Catalytic Deoxygenation Chemistry

Conversion of Phenol and Lignin as Components of Renewable Raw Materials on Pt and Ru-Supported Catalysts

Hydrogenation of phenol in aqueous solutions on Pt-Ni/SiO₂, Pt-Ni-Cr/Al₂O₃, Pt/C, and Ru/C catalysts was studied at temperatures of 150–250 °C and pressures of 40–80 bar. The possibility of hydrogenation of hydrolysis lignin in an aqueous medium in the presence of a Ru/C catalyst is shown. The conversion of hydrolysis lignin and water-soluble sodium lignosulfonate occurs with the formation of a complex mixture of monomeric products: a number of phenols, products of their catalytic hydrogenation (cyclohexanol and cyclohexanone), and hydrogenolysis products (cyclic and aliphatic C₂–C₇ hydrocarbons).

Catalytic Decomposition of Oleic Acid to Fuels and Chemicals: Roles of Catalyst Acidity and Basicity on Product Distribution and Reaction Pathways

The roles of catalyst acidity and basicity playing in catalytic conversion of oleic acid were studied in a fixed-bed micro-reactor at atmospheric pressure. The chemical compositions of the petroleum-like products were obtained and the reaction pathways of different catalysts are discussed. The metal oxides are suitable for upgrading oleic acid into organic liquid products (OLPs). Over 98% oxygen was removed when CaO, MgO, and TiO2 were implemented, whereas a minimum oxygen removal lower than 20% was obtained by using quartz. The oxygen removal was 73% by alumina; however, the light oil yield (to feed) and the valuable product yield received were the highest in all investigated catalysts. The hydrocarbons in OLPs, overwhelmingly presenting in the product, were found to be alkenes and cycloalkenes, followed by saturated hydrocarbons, and then aromatics lower than 4%. For Lewis acidic catalysts, higher acidity of the catalyst is beneficial to deoxygenation but also secondary cracking. CaO has higher dehydrogenation capability than MgO does.

Catalytic Transfer Hydrogenation of Biomass-Derived Substrates to Value-Added Chemicals on Dual-Function Catalysts: Opportunities and Challenges

Aqueous-phase hydrodeoxygenation (APH) of bioderived feedstocks into useful chemical building blocks is one the most important processes for biomass conversion. However, several technological challenges, such as elevated reaction temperature (220-280 °C), high H₂ pressure (4-10 MPa), uncontrollable side reactions, and intensive capital investment, have resulted in a bottleneck for the further development of existing APH processes. Catalytic transfer hydrogenation (CTH) under much milder conditions with non-fossil-based H₂ has attracted extensive interest as a result of several advantageous features, including high atom efficiency (≈100 %), low energy intensity, and green H₂ obtained from renewable sources. Typically, CTH can be categorized as internal H₂ transfer (sacrificing small amounts of feedstocks for H₂ generation) and external H₂ transfer from H₂ donors (e.g., alcohols, formic acid). Although the last decade has witnessed a few successful applications of conventional APH technologies, CTH is still relatively new for biomass conversion. Very limited attempts have been made in both academia and industry. Understanding the fundamentals for precise control of catalyst structures is key for tunable dual functionality to combine simultaneous H₂ generation and hydrogenation. Therefore, this Review focuses on the rational design of dual-functionalized catalysts for synchronous H₂ generation and hydrogenation of bio-feedstocks into value-added chemicals through CTH technologies. Most recent studies, published from 2015 to 2018, on the transformation of selected model compounds, including glycerol, xylitol, sorbitol, levulinic acid, hydroxymethylfurfural, furfural, cresol, phenol, and guaiacol, are critically reviewed herein. The relationship between the nanostructures of heterogeneous catalysts and the catalytic activity and selectivity for C-O, C-H, C-C, and O-H bond cleavage are discussed to provide insights into future designs for the atom-economical conversion of biomass into fuels and chemicals.

Thermochemistry and kinetic analysis for the conversion of furfural to valuable added products

Furfural is a valuable oxygenated compound derived from the thermal decomposition of biomass, and is one of the major problems of bio-oil upgrading. Due to its high reactivity, this compound requires further upgrading to more stable products such as furfuryl alcohol, 2-methylfuran (MF), furan, 2-methyltetrahydrofuran, and tetrahydrofuran. The thermochemical data and kinetic analysis of the reactions involved in the conversion of furfural were investigated by molecular modeling to guide experimental investigations in the process of designing efficient catalysts that allows the control of the reaction pathways in specific directions, towards the production of fuel precursors or chemicals. All calculations for reactants, intermediates, and products were performed using the long range corrected functional WB97XD, with the basis set 6-311+g(d,p), under the density functional theory framework. Thermochemistry results suggest that furfural hydrogenation to form furfuryl alcohol is spontaneous up to a temperature of 523 K, but beyond this temperature the reaction becomes a nonspontaneous process. By contrast, the decarbonylation of furfural was thermodynamically favored at temperatures greater than 523 K. Therefore, furan is a thermodynamically favored product, while furfuryl alcohol is kinetically preferred. Once furfuryl alcohol is formed, the hydrogenolysis path to produce methylfuran is favored kinetically and thermodynamically, compared to the ring-hydrogenation towards tetrahydrofurfuryl alcohol. Gas phase thermodynamic properties and rate constants of the reactions involved in the conversion of furfural were calculated and compared against existing experimental data. This study provides the basis for further vapor phase catalytic studies required for upgrading of furans/furfurals to value-added chemicals. Graphical abstract Furan is a thermodynamically favored product, while furfuryl alcohol is kinetically preferred.