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

- Functional groups on catalyst obviously influence heterogeneous hydroformylation.
- The Rh/AC-80 had the highest n/i ratio of 2.3, almost double to that of raw Rh/AC.
- Abundant functional groups on catalyst suppressed hydrogenation of hexene.

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.

These oxygen-containing functional groups could alter the surface property of catalysts, thus affect the adsorption action and reaction between the active sites and reactants, which was beneficial to improve the selectivity of n-heptanal in hydroformylation.89