Hydrogenation of furfural at the dynamic Cu surface of CuOCeO2/Al2O3 in a vapor phase packed bed reactor

Gas-phase hydrogenation of furfural into value-added chemicals: The critical role of metal-based catalysts

Furfural (FF: aldehyde derivable from lignocellulosic biomass) has been widely recognized as a versatile building block for eco-friendly and sustainable applications to reduce industrial reliance on fossil-fuel carbon sources. Hydrogenation of FF, in particular, is recognized as one of the most effective routes for producing various value-added chemicals (e.g., furfuryl alcohol and 2-methylfuran). The gas-phase FF hydrogenation reaction offers economic and environmental advantages over its liquid-phase counterpart in conversion efficiency, product selectivity, and kinetics. The operation of the former does not require high hydrogen pressures or hazardous solvents while not generating undesirable by-products (due to reduced selectivity toward the ring-opening reaction). In this context, the utility of noble and non-noble metal catalyst systems has been recognized for their potential to induce effective FF hydrogenation in the gas phase. The present review addresses current understandings and recent developments in research on gas-phase FF hydrogenation and the factors governing the performance of metal-based catalysts (e.g., materials and surface chemistry; conversion efficiency; product selectivity; and the mechanisms, pathways, and kinetics of the associated reactions). Current shortcomings and research avenues are also discussed to help establish a roadmap for future development of the gas-phase FF hydrogenation technology and associated disciplines. Overall, the present review is expected to offer much-needed insights into the scalability of metal-based catalytic systems for efficient FF hydrogenation in the gas phase.

The Role of Copper in the Hydrogenation of Furfural and Levulinic Acid

Currently, there is a great interest in the development of sustainable and green technologies for production of biofuels and chemicals. In this sense, much attention is being paid to lignocellulosic biomass as feedstock, as alternative to fossil-based resources, inasmuch as its fractions can be transformed into value-added chemicals. Two important platform molecules derived from lignocellulosic sugars are furfural and levulinic acid, which can be transformed into a large spectrum of chemicals, by hydrogenation, oxidation, or condensation, with applications as solvents, agrochemicals, fragrances, pharmaceuticals, among others. However, in many cases, noble metal-based catalysts, scarce and expensive, are used. Therefore, an important effort is performed to search the most abundant, readily available, and cheap transition-metal-based catalysts. Among these, copper-based catalysts have been proposed, and the present review deals with the hydrogenation of furfural and levulinic acid, with Cu-based catalysts, into several relevant chemicals: furfuryl alcohol, 2-methylfuran, and cyclopentanone from FUR, and γ-valerolactone and 2-methyltetrahydrofuran from LA. Special emphasis has been placed on catalytic processes used (gas- and liquid-phase, catalytic transfer hydrogenation), under heterogeneous catalysis. Moreover, the effect of addition of other metal to Cu-based catalysts has been considered, as well as the issue related to catalyst stability in reusing studies.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Recent Advances in Catalytic Hydrogenation of Furfural

Furfural has been considered as one of the most promising platform molecules directly derived from biomass. The hydrogenation of furfural is one of the most versatile reactions to upgrade furanic components to biofuels. For instance, it can lead to plenty of downstream products, such as (tetrahydro)furfuryl alcohol, 2-methyl(tetrahydro)furan, lactones, levulinates, cyclopentanone(l), or diols, etc. The aim of this review is to discuss recent advances in the catalytic hydrogenation of furfural towards (tetrahydro)furfuryl alcohol and 2-methyl(tetrahydro)furan in terms of different non-noble metal and noble metal catalytic systems. Reaction mechanisms that are related to the different catalytic materials and reaction conditions are properly discussed. Selective hydrogenation of furfural could be modified not only by varying the types of catalyst (nature of metal, support, and preparation method) and reaction conditions, but also by altering the reaction regime, namely from batch to continuous flow. In any case, furfural catalytic hydrogenation is an open research line, which represents an attractive option for biomass valorization towards valuable chemicals and fuels.