TOTEM

Heterogeneous catalysis is a key player in many large-scale industrial processes and holds much promise for meeting current challenges in food, water and energy supplies. In heterogeneous catalysis by metals, the potential of bimetallic nanoparticles (BiM NPs) is undeniable. Indeed, alloying of metal atoms within NPs can lead to improved catalytic activity, selectivity or resistance to poisoning as compared to monometallic NPs. Moreover, in reactions requiring expensive noble metals, considerable financial gain may result from particle downsizing and substitution of noble metals by transition ones. Presently, the capability to design novel and more efficient BiM catalysts is hampered by the lack of a detailed understanding of catalytic reactions, especially because particle structure and surface composition under reaction are unknown most often. Hence, in many catalytic reactions, a clear picture of structure-reactivity relationships is still missing. The general aim of TOTEM project is to gain fundamental atomic-scale insights into the interplay between the surface structuration and catalytic properties of heterogeneous BiM catalysts in conditions as close as possible to catalytic test ones, i.e. at atmospheric pressure and/or at high temperature. This will be achieved by developing time-resolved operando transmission electron microscopy (TEM) to study structural properties of BiM catalysts "in action". Here, we propose to study in near operando the structure of TiO2-supported Au-Cu BiM NPs under two reactions of environmental/industrial interests: the oxidation of carbon monoxide and the selective hydrogenation of butadiene at ambient pressure and in temperatures. Our near operando set-up will couple a JEM-ARM 200F TEM with aberration-correction of the objective lens, a holder-based environmental gas-cell system (E-cell) and a mass spectrometer (MS). The funding of the present project includes the purchase of a MS and the upgrading of an existing gas E-cell to extend the capabilities of the existing in situ platform to near operando conditions for real-time monitoring solid-gas interactions occurring in the E-cell in dynamic gas environments (pressure up to 1 atm and temperature up to 1000 °C). Our TEM approach will be “near operando” since reaction conditions in the E-cell, will be very close to the ones used in laboratory catalytic testing. Changes in gas composition during reaction will be followed either internally (directly in the E-cell) by time-resolved electron-energy loss spectroscopy or externally, by analysing the gas at the outlet of the cell using MS. In parallel, particle structure (morphology, size, crystalline structure) will be studied, at the atomic scale, by chemically-sensitive high-angle annular dark-field STEM imaging and by high resolution TEM imaging with sub-Å resolution and high temporal resolution up to 300 images/second. Additional information on particle composition will be gathered by energy-dispersive X-ray spectroscopy at single particle level. The microscope and MS will be synchronized temporally to unambiguously correlate the structural properties of metallic NPs in gas/temperature conditions and their catalytic performance. In addition to near operando experiments, multiscale structure reconstruction (MSR) model combining first-principle calculations and environmental Wulff construction will be developed to predict the structural evolution of Au-Cu NPs under gas conditions. By combining theory and experiment, we ambition to gain sufficient knowledge into the interplay between the surface structure and the catalytic properties of Au-Cu BiM NPs in the two chosen reactions so as to guide reliably the synthesis of more active and more stable catalysts. This multidisciplinary approach to structure-catalytic activity relationships in heterogeneous catalysis will enable the coordinator to independently strengthen his current research activities and innovate in the field.