Claudia Keijzer

Research: Ultra-pure and structured supports for silver catalysts for ethylene epoxidation

In this project we will explore new approaches to design and assemble high surface area metal oxide nanostructures, with high phase and surface purity. These serve as supports for model catalysts that will be tested in industrially relevant reactions to provide insight on the role of the support, which is useful to optimize existing catalysts. Examples of possible design routes for structured supports^[1] are the use of replicas, sacrificial templates (such as stacked PMMA spheres^[2], Figure 1A), or direct foaming techniques.

A first model reaction that we study is the epoxidation of ethylene, which is very sensitive to impurities, promoters, and non-uniformities, and is highly relevant for industry: with an annual ethylene oxide production of circa 35 · 10⁶ ton, ethylene epoxidation is one of the largest industrial processes worldwide.^[3]The formation of ethylene epoxide by mild oxidation of ethylene is catalysed by silver particles deposited on an α-alumina support. Industrial catalysts show selectivities of around 90%, but only at low conversions. The unwanted side reaction is the complete combustion of ethylene to CO₂.

For these epoxidation catalysts, the support has a large influence on catalyst stability and selectivity towards the desired product. α-Al₂O₃ is used as commercial support for ethylene epoxidation catalysts, because it displays a low volumetric density of surface OH groups, due to both a low OH surface group density (< 1 OH nm^-2) and a low specific surface area (typically 1 m² g^-1, Figure 1B). The OH groups facilitate the unwanted side-reaction of ethylene oxide to eventually CO_2.^[4]. While α-alumina reduces side reactions, its low surface area is disadvantageous for the stability of silver particles. Building on our ultra-pure supports with controlled structure, we aim to gain a better understanding of the influence of support, impurities and promoters on the selectivity and stability of these catalysts. Other industrially relevant model reactions will be considered at a later stage of the project.

Students who are interested in a project related to this research are welcome to contact me!

[1] Studart et al., J. Am. Ceram. Soc., 89 (2006). DOI: 10.1111/j.1551-2916.2006.01044.x

[2] Van den Reijen & Keijzer, Materialia, 4 (2018). DOI 10.1016/j.mtla.2018.10.016

[3] Van den Reijen et al., Catal. Tod., 338 (2019). DOI 10.1016/j.cattod.2019.04.049

[4] Özbek & Van Santen, Catal. Lett., 143 (2013). DOI 10.1007/s10562-012-0957-3

C.V.

2018-2020 Master’s degree in Science and Business Management, Utrecht University

Master thesis at the Inorganic Chemistry and Catalysis group, “Stability of Silver Supported on 3DOM α-Alumina with Varying Cage Size” under supervision of Petra Keijzer and prof. dr. Petra de Jongh

Internship at Dow Consumer Solutions, Terneuzen, The Netherlands

2015-2018 Bachelor’s degree in Chemistry, Utrecht University

1997 Born in Hengelo, The Netherlands