Deactivation Mechanism for Ni-based Dry Reforming Catalysts

Abstract

Dry reforming of methane (DRM) is a promising method for carbon dioxide utilization and hydrogen production, converting CO2 and CH4 into syngas (H2 and CO) using catalysts. Despite its potential, industrial implementation has yet to prevail due to challenges in loss of activity of the catalyst. Carbon deposition (coking) and catalyst particle agglomeration (sintering) occurring during the DRM reaction lead to loss in catalyst activity, thereby lowering hydrogen production yield [1, 7]. This thesis aims to determine whether the addition of alkali promoters on Ni catalysts supported on yttria stabilised zirconia (YSZ) reduces coking and sintering, and whether the catalytic performance and stability is enhanced.

Four samples were analysed: pre and post DRM reaction, with and without promoters, focusing on the comparison between the post reaction samples. Transmission electron microscopy (TEM) imaging was used to examine the various carbon structures formed from coking. Scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-XEDS) mapped the Ni catalyst size distribution to examine sintering. Temperature programmed oxidation (TPO) and catalyst activity measurements were used to examine coking levels and catalytic performance.

The post reaction sample, Ni/YSZ with added alkali promoters, revealed significantly less coking than the post reaction unpromoted Ni/YSZ sample. Sintering levels were comparable in both of the post reaction samples, with an average particle size of 18.8 nm for the alkali promoted sample and 21.8 nm for the unpromoted sample. The alkali promoted sample exhibited a 10% decrease in catalytic activity compared to 20% for the unpromoted sample over a 50-hour reaction period. These findings indicate that the alkali promoted Ni/YSZ sample improved catalytic performance, attributed to the reduction of coking.

Popular Abstract

Turning Harmful Gases into Clean Hydrogen: A Promising Step Towards Sustainable Energy

What if harmful greenhouse gas emissions could be transformed into a cleaner and more sustainable energy source? By using a method called dry reforming of methane (DRM) to convert greenhouse gases into hydrogen, these environmental pollutants can be transformed into valuable fuel. This method could be a promising approach to enhancing the development of sustainable energy while simultaneously combating climate change.

Global warming is an urgent issue, largely driven by the increasing levels of greenhouse gases, particularly carbon dioxide and methane. These gases are emitted in large quantities by industries and the energy sector. For a more sustainable and eco-friendly solution, it is crucial to capture these gases before they are released into the atmosphere. One promising method to capture these gases is DRM, which uses both carbon dioxide and methane to produce hydrogen. However, the process has its challenges. For DRM to work effectively, it relies on catalysts – substances that speed up the process without being consumed themselves. These catalysts though, are prone to carbon buildup – layers of solid carbon that forms on the surface of the catalysts – making the process less effective and leading to reduced hydrogen production over time. Additionally, catalyst particles tend to clump together, further decreasing their effectiveness.

In this thesis, special additives (alkali promoters), were added to the DRM process to examine whether they could prevent carbon from sticking to the surface of nickel catalysts supported on yttria-stabilised zirconia, while also preventing the nickel catalysts from clumping together. Using an advanced imaging technique, electron microscopy, the nickel catalysts could be examined on an atomic level. The findings indicated that the nickel catalysts with these additives performed significantly better than those without, improving the overall efficiency of the DRM process, and hence increasing hydrogen production. While some challenges, like particle clumping, remained, these findings suggest the potential of making DRM a viable industrial process for hydrogen production, reducing greenhouse gases and contributing to a more sustainable future.

• author: Asimakidis, Theodora
• supervisor: Reine Wallenberg; Thomas Willum Hansen
• organization: Centre for Analysis and Synthesis
• course: KASM10 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Dry Reforming of Methane, Nanoparticles, TEM, STEM-XEDS, Nickel, Zirconia, Sustainability, Coking, Sintering, Catalysis, Materials chemistry
• language: English
• id: 9175067
• date added to LUP: 2024-09-26 08:24:39
• date last changed: 2024-09-26 08:24:39