Operando X-ray spectroscopy characterization of nanocatalysts for industrial applications

From 25.07.2017 till 30.06.2019
Grant holder: Alexander Guda
Responsible: Alexander Guda
Members: Yury Rusalev, Aram Bugaev, Andrei Tereshchenko

At elevated temperatures and in reducing atmosphere cerium dioxide is highly nonstoichiometric CeO2-x while the overall fluorite structure is conserved. The high mobility of oxygen vacancies and the ability to reversibly bind and release oxygen with fast kinetics means that cerium oxide is of great importance for applications that require the activation, transportation and storage of oxygen. In heterogeneous catalysis, cerium oxide substrates are used for storing and activating oxygen in three-component catalytic converters for controlling emissions of exhaust gases from internal combustion engines and catalysts for preferential oxidation [1-4]. Electrochemical applications of cerium oxide-based materials include its use as electrolytes in solid oxide fuel cells. In the case of hydrogen production, a two-stage oxidation/reduction cycle is used. The Ce3+ /Ce4+ redox cycle can be controlled by heat from concentrated solar radiation and allows splitting water into its elements, and carbon dioxide into carbon monoxide and oxygen, thereby converting and storing solar energy in chemical bonds. Many optimization attempts have been made to increase the efficiency of conversion of solar energy into fuel: 1) improve the internal properties of the material, such as a higher oxygen storage capacity and higher release rates by doping, and 2) improve heat and mass transfer properties using macroporous structures. Of fundamental importance in the search for better materials is their stability under the influence of a very large number of thermochemical oxidation-reduction cycles [5-8]. However, at present, there is little experimental data on the nature of the electronic and geometric structure of cerium oxide-based materials obtained in operando mode during long-term operation under harsh conditions. Theoretical calculations predict a large number of intermediate phases for cerium oxide, but they are not always detected in diffractograms due to amorphization processes and small crystallites [9]. The determination of structure-property relationships in complex mixed oxides based on cerium dioxide is a motivation for creating an in situ cell for X-ray absorption spectroscopy that can withstand extreme conditions similar to found in industrial applications. Heterogeneous catalytic processes usually occur at the solid-gas interface. The interaction of reacting molecules with the surface of the catalyst reduces the activation barriers for the desired chemical reactions. The catalytic cycle usually includes several steps: adsorption/chemisorption of the reactants on active sites of the catalyst, stepwise conversion of adsorbed molecules to products and desorption of products. The interaction of reaction molecules with the surface of catalysts often leads to changes in the state of oxidation and the local environment of catalytically active atoms. These structural transformations have a characteristic time from microseconds to seconds. To detect the intermediate particles and correlate the rates of their formation and decomposition with the reactivity of the catalyst, it is necessary to rapidly change the reaction conditions to shift the system from the steady state. This can be done by a rapid change in concentration or by initiating a reaction by means of temperature, laser radiation, magnetic fields, etc. By observing intermediate reaction products and quantitatively determining the rates of their transformation under transient conditions with resolving time less than a second provide direct information on the kinetics of a solid. He also gives an idea of the mechanisms of catalytic processes, makes it possible to distinguish active and spectator species and, thus, promotes the rational design of more active or selective catalysts [10-11]. This project aims to synthesize new catalysts based on the porous CeZrO2 matrix on which Au, Pt, Pd and other cheaper 3d metals Cu, Fe, Co nanoparticles of noble metals are deposited and to create a methodology for operando diagnostics of the reactions for the neutralization of harmfull CO, NOx, and SOx. The operando method of X-ray spectral diagnostics of the catalyst operation will allow to optimize the synthesis of catalysts with given properties, to create a nondestructive technique for monitoring the synthesis process, suitable for industrial production, and to explain, at a microscopic level, the dynamics of catalytic reactions with high temporal resolution. These results in the near future will ensure the environmentally friendly use of hydrocarbon raw materials as fuel, and the synthesized samples of nanocatalysts can be used for deep processing of hydrocarbon raw materials. [1] S. Abanades and G. Flamant, Solar Energy, 2006, 80, 1611–1623 [2] W. C. Chueh, C. Falter, M. Abbott, D. Scipio, P. Furler, S. M. Haile and A. Steinfeld, Science (New York, N.Y.), 2010, 330, 1797–801 [3] T. Rager, Chemical Communications, 2012, 48, 10520–10522 [4] I. Ermanoski, J. E. Miller and M. D. Allendorf, Physical chemistry chemical physics : PCCP, 2014, 16, 8418–27. [5] J. E. Miller, A. H. McDaniel and M. D. Allendorf, Advanced Energy Materials, 2014, 4, 1300469–1300469 [6] M. Rothensteiner, Simone Sala, Alexander Bonk, Phys. Chem. Chem. Phys., 2015,17, 26988-26996 [7] J. Paier, Christopher Penschke, and Joachim Sauer, Chem. Rev., 2013, 113 (6), pp 3949–3985 [8] G.N. Vayssilov, Yaroslava Lykhach, Nature Materials 10, 310–315 (2011) [9] M. Cargnello, Vicky V. T. Doan-Nguyen, Science 16 Aug 2013: Vol. 341, Issue 6147, pp. 771-773 [10] Mark A. Newton, Davide Ferri, Grigory Smolentsev, Nature Communications 6, 8675 (2015) [11] Chiarello G. L, Nachtegaal M, Rev Sci Instrum. 2014 July 85(7):074102