Similar experiments were performed with zeolite catalysts. The data obtained with FER are reported in Fig. 6. The IR spectra of the adsorbed species closely correspond to those reported for H-mordenite by Kondo et al.  and attributed to a bridging ethoxy- group. The features of this alkoxy- species disappear in the 473–523 K range, when LC Biotin is produced as the only product. At lower temperature, alkoxy-groups coexist with gas phase ethanol and very small amounts of physisorbed ethanol. In this range, some DEE is formed in the gas phase while ethylene is not observed. These results support the idea that both on alumina and on FER, ethoxy-groups have two reactions paths: in the presence of gaseous or adsorbed ethanol, ethoxy- groups participate to the reaction producing DEE; when gas phase ethanol is no more available and at higher temperature, ethoxy- groups crack to ethylene.
Fig. 6. FT-IR spectra of subtraction gas phase (top) and surface species (bottom) arising from ethanol adsorbed on FER.Figure optionsDownload full-size imageDownload as PowerPoint slide