A study of furfural decarbonylation on K-doped Pd/Al2O3 catalysts

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.

Plasma-Enabled Ligand Removal for Improved Catalysis: Furfural Conversion on Pd/SiO2

A nonthermal, atmospheric He/O2 plasma (NTAP) successfully removed polyvinylpyrrolidone (PVP) from Pd cubic nanoparticles supported on SiO2 quickly and controllably. Transmission electron microscopy (TEM) revealed that the shape and size of Pd nanoparticles remain intact during plasma treatment, unlike mild calcination, which causes sintering and polycrystallinity. Using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), we demonstrate the quantitative estimation of the PVP plasma removal rate and control of the nanoparticle synthesis. First-principles calculations of the XPS and CO FTIR spectra elucidate electron transfer from the ligand to the metal and allow for estimates of ligand coverages. Reactivity testing indicated that PVP surface crowding inhibits furfural conversion but does not alter furfural selectivity. Overall, the data demonstrate NTAP as a more efficient method than traditional calcination for organic ligand removal in nanoparticle synthesis.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

Anodic Cross-Coupling of Biomass Platform Chemicals to Sustainable Biojet Fuel Precursors

Electrocatalytic conversion of biomass platform chemicals to jet fuel precursors is a promising approach to alleviate the energy crisis caused by the excessive exploitation and consumption of non-renewable fossil fuels. However, an aqueous electrolyte has been rarely studied. In this study, we demonstrate an anodic electrocatalysis route for producing jet fuel precursors from biomass platform chemicals on Ni-based electrocatalysts in an aqueous electrolyte at room temperature and atmosphere pressure. The desired product exhibited high selectivity for the jet fuel precursor (95.4%) and an excellent coulombic efficiency of 210%. A series of in situ characterizations demonstrated that Ni²⁺ species were the active sites for the coupling process. In addition, the coupling reaction could be achieved by generating radical cations and inhibiting the side reaction. First, the electrochemical process could activate the furfural (FF) molecule and generate radical cations, resulting in an average of 2.0 times chain propagation. The levulinic acid (LA) molecules played a vital role in the coupling reaction. The adsorption strength of LA on Ni₃N was higher than that of FF, which could inhibit the side reaction (the oxidation of FF) and achieve high selectivity. Meanwhile, the LA molecules were adsorbed on the Ni₃N surface and then disrupted the formation of Ni³⁺ species, thus favoring the coupling reaction. This work demonstrates an efficient route to produce jet fuel precursors directly from biomass platform chemicals and provides a comprehensive understanding of the anodic coupling process.

Mixed Oxides Derived from Hydrotalcites Mg/Al Active in the Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol

Herein, a family of Mg/Al hydrotalcites was synthesized as catalytic precursors of MgAlOx mixed oxides. Both hydrotalcites and mixed oxides were characterized and the mixed oxides were tested in the reduction of furfural to yield furfuryl alcohol by MPV reaction using isopropanol as hydrogen donor. Different catalytic parameters were tested, such as the type of alcohol, calcination temperature of the hydrotalcite, and reaction temperature. Furfural and isopropanol were adsorbed on the MgAl-3 catalyst to follow the species adsorbed on the catalyst by FTIR analysis. The results showed that the isopropanol was activated as isopropoxide and furfural changed the adsorption site with increasing temperature but maintaining the h1-conformation. The catalytic performances were associated with the basicity of the catalysts and the deactivation processes have been attributed to the existence of adsorbed species on the surface, mainly due to furfural-derived compounds. The catalysts were reused in three consecutive cycles showing a sharp drop of catalytic activity. To recover the activity, the catalysts were calcined at 500 °C but the activity was only partially recovered. The XPS analysis after reactivation showed that the catalyst surface was modified due to the segregation of hydroxides of Mg and Al.

Ni-Cu/Al2O3 from Layered Double Hydroxides Hydrogenates Furfural to Alcohols

The hydrogenation of furfural is an important process in the synthesis of bio-based chemicals. Copper-based catalysts favor the hydrogenation of furfural to alcohols. Catalytic activity and stability were higher at a Ni-to-Cu atomic ratio of 1:1 and 1.5:0.5 compared to 0.5:1.5. Here, we prepared Ni-Cu/Al2O3 hydrogenation catalysts derived from layered double hydroxides (LDHs). Catalysts calcined at 673 K and reduced at 773 K with nominal Ni/Cu atomic ratios y/x = 1.5/0.5, 1/1 and 0.5/1.5 were characterized by XRD, FESEM-EDX, H2-TPR, XPS, FAA and BET. Their activity was tested at 463 K and in a 0.05 g g−1 furfural solution in ethanol, and the space velocity in a packed-bed reactor (PBR) was 2.85 gFF gcat−1 h−1. In a slurry reactor (SSR) at 5 MPa H2 and a contact time of 4 h, conversion was complete, while it varied from 91 to 99% in the PBR. Tetrahydrofurfuryl alcohol (TFA) was the main product in the SSR, with a selectivity of 32%, 63% and 56% for Ni0.5Cu1.5Al1, Ni1Cu1Al1 and Ni1.5Cu0.5Al1, respectively. The main product in the atmospheric PBR was furfuryl alcohol (FA), with a selectivity of 57% (Ni0.5Cu1.5Al1), 61% (Ni1Cu1Al1) and 58% (Ni1.5Cu0.5Al1). Other products included furan, methylfuran, 1-butanol and 1,2-pentanediol. Ethyl tetrahydrofurfuryl ether and difurfuryl ether were also formed via the nucleophilic addition of furfural with ethanol and furfuryl alcohol.

Green synthesis of zero-valent iron nanoparticles and loading effect on activated carbon for furfural adsorption

The adsorption techniques are extensively used in dyes, metronidazole, aniline, wastewater treatment methods to remove certain pollutants. Furfural is organic in nature, considered a pollutant having a toxic effect on humans and their environment and especially aquatic species. Due to distinct characteristics of the adsorption technique, this technique can be utilized to adsorb furfural efficiently. As an environmentally friendly technique, the pomegranate peel was used to synthesized activated carbon and nanostructure of zerovalent iron impregnated on the synthesized activated carbon. The physicochemical and crystallinity characterization was done using Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and Field emission scanning electron microscopy (FESEM). The nanoparticles are porous in structure having 821.74 m²/g specified surface area. The maximum amount of the adsorbent pores in the range of 3.08 nm shows the microporous structure and enhancement in adsorption capacity. The effects of increment in concentration of adsorbent, pH, reaction contact time and adsorbent dose, isothermal and kinetic behaviour were investigated. At the UV wavelength of 227 nm furfural adsorption was detected. The separation of the furfural from the aqueous solution was calculated at the 1 h reaction time at the composite dosage of 4 g/L, 250 mg/L adsorbent concentration and pH kept at 7. The 81.87% is the maximum removal attained by the nanocomposite in comparison to the activated carbon is 62.06%. Furfural adsorption was also analyzed by using the equations of isothermal and kinetics models. The adsorption process analysis depends on the Freundlich isotherm and Intra-particle diffusion than the other models. The maximum adsorbent of the composite was determined by the Langmuir model which is 222.22 mg/g. The furfural removal enhances as the adsorbent dose enhances. The developed zerovalent iron nanoparticles incorporated on activated carbon (AC/nZVI) from pomegranate peel extract are feasible as an efficient and inexpensive adsorbent to eliminate furfural from a liquid solution.

Advances in Diels-Alder/aromatization of biomass furan derivatives towards renewable aromatic hydrocarbons

The effective upgrading of renewable resources into high value-added chemicals is of great significance to achieve the sustainable economic development, as well as the implementation of carbon neutral technologies practically....

Synthesis and Characterization of Nickel(II) Homogeneous and Supported Complexes for the Hydrogenation of Furfural to Furfuryl Alcohol

Nickel(II) complexes have been synthesized and characterized using nuclear magnetic resonance (NMR), infrared spectroscopy, high resolution mass spectroscopy, and elemental analysis. The complexes were evaluated as pre-catalysts in the direct hydrogenation of furfural to furfuryl alcohol. The pre-catalysts C1 and C4 gave higher furfural conversion (97% and 96%, respectively), as a result, they were also evaluated in the transfer hydrogenation of furfural using formic acid as the hydrogen source where higher furfural conversion (93%) was obtained and selectivity (100%) toward the formation of furfuryl alcohol at 4 h. The catalyst C1 was recycled three times with and it was observed that the catalytic activity might be due to a mixture of both molecular catalysis and nanoparticles, as evidenced by the decrease in activity in mercury poisoning experiments. The hydrogenation reactions were also extended to alpha-β unsaturated substrates and were selective toward saturation of the carbonyl functionality over alkene groups.

Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural

Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

Glucose–Carbon Hybrids as Pt Catalyst Supports for the Continuous Furfural Hydroconversion in Gas Phase

Glucose–carbon hybrids were synthetized with different carbon materials, namely carbon nanotubes, reduced graphene oxide, carbon black and activated carbon by a hydrothermal treatment. These carbon hybrids were used as Pt-supports (1 wt.%) for the furfural (FUR) hydroconversion in the gas phase at mild operating conditions (i.e., P = 1 atm and T = 200 °C). The physicochemical properties (porosity, surface chemistry, Pt-dispersion, etc.) were analyzed by different techniques. Glucose–carbon hybrids presented apparent surface areas between 470–500 m2 g−1, a neutral character and a good distribution of small Pt-nanoparticles, some large ones with octahedral geometry being also formed. Catalytic results showed two main reaction pathways: (i) FUR hydrogenation to furfuryl alcohol (FOL), and (ii) decarbonylation to furane (FU). The products distribution depended on the reaction temperature, FOL or FU being mainly produced at low (120–140 °C) or high temperatures (170–200 °C), respectively. At intermediate temperatures, tetrahydrofurfuryl alcohol was formed by secondary FOL hydrogenation. FUR hydroconversion is a structure-sensitive reaction, rounded-shape Pt-nanoparticles producing FU, while large octahedral Pt-particles favor the formation of FOL. Pt-catalysts supported on glucose–carbon hybrids presented a better catalytic performance at low temperature than the catalyst prepared on reference material, no catalyst deactivation being identified after several hours on stream.

Insights into the catalytic mechanism of 5-hydroxymethfurfural to phthalic anhydride with MoO3/Cu(NO3)2 in one-pot

A synthetic approach to obtain renewable phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) with a yield of 63.2% using MoO₃/Cu(NO₃)₂ as a catalyst in one pot.

Vapor-Phase Furfural Decarbonylation over a High-Performance Catalyst of 1%Pt/SBA-15

A high-performance Pt catalyst supported on SBA-15 was developed for furfural decarbonylation. Compared to Pt catalysts loaded on microporous DeAl-Hbeta zeolite and hierarchical micro-mesoporous MFI nanosheet (NS) materials, the 1%Pt/SBA-15 catalyst afforded notably higher activity, furan selectivity and stability owing to the negligible acid sites and proper mesopores on the SBA-15 support. Among a set of 1%Pt/SBA-15 catalysts bearing Pt nanoparticles (NPs) with sizes of 2.4–4.3 nm, the catalyst with 3.7 nm Pt NPs afforded the highest furan selectivity. Over the optimal catalyst, 88.6% furan selectivity and ca. 90% furfural conversion were obtained at 573 K and a high weight hourly space velocity (WHSV) of 16.5 h−1. Moreover, the reaction temperatures at 440–573 K and the ratios of H2 to furfural at 0.79–9.44 did not affect the reaction selectivity notably, showing that the reaction over 1%Pt/SBA-15 can be conducted over a wide range of conditions. The catalyst was stable under the harsh reaction conditions and lasted for 90 h without significant deactivation, demonstrating the superior property of SBA-15 as a catalyst support for furfural decarbonylation.

Furfural to 1,4-Butanediol/Tetrahydrofuran - A Detailed Catalyst and Process Design

The feasibility to convert furan, a direct derivative of furfural, to a mixture of 1,4-butanediol (BDO) and tetrahydrofuran (THF) is demonstrated with industrially acceptable performances using mm-sized pellets of a carbon-supported RePd catalyst for 2000 h of operation. The reaction schemes were unraveled by spiking potential reaction intermediates and a full kinetic model was developed. Finally, we developed a comprehensive process flow scheme that integrates the conversion of furfural to furan, the recovery and purification of furan, its reductive hydration to BDO/THF as well as the recovery and purification of BDO and THF. This process concept appears economically viable at current furfural, BDO and THF market prices.

Integrating Biomass into the Organonitrogen Chemical Supply Chain: Production of Pyrrole and d-Proline from Furfural

Production of renewable, high-value N-containing chemicals from lignocellulose will expand product diversity and increase the economic competitiveness of the biorefinery. Herein, we report a single-step conversion of furfural to pyrrole in 75 % yield as a key N-containing building block, achieved via tandem decarbonylation-amination reactions over tailor-designed Pd@S-1 and H-beta zeolite catalytic system. Pyrrole was further transformed into dl-proline in two steps following carboxylation with CO₂ and hydrogenation over Rh/C catalyst. After treating with Escherichia coli, valuable d-proline was obtained in theoretically maximum yield (50 %) bearing 99 % ee. The report here establishes a route bridging commercial commodity feedstock from biomass with high-value organonitrogen chemicals through pyrrole as a hub molecule.

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.

Biochar as a catalytic material for the production of 1,4-butanediol and tetrahydrofuran from furan

Biomass valorization is emerging as a new trend for the synthesis of materials for various environmental applications. In this connection, a biochar resulting from pyrolysis of rice straw was employed as a catalytic material for the conversion of hemicellulose-derived furan into value-added platform chemicals such as 1,4-butanediol (1,4-BD) and tetrahydrofuran (THF). The biochar was used as catalyst support of bifunctional Ru-Re catalyst. Two different catalysts were prepared: a conventional activated carbon (AC)-supported Ru-Re catalyst (Ru-Re/AC) and a biochar-supported Ru-Re catalyst (Ru-Re/biochar). The Ru-Re/biochar had a different form of Re species from the Ru-Re/AC, resulting in different reducibility. The difference of reducibility between the two was attributed to alkali metal present in the biochar such as potassium. The Ru-Re/biochar had a 17 times lower metal dispersion on the surface than the Ru-Re/AC, ascribed to a lower surface area of the biochar than the AC. Catalytic activities of the catalysts with regard to reaction rate per available surface active site for transforming furan to 1,4-BD and THF were measured. The Ru-Re/AC was 3 times less active than the Ru-Re/biochar. This study not only provides a way to efficiently use biomass both for environmental catalysts and for feedstock of producing value-added platform chemicals, but also shows potential of biochar for the replacement of typical catalysts employed in biorefinery.

One-Pot Synthesis of Renewable Phthalic Anhydride from 5-Hydroxymethfurfural by using MoO3 /Cu(NO3 )2 as Catalyst

Herein, a synthetic pathway to renewable phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) in one pot is reported. The commonly available catalysts MoO₃ and Cu(NO₃ )₂ play a crucial role in integrating the multiple steps of the reaction, namely decarbonylation of HMF to active furyl intermediate (AFI), oxidation of HMF to maleic anhydride (MA), Diels-Alder cycloaddition of AFI and MA, and subsequent dehydration, in one pot. Under mild reaction conditions, a 63.2 % yield of PA is obtained from HMF. Compared with the currently reported route to renewable PA based on the Diels-Alder cycloaddition of biomass-derived MA and furan, this convenient one-pot synthesis represents a great improvement in efficiency.

Bio-Based Chemicals from Renewable Biomass for Integrated Biorefineries

The production of chemicals from biomass, a renewable feedstock, is highly desirable in replacing petrochemicals to make biorefineries more economical. The best approach to compete with fossil-based refineries is the upgradation of biomass in integrated biorefineries. The integrated biorefineries employed various biomass feedstocks and conversion technologies to produce biofuels and bio-based chemicals. Bio-based chemicals can help to replace a large fraction of industrial chemicals and materials from fossil resources. Biomass-derived chemicals, such as 5-hydroxymethylfurfural (5-HMF), levulinic acid, furfurals, sugar alcohols, lactic acid, succinic acid, and phenols, are considered platform chemicals. These platform chemicals can be further used for the production of a variety of important chemicals on an industrial scale. However, current industrial production relies on relatively old and inefficient strategies and low production yields, which have decreased their competitiveness with fossil-based alternatives. The aim of the presented review is to provide a survey of past and current strategies used to achieve a sustainable conversion of biomass to platform chemicals. This review provides an overview of the chemicals obtained, based on the major components of lignocellulosic biomass, sugars, and lignin. First, important platform chemicals derived from the catalytic conversion of biomass were outlined. Later, the targeted chemicals that can be potentially manufactured from the starting or platform materials were discussed in detail. Despite significant advances, however, low yields, complex multistep synthesis processes, difficulties in purification, high costs, and the deactivation of catalysts are still hurdles for large-scale competitive biorefineries. These challenges could be overcome by single-step catalytic conversions using highly efficient and selective catalysts and exploring purification and separation technologies.

How Catalysts and Experimental Conditions Determine the Selective Hydroconversion of Furfural and 5-Hydroxymethylfurfural

Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.

Low-Temperature Continuous-Flow Dehydration of Xylose Over Water-Tolerant Niobia-Titania Heterogeneous Catalysts

The sustainable conversion of vegetable biomass-derived feeds to useful chemicals requires innovative routes meeting environmental and economical criteria. The approach herein pursued is the synthesis of water-tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia-titania skeleton building up a hierarchical open-cell network of meso- and macropores, and tailored for use under continuous-flow conditions. The materials were characterized by spectroscopic, microscopy, and diffraction techniques, showing a reproducible isotropic structure and an increasing Lewis/Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as a representative application. The efficiency of the catalyst was found to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2 wt % niobium resulted in the highest furfural yield at 140 °C under continuous-flow conditions, by using H₂ O/γ-valerolactone as a safe monophasic solvent system. The interception of a transient 2,5-anhydroxylose species suggested the dehydration process occurs via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the Lewis acid sites (LAS)/Brønsted acid sites (BAS) ratio and indicated a significant contribution of xylose-xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage.

Highly Efficient Gas-Phase Oxidation of Renewable Furfural to Maleic Anhydride over Plate Vanadium Phosphorus Oxide Catalyst

Maleic anhydride (MAnh) and its acids are critical intermediates in chemical industry. The synthesis of maleic anhydride from renewable furfural is one of the most sought after processes in the field of sustainable chemistry. In this study, a plate vanadium phosphorus oxide (VPO) catalyst synthesized by a hydrothermal method with glucose as a green reducing agent catalyzes furfural oxidation to MAnh in the gas phase. The plate catalyst-denoted as VPO_HT -has a preferentially exposed (200) crystal plane and exhibited dramatically enhanced activity, selectivity and stability as compared to conventional VPO catalysts and other state-of-the-art catalytic systems. At 360 °C reaction temperature with air as an oxidant, about 90 % yield of MAnh was obtained at 10 vol % of furfural in the feed, a furfural concentration value that is much higher than those (<2 vol %) reported for other catalytic systems. The catalyst showed good long-term stability and there was no decrease in activity or selectivity for MAnh during the time-on-stream of 25 h. The high efficiency and catalyst stability indicate the great potential of this system for the synthesis of maleic anhydride from renewable furfural.

The effect of potassium on Cu/Al2O3 catalysts for the hydrogenation of 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan in a fixed-bed reactor

The highly efficient selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved in a fixed-bed reactor by using inexpensive potassium-doped Cu/Al₂O₃ catalysts.

Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity

Decarbonylation of furfural to furan was efficiently catalyzed by ZrO₂ -supported Pd clusters in the liquid phase under a N₂ atmosphere without additives. Although Pd/C and Pd/Al₂ O₃ have frequently been used for decarbonylation, Pd/ZrO₂ exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO₂ . ZrO₂ with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al₂ O₃ despite their high surface areas. The catalytic activity of Pd/ZrO₂ was enhanced with a decrease in particle size, and the smallest Pd/ZrO₂ was the most active catalyst for decarbonylation. When CeO₂ was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO₂ with a high surface area, with a strong interaction through the formation of a Pd-O-Ce bond, which led to a lower catalytic activity than that of Pd/ZrO₂ . This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO₂ maintained its catalytic activity until its sixth use.