ABSTRACT
The conversion of synthesis gas (CO + H2) to alcohols and hydrocarbons using heterogeneous catalysts is well known. The production of CH3OH using Cu/ZnO catalysts is practiced commercially [1], as is the production of gasoline and diesel fuels via the Fischer-Tropsch synthesis using Fe or Co catalysts [2,3]. The selective conversion of synthesis gas to liquid fuels provides a route to renewable fuels that is almost CO2 neutral if the synthesis gas is produced from biomass. Our interest is in the selective conversion of synthesis gas to ethanol for use as a fuel or fuel additive. Several catalysts, based on metals such as Cu, Co, Pd, and Fe, have been investigated for the higher alcohol synthesis [4], but few reports on the synthesis of ethanol from synthesis gas are available. Rhodium-based catalysts are able to produce oxygenates from synthesis gas [4,5]. The addition of appropriate promoters such as Mn enhances the rate of formation of these oxygenates, especially in the case of ethanol [5-10]. Mo-based catalysts also have high selectivity toward higher alcohols when Mo is doped with alkali metals [11]. Mo2O3 has also been used for the syngas conversion reaction [12], although high ethanol selectivity was not achieved. The highest selectivity for ethanol has been reported on MoS2 catalysts [13]. Interestingly, MoP supported on metal oxides (Al2O3 and SiO2) has been investigated as an alternative to MoS2 catalysts for hydrodenitrogenation and hydrodesulfurization reactions [14,15]. Although there are no reports on the use of MoP for synthesis gas conversion to alcohols or hydrocarbons, previous researchers have suggested that metal phosphides may have good activity in other hydrogenation reactions, such as synthesis gas conversion to hydrocarbons and alcohols [16].
