(621dm) Selective Hydrodeoxygenation of Furfural to 2-Methylfuran Using Fe-Cu/Silica Catalyst

Introduction

Furfural, derived from hemicellulose through hydrolysis and dehydration, is as a promising platform chemical for biofuels production. Furfural, however, cannot directly be used as fuel because it is oxygen rich and self-polymerize when exposed to air or light and has to be transformed into a more suitable species. Furfural can be source of numerous derivatives, which can be either substitutes of fossil fuels or be used as fine chemicals. Among these species 2-methylfuran is specially promising as a biofuel or biodiesel additive.

Supported Cu on silica is a mild hydrogenation catalyst that only hydrogenates the carbonyl group of furfural to from furfuryl alcohol. In this report, we described the properties of iron-containing Cu-based catalysts that show much higher reactivity and very high selectivity towards 2-methylfuran. Furthermore, we found that the catalyst pre-activation condition can have a large effect on the selectivity. Catalyst that calcined and pre-reduced at 210 ^oC will selectively produce furfuryl alcohol, while that pre-reduced at 270 ^oC will shift the selectivity to 2-methylfuran.

Materials and Methods

Silica supported Cu-Fe catalysts were prepared by incipient wetness co-impregnation method. The copper loading is 1 wt.% and the atomic ratios of Cu/Fe are 1:0, 9:1, 7:1 and 0 : 1. The catalysts will be reduced at a proper temperature before reaction.

The catalysts were tested in a flow micro reactor. Furfural was fed continuously into the reactor using a syringe pump. All the gas transfer lines were heated to ensure a uniform temperature and avoid product condensation. The reaction products were analyzed on line using a gas chromatograph.

Results and Discussion

The reaction network of furfural on Cu is a two-step series reaction from furfural to furfuryl alcohol and then to 2-methylfuran (Scheme 1). We have found that the addition of Fe (0-0.15% w/w) to Cu (1% w/w) could increase the reaction rates by a factor greater than 3 without any loss in selectivity (Figure 1). However if the pre-reduction was performed at a higher temperature (270 ^oC), a selectivity shift was observed as shown in Table 1. Considering the shift was only applicable to Cu-Fe/SiO₂ catalyst instead of Cu, we investigated the reactivity of the 1 wt.% Fe. The results showed that Fe was not very reactive with furfural, but could convert furfuryl alcohol to 2-methylfuran very fast. Temperature programmed reduction profile suggested Cu was fully reduced at 270 ^oC, while Fe was most likely only partially reduced (a mixture of Fe^II and Fe^III). An in-situ DRIFT study suggested that Fe^II species were formed on the surface, as indicated by the adsorption of CO. Our further in-situ XANES study confirmed that iron was partially reduced to +2.7, which was found to be responsible for the high hydrogenation performance of the catalyst.

Scheme 1. Series reaction network of furfural

Figure 1.  Catalytic activity of the Cu-Fe/silica catalysts. The Cu loading are all 1% and the atomic ratio of Cu to Fe is as labeled. Reaction conditions: 1 atm, 210 ^oC, 50 mL/min of H₂ flow, 0.1 mL/hr of furfural, m_cat = 50 mg.

Table 1. Selectivity shift of the Cu-Fe (7:1)/SiO₂

Significance

2-Methylfuran is an excellent bio-fuel candidate, which is the hydrodeoxygenation product of furfural. This work presented a promising catalyst that can selective convert furfural to 2-methylfuran.

References

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