Catalytic Upgrading of Biomass Model Compounds: Novel Approaches and Lessons Learnt from Traditional Hydrodeoxygenation – a Review

Abstract

Catalytic hydrodeoxygenation (HDO) is a fundamental process for bio-resources upgrading to produce transportation fuels or added value chemicals. The bottleneck of this technology to be implemented at commercial scale is its dependence on high pressure hydrogen, an expensive resource which utilization also poses safety concerns. In this scenario, the development of hydrogen-free alternatives to facilitate oxygen removal in biomass derived compounds is a major challenge for catalysis science but at the same time it could revolutionize biomass processing technologies. In this review we have analysed several novel approaches, including catalytic transfer hydrogenation (CTH), combined reforming and hydrodeoxygenation, metal hydrolysis and subsequent hydrodeoxygenation along with non-thermal plasma (NTP) to avoid the supply of external H 2 . The knowledge accumulated from traditional HDO sets the grounds for catalysts and processes development among the hydrogen alternatives. In this sense, mechanistic aspects for HDO and the proposed alternatives are carefully analysed in this work. Biomass model compounds are selected aiming to provide an in-depth description of the different processes and stablish solid correlations catalysts composition-catalytic performance which can be further extrapolated to more complex biomass feedstocks. Moreover, the current challenges and research trends of novel hydrodeoxygenation strategies are also presented aiming to spark inspiration among the broad community of scientists working towards a low carbon society where bio-resources will play a major role. Figure 1. Three basic phenylpropane monomers: (1) p-coumaryl alcohol; (2) coniferyl alcohol; (3) sinapyl alcohol.

Emphasis on the Properties of Metal‐Containing Zeolites Operating Outside the Comfort Zone of Current Heterogeneous Catalytic Reactions

“…[91] However,d ue to the significant content of impurities such as water and oxygen, bio-oils obtained from the CFP of biomass such as lignin must be upgraded by hydrodeoxygenation (HDO) before they can be used or blended with conventional petrochemical products. [92] Zeolites have been ap rimary target of research efforts in both CFP and HDO,i np articular ZSM-5, due to its selectivity towards gasoline-range alkenes and aromatics. [93] While an enormous number of zeolite catalysts have been tested for optimizing the bio-oils obtained from CFP,o nly as mall number of studies have investigated the long-term stability of pristine zeolites, [68a, 94] and to best of our knowledge,very little information concerning the long-term stability of metalcontaining zeolites has been reported.…”

Mild Hydrodeoxygenation of Phenols into Cycloalkanes under Ambient Hydrogen Pressure over a Ni/H‐Beta Catalyst

“…However, they still require high pressure H 2 (2‐5 MPa). Besides, known atmospheric HDOs by base metal catalysts are performed at high temperatures (250 °C or higher) . Herein, we wish to report that Ni/H‐Beta catalyzes the HDO of phenols into cycloalkanes in octane at 110 °C under atmospheric pressure H 2 .…”

Effects of metal promoters in bimetallic catalysts in hydrogenolysis of lignin derivatives into value‐added chemicals

“…have proposed a number of bimetallic catalysts with bifunctional effects in the HDO of pyrolysis oil and model compounds, in which the hydrogenating sites provide activated hydrogen while the oxyphilic metal promote the cleavage of C−O bonds. And Jin et al [30] . have concluded that the employment of bimetallic catalysts in biomass conversion is a promising strategy, which could achieve higher catalytic activity under relatively mild reaction conditions, reduce the hydrogen consumption and avoid the use of acid supports that are prone to coke and rapid deactivation.…”