Design and testing of an operando-Raman annular reactor for kinetic studies in heterogeneous catalysis

In this work, we present a novel experimental tool that integrates in situ Raman spectroscopy and an annular reactor for the operando-Raman kinetic analysis of heterogeneous catalytic reactions. The proposed configuration can monitor via Raman spectroscopy the catalytic surface under kinetically limited reaction conditions, with reliable product analysis, thus retaining the main features of both Raman spectroscopy and kinetic investigation in an annular reactor. We report a thorough description of the key constraints in developing online Raman spectroscopic tools for kinetic investigations. These constraints are considered in the design, assembly and testing of the experimental method by minimizing the mutual invasiveness of the Raman spectroscopy and of the annular reactor configurations. Show-cases of dry reforming and partial oxidation of CH4 on Rh catalysts are used to establish proof of concept of the method, demonstrating the acquisition of time-resolved Raman spectroscopic data under kinetically relevant conditions. Experiments both on clean and coked Rh surfaces reveal that well-structured graphitic deposits are likely to form during DR. During CPO, instead, the presence of O-2 and H2O limits the formation of organized graphitic-like carbonaceous species. On a more general basis, this reactor allows a detailed structural characterization of a catalyst material during the reaction and at conditions of temperature, pressure and composition relevant to catalysis. Therefore, it is an important breakthrough for the simultaneous collection of spectroscopic and kinetically relevant data for the investigation of the structure-activity relationship in heterogeneous catalysis.