Transformation of syngas to valuable oxygenated products over Rh-MnOx/SiO₂, Rh-Co/ZrO₂ and Rh-Cu/ZrO₂ catalysts

The conversion of syngas into higher alcohols was examined using bimetallic Rh-Co, Rh-Cu, and multimetallic RhCuPd catalysts, all of which were supported on ZrO₂. This process was also studied using a MnOx-promoted Rh/SiO₂ catalyst. These experiments were conducted within a temperature range of 225–300 °C, under a pressure of 30 bar, and with a H₂/CO ratio of 2. The catalysts were characterized using a variety of physicochemical methods, including Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Carbon Monoxide Diffuse Reflectance Infrared Fourier Transform Spectroscopy (CO DRIFTS). The Rh particle sizes in the fresh catalysts were found to be less than 3 nm. The Rh-Co catalyst supported on ZrO₂ exhibited the highest selectivity to ethanol, achieving 38 % at a CO conversion rate of 58 % at 275 °C. This catalyst also demonstrated a chain growth probability of 0.35 for alcohols. A slightly higher chain growth probability was observed with the Rh-MnOx/SiO₂ catalyst, although this also resulted in the formation of substantial amounts of acetic acid. Interestingly, this acetic acid could be converted into ketones when RhMnOx was used in conjunction with Pd/ZrO₂.