Stability improvement to a ruthenium catalyst for partial oxidation of methane

Abstract

Catalytic partial oxidation of methane (CPOM) is an energy-efficient alternative to steam reforming, the currently prevailing method for energy production from natural gas. Hulteberg Chemistry & Engineering AB has developed a catalyst for the partial oxidation of methane into syngas, for use in solid oxide fuel cells. In its current form, the catalyst rapidly deactivates, causing increased material cost and a need for frequent stopping of the process to regenerate the catalyst. This thesis focuses on improvements to the stability of the catalyst to increase its lifetime and thus commercial viability.
Several new granular catalyst formulations were prepared and tested for activity, selectivity and stability in a lab-scale reactor. All catalysts were supported on magnesia-alumina and used low loadings of ruthenium as the main component of the active phase. Modifications were made to the support by adding magnesium, and to the active phase by doping with platinum or palladium. The activity tests showed that all tested catalysts were active for CPOM, with methane conversion and selectivity towards syngas close to the thermodynamic equilibrium. The activity was virtually unaffected by varying the space velocity from 10,000 to 160,000 h-1. Long-term stability tests found that the addition of 10 wt% magnesium to the catalyst support significantly increased stability, although deactivation continued at a reduced rate even after 100 hours. Through kinetic modelling, a catalyst half-life of 123 hours was determined for the modified catalyst compared to 69 hours for the standard catalyst.
Characterization of the long-term tested catalysts by pulse chemisorption found that the modified catalyst had a surface area of 0.21 m2/gsample, compared to 0.14 m2/gsample for the standard catalyst, indicating that addition of magnesium increases stability during the calcination and reduction.
Overall, the increased stability by the addition of magnesium gives a good starting point for further research. Several prepared formulations are yet to be long-term tested and characterized; doing this could result in further improvements to catalyst stability.

Popular Abstract

Natural gas will likely remain an important energy source for years to come, as it is still abundant, cheap and cleaner burning than coal. During the transition from fossil resources into renewable energy, our society depends on natural gas if we want to avoid using coal, a dependence which has become particularly evident during the ongoing war in Ukraine. The main process for turning natural gas into energy is called steam reforming, but there are other processes which may be more energy-efficient and less wasteful in some situations. If energy producers can use these improved processes to reduce environmental impact in the short run, the benefits could be substantial in terms of reduced carbon emissions.
One of the processes being studied is called catalytic partial oxidation of methane, or CPOM, and is the focus of this master thesis. Methane is the main component of natural gas, and partial oxidation means burning the methane with less oxygen than during normal combustion. The product of the combustion is energy and so-called syngas, a mixture of carbon monoxide and hydrogen gas. Syngas can be used for many different applications; for example to make chemicals, or to be used in fuel cells for energy.
To make the process require less energy to initiate, a catalyst is used. Catalysts come in many shapes and sizes, but the catalysts used in this project look like small grains of sand. The grains are speckled all over with ruthenium, a noble metal that helps the gas molecules find and interact with each other. A common problem with catalysts is deactivation – the worsening of catalyst performance over time. Developing catalysts that stay active for longer is therefore very interesting as a research topic, as it reduces the cost of the catalyst and less material is wasted. This thesis focuses on ways to reduce the deactivation while making sure that the catalyst still works for CPOM. New catalysts were made by making educated guesses about what changes to the recipe could make it more stable. The catalysts were then tested in a small-scale reactor where CPOM occurred at conditions similar to in a real fuel cell. Which catalyst did best was decided by looking at the concentration of methane and other gases after the reaction and comparing between catalysts. The catalysts were also examined with a special analysis technique to try to explain how the catalyst properties are different from each other.
In the end, this work found that adding magnesium to the grains helped made the catalyst last almost twice as long, depending on how you count. It was also found that the catalyst with magnesium had a larger surface area than the one without. All the tested catalysts, which included some using different metals together with ruthenium, as well as ruthenium in different concentrations, were active for CPOM, although not all were able to be completely tested as each test took a long time to perform, so it is still unknown how stable they are. More tests are probably needed before the catalyst can be seen as completely stable, but the results give a good starting point for further work.

• author: Axelsson, Melker
• supervisor: Christian Hulteberg
• organization: Chemical Engineering (M.Sc.Eng.)
• course: KETM05 20222
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: catalysis, reaction engineering, kinetics, partial oxidation, chemical engineering
• language: English
• id: 9106211
• date added to LUP: 2023-01-16 13:43:22
• date last changed: 2023-01-16 13:43:22