Non-thermal plasma activates metal-organic frameworks (MOFs) for challenging catalytic reactions
Researchers at The University of Manchester together with colleagues in Belfast and Chiang Mai University (Thailand) have proposed and developed innovative low-temperature plasma processes to activate the intrinsic catalytic properties and to sustain the stability of Metal-organic frameworks (MOFs) for the challenging catalysis of the water-gas shift reaction which normally only occurs at high temperature. Importantly, the stability of MOFs is sustained under plasma activation and in the presence of water. The method has been proven to be generic, and therefore has the potential to be a platform technology enabling the utilisation of MOFs for a wider range of catalysis research, such as SCR for emission control.
Metal-organic frameworks (MOFs), are crystalline porous materials constructed by connecting metal ions/clusters with organic linkers (such as multi-dentate carboxylates). The highly dispersed and uniformly distributed metal sites can be tailored in MOFs, endowing them the great yet versatile capacity for various applications such as catalysis. However, to date, MOFs have found poor thermal and hydrolytic stability issues in catalysis. This severely restricts their applications in conventional catalysis involving thermal treatment and/or use of water.
MOFs containing open metal sites (OMSs, i.e. coordinatively unsaturated metal sites), such as Cu-HKUST-1, have shown great promise for optimal guest binding, resulting in desirable adsorption and catalysis. However, the most challenging feature of using MOFs with OMSs in heterogeneous catalysis lies in the role of OMSs, which have to provide a balance between activity and stability during the reaction under heating or the presence of water or both. We investigated the behaviour of a MOF (Cu-HKUST-1) during the challenging water-gas shift reaction (WGSR) assisted by non-thermal plasma (NTP, Argon as the discharge gas). Cu OMSs in HKUST-1, showed excellent catalytic activity for the WGSR under NTP conditions. The plasma promoted the dissociation of H2O supplying OH (a key intermediate) to enable the WGSR, as well as preventing the water-induced decomposition of HKUST-1, resulting in an enhanced stability. Additionally, the stability enhancement of MOFs induced by plasma treatment proved as a general phenomenon, as evidenced using HKUST-1 in combination with various SEDs and discharge gases, as well as using Cu-MOF-74 or Cu(bdc)(ted)0.5 MOFs with Ar plasma
By using this strategy, we, along with other colleagues, are now exploring a wide range of scientific catalytic systems to gain insight into the synergy of MOFs-catalysis and NTP-activation.
During the process of publishing the findings of our research in the Nature Catalysis, we have received instructive, constructive and critical comments and suggestions for the referees, which helped us significantly to improve the quality of the manuscript. Herein, we would like to express our sincerest gratitude to them.
This work was kindly supported by the Royal Society (RG160031), European Community’s Seventh Framework (FP7)/People-Marie Curie Actions Programme (RAPID under Marie Curie Grant agreement no. 606889) and Engineering and Physical Sciences Research Council, UK (UK Catalysis Hub Consortium, Portfolio Grant nos EP/K014706/2, EP/K014668/1, EP/K014854/1, EP/K014714/1 and EP/I019693/1).