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 analyzed several novel
approaches, including catalytic transfer hydrogenation (CTH),
combined reforming and hydrodeoxygenation, metal hydrolysis
and subsequent hydrodeoxygenation along with non-thermal
plasma (NTP) in order to avoid the supply of external H2. 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 analyzed in this work.
Biomass model compounds are selected aiming to provide an indepth
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.
Mo2C is an effective catalyst for chemical CO2 upgrading via reverse water-gas shift (RWGS). In this work, we demonstrate that the activity and selectivity of this system can be boosted by the addition of promoters such as Cu and Cs. The addition of Cu incorporates extra active sites such as Cu+ and Cu0 which are essential for the reaction. Cs is an underexplored dopant whose marked electropositive character generates electronic perturbations on the catalyst?s surface leading to enhanced catalytic performance. Also, the Cs-doped catalyst seems to be in-situ activated due to a re-carburization phenomenon which results in fairly stable catalysts for continuous operations. Overall, this work showcases a strategy to design highly efficient catalysts based on promoted ²-Mo2C for CO2 recycling via RWGS.
An innovative route for bio?compounds upgrading via ?hydrogen?free? hydrodeoxygenation (HDO) is proposed and evaluated using guaiacol as a model compound in a high?pressure batch reactor. Experimental results showed that noble metal supported on activated carbon catalysts are able to conduct tandem multiple steps including water splitting and subsequent HDO. The activity of Ru/C catalyst is superior to other studied catalysts (i.e. Au/C, Pd/C and Rh/C) in our water?only HDO reaction system. The greater dispersion and smaller metal particle size confirmed by the TEM micrographs accounts for the better performance of Ru/C. This material also presents excellent levels of stability as demonstrated in multiple reciclabylity runs. Overall, the proposed novel approach confirmed the viability of oxygenated bio?compounds upgrading in a water?only reaction system suppressing the need of external H2 supply and can be rendered as a fundamental finding for the economical biomass valorisation to produce added value bio?fuels.
This work showcases an innovative route for biocompound upgrading via hydrodeoxygenation (HDO) reactions, eliminating the need for external high-pressure hydrogen supply. We propose the use of water as reaction media and the utilization of multifunctional catalysts that are able to conduct multiple steps such as water activation and HDO. In this study, we validate our hypothesis in a high-pressure batch reactor process using guaiacol as a model compound and multicomponent Ni-based catalysts. In particular, a comparison between ceria-supported and carbon/ceria-supported samples is established, the carbon-based materials being the suitable choice for this reaction. The physicochemical study by X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and temperature-programmed reduction reveals the greater dispersion of Ni clusters and the strong metal-support interaction in the carbon/ceria-based samples accounting for the enhanced performance. In addition, the characterization of the spent samples points out the resistance of our catalysts toward sintering and coking. Overall, the novel catalytic approach proposed in this paper opens new research possibilities to achieve low-cost bio-oil upgrading processes.
Catalytic hydrodeoxygenation (HDO) is a fundamental and promising route for bio-oil upgrading to produce petroleum-like hydrocarbon fuels or chemical building blocks. One of the main challenges of this technology is the demand of high-pressure H2, which poses high costs and safety concerns. Accordingly, developing cost-effective routes for biomass or bio-oil upgrading without the supply of commercial H2 is essential to implement the HDO at commercial scale. This paper critically reviewed the very recent studies relating to the novel strategies for upgrading the bio-feedstocks with ?green? H2 generated from renewable sources. More precisely, catalytic transfer hydrogenation/hydrogenolysis (CTH), combined reforming and HDO, combined metal hydrolysis and HDO, water-assisted in-situ HDO and non-thermal plasma (NTP) technology and self-supported hydrogenolysis (SSH) are reviewed herein. Current challenges and research trends of each strategy are also proposed aiming to motivate further improvement of these novel routes to become competitive alternatives to conventional HDO technology.
Jin Wei, Pastor-Pérez Laura, Villora-Pico Juan J., Pastor-Blas Mercedes M., Sepúlveda-Escribano Antonio, Gu Sai, Charisiou Nikolaos D., Papageridis Kyriakos, Goula Maria A., Reina Tomas R. (2019) Catalytic Conversion of Palm Oil to Bio-Hydrogenated Diesel over Novel N-Doped Activated Carbon Supported Pt Nanoparticles, Energies 13 (1)
Bio-hydrogenated diesel (BHD), derived from vegetable oil via hydrotreating technology, is
a promising alternative transportation fuel to replace nonsustainable petroleum diesel. In this work,
a novel Pt-based catalyst supported on N-doped activated carbon prepared from polypyrrole as the
nitrogen source (Pt/N-AC) was developed and applied in the palm oil deoxygenation process to
produce BHD in a fixed bed reactor system. High conversion rates of triglycerides (conversion of
TG > 90%) and high deoxygenation percentage (DeCOx% = 76% and HDO% = 7%) were obtained
for the palm oil deoxygenation over Pt/N-AC catalyst at optimised reaction conditions: T = 300 æC,
30 bar of H2, and LHSV = 1.5 h?1
. In addition to the excellent performance, the Pt/N-AC catalyst
is highly stable in the deoxygenation reaction, as confirmed by the XRD and TEM analyses of the
spent sample. The incorporation of N atoms in the carbon structure alters the electronic density of the
catalyst, favouring the interaction with electrophilic groups such as carbonyls, and thus boosting the
DeCOx route over the HDO pathway. Overall, this work showcases a promising route to produce
added value bio-fuels from bio-compounds using advanced N-doped catalysts.