Live observations of catalysts using high-pressure scanning probe microscopy

Abstract

Recently it has become clear that essential discrepancies exist between the behavior of catalysts under industrial conditions and the (ultra)high vacuum conditions of traditional laboratory experiments. Differences in structure, composition, reaction mechanism, activity, and selectivity have been observed. These differences indicated the presence of the “pressure gap”, and made it clear that meaningful results can only be obtained at high pressures and temperatures. This chapter focuses on the development of scanning probe microscopy for operando observations of active model catalysts. We have developed instrumentation that combines an ultrahigh vacuum environment for model catalyst preparation and characterization with a high-pressure flow reactor cell, integrated with either a scanning tunneling microscope or an atomic force microscope. We combine the structural observations obtained under high-pressure, high-temperature conditions with time-resolved mass spectrometry measurements on the gas mixture leaving the reactor. In this way, we can correlate structural changes of the catalyst due to the gas composition with its catalytic performance. This chapter provides an overview of the instruments we developed and illustrates their performance with results obtained for different model catalysts and reactions.