Effect of carbon support and functionalization on the synthesis of rhenium carbide and its use on HDO of guaiacol

The effect of the choice of carbon support (activated carbon, carbon nanofiber, graphite, and multiwalled carbon nanotube) on the formation of rhenium carbide was evaluated in the hydrodeoxygenation of guaiacol, a pyrolysis oil model compound. Catalysts were prepared by incipient wetness impregnation, carburized at 650oC under a 25/75 mixture of ethylene/hydrogen, and characterized by XRD, N2-physisorption, TPD, TPR, NH3-TPD, and XPS. The characterization results gave evidence that the choice of support affected the carburization of rhenium, a likely consequence of the nature of oxygen function groups on the supports. Indeed, poor carburization of Re occurred over the carbon nanofiber support, which was rationalized by a lack of carboxylic groups on the support. The study showed that the sites mainly responsible for converting guaiacol could be identified by quantification of CH4 mass signals during TPR measurements. This is an important finding to unravel the critical properties responsible for the HDO catalysis of carburized Re. Most of the catalysts were effective at converting guaiacol to phenol and a few, especially Re/MWCNT-O+ and Re/HSAG, were active for the hydrogenolysis of phenol to benzene (with benzene selectivity reaching 50% at guaiacol conversion of 98%). This indicates that this class of catalysts show great promise in converting guaiacol to desirable aromatic hydrocarbons.