Bert M. Weckhuysen is Distinguished University Professor of Catalysis, Energy and Sustainability at Utrecht University, The Netherlands. He is the (co-)editor of four books and (co-)authored more than 700 peer reviewed publications. He serves on the editorial and/or advisory boards of several journals (e.g., Angewandte Chemie International Edition, Chemical Society Reviews, and ChemCatChem). He is a recipient of the Royal Netherlands Chemical Society Golden Medal (2006), the International Catalysis Award (2012), the prestigious Dutch Spinoza Prize (2013), and honorary fellow of the Chinese Chemical Society (since 2020). Together with his research group, he works to deepen the fundamental understanding of how catalyst materials work and deactivate thereby making use of operando spectroscopy and microscopy. Anne-Eva Nieuwelink is project manager at the Dutch Advanced Research Center Chemical Building Blocks Consortium (ARC CBBC), and the coordinator of the gravitation program Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC). She has a joint PhD degree from Utrecht University and Twente University, both located in the Netherlands, focusing on single catalyst particle diagnostics, using microfluidics and spectroscopy.

• 1. Introduction PART A: IMPORTANT APPLICATIONS2. Heterogeneous Catalysis 3. Homogeneous Catalysis 4. Photo- and Electrocatalysis 5. Batteries6. Fuel Cells PART B: TECHNIQUES AND METHOD DEVELOPMENT7. Introduction8. Advances in Operando Microscopy 9. Operando Surface Science10. Advances in Operando Spectroscopy11. Computational Operando Characterization12. Emerging Methods: Exploring the Time Domain 13. Advances in Data Analysis 14. Outlook

Bert M. Weckhuysen is Distinguished University Professor of Catalysis, Energy and Sustainability at Utrecht University, The Netherlands. He is the (co-)editor of four books and (co-)authored more than 700 peer reviewed publications. He serves on the editorial and/or advisory boards of several journals (e.g., Angewandte Chemie International Edition, Chemical Society Reviews, and ChemCatChem). He is a recipient of the Royal Netherlands Chemical Society Golden Medal (2006), the International Catalysis Award (2012), the prestigious Dutch Spinoza Prize (2013), and honorary fellow of the Chinese Chemical Society (since 2020). Together with his research group, he works to deepen the fundamental understanding of how catalyst materials work and deactivate thereby making use of operando spectroscopy and microscopy. Anne-Eva Nieuwelink is project manager at the Dutch Advanced Research Center Chemical Building Blocks Consortium (ARC CBBC), and the coordinator of the gravitation program Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC). She has a joint PhD degree from Utrecht University and Twente University, both located in the Netherlands, focusing on single catalyst particle diagnostics, using microfluidics and spectroscopy.

• 1. Introduction PART A: IMPORTANT APPLICATIONS2. Heterogeneous Catalysis 3. Homogeneous Catalysis 4. Photo- and Electrocatalysis 5. Batteries6. Fuel Cells PART B: TECHNIQUES AND METHOD DEVELOPMENT7. Introduction8. Advances in Operando Microscopy 9. Operando Surface Science10. Advances in Operando Spectroscopy11. Computational Operando Characterization12. Emerging Methods: Exploring the Time Domain 13. Advances in Data Analysis 14. Outlook