Prospects and challenges for autonomous catalyst discovery viewed from an experimental perspective

The urgency with which fundamental questions of energy conversion and the sustainable use of raw materials must be solved today requires new approaches in catalysis research. One way is to couple high-throughput experiments with machine learning methods in autonomous catalyst development. The fact that the active form of a catalyst is only created under working conditions and that the catalytic function is always in a very complex relationship with a number of physical and chemical properties of the material makes it essential to integrate operando experiments into systems of autonomous catalyst development. The analysis of the current state of the art and knowledge revealed a lack of integration of the numerous, technically very different unit operations in catalyst discovery and a great need for new developments in online and in situ analytics, especially in catalyst synthesis. To pave the way for autonomous processing of work packages by robots, it is proposed to advance the automation of single unit operations currently performed by human researchers by introducing standard operating procedures described in handbooks. The work according to rigorous protocols produces, on the one hand, reliable data that can be evaluated using artificial intelligence and facilitates on the other hand the automation. Special attention should be paid to the acquisition and real-time evaluation of analytical data in in situ and operando experiments as well as the automatic storage of data and metadata in databases

Single-Site Vanadyl Species Isolated within Molybdenum Oxide Monolayers in Propane Oxidation

The cooperation of metal oxide subunits in complex mixed metal oxide catalysts for selective oxidation of alkanes still needs deeper understanding to allow for a rational tuning of catalyst performance. Herein we analyze the interaction between vanadium and molybdenum oxide species in a monolayer supported on mesoporous silica SBA-15. Catalysts with variable Mo/V ratio between 10 and 1 were studied in the oxidation of propane and characterized by FTIR, Raman, and EPR spectroscopies, temperature-programmed reduction, UV/vis spectroscopy in combination with DFT calculations, and time-resolved experiments to analyze the redox properties of the catalysts. Molybdenum oxide (sub)monolayers on silica contain mainly dioxo (Si–O−)2Mo(═O)2 species. Dilution of silica-supported vanadium oxide species by (Si–O−)2Mo(═O)2 prevents the formation of V–O–V bonds, which are abundant in the pure vanadium oxide catalyst that predominantly contains two-dimensional vanadium oxide oligomers. Existing single vanadyl (Si–O−)3V(═O) sites and neighboring (Si–O−)2Mo(═O)2 sites do not strongly interact. The rates of reduction in propane and of oxidation in oxygen are lower for single metal oxide sites compared to those for oligomers. The rate of propane oxidation correlates with the overall redox rates of the catalysts but not linearly with the chemical composition. Retarded redox behavior facilitates selectivity toward acrolein on single-site catalysts. The abundance of M–O–M bonds is more important in terms of activity and selectivity compared to the nature of the central atom (molybdenum versus vanadium)