Palladium Supported on Polystyrene (Pd@PS) for the Catalytic Synthesis of 2,5‐Dimethylfuran (2,5‐DMF) From Biomass‐Derived 5‐Chloromethylfurfural (CMF) at Ambient Temperature

ABSTRACT

2,5‐Dimethylfuran (2,5‐DMF), a renewable biofuel with promising properties, highlights the importance of biomass conversion as a key strategy for sustainable energy production. In this study, we report a facile synthesis of 2,5‐DMF from 5‐chloromethylfurfural (CMF) using polymer‐supported nano‐composite material (Pd@PS) as a catalyst at 35°C in 3 h under a H₂ atmosphere. The developed methodology provides an excellent tentative carbon conversion efficiency percentage (90%), high atom economy (64%), and low environmental factor (E‐factor) (1.15, normalized value 50%), indicating sustainability and a green chemistry matrix. These studies also aligned with the UN Sustainable Development Goals 7 and 12, contributing to the global transition toward cleaner and more sustainable chemical manufacturing by valorizing biomass‐based feedstocks. Additionally, the CMF has been synthesized from raw biomass sources, like banana peel waste, sugarcane bagasse, rice straw, and corn cobs, with yields ranging from 8 to 15 wt% and carbon conversion efficiency (tentative) between 25% and 54%. Furthermore, the developed protocol offered an efficient and scalable process (up to 5.0 g) for the production of biofuel, with superior catalytic activity and high recyclability up to six cycles. Moreover, total turnover and turnover frequency numbers were found to be 59.89 and 59.89 h⁻¹, respectively.

The biomass‐derived 5‐chloromethylfurfural (CMF) is selectively converted to 2,5‐dimethylfuran (2,5‐DMF), a bio‐based fuel with remarkable properties, using a polymer‐supported nanocomposite material (Pd@PS) as a catalyst under a hydrogen atmosphere. This work presents a sustainable strategy combining catalyst engineering and green chemistry to access a vital building block for renewable polymer production.

1. Introduction

The advancement of eco‐friendly, lignocellulosic biomass valorization for the production of highly valuable chemicals and biofuels is considered a sustainable alternative to traditionally used petroleum‐based molecules [1]. Among these, 5‐chloromethylfurfural (CMF) and 2,5‐dimethylfuran (2,5‐DMF) received considerable interest as biomass‐derived high‐value chemicals [2, 3]. In this study, from the viewpoint of sustainable development, 2,5‐DMF has emerged as a potential biofuel because of its excellent fuel properties and wide applications in the pharmaceutical and aroma industries [4, 5]. In addition, it serves as an intermediate for the production of high‐value fuels and petrochemicals, such as p‐xylene [6]. Similarly, CMF has also emerged as a promising platform molecule due to its greater stability, less hygroscopic nature, lower polymerization tendency, ease of handling, and structural and chemical properties similar to those of comparatively unstable HMF [7, 8]. These advantageous properties make CMF an attractive furan‐based platform chemical for the sustainable production of fuels, solvents, and value‐added chemicals such as 2,5‐DMF, 2,5‐diformylfuran (DFF), 2,5‐furandimethanol (FDM), and 2,5‐hexanedione (HDO) [9, 10, 11, 12].

Hence, considering the importance of sustainable energy alternatives, significant research efforts have been made in this direction. In general, the synthesis of 2,5‐DMF depends on the catalytic reduction of HMF by using several noble and transition metal catalysts [13, 14]. However, the large‐scale synthesis of 2,5‐DMF from HMF as an initial substrate is constrained by several challenges, including the complexity of the reaction process, difficulties in product separation, and instability of HMF. Moreover, only limited advancements have been reported for the conversion of CMF to 2,5‐DMF till date. In 2008, Mascal et al. reported a two‐step process, wherein the aldehyde group of CMF was initially protected to form an acetal intermediate, followed by hydrogenation over a Pd/C catalyst under a hydrogen atmosphere, achieving an 81% yield of 2,5‐DMF [15]. Similarly, Li and co‐workers also employed CMF as an initial feedstock to produce 2,5‐DMF by using Pd/C, and polymethylhydrosiloxane (PMHS) as the hydrogen source, and obtained 96% yield of the corresponding product at 45°C under n‐butanol solvent [16]. Moreover, recently, Zeng's group reported a method using a Pd/CNT catalyst, achieving a 92% yield of the desired product from the conversion of CMF. In this report, the author also explains the role of the in situ formation of Pd‐Cl active sites for the high selectivity of the process [11]. All these significant advancements are made to produce 2,5‐DMF from CMF (Scheme  1a). However, there are challenges which need to be addressed, such as a complex reaction procedure utilizing protection/deprotection of aldehyde functional group, difficult catalyst preparation, catalyst recyclability, use of costly hydrogen donors, large‐scale production of 2,5‐DMF, and the utilization of raw biomass to produce starting substrate (CMF) to produce 2,5‐DMF. Also, the synthesis of CMF from raw biomass has been rarely reported, posing an inherent challenge for the direct conversion of raw biomass to CMF. In the early 20th century, CMF was successfully synthesized for the first time by using inulin and cellulose biomass feedstock [17]. Recently, CMF synthesis was targeted from biomass‐based substrates, including bagasse pulp, bamboo pulp, eucalyptus pulp, and pretreated lignocellulosic residues (sugarcane bagasse, eucalyptus kraft pulp, and corn stover) by using various reagent systems such as metal salts (CrCl₃ and ZnCl₂), deep eutectic solvent (ChCl/AlCl₃·6H₂O/oxalic acid), and HCl/organic solvent biphasic processes [18, 19, 20, 21]. However, the direct utilization of raw biomass feedstock for the synthesis of CMF remains challenging due to the complex nature of biomass. This approach has attracted the world's scientific community working in this area, for both commercial and laboratory‐scale production of CMF. Therefore, these challenging findings motivated us to develop a process for the direct utilization of lignocellulosic biomass feedstock in CMF production and to develop a stable, recyclable, and economically viable catalyst for an efficient, scalable process for 2,5‐DMF production from CMF.

SCHEME 1.

Comparative analysis of earlier protocols with our present work for CMF to 2,5‐DMF production.

Our research group has been actively working for the past decade on the valorization of various biomass feedstocks (such as sugarcane bagasse, de‐oiled lemongrass, rice straw, and corn cobs) into furan‐based compounds (HMF and furfural) and on the development of nanocomposite materials for applications in various organic transformations [22, 23, 24, 25, 26]. In the present work, the polymer‐supported Pd@PS catalyst exhibits synergetic effects with Pd nanoparticles and polystyrene support which shows remarkable catalytic activity for the selective conversion of CMF to 2,5‐DMF under molecular H₂ gas and comparatively mild reaction conditions. The basic and porous nature of the polymer support with well‐dispersed Pd nanoparticles on the surface facilitates efficient hydrogen activation and C─Cl bond cleavage to generate the targeted product. Additionally, the catalyst was recyclable up to six cycles, and the synthesis of CMF to 2,5‐DMF was scaled up to 5.0 g (Scheme 1b).

2. Results and Discussion

Over the past decade, our research group has been actively engaged in designing, synthesizing, and utilizing the polystyrene‐supported metal nanocomposites as sustainable catalysts for a wide range of organic transformations, along with biomass valorization into high‐value platform chemicals [27, 28]. In the present study, we employed various biomass feedstocks to synthesize CMF in appreciable yields. Furthermore, the synthesized CMF has been targeted for the synthesis of 2,5‐DMF by using a polymer‐supported nanocomposite material as a heterogeneous catalyst. This heterogeneous catalytic system performed efficiently, highlighting its potential in the sustainable valorization of biomass‐derived compounds to high‐value chemicals.

2.1. Preparation and Characterization of Pd@PS Catalyst

The polymer‐supported palladium (Pd@PS) nano‐catalyst was prepared by using our previously developed reduction‐deposition protocol, employing Pd(OAc)₂ as the palladium source and Amberlite IRA 900 Cl⁻ resin as the solid support, and recharacterized using various techniques (see Supporting Information) [25, 26, 27]. The morphology and dispersion of synthesized palladium nanoparticles (Pd NPs) on solid support were initially investigated on a scanning electron microscope (SEM) instrument. The SEM images revealed spherical polystyrene beads with a relatively smooth surface and homogeneous distribution of Pd NPs across the support at both low and high magnifications (Figure S1b–d). Also, energy‐dispersive X‐ray spectroscopy (EDS) analysis of the Pd@PS showed the presence of Pd NPs at a characteristic peak at 2.7 keV, as depicted in Figure S1e. To gain information about the oxidation state and chemical composition of the developed Pd@PS nanocomposite, the X‐ray photoelectron spectroscopy (XPS) analytical technique was used, and two characteristic peaks with binding energies of 335.4 eV and 340.6 eV were obtained, which correspond to the 3d_5/2 and 3d_3/2 energy states of Pd metal, respectively (Figure S1f). These peaks confirm the presence of the Pd (0) oxidation state of palladium metal [29]. Furthermore, the physical properties of the catalyst, such as surface area and porosity, were investigated using Brunauer–Emmett–Teller (BET) analysis. The hysteresis loop (adsorption–desorption isotherm) confirmed the porous structure of the catalyst, which falls under the type IV category (Figure S1g), and the average pore size indicates that the support used for catalyst preparation is a mesoporous material. Furthermore, we observed that the polymer support had a surface area around 20.59 m²/g, with an average pore radius ≈ of 33.5 nm (see inset of Figure S1g) and a pore volume of 0.345 cc g⁻¹. The structure and crystalline nature of Pd@PS were determined by the powder X‐ray diffractometer (P‐XRD) technique (Figure S1h). The diffractometer of the synthesized Pd@PS catalyst showed two crystallographic planes, (111) and (200), with Bragg reflections at 2θ values of ∼40° and ∼46°, respectively [29]. The following peaks confirmed the face‐centered cubic (FCC) structure of Pd NPs. Additionally, P‐XRD analysis confirmed the crystalline structure of the Pd@PS catalyst, which possesses the (111) and (200) lattice planes, as also observed in the TEM and SAED analysis. The CO₂‐TPD profile of the developed catalyst shows three distinct desorption peaks at 122.1°C (0.012 mmol g^{− 1}), 232.4°C (0.262 mmol g^{− 1}), and 430.7°C (0.200 mmol g^{− 1}), representing the weak, moderate, and strong basic sites, respectively, as presented in Figure S1i. Based on these findings, the Pd@PS catalyst possesses a combination of strong and moderate basicity based on the conventional classification of desorption temperatures, with a small contribution from weak basic sites, as also confirmed by our previous study [29]. Also, the theoretical Pd loading in the Pd@PS catalyst is 0.47 wt%, which is in close agreement with the experimentally determined value of 0.42 wt%, as confirmed by ICP‐AES analysis (see Supporting Information).

Whereas the HR‐TEM, HAADF‐STEM, and the corresponding EDX elemental mapping analysis revealed that the Pd NPs are uniformly settled across the surface of the polymer support with no aggregation of metal nanoparticles (Figure S2a–c and f–i). Additionally, using Image‐J software on the TEM image (Figure S2b, 50 nm), the average particle size of the synthesized catalyst was determined to be approximately 1.98 nm (Figure S2d). Moreover, the selected area electron diffraction (SAED) analysis also exhibited concentric Debye–Scherrer diffraction rings attributed to the (111) and (200) planes of crystalline palladium metal (Figure S2e). These results collectively confirmed the formation of nanocrystalline Pd particles with a high degree of dispersion on the polymer matrix [30].

2.2. Process Development for the Synthesis of CMF From Different Biomass Substrates (Banana Peel Waste, Corn Cob, Rice Straw, and Sugarcane Bagasse)

In this study, banana peel waste was chosen as a model substrate to develop a selective and scalable approach for CMF synthesis. First, 1.0 g of dried powder banana peel waste was added to a neat and dry round‐bottom flask, solvated with 10 mL of dichloroethane (DCE) solvent, and further 100 mg of lithium chloride (LiCl) and 1.0 mL of concentrated (conc.) hydrochloric acid (HCl) was added to the reaction mixture and stirred for 18 h at 80°C under reflux conditions as shown in Figure 1. This reaction condition resulted in the formation of 102 mg isolated yield (10.2 wt%) of CMF. Moreover, we have also explored other biomass wastes, such as corn cobs, rice straw, and sugarcane bagasse, using optimized reaction conditions and obtaining 8 to 15 wt% of CMF, respectively (see Supporting Information for more detail optimization study).

FIGURE 1.

Reaction conditions: biomass (1.0 g), LiCl (10 wt%, 100 mg), HCl (1.0 mL), and DCE (10 mL), 18 h, 80°C.

2.3. Catalytic Performance of Developed Pd@PS for the Synthesis of 2,5‐DMF From Biomass‐Derived CMF

To determine the best reaction conditions, we critically investigated various parameters, including catalyst quantity, hydrogen pressure, solvent, temperature, reaction time, and type of catalyst for converting CMF to the targeted product. In this investigation, we performed all the reactions in a stainless‐steel high‐pressure reactor (25 mL) equipped with a pressure gauge. We started our optimization study by charging a high‐pressure reactor with the addition of CMF (0.50 mmol, 72.25 mg, 58 µL), Pd@PS (2 mol%, 0.01 mmol, 224.8 mg), and tetrahydrofuran (THF, 6 mL) as the solvent. Then the reactor was finally filled with hydrogen gas (20 bar) and stirred at 35°C for 3 h in an oil bath (Table 1, entry 1). After the completion of the reaction, the crude was analyzed on a gas chromatography–mass spectrometry (GC–MS) to identify all possible and desired products. Surprisingly, this reaction condition resulted in the > 99.0% conversion of CMF for the formation of targeted products (2,5‐DMF) and other reduced products such as 2,5‐dimethyltetrahydrofuran and 2,5‐hexanedione. To reduce the formation of other by‐products, we decreased the catalyst loading from 2 to 1.5 mol% and the hydrogen gas pressure from 20 to 15 bar. These reaction conditions increases the yield of 2,5‐DMF and reduces the over reduction of 2,5‐DMF (38%–60% GC yield, Table 1, entries 2 and 3). Furthermore, when the hydrogen gas pressure decreased from 15 to 10 bar, the selectivity rate of 2,5‐DMF formation increased to 71%, with a conversion of > 99% (Table 1, entry 4). Surprisingly, when the reaction was performed at 7 bar under the identical reaction conditions, it gave the highest yield (86%) of the targeted product, 2,5‐DMF with minimal formation of by‐products (< 4.0) (Table 1, entry 5). However, when the hydrogen gas pressure was further reduced from 7 to 5 bar, and the catalyst loading was reduced from 1.5 to 1 mol%, the yield of the desired product (2,5‐DMF) decreased, as shown in Table 1, entries 6 and 7. Moreover, when the Pd@PS catalyst and hydrogen gas were employed individually under identical reaction conditions, no product formation was noticed (Table 1, entries 8–10). This observation highlights the importance of the catalyst and hydrogen environment for the overall conversion to 2,5‐DMF. In addition, when the reaction was conducted with Pd(OAc)₂ under the identical optimal conditions, the conversions of CMF were > 99.0%, and there was a significant decrease in the yield of 2,5‐DMF (Table 1, entry 11).

TABLE 1.

Optimization study. ^a

				Product yield (%)
Entries	Catalysts loading (mol%)	H2 Pressure (bar)	CMF conversion (%)	2,5‐DMFb	5‐MFc	Other reduced products
1	Pd@PS (2)	20	>99	23.0	—	>50.0
2	Pd@PS (1.5)	20	>99	38.0	—	>40.0
3	Pd@PS (1.5)	15	>99	60.0	—	>30.0
4	Pd@PS (1.5)	10	>99	71.0	—	>13.0
5	Pd@PS (1.5)	7	>99	86.0	—	<4.0
6	Pd@PS (1.5)	5	>99	81.0	0.3	0.0
7	Pd@PS (1.0)	7	>99	74.0	12.0	0.0
8d	Pd@PS (1.5)	—	—	—	—	—
9e	—	7	—	—	—	—
10f	—	—	—	—	—	—
11g	Pd(OAc)2 (1.5)	7	>99	59.0	13.0	—

^a Reaction conditions: CMF (72.25 mg, 0.50 mmol), Pd@PS (2.0–1.0 mol%), THF (6 mL), and H₂ (bar), 3 h.

^b GCMS yield.

^c UPLC yield.

^d Without hydrogen pressure.

^e Without catalyst.

^f Without hydrogen pressure and a catalyst.

^g Reaction with Pd(OAc)₂. Reaction was performed at 35°C. All reactions were performed in a hydrothermal reactor.

In this study, we have also screened other solvents apart from THF, including ethanol (EtOH), methanol (MeOH), 2‐butanol, and t‐butanol. However, the corresponding desired product was obtained in low yield, accompanied by the formation of 5‐methyl furfural (5‐MF) and other reduced products (Figure 2a). Following the solvent optimization, the effect of reaction temperature on the conversion of CMF to 2,5‐DMF was studied. During this study, we found that reducing the temperature to 25°C, conversion and selectivity (65% and 19%) both were decreased, while increasing the temperature to 45°C, resulted in >99% conversion of CMF with the generation of 44% of 2,5‐DMF along with other reduced products (34%) as described in Figure 2b.

FIGURE 2.

(a) Role of solvent; (b) effect of temperature; and (c) role of catalyst for the transformation of CMF to 2,5‐DMF. Reaction conditions: CMF (0.50 mmol), catalysts (1.5 mol%), THF (6 mL), 7 bar H₂, 35°C for 3 h.

Therefore, the ideal reaction temperature for this transformation was found to be 35°C, ensuring complete conversion and maximum product selectivity. Further, we performed the reaction using commercially available heterogeneous catalysts Pd/C (5 wt%) and Pd/Al₂O₃ (5 wt%) under the same optimal reaction conditions, and the results are depicted in Figure 2c. These results indicate that Pd/C and Pd/Al₂O₃ were less effective than the Pd@PS nano‐catalyst, which might be due to the larger proportion of polymer support which provides better gas holding capacity and enhance the probability of interaction with highly reactive Pd NPs, and both in combination playing a synergistic role to achieve the high yield of the product [31]. After the optimization study, we achieved the following best‐optimized reaction conditions: CMF (0.50 mmol, 72.25 mg, 58 µL), Pd@PS (1.5 mol%, 0.0075 mmol, 168.7 mg) in THF solvent (6 mL) under molecular hydrogen (7 bar) as reducing agent at 35°C for 3 h, which gave the best result with >99% conversion and 86% yield of targeted product (Table 1, entry 5). In this study, we have further evaluated the turnover number (TON) and turnover frequency (TOF) based on the amount of product formed per mole of active Pd ion [32, 33]. Under the optimized reaction conditions (after 1 h of reaction), the Pd catalyst showed a TON of 59.89 and a TOF of 59.89 h^{− 1} (see Supporting Information for detailed calculation).

2.4. Reaction Mechanism

The formation of 2,5‐DMF from CMF generally proceeds through the following pathways: The reaction starts with the hydrodechlorination of the chloride ion (⁻Cl in the CMF). During time‐based study, we observed that the 5‐MF(II) formed as an intermediate in the initial step of the reaction, which is further confirmed by GC–MS analysis (see Supporting Information). This intermediate might be formed following the metallic Pd⁰ species (confirmed by X‐PS analysis), which promotes the hydrodechlorination of ⁻Cl in the CMF molecule. In the subsequent step, the reduction of the ^–CHO group of intermediate (II) forms an intermediate (III) (5‐MFA), which subsequently undergoes a hydrogenolysis and generating 2,5‐DMF as the desired product. Based on these findings, we propose a plausible reaction mechanism under optimized conditions utilizing a palladium (Pd) catalyst, in combination with hydrogen gas (Scheme 2).

SCHEME 2.

A plausible reaction mechanism for the conversion of CMF to 2,5‐DMF.

2.5. Reaction Kinetics Study

Based on the previous reports and a time‐based study, we calculated the reaction kinetics of the reaction, as shown in Figure 3a,b. The reaction was conducted with an optimized amount of Pd@PS catalyst, which provides the adsorption site for the CMF and hydrogen molecules onto its active sites, thereby facilitating the hydrodechlorination of the chloro group under constant temperature and hydrogen pressure. In the following reaction pathway, formation of 5‐MF from CMF and HMF was assumed to be the initial step, and the rate constants of K₁CMF and K₁HMF were found to be 0.0434 and 0.0152 min⁻¹, respectively (Figure 3e). These results demonstrate that our developed catalyst (Pd@PS) promotes dechlorination over deoxygenation. The rate constant (K₂CMF = 0.0102 min⁻¹ and K₂HMF = 0.0031 min⁻¹) indicates that the conversion of 5‐MF is a fast reaction and forms 5‐MFA and 2,5‐DMF, respectively (Figure 3e). However, we are unable to calculate the K₃CMF because of the rapid conversion of 5‐MFA to 2,5‐DMF. Notably, during this course, we observed that the yield of 2,5‐DMF was lower in the case of HMF substrate as compared to the yield obtained from the conversion of CMF to 2,5‐DMF, due to the rapid hydrodechlorination reaction as shown in Figure 3e, which was also supported by the calculated rate constant values (K₁ and K₂) (see Supporting Information). Finally, the obtained result concluded that the decay of concentration of CMF versus time follows the pseudo‐first‐order reaction kinetics pathways as shown in Figure 3c,d [11].

FIGURE 3.

Kinetic reaction model to produce 2,5‐DMF from (a) CMF, (b) HMF; (c) reaction profile of time versus concentration (mmol); (d) time versus concentration (ln (CMF)/mmol) of reactant; (e) reaction rate constants (bar) and ratios (symbol) for each reaction step. Reaction conditions: 0.50 mmol (CMF and HMF with 1.5 mol% catalyst), THF (6 mL), 7 bar H₂, 35°C, 10–180 min.

2.6. Gram‐Scale Reaction for 2,5‐DMF Production

To evaluate the viability of our developed method, we performed the gram‐scale synthesis of 2,5‐DMF. The reaction was carried out by using biomass‐derived CMF (34.5 mmol, 5.0 g), Pd@PS (1.5 mol%, 0.51 mmol.), and THF (50 mL) in a 250 mL high‐pressure hydrothermal reactor (SS‐316), and the mixture was stirred at 35 °C for 3 h under the hydrogen pressure (7 bar). After completion, the reaction mixture was analyzed by GC–MS, yielding 70% of the desired product (GC yield), corresponding to a 95% conversion of CMF (Figure 4). These findings confirm that the developed method is effective for gram‐scale synthesis and holds promise for future scale‐up applications.

FIGURE 4.

Scale‐up synthesis of 2,5‐DMF from biomass‐derived CMF.

2.7. Hot Filtration and Catalyst Recyclability Test

To understand the heterogeneous nature of the Pd@PS catalyst, we conducted a hot‐filtration test using CMF as the standard substrates. We have removed the catalyst after 45 min and continued the reaction for another 2.15 h. The hot filtration test clearly shows that no further increase in the yield of 2,5‐DMF is observed, suggesting heterogeneous behavior of the developed Pd catalyst (Pd@PS) in the reaction (Figure 5a). Furthermore, the recyclability and stability of heterogeneous catalysts play a vital role in the efficient hydrodechlorination and hydrogenolysis of CMF to produce 2,5‐DMF. In the present study, we examined the recyclability of Pd@PS Nps by conducting reactions with CMF under the established protocol. Following each reaction cycle, the Pd@PS catalyst was recovered by filtration, thoroughly washed with acetone, and dried under reduced pressure before reuse. The catalyst exhibited sustained activity over four consecutive cycles, with only a marginal decline in performance in the fifth and sixth cycles (Figure 5b). Thereafter, we performed the SEM and TEM analysis of the recycled catalyst after six runs (see Supporting Information), which showed that agglomeration occurs between the Pd NPs, resulting in a decrease in the number of active sites of the nano catalyst. Therefore, the Pd NPs agglomeration might be the reason for the minor loss in catalytic efficiency. This observation is in agreement with our previous findings [34, 35, 36].

FIGURE 5.

(a) Hot filtration test; (b) recyclability test of Pd@PS for the conversion of CMF to 2,5‐DMF.

2.8. Evolution of Green Chemistry Parameters

The green chemistry metrics of the developed process were evaluated using the carbon conversion efficiency, the environmental factor (E‐factor), and atom economy (AE), analysis based on previously reported equations [37, 38]. The conversion of various lignocellulosic biomass to CMF exhibited a carbon conversion efficiency between 25% and 54% with an experimental E‐factor of 20.22 (see Supporting Information for detailed calculations).

Furthermore, the subsequent conversion of CMF to 2,5‐DMF shows an atom economy of 64%, considering the stoichiometric utilization of three moles of H₂, along with a high carbon conversion efficiency of 90%. The calculated E‐factor for this step was found to be 1.15 (normalized to 50% yield) as shown in Figure 6, indicating an efficient and environmentally favorable catalytic protocol (see Supporting Information). The relatively low E‐factor value obtained indicated the high selectivity of the supported Pd catalyst toward the hydrogenolysis of CMF to 2,5‐DMF under mild reaction conditions. Furthermore, the molecular hydrogen serves as a clean reducing agent, and the recyclability of the developed leads to improved sustainability of the process.

FIGURE 6.

Representation of the green chemistry matrix for the conversion of CMF to 2,5‐DMF.

3. Conclusion

The biofuel 2,5‐DMF has been successfully synthesized from biomass‐derived CMF using a polymer‐supported nanocomposite material (Pd@PS) catalyst at 35°C and H₂ pressure, with an 86% yield of the targeted product and >99% conversion of CMF. The developed catalyst shows excellent stability and recyclability up to six reaction cycles, with only a slight decrease in the fifth and sixth cycles due to agglomeration between the Pd Nps. Additionally, the effects of various reaction parameters, including catalyst characterization, rate constants, and reaction pathways, were investigated exclusively. Moreover, the developed methodology with 90% carbon conversion efficiency percentage, 64% atom economy, acceptable E‐factor, and high recyclability of the catalyst and gram‐scale (5.0 gm) synthesis of 2,5‐DMF highlights the green chemistry matrix and potential for commercial‐scale implementation of the developed protocol. Finally, with all these investigations, the developed process may benefit the sustainable upgradation of biomass‐based fuels and other value‐added chemicals for commercialization.

4. Experimental Section

4.1. Materials and Methods

The standard furanic chemicals, such as 2,5‐dimethylfurfural (DMF, 99%), 5‐methylfurfural (5‐MF, 99%), 5‐methylfurfural alcohol (5‐MFA, 99%), deuterated chloroform (CDCl₃, 99%), tert‐butanol, and palladium acetate Pd(OAc)₂), were purchased from Sigma‐Aldrich. 2‐Butanol (98.00%) and tetrahydrofuran (THF) (99.50%) were purchased from Central Drug House (P) Ltd. Acetonitrile (99.80%), silica gel 60–120, methanol (99.80%), and anhydrous sodium sulfate (99.50%) were acquired from SD Fine‐Chem Limited (SDFCL). Across Organics provided the polystyrene‐based amberlite IRA‐900 Cl‾ resin (PS). All reactions were monitored using thin‐layer chromatography (TLC) with silica gel 60 F254 plates from Merck and analyzed in a UV light detector chamber.

4.2. General Experimental Procedure for the Catalytic Conversion of CMF to 2,5‐DMF

A high‐pressure reactor (25 mL) made up of stainless steel (NV enterprises Moc: SS316L) equipped with a pressure gauge was used for the synthesize 2,5‐DMF from CMF. This reactor was charged with CMF (0.50 mmol), Pd@PS (2.0–1.0 mol%), and tetrahydrofuran (THF) (6.0 mL) and H₂ gas. Then the reactor was placed in oil based with preheated reaction temperature (35°C). Once the reaction was completed, the hydrogen pressure was released from the reactor. Then the sample was taken from the mixture, filtered, and analyzed on GC–MS (Agilent 5977C GC/MSD) analytical technique. The final conversion of CMF and the yield of relevant products, carbon conversion efficiency, atom economy (AE), and the environmental factor (E‐factor) analysis based on previously reported equations were calculated as follows:

$$\mathrm{Conversion}\left(\%\right)=1-\left(\frac{\mathrm{mmol}\mathrm{of}\mathrm{CMF}\mathrm{in}\mathrm{product}}{\mathrm{mmol}\mathrm{of}\mathrm{CMF}\mathrm{in}\mathrm{substrate}}\right)\times 100\%$$ (1)

$$\mathrm{Yield}\left(\%\right)=\left(\frac{\mathrm{mmol}\mathrm{of}\mathrm{product}}{\mathrm{mmol}\mathrm{of}\mathrm{CMF}\mathrm{in}\mathrm{substrate}}\right)\times 100\%$$ (2)

$$\begin{array}{ccc}& & \mathrm{Carbon}\mathrm{conversion}\mathrm{efficiency}\left(\%\right)\hfill \\ & & =\left(\frac{\mathrm{moles}\mathrm{of}\mathrm{carbon}\mathrm{in}\mathrm{product}}{\mathrm{moles}\mathrm{of}\mathrm{carbon}\mathrm{in}\mathrm{the}\mathrm{intial}\mathrm{substrate}/\mathrm{biomass}}\right)\times 100\%\hfill \end{array}$$ (3)

$$\mathrm{E}-\mathrm{factor}=\frac{\mathrm{Total}\mathrm{amount}\mathrm{of}\mathrm{waste}}{\mathrm{Total}\mathrm{amount}\mathrm{of}\mathrm{product}}$$ (4)

$$\mathrm{Atom}\mathrm{economy}\left(\%\right)=\left(\frac{\mathrm{Molecular}\mathrm{weight}\mathrm{of}\mathrm{the}\mathrm{product}}{\mathrm{Molecular}\mathrm{weight}\mathrm{of}\mathrm{the}\mathrm{reactant}}\right)\times 100\%$$ (5)

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

General information about materials, methods, optimization procedures, detailed calculations, and analytical and spectral data is all provided in the Supporting Information [22, 39].

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.