Periodic Reporting for period 1 - CURVEO (Selective ethylene oxidation on novel curved model catalysts)
Reporting period: 2022-06-01 to 2024-05-31
The CURVEO project aims to advance our understanding of selective ethylene epoxidation. Silver-based (Ag) model catalysts were employed to investigate how different surface structures influence the reaction mechanism.
Ethylene oxide (EO), a valuable chemical for various industrial applications, is produced through the direct oxidation of ethylene using silver-based catalysts. Traditional surface science techniques face limitations in replicating real industrial conditions, referred to as the materials and pressure gaps. The pressure gap highlights the disparity between ultra-high vacuum (UHV) conditions in laboratories and the high-pressure conditions in industrial processes. The materials gap points to the difference between idealized research surfaces and the complex, heterogeneous surfaces of industrial catalysts.
CURVEO bridges these gaps by studying selective ethylene epoxidation under near-ambient pressure conditions in atomic detail. The project systematically characterizes different surface species and intermediates, studies their occurrence during active reaction conditions, and correlates changes in reactivity with specific surface features. This is an important step to elucidate the various pathways occurring in parallel on real catalytic materials with complex surfaces.
Ethylene oxide (EO), a valuable chemical for various industrial applications, is produced through the direct oxidation of ethylene using silver-based catalysts. Traditional surface science techniques face limitations in replicating real industrial conditions, referred to as the materials and pressure gaps. The pressure gap highlights the disparity between ultra-high vacuum (UHV) conditions in laboratories and the high-pressure conditions in industrial processes. The materials gap points to the difference between idealized research surfaces and the complex, heterogeneous surfaces of industrial catalysts.
CURVEO bridges these gaps by studying selective ethylene epoxidation under near-ambient pressure conditions in atomic detail. The project systematically characterizes different surface species and intermediates, studies their occurrence during active reaction conditions, and correlates changes in reactivity with specific surface features. This is an important step to elucidate the various pathways occurring in parallel on real catalytic materials with complex surfaces.
The project investigated the reactivity of different surface sites on Ag catalysts during ethylene epoxidation. The reaction was studied under near-ambient pressure conditions but with well-defined catalyst surfaces.
At the outset of the project, a comprehensive characterization of Ag surfaces was carried out, using techniques such as Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). These methods allowed for detailed analysis of various Ag surfaces, including flat and curved crystals with different step types, and provided insights into surface species under both ultra-high vacuum and near-ambient pressure conditions.
One of the key findings of the project was the differentiation between nucleophilic and electrophilic oxygen species on different Ag surfaces, while simultaneously tracking product formation. It was found that steps exhibited higher selectivity for electrophilic oxygen, which is crucial for EO production. However, stepped surfaces were more prone to ethylene cracking and surface poisoning, while flat (111) surfaces provided more stable conditions for consistent product formation. These findings underscore the importance of surface stability for optimal catalytic performance.
Efforts to fabricate stable Ag nanoparticle arrays on oxide supports encountered unforeseen challenges, particularly due to the instability of Al2O3 films in reaction EO-selective conditions. As a result, the project maintained a focus on experiments with Ag surfaces. The use of near-ambient pressure XPS (NAP-XPS) proved successful in observing reactions under near-realistic conditions. Various oxygen- and carbon-containing species were identified, including electrophilic and nucleophilic oxygen, carbonates, and reaction products such as CO2 and EO. We gained new insights on the interplay of these species in different pressures, gas mixes, temperatures, and on different surfaces.
Throughout the project, the researcher gained extensive expertise in advanced spectroscopy techniques and project management skills. During the two years of this project, the researcher established active collbaorations with five international research groups. She has contributed six talks at conferences (three invited).
At the outset of the project, a comprehensive characterization of Ag surfaces was carried out, using techniques such as Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). These methods allowed for detailed analysis of various Ag surfaces, including flat and curved crystals with different step types, and provided insights into surface species under both ultra-high vacuum and near-ambient pressure conditions.
One of the key findings of the project was the differentiation between nucleophilic and electrophilic oxygen species on different Ag surfaces, while simultaneously tracking product formation. It was found that steps exhibited higher selectivity for electrophilic oxygen, which is crucial for EO production. However, stepped surfaces were more prone to ethylene cracking and surface poisoning, while flat (111) surfaces provided more stable conditions for consistent product formation. These findings underscore the importance of surface stability for optimal catalytic performance.
Efforts to fabricate stable Ag nanoparticle arrays on oxide supports encountered unforeseen challenges, particularly due to the instability of Al2O3 films in reaction EO-selective conditions. As a result, the project maintained a focus on experiments with Ag surfaces. The use of near-ambient pressure XPS (NAP-XPS) proved successful in observing reactions under near-realistic conditions. Various oxygen- and carbon-containing species were identified, including electrophilic and nucleophilic oxygen, carbonates, and reaction products such as CO2 and EO. We gained new insights on the interplay of these species in different pressures, gas mixes, temperatures, and on different surfaces.
Throughout the project, the researcher gained extensive expertise in advanced spectroscopy techniques and project management skills. During the two years of this project, the researcher established active collbaorations with five international research groups. She has contributed six talks at conferences (three invited).