Resolving kinetics and dynamics of a catalytic reaction inside a fixed bed reactor by combined kinetic and spectroscopic profiling

Abstract

The oxidative dehydrogenation of ethane to ethylene was studied using a MoO₃ based catalyst supported on γ-alumina spheres. The measurement of species and temperature profiles through a fixed bed reactor shows for the first time the reaction pathways inside the catalyst bed directly. Oxidative dehydrogenation of ethane to ethylene and water occurs on the redox sites of MoO₃ only in the presence of gas phase oxygen. Further oxidation of the product ethylene to carbon dioxide occurs as a subsequent reaction step by lattice oxygen of MoO₃. Deep oxidation of ethylene to COv is the only existing reaction in the absence of gas phase oxygen reducing MoO₃ to MoO₂. Oxidation of CO and C₂ H₆ by lattice oxygen does not occur. The reduction of the catalyst can be followed by in situ fiber Raman spectroscopy as a function of the oxygen partial pressure. The in situ Raman measurements are complemented by ex situ micro-Raman spectroscopy and X-ray diffraction. The combined measurement of kinetic and spectroscopic reactor profiles presents a novel approach in in situ catalysis research to establish catalyst structure–function relationships under technically relevant conditions of temperature and pressure

Investigating dry reforming of methane with spatial reactor profiles and particle‐resolved CFD simulations

“…The catalytic spheres act like a species mass sink in which the reacting mass is diffusing before but also after the actual catalyst bed. Such behavior was also observed experimentally by the capillary technique in a catalytic honeycomb reactor and in a fixed‐bed reactor . Syngas, that is, CO and H 2 , is produced with an almost linear slope, whereas CO shows a steeper gradient.…”

“…One of the most widely used techniques is a capillary that can be moved axially inside the catalytic reactor measuring temperature and species profiles by sucking gas into the probe. With this technique catalytic foams have been investigated, as well as catalytic fixed‐bed reactors, and catalytic monoliths . Recently, a dispute arose about the influence of the capillary probe on the measurement, in particular in honeycomb monoliths, compare, Gohuet et al vs. Hettel et al If possible, the effect of the probe should be considered and/or quantified.…”

Fabrication of MoS2 Nanowire Arrays and Layered Structures via the Self‐Assembly of Block Copolymers

“…These are consistent with the E 1 2g vibrational Mo–S bond along the base plane and the A 1g vibration of sulfur along the vertical axis, respectively . At 300 ºC, a small shoulder peak was observed at about 460 cm −1 due to the presence of MoO 2 . This suggests incomplete sulfurization at the lower temperatures used.…”

Heterogeneous Catalysis

“…These simplifications are, however, not valid in the vast majority of all practical reactors and laboratory experiments aiming at measuring catalytic performances 13b. 154 Rather, considerable gradients in the chemical potential are present along the typical packed bed of a catalytic experiment. As many reactions have an associated heat exchange, energy flux gradients appear parallel as well as perpendicular to the central axis of the reactor and have a significant effect on the chemical potential.…”