Effect of FeO_x Modification of Al₂O₃ on Its Supported Au Catalyst for Hydrogenation of 5-Hydroxymethylfurfural

Abstract

To enhance the hydrogenation activity of alumina supported Au (Au/Al2O3) catalyst for selective hydrogenation of 5-hydroxy­methyl­furfural (HMF), an important biomass-derived aldehyde, Al2O3 support was modified with iron oxide (FeO x ). The apparent catalytic activity of the FeO x /Al2O3 supported Au (Au/FeO x /Al2O3) catalysts increased as an increase of Fe loading up to 10 wt % (3–4 times higher than Au/Al2O3). When the Fe loading was more than 10 wt %, the apparent catalytic activity decreased, and Au/α-Fe2O3 showed much lower activity than Au/Al2O3. The Fe K-edge X-ray absorption fine structure (XAFS) spectra and the atomic scale observation using aberration corrected scanning transmission electron microscopy (Cs-STEM) suggested positive and negative effects of FeO x support. As the positive effect, FeO x promotes formation of Au clusters by reduction of Au single atoms having low or no catalytic activity for the hydrogenation. On the other hand, as the negative effect, FeO x , more specifically, large α-Fe2O3, can form buried structure of Au clusters in FeO x due to reduction of α-Fe2O3 to Fe metal by H2 pretreatment. The buried structure of Au clusters is responsible for the decrease of hydrogenation activity at high Fe loading. In contrast, dispersed Fe2O3 species of Au/FeO x /Al2O3 with less than 20 wt % of Fe loading was not subjected to the reduction of Fe2O3 species to Fe metal, and the Au clusters were exposed on the support surface. Therefore, the dispersed Fe2O3 on Al2O3 is effective to enhance the activity of Au catalysts for the hydrogenation because of the formation of exposed small Au clusters.

Advances in porous and nanoscale catalysts for viable biomass conversion

“…28B). Ohyama et al 346 demonstrated that addition of Fe (up to 10 wt%) to Au/Al 2 O 3 catalyst could improve its catalytic efficiency by 3-4 times in the hydrogenation of HMF to BHF, due to the formation of abundant surfaceexposed Au nanoclusters (entry 5, Table 4). However, the activity of Au/FeO x /Al 2 O 3 catalyst was decreased drastically with further increase of Fe content (greater than 10 wt%), because of Table 4).…”

Catalytic valorization of lignocellulosics: from bulk biofuels to value‐added chemicals

“…In the hydrogenation of HMF, the SACs (Au/FeO X /Al 2 O 3 ) has a better catalytic performance than traditional catalyst Au/Al 2 O 3. 61 …”

Heterogeneous Catalytic Upgrading of Biofuranic Aldehydes to Alcohols

“…For example, both the reaction temperature and hydrogen pressure are high (120°C, 6.5 MPa). In order to make Au/Al 2 O 3 hold excellent catalytic performance under mild reaction conditions, Ohyama et al doped iron oxides with the support Al 2 O 3 , and the resulting catalyst (Au/FeO x /Al 2 O 3 ) is highly selective for the reduction of 5-hydroxymethylfurfural to BHMF, giving 5-hydroxymethylfurfural conversion and BHMF yield both in 96% at 80°C and 3 MPa H 2 for 2 h (Ohyama et al, 2016).…”