Reaction pathways of biomass-derived furfural on non-precious metal and metal carbide surfaces
Date
2015
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Publisher
University of Delaware
Abstract
Furfural is one of the most important platform chemicals in biomass conversion. It can be readily produced from the hemicellulose-rich biomass such as corncob and oat hull, etc. The conversion of furfural can produce a wide range of alternative fuels and chemicals which are traditionally obtained from petroleum-based feedstock. Hydrodeoxygenation (HDO) is one of the most important reactions for upgrading furfural. In this dissertation, non-precious metal based bimetallic and metal carbide catalysts were developed for upgrading furfural to value-added fuels and chemicals, especially through HDO to produce 2-methylfuran. Emphasis was put on investigating the adsorption configurations and reaction pathways of furfural on these bimetallic and metal carbide surfaces through the combination of density functional theory (DFT) calculations and surface science experiments. First, the reaction pathways of furfural on different monometallic surfaces were studied by temperature programmed desorption (TPD) experiments. The results were correlated with the interactions between the functional groups of furfural and the metal surfaces. The interactions were investigated by comparing the bond lengths of furfural in gas phase with those of adsorbed furfural on the metal surfaces through DFT calculations. Then bimetallic surfaces were used to tune the interactions between the functional groups of furfural and the metal surfaces in order to enhance the activity for desired reaction pathways. The reaction pathways of furfural on Cu(111) and NiCu bimetallic surfaces were further investigated by using the high resolution electron energy loss spectroscopy (HREELS) in order to determine how the formation of the bimetallic structure enhanced the HDO pathway to produce 2-methylfuran. The different reaction pathways on Cu(111) and the NiCu bimetallic surfaces were explained by the different adsorption configurations of furfural on these surfaces. The ability to dissociate H 2 could also play a role in determining the reaction pathways. The reaction pathways of furfuryl alcohol were also investigated on these surfaces. Second, Molybdenum carbide (Mo2C) was developed as a promising deoxygenation catalyst, especially for the HDO of furfural to produce 2-methlylfuran. The deoxygenation of several C3 oxygenates on the Mo2C surface was investigated by TPD and HREELS. A common intermediate was observed by HREELS for the deoxygenation of propanal and 1-propanol. The different deoxygenation selectivity for the reactions of propanal and 1-propanl was attributed to the different activation barriers for the side reactions of these molecules on the Mo 2 C surface. Combination of DFT calculations, surface science experiments on model surfaces and flow reactor evaluation on porous catalysts demonstrated that Mo2C was a promising catalyst for the HDO of furfural to produce 2-methylfuran. This result opens a potential route to produce fuels from the hemicellulose part of biomass.