Noble metal replacement in catalytic biomass conversion

The increasing demand for fuels and chemicals must face diminishing fossil resources and rising environmental problems. Lignocellulosic biomass is a renewable nonfossil carbon energy source, which avoids the food-versus-fuel debate and can reduce CO2 emissions. Furfural derives from biomass through hemicellulose conversion by hydrolysis and further xylose cyclodehydration. Its molecular structure is highly functionalized and allows obtaining value-added chemicals containing oxygen atoms. Progressive steps of furfural selective hydrogenation and hydrogenolysis result mainly in C5 chemicals. Although noble metal-based catalysts effectively transform biomass resources, they have high costs and limited availability. Transition metals constitute a possible alternative. For example, Villa et al. reported the application of Mo and W carbide in benzyl alcohol oxidation. Furthermore, many papers reported that the introduction of transition metal to noble-metals based catalysts had a significant influence on the catalytic activity and selectivity. Here, we investigated the behavior of Pt supported on activated carbon (AC) from birch in furfural hydrogenation. Furthermore, we modified the same AC with Mo. Precursor was (NH4)6Mo7O24 ∙4H2O, dissolved in water, then mixed with AC for 16 h and dried at 105 °C before calcination (350 °C for 5 h under N2 atmosphere) (Fig. 1). Finally, we supported Pt on Mo/AC in order to investigate the synergistic effect of the bimetallic system. Furfural hydrogenation reactions occurred in a batch autoclave at 50 °C and 3 bar of hydrogen. Catalyst (substrate/metal ratio=500, mol/mol) was suspended in 10 ml of furfural solution (0.3 M in EtOH). GC analyses showed the furfural conversion and products formation over time (6 h). Both Pt and Mo supported on AC were able to convert furfural. This latter is hydrogenated to furfuryl alcohol and tetrahydrofurfuryl alcohol. Also, GC analysis showed the formation of the ether from the reaction between substrate and solvent. However, we found a different products distribution comparing the two metals. Moreover, the presence of Mo influenced both the activity and selectivity of the Pt-supported catalyst, showing a different ratio between alcohols and ether.