Recent advances in dynamic chemical characterization using Temporal Analysis of Products

The Temporal Analysis of Products (TAP) technique is a pulse response methodology that reveals the time-dependent evolution of chemical processes between a gas phase molecule and a solid surface. By simplifying both the transport and kinetic processes the complexity of a multistep chemical processes can be distilled to where the underlying fundamental steps can be distinguished. Moreover, the technique is applicable to real materials (e. g. industrial catalysts) and hence the complexity of the solid is studied intact; a 'top-down' approach. In this short review we discuss key theoretical advancements in the interpretation of pulse response data; though not yet widely implemented, we will highlight the broader impacts of the Y-Procedure method [1(..)], momentary equilibrium phenomena [2(..)] and kinetic coherency discrimination [3(..)] over more commonly used analysis techniques. The conventional TAP approach for mechanism development is well-laid out in a recent work focused on the upgrading of ethanol to higher hydrocarbons. This includes detailed comparison of the time characteristics of reactant, intermediate and product pulses in both single pulse and pump/probe modes [4(..)]. This work calls to mind some of the challenges in the conventionally used residual gas analyzer for pulse response detection of homologous products. A new detection method using photoelectron photoion coincidence spectroscopy (PEPICO) was recently demonstrated for a TAP-like setup [5(..)]. This method presents the exciting opportunity to better resolve complex product spectra and even isomeric species. This enables the mechanistic detail of the TAP technique to be applied to more complex probe molecules as are needed for the study of biomass conversion processes. Finally, we discuss directions for the future development of instrumentation that can directly connect this rich kinetic data to features of catalyst structural and composition.