Modelling a reactor cell for operando IR studies: From qualitative to fully quantitative kinetic investigations

- Gas fluid dynamics in an IR reactor cell was modelled using computational fluid dynamics.
- The IR cell consists in a combination of ideal reactors both in series and parallel.
- Kinetic constant for methanol/methoxy exchange on CeO2 was obtained from operando SSITKA.
- Moving from a disk to a square sample holder led to a quasi perfect plug-flow reactor.
- Better estimation of the kinetic constant enabled by the optimized reactor geometry.

Operando infrared spectroscopy is often used qualitatively to elucidate reaction mechanisms thanks to the observation of the catalyst under actual operating conditions. Besides, in principle such technique can also provide quantitative information that can be used to describe detailed chemical kinetics (spectrokinetic approach). However, the collected kinetic information are relevant only if the gas fluid dynamics inside the reactor cell is well known and can be precisely described. In fact, to perform a reliable kinetic analysis, it is essential to correctly model the flow in the reactor cell and to couple this model with the mass balances. To demonstrate the importance of this aspect, in this work the SSITKA (Steady State Isotopic Transient Kinetic Analysis) approach was exploited within an operando FTIR reactor to study the methanol adsorption onto ceria, herein selected as model probe reaction. A conventional round sample holder with round catalyst wafer and a novel square sample holder with square catalyst pellet have been used. Although the conventional round sample holder shows a satisfactory behaviour, the modified sample holder leads to a virtually perfect plug-flow reactor, which will simplify data computing, provide a better fit of the experimental data and more accurate estimates of the kinetic parameters.

178