In-situ spectroscopic probes are powerful tools to monitor the liquid-phase composition of solutions or suspensions under reaction conditions, with several advantages over conventional ‘off-line’ analysis methods, such as GC, HPLC, NMR or MS. These conventional techniques require withdrawal of samples from the reaction medium, which reduces the reaction volume and can be difficult to conduct if reactions are carried out at pressure. Another advantage over the ‘off-line’ analysis methods is that these techniques are relatively fast, and it is possible to detect unstable ‘short-lived’ reaction intermediates. Furthermore, it might be possible to detect reaction species adsorbed on, or interacting with the catalyst surface. These advantages make the probe technique very suitable for both kinetic and mechanistic studies. Here we built an autoclave with a rare combination of three spectroscopic probes (ATR-IR, Raman, and UV/vis) to investigate heterogeneous catalysis in the liquid-phase.
In-situ ATR-IR spectra during aldol condensation on Mg-AlOx (850 oC):
In-situ UV-vis spectra during aldol condensation on Mg-AlOx (850 oC):
IR spectra of reactant and product in different phases:
IR spectra of reactant and product in emulsion and trends of IR bands during aldol condensation in O/W emulsion:
(1) Solvent effect on the IR spectra of acetone and furfural is observed.
(2) Reactants are mainly in the aqueous phase; condensation product is mostly in the oil phase.
(3) The continuous component of the emulsion has a stronger IR signal than the globular component.
(4) ATR-IR spectral features of acetone and furfural in the O/W emulsion are similar to those in aqueous phase as a consequence of (2) and (3).
(5) The observed rate in O/W emulsion by ATR-IR spectroscopy is slow at the beginning because of (2), (3) and phase migration of reactants and products.