Energy Scientific Progress
The Energy theme of the UK Catalysis has undertaken a wide range of liquid and gas phase projects related to energy conversion catalytic technologies. All the projects have involved strongly multidisciplinary teams utilising expertise from around the UK and internationally which has been facilitated by the funding mechanism from the Hub grant. Highlights of some of the projects are described:
The aim of the project was to assess the impact of plasma on a reaction that is a key step in the production of clean hydrogen for refineries and fuel cell applications. It has been demonstrated that hybrid plasma-catalysis can lead to extremely low temperature water gas shift catalysis.
Probing a Non-Thermal Plasma Activated Heterogeneously Catalyzed Reaction Using in Situ DRIFTS-MS C. E. Stere, W. Adress, R. Burch, S. Chansai, A. Goguet, W. G. Graham, and C. Hardacre, ACS Catal., 2015, 5 (2), pp 956–964 DOI: 10.1021/cs5019265
Chemical looping dry reforming of methane using mixed oxides of iron and cerium: the use of an oxidation state operating window for selectivity improvement
Mixed oxides of iron and cerium with various iron loadings were synthesised and tested as oxygen carriers in the chemical looping dry reforming of methane (CL-DRM). The reactivity during the CL-DRM significantly increased when iron and cerium are forming a mixed oxide due to the dispersion of the iron oxide particles on the cerium oxide surface and a synergetic interaction between both iron and cerium oxides. By careful control of the Fe2O3/CeO2 ratio the activity of the oxygen carrier material could be adjusted to substantially favour oxidation of methane to syngas and inhibit both total oxidation of methane and carbon deposition. Furthermore, controlling the oxidation state of the oxygen carrier was used to influence product selectivity. Such use of an oxidation state operating window could potentially be used to improve future chemical looping processes. The collaboration between the partners under the auspices of the Catalysis Hub provided access to a unique range of reactor types (both differential and integral) in order to perform the work.
Following a screening process, high activity Pt-Sn bimetallic electrocatalysts were developed for the oxidation of n-butanol at potentials ca. 500 mV lower than that found for pure Pt. Importantly, for the first time it has been shown that, the surface does not permanently deactivate on cycling but can, by increasing the mass transport, retain its high activity. This provides the basis for an engineered solution to the n-butanol electrooxidation for efficient fuel cell operation. The multidisciplinary approach to the research has been critical to developing this process requiring both engineering and fundamental science to understand and design the system. Interaction between the centres has been significant which has been promoted by the Hub approach.
Environmental analysis of the chemical looping separation technology used for oxy-fuel combustion and electricity production
The environmental burdens of this CO2 capture technology have been quantified by means of the Life Cycle Assessment (LCA) methodology and compared to conventional and renewable electricity production systems. Significant savings on greenhouse gas emissions (245%) have been determined as being possible when compared to the electricity grid mix in Europe and 135% when compared to electricity production from wind. The collaborative approach developed within the Hub has allowed the LCA team to interact strongly with engineers to enable the quantification of the mass and energy balances of the systems under study, which have directly been fed into the environmental analysis.
The aim of the project was to assess the impact of plasma on a reaction, a key step in the production of clean hydrogen for refineries and fuel cell applications. It has been demonstrated that hybrid plasma-catalysis can lead to extremely low temperature water gas shift reactions, allowing the kinetics of the catalytic process, conventionally determined by the applied temperature, to be disconnected from the thermodynamic limitations of an exothermic reaction. The experimental results have been used to validate a kinetic model; developed to understand how to specifically develop catalysts for plasma activated processes. This project required a close collaboration with researchers from four universities with expertise in theory, kinetics, plasma, spectroscopy and engineering which has been promoted by the Hub model.
The Hub has enabled the establishment of a new team focusing on structure-activity relationships for complex transition metal oxides, bringing together expertise on material synthesis and electrocatalysis, solid state surface and bulk structural analysis and Density Functional Theory. Multicomponent metal oxides have the potential to replace costly Pt-based materials for oxygen electrocatalysts in PEM fuel cells and electrolysers. However, rationalising the properties of these materials is highly challenging due to the generation of multiple crystal phases, elemental segregation, oxygen vacancies etc. Synchrotron X-ray absorption/fluorescence spectroscopy has provided a powerful approach to uncover structure-activity relationships in this area. For example, in LaxCa1-xMnO3 Mn (III) states undergo a reduction step which activates the 4e- oxidation reduction process while the A-site in the oxides structure plays a key role on establishing the initial Mn oxidation state and the extent of surface elemental segregation. Access to the B18 beamline at Diamond, via the Hub allocated BAG has been pivotal in establishing these key observations which are now being developed as more efficient electocatalysts.