A review on reactivity and stability of heterogeneous metal catalysts for deoxygenation of bio-oil model compounds

A review on reactivity and stability of heterogeneous metal catalysts for deoxygenation of bio-oil model compounds

Catalytic deoxygenation is a fundamental process for bio-oil upgrading due to its high oxygen contentwhich will result in lower heating value, corrosion and instability issues. The discovery of an excellentheterogeneous deoxygenation metal catalyst with high deoxygenation activity is a necessarybreakthrough for an optimized bio-oil catalytic deoxygenation. For an effective deoxygenation supportedmetal catalyst, properties such as high H2 sticking coefficient, optimal metal-oxygen bond strength andsuitable acid strength from support are needed to ensure facile scission of C O bonds and activation ofH2 and O-containing compounds. Metals such as Fe, Ru, Sn, W, Zr and supports such as C, TiO2, ZrO2 whichare oxophilic were also observed to enhance direct removal of oxygen from O-containing compounds dueto their high C O and C¼O bond affinities. The choice of support is important to ensure it has optimalphysicochemical properties for facile deoxygenation and the optimal acid strength to enhance C Ohydrogenolysis activity while minimizing coke formation. The choice of metal is dependent on the type ofmodel compound since different metals catalyze different reaction pathways of the deoxygenation ofmodel compounds. This review presents on the use of heterogeneous metal catalysts in thedeoxygenation of bio-oil model compounds through several perspectives which are catalytic properties,reaction conditions, deactivation and regeneration of metal catalysts. In addition, several outlooks on thefeasible range of reaction condition for catalytic deoxygenation and criteria of excellent deoxygenationsupported metal catalysts were also expressed in this article based on the studies on the literatures.

Catalytic deoxygenation is a fundamental process for bio-oil upgrading due to its high oxygen contentwhich will result in lower heating value, corrosion and instability issues. The discovery of an excellentheterogeneous deoxygenation metal catalyst with high deoxygenation activity is a necessarybreakthrough for an optimized bio-oil catalytic deoxygenation. For an effective deoxygenation supportedmetal catalyst, properties such as high H2 sticking coefficient, optimal metal-oxygen bond strength andsuitable acid strength from support are needed to ensure facile scission of C O bonds and activation ofH2 and O-containing compounds. Metals such as Fe, Ru, Sn, W, Zr and supports such as C, TiO2, ZrO2 whichare oxophilic were also observed to enhance direct removal of oxygen from O-containing compounds dueto their high C O and C¼O bond affinities. The choice of support is important to ensure it has optimalphysicochemical properties for facile deoxygenation and the optimal acid strength to enhance C Ohydrogenolysis activity while minimizing coke formation. The choice of metal is dependent on the type ofmodel compound since different metals catalyze different reaction pathways of the deoxygenation ofmodel compounds. This review presents on the use of heterogeneous metal catalysts in thedeoxygenation of bio-oil model compounds through several perspectives which are catalytic properties,reaction conditions, deactivation and regeneration of metal catalysts. In addition, several outlooks on thefeasible range of reaction condition for catalytic deoxygenation and criteria of excellent deoxygenationsupported metal catalysts were also expressed in this article based on the studies on the literatures.