Hydrogenation of phenol with supported Rh catalysts in the presence of compressed CO2: Its effects on reaction rate, product selectivity and catalyst life

Abstract

Hydrogenation of phenol to cyclohexanone and cyclohexanol in/under compressed CO 2 was examined using commercial Rh/C and Rh/Al 2 O 3 catalysts to investigate the effects of CO 2 pressurization on the total conversion and the product selectivity. Although the total rate of phenol hydrogenation with Rh/C was lowered by the presence of CO 2 , the selectivity to cyclohexanone was improved at high conversion levels > 70%. On the other hand, the activity of Rh/Al 2 O 3 was completely lost in an early stage of reaction. The features of these multiphase catalytic hydrogenation reactions using compressed CO 2 were studied in detail by phase behavior and solubility measurements, in situ high pressure FTIR for molecular interactions of CO 2 with reacting species and formation/adsorption of CO on the catalysts, and simulation of reaction kinetics using a simple model. The CO 2 pressurization was shown to suppress the hydrogenation of cyclohexanone to cyclohexanol, improving the selectivity to cyclohexanone.The formation and adsorption of CO were observed for the two catalysts at high CO 2 pressures in the presence of H 2 , which was one of important factors retarding the rate of hydrogenation in the presence of CO 2 . It was further indicated that the adsorption of CO on Rh/Al 2 O 3 was strong and caused the complete loss of its activity.

Effect of size and oxidation state of size-controlled rhodium nanoparticles on the aqueous-phase hydrodechlorination of 4-chlorophenol

“…Cyclohexanone and cyclohexanol result from hydrogenation of phenol while cyclohexanol is also produced from cyclohexanone hydrogenation. This reaction scheme is in good agreement with that proposed by Fujita et al [47] for the hydrogenation of phenol using supported Rh catalysts. Other useful reaction scheme has been proposed by Diaz et al [11] for the HDC of 4-CP using alumina-supported Pd, Pt and Rh catalysts.…”

“…8, the following kinetic model is proposed for the HDC process to gain insight into the issue. This model is similar to that proposed by Fujita et al [47] for the hydrogenation of phenol using Rh-based catalysts, but including the step of HDC of 4-CP to phenol.…”

A multiphase reaction medium including pressurized carbon dioxide and water for selective hydrogenation of benzonitrile with a Pd/Al2O3 catalyst

“…For example, in hydrogenation of phenol with Rh catalysts supported on C and Al 2 O 3 , the Rh/C does not lose its activity during the reaction but the Rh/Al 2 O 3 is easily deactivated at an early stage of reaction [17]. This difference is caused by weak and strong adsorption of CO (originating from CO 2 ) on the former and latter catalysts, respectively, as proved by in situ FTIR measurements.…”

“…In the present work, the features of such a reaction system have been studied in detail for the selective hydrogenation of BN to the primary amine of benzylamine (BA) with a Pd/Al 2 O 3 catalyst. The hydrogenation runs were conducted under different conditions and molecular interactions among the substrate, CO 2 , water, and the catalyst were measured by in situ high-pressure FTIR methods [16,17] in order to elucidate the roles of CO 2 and water. The medium of gas (H 2 , CO 2 ) -liquid (water) -liquid (BN) -solid (catalyst) has been confirmed to be effective for the selective production of BA by BN hydrogenation with no catalyst deactivation.…”

In situ FTIR study on the formation and adsorption of CO on alumina-supported noble metal catalysts from H2 and CO2 in the presence of water vapor at high pressures

“…Using in situ high pressure FTIR techniques, a few authors investigated this phenomenon important in catalytic hydrogenation and other reactions in the presence of dense phase CO 2 . [9][10][11][12][13][14][15] Baiker et al used attenuated total reflection infrared spectroscopy (ATR-IR) to follow the reaction of CO 2 with H 2 over alumina-supported Pt catalyst in the form of thin film in cyclohexane at 313 K. 9,10,12 It is indicated that carbonate-like species are formed from CO 2 adsorbed on the support and then react with H 2 , forming CO. The formation of CO was responsible for the catalyst deactivation observed in hydrogenation of ethyl pyruvate in supercritical CO 2 .…”