Description of an operando setup for investigating syngas conversion to hydrocarbons and methanol
Résumé
Synthetic fuels and base chemicals can be obtained from both fossil and renewable sources through the conversion of synthesis gas (syngas, a mixture of carbon oxides and dihydrogen). Understanding the selectivity pattern to various products of interest of a given catalyst is paramount to derive structure/activity relationship. Operando DRIFT (diffuse reflectance FT-IR) spectroscopy can be of help to determine the relevance of surface species in the formation of products. In the case of a Co-Mg-O sample, it was shown that the surface formates species observed by DRIFTS were irrelevant in the formation of ethane [1]. A new setup was developed combining a DRIFTS reaction cell for operando surface characterisation and an IR gas cell and mass spectrometer for the on-line analysis of the reactor cell effluents (Fig. 1). DRIFTS spectra of excellent quality (see carbonyls and formates bands in Fig. 1) could be obtained in 10 s with less than 10 mg of sample, for which the contribution of gas-phase CO could be perfectly subtracted. The IR-cell exhibited a 2 m-long pathlength that enabled measuring concentration of reaction products in the ppm range. The system could thus be operated under differential conditions and the primary reaction products could be detected. The system can be operated up to 5 bars of absolute pressure. Preliminary results collected over a Co-based catalyst (Fig. 2) show that the reaction order in CO was globally positive and methane and propene were the main reaction products, while only trace amounts of methanol were detected. The relation between the various surface species and reaction products will be discussed. 1] J. Schweicher, A. Frennet, N. Kruse, H. Daly, F.C. Meunier, J. Phys. Chem. C 114 (2010) 2248.