promising, there are multiple challenges with the predominant current approach, thermal catalysis [3,4]. First, this process requires harsh reaction conditions, particularly the need for high reaction temperatures ranging from 700–1100ºC. High temperatures require immense energy, leading to an expensive and dangerous system. Second, the immense heat creates the possibility of side reactions, especially the complete removal of hydrogen atoms from carbon and thus the formation of useless and unwanted products such as atomic carbon and carbon dioxide.
To combat these issues, my research, supported by a Summer Undergraduate Research Fellowship (SURF), implemented a photocatalytic approach [5]. The key advantage of photocatalysis is the facilitation of reactions under ambient temperature and normal pressure using light, reducing the risk and cost associated with thermal catalysis. This replacement of thermal energy with light energy allows for the use of sunlight, resulting in a green conversion process. Furthermore, photocatalysis can lead to increased conversion and consequently a greater production of ethane. This is an extremely promising direction in the reduction of greenhouse emissions while also creating the financial incentive of creating more valuable fuels with relatively low energy input.
Research Methods
My research aimed to develop an effective catalyst for converting methane to ethane using light as the driving energy for the reaction. I first identified an effective method to hold my catalysts on our homemade flow reactor. The flow reactor allows gas (methane and helium) to enter and exit continuously and allows us to test the activity of the catalyst. I designed and printed a few 3D sample holders made of plastic that held my catalysts and promoted an optimal flow of gas through the reactor. Through multiple tests and redesigns, I landed on a sample holder that I believed to be optimal. The remainder of my summer then focused on designing and testing catalysts, which consisted of four steps: synthesis of catalyst, calcination (heat treatment), structural characterization of the catalyst, and activity testing.
The first step was to identify and synthesize my catalyst. Based on prior research, I chose to use phosphotungstic acid, loaded with gold nanoparticles supported on the metal oxide titanium dioxide. The phosphotungstic acid and gold act as the active species, while titanium dioxide increases the surface area of the catalyst.
During synthesis, phosphotungstic acid and titanium dioxide were suspended in water, and the mixture was stirred and heated to around 50ºC. Because my catalyst is modified with gold, I used a specific amount of gold solution and added it dropwise to the suspended catalyst. This mixture was left to stir for two hours and removed from the beaker into a round bottom flask. Water was removed by using rotary evaporation and a vacuum oven. The drying step was performed overnight, so I returned the next day to remove my catalyst from the flask. While developing my catalyst, I observed that the amount of gold had a significant effect on methane conversion and product distribution. Because of this, I varied gold loading until I landed on an apparent best design that showed the maximum methane conversion and ethane production.
Following synthesis, the catalyst was calcined at high temperatures to remove impurities. I found that by varying the temperature, I could greatly alter the longevity of conversion and production of ethane. Therefore, I altered calcination temperatures to find a catalyst that had the best longevity as well as activity for methane conversion.
An important step following the synthesis of a catalyst is characterization. This involves using instruments to better understand properties associated with my catalysts, including structure, composition, acidity, and response to heat. I performed two characterizations: Raman Spectroscopy and Thermogravimetric Analysis (TGA). Raman spectroscopy uses a laser that reflects off the sample to determine vibrational modes, crystal structures, and composition. This method allowed me to identify the presence of phosphotungstic acid in my catalyst, which confirmed the synthesis was successful. TGA is used to identify how a sample responds to an increased temperature. The heat flow and the mass of the sample are measured as the temperature is slowly and incrementally increased from room temperature to a high temperature (up to 800 ºC). Using TGA, I was able to identify a shift in the crystal structure of my catalyst which helped me find an optimal calcination temperature. I incrementally lowered calcination temperature until I identified a catalyst that had both the optimized ethane production and a much-improved longevity.
Following synthesis and characterization, the catalyst’s performance must be tested. This is known as an activity test and was the most time-consuming part of my summer. First, I loaded the catalyst into a homemade flow reactor by placing it onto the sample holder I designed earlier. The reactor was then sealed and tested for leaks to ensure a pure atmosphere. A mixture of methane and helium were then pushed through the reactor. Once the reactor reached a steady state (consistent and stable flow of gases), we activated an Xe lamp at a power level of 300W. This provided the energy necessary for the catalyst to facilitate the coupling of two methane molecules to form one ethane and hydrogen molecule. Because the product gases—methane, carbon dioxide, and ethane—are colorless and odorless, a gas chromatograph is needed to analyze the gases exiting the flow reactor. This instrument separates the gas stream into its pure components and gives an output in peaks. Using the area under the peaks, quantitative amounts of each gas can be found. Through data analysis of each activity test, I determined how much methane reacted and the amount of ethane and carbon dioxide produced.
Preliminary Findings
Figure 1. Effect of calcination temperatures on photocatalytic methane conversion to ethane.
Through variations in calcination temperature, reactor design, and gold loading, I successfully synthesized a catalyst that was effective and stable for ethane production in a flow reactor. Notably, I identified a gold modified phosphotungstic acid catalyst to be an effective photocatalyst for methane coupling. Through results obtained from the gas chromatograph, I saw the clear formation of ethane when the catalyst was exposed to light from the Xe lamp. Once the light was turned on, ethane production increased rapidly until it reached a value where it plateaued, as shown in Figure 1.
Comparatively, when under no irradiation, no formation of ethane or other products were observed. This reaction proceeds at room temperature and is selective towards ethane production. These results are significant because methane can be converted to a more valuable fuel without the need for immense energy input that is required for thermal catalysis.
Future Plans
Through SURF, I obtained key results that will direct my project’s future. During fall 2024, I am continuing to run activity tests, focusing on gold loading amounts and calcination temperature to find an optimal combination for my catalyst. In addition, I am redesigning the sample holder in the flow reactor. During each activity test conducted over the summer, I noticed a large production of carbon dioxide in addition to the expected ethane. This came as a bit of a surprise, as there is no gaseous oxygen present in the system. Through further investigation, I found that under the heat generated by the lamp, the plastic that comprised the sample holder was decomposing and releasing carbon dioxide. This was a major finding as it meant my catalyst was far more selective towards ethane than I previously thought. Therefore, I am redesigning my sample holder to use stainless steel instead of plastic. The stainless steel sample holder will not react with the reactant gas leading to more accurate results. Through these modifications I hope to identify a catalyst that is nearly 100% selective towards ethane production.
I plan to further my research by adding an oxidative species to regenerate my catalyst. Without the use of an oxidant, the reaction is thermodynamically limited, and thus only a limited amount of methane can react. I plan to test varying oxidative species such as oxygen, water, and hydrogen peroxide to determine the effect these have on my catalyst’s performance. By doing so, I hope to increase catalyst activity for enhanced methane conversion while maintaining the high selectivity of my current catalyst.
In the immediate future, I will present at the 2024 American Institute for Chemical Engineers (AIChE) annual conference in San Diego, allowing me to share my results and connect with other researchers. My SURF experience solidified my desire to obtain my PhD and sparked my interest in clean energy, which is now a field I hope to work in after school. I have found the energy field to be fascinating and rewarding as it has a positive impact on the world around us.
I would like to express my deepest gratitude to my advisor, Dr. Nan Yi, for supporting me and guiding me through this project. Additionally, I'm grateful for the assistance in lab training and project guidance I received from Seth Drahusz. Without their contributions, my project wouldn't have been nearly as successful. I would also like to thank Dracy Silver for her incredible help in manufacturing my new sample holder out of steel. Lastly, without the funding from the Hamel Center for Undergraduate Research I would not have been able to complete this project. For this I am grateful as well as for the direction this research has given my future career.
References
[1] Catalysis Science & Technology, 2014, 4, 2397-2411.
[2] Catalysis Today, 2000, 63, 165-174.
[3] Energy & Environmental Science, 2014, 7, 2580-2591.
[4] Chem Catalysis, 2023, 3, 100437.
[5] Carbon Future 2023, 1, 920004.
Author and Mentor Bios
Jack Sullivan is a chemical engineering major from Plymouth, New Hampshire, who will graduate from UNH in May 2026. He is a student ambassador for the Hamel Center for Undergraduate Research and a member of UNH’s Energy Club. In 2024, Jack received a Summer Undergraduate Research Fellowship (SURF) from the Hamel Center to complete the research described in this research brief.
Nan Yi is an associate professor in the Department of Chemical Engineering at UNH where he has taught since 2015. He specializes in catalysis science, which is a great passion of his along with STEM outreach. Dr. Yi teaches core chemical engineering classes and electives that discuss how the various forms and uses of energy impact the environment. Since 2016, Dr. Yi has mentored several Inquiry authors and numerous students who received grants from the Hamel Center for Undergraduate Research, including: seven Research Experience and Apprenticeship Program (REAP) awardees; eight Summer Undergraduate Research Fellowship (SURF) awardees; and six Undergraduate Research Award (URA) recipients.
Copyright © 2024 Jack Sullivan
