In view of the diminishing oil resources and the ongoing climate change, the use of efficient and environmentally benign technologies for the utilization of renewable resources has become indispensible. Therein, hydrogenolysis reactions offer a promising possibility for future biorefinery concepts. These reactions result in the cleavage of C-C and C-O bonds by hydrogen and allow direct access to valuable platform chemicals already integrated in today's value chains. Thus, hydrogenolysis bears the potential to bridge currently available technologies and future biomass-based refinery concepts. This Review highlights past and present developments in this field, with special emphasis on the direct utilization of cellulosic feedstocks.

Hydrogenolysis Goes Bio: From Carbohydrates and Sugar Alcohols to Platform Chemicals

Angesichts begrenzter Reserven fossiler Rohstoffe und einem Voranschreiten des Klimawandels werden effiziente und umweltfreundliche Technologien zur Nutzbarmachung erneuerbarer Rohstoffe unerlasslich. Dabei stellt die Hydrogenolyse eine vielversprechende Reaktion fur zukunftige Bioraffineriekonzepte dar. Sie resultiert in einer C-C- und C-O-Bindungsspaltung mit Wasserstoff und erlaubt einen direkten Zugang zu nutzlichen Plattformchemikalien, die bereits heute Teil der Wertschopfungsketten der chemischen Industrie sind. Aus diesem Grund birgt die Hydrogenolyse das Potential, existierende Wertschopfungsketten und zukunftige Bioraffineriekonzepte zu verbinden. Dieser Aufsatz stellt vorausgegangene und aktuelle Entwicklungen in diesem Bereich mit besonderem Augenmerk auf der direkten Umsetzung von Cellulose als Rohstoffe dar.

Hydrogenolyse goes Bio: Von Kohlenhydraten und Zuckeralkoholen zu Plattformchemikalien

Publisher Summary This chapter explains the decomposition of saccharides by heat devoted to the caramelization of saccharides and their pyrolysis above 250°. Caramelization belongs to the group of so-called “browning reactions.” Caramel has a brown color and it originates from various sugars when they are heated, either dry, or in concentrated solutions. The quality of a caramel depends on its source as well as on the parameters of the process of its manufacture. Caramel is manufactured to change and improve the appearance (color) of many food products; the enhancement of the flavor of food is also important. The chemical nature of caramel depends on the conditions of the caramelization and the source, at least in the terminal period of their processing. Ever since it was suspected that caramels are biologically active, the daily uptake levels for them have been calculated and announced. The pyrolysis of sugars has been studied because carbohydrates could be considered as a source of technically important products. Moreover, these studies were intended to contribute to the knowledge of the chemistry of caramelization.

The Thermal Decomposition of Carbohydrates. Part I. The Decomposition of Mono-, Di-, and Oligo-Saccharides

Glucose is the most abundant platform molecule of biomass in nature. High value-added chemicals and liquid fuels can be obtained by selectively breaking C–C/C–O bonds and removing surplus oxygen in glucose. This article focuses on glucose hydrogenolysis over a wide variety of transition metal catalysts (Cu/C, Ni/C, Pt/C, Pd/C, Ru/C, Rh/C, Ir/C). Liquid and gas phase after reaction mainly contain three types of products such as polyols, alkanes, furans. Many value-added chemicals and liquid fuels were obtained, such as sorbitol, 1,2-propanediol, ethylene glycol, 2,5-dimethylfuran, 2,5-dimethyltetrahydrofuran, hexane, etc. Different metal catalysts showed different selectivities to these products. Typically, at hydrogenation conditions of 453 K and 4.0 MPa, glucose was largely converted to C1 products over the Ru/C catalyst. Pd/C selectively converted glucose into C2 and C3 products. C6 products were most selective over Pt/C. The hydrogenation/hydrogenolysis capabilities of different metals for C–C and C–O bonds, the endocyclic C C and C–O–C bonds are also quite different. For example, Pt/C provides the weakest hydrogenolysis activity to C–O and C–C bonds. Ru/C possesses the highest activity to C–C and C–O bond cleavage. Meanwhile, it is most active for C–O–C bond hydrogenation in glucose at low temperature. Cu/C exhibits the weakest endocyclic C C bond hydrogenation activity in furan ring. The reaction pathway of glucose hydrogenolysis over different metal catalysts was also outlined.

Aqueous-phase hydrogenolysis of glucose to value-added chemicals and biofuels: A comparative study of active metals

Carbon black (CB) supported Ni, Fe, or Fe-Ni alloy catalysts were synthesized by sol-gel to elucidate the reaction pathways over each catalyst, as well as synergistic effects in glucose to sorbitol hydrogenation. The bimetallic materials presented small and alloyed nanoparticles that were richer in reduced metallic sites at the surface than their monometallic counterparts. Glucose isomerization to fructose was favoured over Fe/CB, while glucose hydrogenation to sorbitol is the dominating pathway over Ni/CB catalyst. By contrast, sorbitol production was promoted and undesired isomerization was suppressed when Fe and Ni formed a nanoalloy. In addition, the alloy catalyst presented better stability than the corresponding monometallic catalyst. A comparison with a mechanical mixture of Fe/CB and Ni/CB monometallic catalysts demonstrated the synergy at the nanoscale in the alloy. By comparing different Fe:Ni ratios, the 1:1 formulation was identified as the best compromise to achieve a high activity while maintaining high sorbitol selectivity.

Synergistic effects altering reaction pathways: The case of glucose hydrogenation over Fe-Ni catalysts

The effect of five different types of catalyst and the concentration both of glucose and catalyst on the rate of the catalytic hydrogenation of glucose has been investigated.

Factors Affecting the Catalytic Hydrogenation of D-Glucose. Part I. Effect of Type of Catalyst and Concentrations of both Glucose and Catalyst

The effect of different degrees of pressure and temperature on the rate of the catalytic hydrogenation of glucose has been investigated.

Factors Affecting the Catalytic Hydrogenation of D-Glucose Part II. Effect of Pressure and Temperature†

Hydrogenolysis of corn syrup was carried out at 170°C and 60 at pressure. After 3 h 92.3% of the glucose content of the syrup was converted into sorbitol.

The Hydrogenolysis of Commercial Corn Glucose Syrup

In ethanolic solution the rate of hydrogenation of glucose was highly increased. When the hydrogenation was carried out in aqueous solution at pH 8, 170 °C and 60 at pressure the time required for complete hydrogenation decreased from 6 to 1 h. The re-use of catalyst was also investigated.

Factors Affecting the Catalytic Hydrogenation of D‐Glucose. Part IV. Effect of Solvent‐Catalyst Concentration at High Pressure, Temperature and pH 8 and the Re‐use of Catalyst

The rate of hygrogenation was highly increased by carrying out the reaction at pH 8. Addition of some metals and metal salts, especially calcium sulphate, highly increased the rate of hydrogenation at pH 6.8.

J. Ghali

Papers

Factors Affecting the Catalytic Hydrogenation of D-Glucose. Part I. Effect of Type of Catalyst and Concentrations of both Glucose and Catalyst

Factors Affecting the Catalytic Hydrogenation of D-Glucose Part II. Effect of Pressure and Temperature†

The Hydrogenolysis of Commercial Corn Glucose Syrup

Factors Affecting the Catalytic Hydrogenation of D‐Glucose. Part IV. Effect of Solvent‐Catalyst Concentration at High Pressure, Temperature and pH 8 and the Re‐use of Catalyst

Factors Affecting the Catalytic Hydrogenation of D‐Glucose. Part III. Effect of pH‐Value and Promotors