上海科技大学知识管理系统

Ethanol has great application prospects given it is an important essential chemical and a substitute for traditional energy sources. Currently, ethanol production is achieved through grain fermentation and petroleum-based ethylene hydration. However, the inefficient fermentation processes and increasingly depleted crude oil resources hinder the large-scale production of ethanol. Therefore, the development of alternative technologies for ethanol production has become an important issue. The direct production of ethanol from syngas (CO + H-2) is considered to be a new strategy to acquire high value-added products and achieve clean utilization of carbonaceous resources such as coal, natural gas, and biomass. Supported Rh-based catalysts have been extensively studied as the most promising and effective systems for the direct production of ethanol from syngas. The use of promoters and supports is generally effective in increasing the activity and ethanol selectivity of supported Rh-based catalysts. Fe is widely used in the research on Rh-based catalysts, as it is one of the most effective promoters for enhancing ethanol selectivity. In this work, with the aim of exploring the role of the support, we used the incipient wetness impregnation method to prepare Fe-promoted Rh-based catalysts supported by CeO2, ZrO2, and TiO2 for the synthesis of ethanol from syngas. CO conversion of CO on the RhFe/TiO2 catalyst was as high as 18.2% under the reaction conditions of 250 degrees C and 2 MPa, and the selectivity to ethanol in the alcohol distribution was 74.7%, which was much higher than that observed with RhFe/CeO2 and RhFe/ZrO2 under the same conditions. The characterization results showed that the specific surface of the catalyst followed the order RhFe/CeO2 < RhFe/ZrO2 < RhFe/TiO2; the dispersion of Rh increased sequentially, and the particle size decreased in the same order. A larger specific surface area may favor the dispersion of the Rh species, and the highly dispersed Rh species would imply a greater number of active sites on the surface of the support. The results of H-2-temperature-programmed reduction indicated possible interactions between Rh and the support as well as between Rh and Fe, and partial reduction of TiO2 under the experimental reduction conditions; however, the other supports did not undergo reduction. The results of X-ray photoelectron spectroscopy indicated that the RhFe/TiO2 catalyst had the largest amount of Rh-0 as well as Rh+ species. Thus, this catalyst has more (Rh-x(0)-Rh-y(+))-O-Fe delta+ active sites for the synthesis of ethanol, which greatly increases the ethanol selectivity. CO-temperature programmed desorption was used to confirm the CO adsorption capacity of different catalysts. The results showed that TiO2 enhances the adsorption of CO due to the presence of more O vacancies and Ti3+ ions, which is beneficial to the improvement of the catalyst activity.