Intial period:
To achieve our aim, we compared Cu-SSZ-13 samples prepared by two different methods to induce the formation of different copper species within the framework: the first synthesized via a standard wet ion exchange method known to produce an efficient SCR catalyst material, and the second prepared by a solid state incorporation method. In particular, the presence of copper aluminate species, which has previously been associated with the deactivation of Cu-zeolites, is considered as a site for preferential nitrate formation. To demonstrate this correlation, the samples were studied using an ambitious combination of two synchrotron techniques at the Diamond Light Source. The hard X-ray nanoprobe on beamline I14 was used to generate X-ray fluorescence (XRF) and X-ray absorption near edge structure (XANES) maps, providing detailed characterization of the catalysts. The multimode infrared imaging and micro-spectroscopy (MIRIAM) beam on B22 was then used to identify vibrational modes of nitrate components under operando conditions. Furthermore, density functional theory (DFT) using a quantum mechanics/molecular mechanics (QM/MM) approach was employed to elucidate the reaction pathway for formation of N2O over Cu-SSZ-13 catalyst.
Final period- overview of the results:
Our resutls provide another perspective to elucidate the role of Cu speciation in NH3-SCR reaction. The data implied that catalyst performance in a reaction might be affected by the synthesis process. Spectroscopic techniques, including operando XANES, UV-Vis, Raman provided indirect evidence for the Cu speciation by detecting changes in the Cu coordination environment. While the XANES indicates the presence of a linear copper species such as CuAlO2, the data generated is not able to comment on what this species might ‘look’ like or how it might be distributed. Given that both samples have been subjected to standard high temperature activations and gas experiments, it is expected that the Cu(I) species must be stable, making a compound such as an aluminate phase one such possibility. Based on the higher production rate of N2O, this would also indicate that the species should be readily accessible. By exclusion, a crystalline phase might not constitute a large enough surface area to be considered ‘readily accessible’, meaning it may instead be a disperse species occurrent throughout the sample. Operando IR micro-spectroscopy pointed to the early formation of a new intermediate along with consumption of nitrate species and adsorption of NH3 on acid sites; attention should be paid to the Cu local environment that is closely correlated with the evolution of N2O. According to DFT calculation results both the adsorbed NH4+ and NO3- ions can be associated with CuAlO2 with a similar energy barrier and facilitate the generation of intermediate [(Al2O4Cu)HNO3, NH3] species during the NH3-SCR reaction. This may also explain why the presence of a linear copper species such as CuAlO2 significantly influences the local environment of Cu species towards N2O formation.
Exploitation and dissemination:
This research has been presented in national and international conferences, invited talk and seminars:
1- 6th UK Catalysis Conference, Loughborough, UK.
2- ICEC, 11th International Conference on Environmental Catalysis, UK.
3- UCL Chemistry seminars, UK
4- UK Catalysis Hub seminars, UK
5- Posters for Scientific Advisory Board, Research Complex at Harwell, UK.
Invited talk:
1- Chemical Engineering Lectures, The University of Edinburgh, UK.
2- Diamonds Seminar, Diamond Light Source, UK.
