Enhancing catalytic performance of activated carbon supported Rh catalyst on heterogeneous hydroformylation of 1-hexene via introducing surface oxygen-containing groups

Activated carbon supported rhodium (Rh/AC) catalysts with different amounts of oxygen-containing functional groups were prepared by nitric acid (HNO₃) treatment at varied temperatures. Thermal analyses of Rh/AC catalysts with or without this acidic treatment were characterized by thermogravimetric analysis (TGA) and temperature programmed desorption (TPD). The change of surface oxygen-containing functional groups was characterized by Fourier transform infrared spectrometry (FTIR) and X-ray photoelectron spectroscopy (XPS). These characterization results indicated that the amount of oxygen-containing functional groups increased with the treatment temperature. The influence of these oxygen-containing functional groups on the products selectivities in heterogeneous hydroformylation reaction was investigated in detail. These abundant functional groups were benefited to improve the selectivity of n-heptanal, resulting in higher n/i (normal to iso) ratio of heptanal. The Rh/AC catalyst being treated at 80 °C had the highest n/i ratio of 2.3, due to the maximum amount of oxygen-containing functional groups, which was almost double to that of raw Rh/AC catalyst. Moreover, abundant functional groups on catalyst suppressed hydrogenation of hexene, decreasing the selectivity of hexane from 4.9% of raw Rh/AC to 0.2%. These findings disclosed that these oxygen-containing functional groups on catalysts played an extremely important role in improving the catalytic performance of heterogeneous hydroformylation reaction, providing a new viewpoint for the studies on heterogeneous hydroformylation.