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Contenuto archiviato il 2024-06-18

Addressing global sustainability challenges by changing perceptions in catalyst design

Final Report Summary - AFTERTHEGOLDRUSH (Addressing global sustainability challenges by changing perceptions in catalyst design)

Catalysis underpins almost all chemical processes in the modern world, contributing to over 90% of all chemical manufacturing processes. It also provides sustainable solutions to some of the most pressing global problems faced today. In recent decades there has been a ‘gold rush’ in the field of heterogeneous catalysis whereby the precious metal that was previously considered inert was demonstrated to be remarkably effective at catalysing a myriad of reactions. This led to a step-change in the approach to catalyst design but the rate of catalyst discovery has not kept pace with the increasing demand for sustainable technologies. The After the Gold Rush project set out to challenge the pre-conceptions of the research community by using fresh methodologies and new approaches to design high-performance catalysts using metals other than gold.
Energy vectors were one of our main themes and we focussed on two reactions that can be used to produce clean hydrogen for fuel cells in this context: the low-temperature water-gas shift reaction and NH3 dissociation into N2 and H2. For the former reaction, our studies showed that the formation of a nano-alloy was not effective in stabilising the benchmark Au catalyst and reduced the activity of the catalyst. We then went on to discover the underlying processes that cause catalyst deactivation and consequently designed a catalyst that exhibited enhanced stability on-stream. For the latter reaction, we designed catalysts for the dissociation of NH3 by computationally modelling the catalyst surface and extracting information that led us to discover a promising class of bimetallic catalysts. Methanol is an important platform chemical and also a potential fuel for the future. We discovered a new sustainable synthetic route to methanol from glycerol, using a basic metal oxide catalyst. This has been patented and also resulted in funding for future projects.
Using novel methodologies was also an important theme of the project and we used such methods to great effect. Supercritical CO2 as an anti-solvent was used to synthesise a perovskite material for N2O dissociation. Due to its enhanced surface area, possible only through using this methodology, it performed better than the best catalysts of its type. This same methodology was used to synthesise georgeite, a rare mineral that is also a precursor to a remarkably active water-gas shift catalyst.
We have demonstrated that CO2 could be used a mild oxidant to transform propane into propene over a ceriumbased catalyst. This new catalytic process, which has been disclosed in a patent filing (PCT/GB2016/052495) has the potential to show substantial benefits over existing alkane-dehydrogenation processes such as STAR, Oleflex and Catofin. We have also used CO2 in the synthesis of cyclic carbonates, showing that cyclic carbonates can be formed directly from high energy molecules (alkenes) in a one-pot reaction under mild conditions.
Our work on the epoxidation of linear alkenes demonstrated that the reaction can be catalysed by a graphitic oxide catalyst, structurally related to graphene, without the need for gold or expensive oxidant reactants; ambient air was all that was required.
In the latter stages of the programme we focussed on convergence of the component themes. This involved applying the knowledge gained from the earlier parts of the programme to new problems in catalysis. Of particular note was the development of an extremely selective hydrogen peroxide synthesis catalyst, composed of a tin-palladium nanoalloy. Previously gold-palladium nanoalloy catalysts were the benchmarks but our discovery demonstrated that gold was not necessary. Further, we demonstrated that gallium, nickel, zinc, indium, and cobalt could also be used to replace gold. Two patents were granted as a result of this work. Similar work was performed on the replacement of Au in the Au-Pd nanoparticles for oxidation of toluene.
The main objectives of the After the Gold Rush project were to change perceptions in catalyst design by developing highly efficient catalysts for some of the most intractable global challenges. The replacement of gold with other metals was also an important aspect of our project. The examples given above demonstrate that we were able to achieve our objectives in each area of investigation and we expect that the pre-conceptions that we have challenged will continue to pave the way for the discovery of new, highly efficient catalysts.