Next Article in Journal
Preparation of Oxygen Reduction Catalyst Electrodes by an Efficient Electrodeposition Method on HNO3-Activated Carbon Paper
Previous Article in Journal
A Review on the Research Progress of Zeolite Catalysts for Heavy Oil Cracking
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 15
Issue 4
10.3390/catal15040402
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Waste Incineration Fly Ash-Based Bifunctional Catalyst for Upgrading Glucose to Levulinic Acid

by
Rui Zhang
1,*,
Han Wu
1,
Jiantao Li
1,
Dezhi Chen
2,
Shimin Li
1,
Jiale Chen
1,
Xiaoyun Li
3,
Jian Xiong
4,
Zhihao Yu
5 and
Xuebin Lu
4
1
School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin 300384, China
2
School of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
3
School of Agriculture and Biotechnology, Sun Yat-sen University, Shenzhen 518107, China
4
School of Ecology and Environment, Tibet University, Lhasa 850000, China
5
School of Environmental Science and Engineering, Tianjin University, Tianjin 300350, China
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(4), 402; https://doi.org/10.3390/catal15040402
Submission received: 3 March 2025 / Revised: 14 April 2025 / Accepted: 16 April 2025 / Published: 19 April 2025
(This article belongs to the Section Biomass Catalysis)
Browse Figures
Versions Notes

Abstract

:
The safe and resource-efficient utilization of waste incineration fly ash (WIFA) has emerged as a pressing challenge in solid waste management. In this work, WIFA was used to prepare a bifunctional catalyst (Metalsx/4@WIFA-S) for the production of levulinic acid (LA) from glucose. The yield of LA was 42.3% with water as the solvent. Moreover, adding 20% γ-valerolactone (GVL) to the system increased the yield to 50.7%. Reaction kinetics and molecular dynamics simulations were applied to elucidate the mechanism by which the solvent system enhanced the catalytic performance of the Metalsx/4@WIFA-S catalyst. Additionally, the environmental risks of WIFA in the preparation of catalysts were evaluated. The dioxin decomposition rate in the catalyst was calculated to be 99.87%, effectively achieving the detoxification of the catalyst. The concentration of heavy metals in the hydrolysate complied with emission standards, thereby reducing environmental risk. This study confirms that waste incineration fly ash-based bifunctional catalysts are effective and safe catalysts with great potential for application in biomass catalysis.

Graphical Abstract

1. Introduction

Incineration is currently the predominant method for municipal solid waste, and the fly ash generated from this process, known as waste incineration fly ash (WIFA), is classified as a hazardous waste at the national level [1]. The improper disposal of toxic substances, including dioxins and heavy metals, in WIFA can lead to severe pollution of the atmosphere, water, and soil, thereby posing a significant threat to environmental health [2]. Although WIFA possesses carcinogenic and toxic properties [3], its abundant metal and other content render it a valuable resource for recycling [4]. The objectives of decomposing dioxins, stabilizing heavy metals, and reusing carbon fractions are crucial in addressing the environmental impact of WIFA. Hence, urgent efforts are required to develop a safe and economically valuable technology for WIFA disposal in the current scenario [5].
Existing WIFA treatment technologies are primarily aimed at reducing the leachability of heavy metals and breaking down dioxins. As reported, the dioxin concentrations in fly ash from municipal solid waste incineration are about 2.8–190 ng/g [6]. The current technologies that can efficiently dispose of organics such as dioxins include low- and medium-temperature heat treatment and mechanochemical methods [7]. Wu et al. [7] used heating for dioxin removal from WIFA and found that when the heating temperature was higher than 350 °C, the structure of dioxin was significantly disrupted. In addition, the major elements of heavy metals in WIFA include Zn, Pb, Cu, Cr, Cd, and Ni with contents of 4136–19311, 1473–5670, 370–1061, 240–261.4, 40.1–412.5, and 60.8–185.2 mg/kg, respectively [6]. The corresponding methods, such as cement solidification and chemical stabilization, are universal. Greef et al. [8] found that it typically required 300 to 400 kg of cement per ton of fly ash, which undoubtedly increased the volumetric and weight burdens of subsequent landfills. Furthermore, the poor long-term stability and durability of the cement-cured product due to chlorine salts increased the secondary leaching risk of heavy metals [9]. Ma et al. [10] found that the addition of chelating agents (dithiocarbamate) during the cement curing process can encapsulate heavy metals in the three-dimensional structure of cementitious curing products. Currently, existing WIFA treatment technologies mainly focus on the immobilization of heavy metals or dioxin degradation, but they seldom solve these two problems simultaneously. Therefore, it is necessary to develop a technology that can simultaneously treat heavy metals and dioxins in WIFA to realize the resource utilization of WIFA.
Under the background of sustainable development and circular economy, the resource utilization of WIFA before terminal disposal has attracted wide attention. WIFA is often used in catalysis due to its richness in alkali metals and mineral components. WIFA can be utilized as a catalyst in pyrolysis to improve the quality of the product. Yu et al. [11] used co-pyrolysis to dispose of sludge containing sludge and WIFA, and they showed that the addition of 20 wt% WIFA at 600 °C promoted the cracking of heavy oil components and increased the content of light aromatics, thus improving the oil quality. In addition, the addition of WIFA was found to inhibit the polymerization and condensation reactions of macromolecular compounds and reduce coke formation. Chen et al. [12] used a hydrothermal method to modify municipal waste incineration fly ash. The fly ash was first treated in NaOH solution at 130–150 °C for 24 h, then washed with HCl solution and pH-adjusted to 7 with water, and dried to obtain modified fly ash. Subsequently, Mn-Ce composite oxides were loaded on the modified fly ash to prepare catalysts. It was used to catalyze the reduction of NO by NH3 and achieved 93% NO conversion. Feng et al. [13] synthesized zeolites from waste incineration fly ash for the preparation of γ-valerolactone (GVL). Under optimal conditions, the GVL yield reached 94%, which was comparable to the performance of commercial catalysts. In addition, by testing the heavy metal content in the reaction solution, it was found that the zeolite structure was conducive to immobilizing heavy metals in the pore structure, and the heavy metal leaching values were all in accordance with the standards. In summary, WIFA has the potential and advantage to provide cost-effective new materials for environmental catalytic applications. However, there are few reports on the preparation of catalysts from WIFA, and the key issues such as the corresponding catalysis mechanism need further study. Additionally, the analysis of toxicants in the catalysts based on WIFA has not yet been explored in the literature. Therefore, it is important to study the catalytic performance of the catalysts based on WIFA and its environmental risks.
This study introduces a method for the high-value utilization of WIFA. In this study, a WIFA-based bifunctional catalyst (Metalsx/4@WIFA-S) was synthesized by sulfonation and wet impregnation techniques using WIFA as a catalyst precursor. This study evaluates the catalytic performance of Metalsx/4@WIFA-S catalysts using LA production from glucose conversion as a model reaction. The effects of various solvent systems on enhancing catalytic performance were thoroughly investigated. In addition, the environmental risks of WIFA in the preparation of catalysts were evaluated, including the decomposition of dioxins and the leaching of heavy metals. This novel approach may enrich the theoretical framework for the high-value conversion of WIFA and provide novel catalytic materials for the field of biomass catalysis.

2. Results and Discussion

2.1. Effect of Different Metals and Loading Rates on the Preparation of LA from Glucose

Figure 1 is a schematic diagram of the reaction pathway for the conversion of glucose to LA, in which the molecular rearrangement during glucose isomerization is a key step in the conversion of glucose to LA. In this case, the metal loaded on WIFA-S (WIFA loaded with sulfonic acid moiety) can act as a Lewis acid site to promote aldose ketose isomerization [14]. Therefore, it was necessary to screen the loaded metals to assess the effect of synergistic interaction of the metal (Lewis acid) with WIFA-S (Brønsted acid) on the conversion of glucose to LA. Transition metals with larger atomic sizes facilitate the generation of spatial effects at acidic sites, thereby enhancing glucose conversion [15]. Therefore, Fe, Al, Zn and Cu were adopted as Lewis acidic sites in this paper. As shown in Figure 2, the glucose conversion reached 96.1%, 97.7%, 95.2% and 96.6%, respectively. When different metals acted as Lewis acidic sites, CuCl2 increased LA yield significantly more than FeCl3, AlCl3, and ZnCl2. This result is consistent with previous studies [16].
A small amount of fructose (1–2%) was detected in the derived products, probably due to the rapid dehydration reaction of fructose to LA and formic acid (FA). However, the yields of LA and FA were relatively low with the catalysis of Al2/4@WIFA-S and Zn2/4@WIFA-S, which were 21.3% and 16.6%, respectively. The results showed that AlCl3 and ZnCl2 as Lewis acids may not be able to isomerize glucose to fructose well enough to support the continuation of this multistep cascade reaction to downstream products.
When CuCl2 and FeCl3 were used as Lewis acids, the yields of the target product, LA, were 39.2% and 34.9%, respectively. From the yield point of view, both CuCl2 and FeCl3 have good synergistic effects with WIFA-S catalysts, although CuCl2 has a better effect than FeCl3 with WIFA-S catalysts. The high LA yield with the Cu2/4@WIFA-S catalyst was attributed to the sites on CuCl2 as a Lewis acid, which provided unsaturated metal centers, increased the acidity, decreased the hydrophobicity of WIFA-S, and thus favored the -OH binding of glucose. It was proved that Cu2+ was able to polarize the C-O bond of the carbon cation to form a bidentate complex, which promoted the electron transfer and reaction rate [17]. Therefore, Cux/4@WIFA-S was selected as the best catalyst for subsequent studies.
The proportion of Cu loading in this cascade reaction has an important influence on the rate-limiting step of glucose isomerization. The distribution of downstream products in the conversion of glucose to LA as a function of the Cu loading ratio is shown in Figure 3. As shown in Figure 3, the yield of the target product, LA, was only 14.9% without the addition of Cu, which is probably due to the small amount of metal elements in WIFA-S. However, when Cu was introduced, the yield of LA increased significantly, indicating that Cu can play an important catalytic role as a Lewis acid. The target product, LA, reached its peak when the catalyst was Cu1/2@WIFA, and further increasing the Cu loading led to a decrease in the yield of LA. This implies the existence of an optimal Brønsted/Lewis acid ratio for the formation of LA and that an excess of Lewis acid promotes side reactions, resulting in the degradation of carbohydrates and intermediates into humic acid. Consequently, Cu1/2@WIFA was identified as the optimal catalyst.

2.2. Catalyst Characterization

Figure 4 shows the SEM and EDS images of Zn2/4WIFA-S, Fe2/4WIFA-S, Al2/4WIFA-S, and Cu2/4WIFA-S catalysts. Figure 4A shows the morphology of the catalysts, which can be seen to change after the impregnation of Zn, Fe, Al, and Cu elements onto WIFA-S (Figure 5A) by wet impregnation. After the impregnation of Zn, Fe, Al, and Cu elements onto FA-S by wet impregnation, the surface of the catalysts became irregular with many wrinkles and fragments as compared to the WIFA-S catalysts (Figure 5A). This phenomenon may be attributed to the interaction between the mentioned metal chlorides and the carbon material during wet impregnation, resulting in uneven adsorption onto the carbon surface and the subsequent aggregation of metal chlorides [17]. Figure 4B shows the distribution of Zn, Fe, Al, and Cu metals over the WIFA-S catalyst by wet impregnation. The Zn, Fe, Al, Cu, and S elements in the catalysts were relatively uniformly distributed on the surface of the catalyst precursors. This indicated that the successful loading of metals did not change the original S-element distribution in the WIFA-S catalyst
Figure 6 shows the FT-IR curves of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts. As shown in Figure 5, Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts all showed obvious characteristic peaks around 3400 cm−1, indicating O-H stretching vibration peaks in the oxygen-containing functional groups. These four catalysts all showed characteristic peaks around 1580 cm−1, corresponding to C=C stretching vibration in the aromatic ring [18]. The characteristic peak at 1154 cm−1 corresponded to the stretching vibration peak of -SO3H, which also confirmed the successful loading of sulfonic acid groups [19].
NH3-TPD (ammonia temperature-programmed desorption) is an experimental method to characterize the amount of catalyst acid. Different acidic sites will desorb at different temperatures, and information such as desorption peaks, desorption temperature sites, etc., can be obtained from the obtained TPD profile. The NH3-TPD spectra of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts are shown in Figure S2, and a quantitative analysis is in Table 1. These four catalysts all showed weakly acidic peaks at 90–150 °C, which may be produced by the acidic sites of -OH or -COOH. The highest amount of weak acidic sites for the Cu2/4@WIFA-S catalyst was 8.273 mmol/g. Strong acid peaks appeared at 580–650 °C, probably generated by the acidic sites of -SO3H and metal. The highest amount of strong acidic sites for the Cu2/4@WIFA-S catalyst was 16.069 mmol/g. It was reported that the distribution of downstream products is closely linked to the amount of acid, and that glucose tends to produce LA in strongly acidic environments [20]. This observation is in agreement with the experimental results shown in Figure 1, which can be ascribed to the favorable catalytic performance of Cu2/4@WIFA, attributed to its acidic nature.
The pore structure of catalysts has important effects on catalytic reactions, such as affecting the diffusion efficiency and providing variable active sites for catalytic reactions [21]. Therefore, the pore structure parameters of catalysts should have a synergistic effect on the generation of LA. In this work, the surface parameters of the prepared Metalsx/4@WIFA-S catalysts were analyzed, with the results shown in Table 1. The specific surface area, pore volume, and pore size of the Metals2/4@WIFA-S catalyst are smaller than those of the WIFA-S catalyst. It may be because the metal particles occupied the pore space of the WIFA-S catalysts, thus leading to the reduction in the specific surface area of Metalsx/4@WIFA-S catalysts.

2.3. Catalyst Performance Evaluation

The catalytic performance of Metalsx/4@WIFA-S in the pure H2O system was evaluated. As we all know, reaction temperature and time, as key parameters in the reaction producing LA from glucose, affect the course of the reaction and the selectivity of the products [22]. The distribution of downstream products in the conversion of glucose to LA as a function of reaction temperature is shown in Figure 7A. Figure 7A shows that both LA and FA showed a trend of increasing and then decreasing with increasing temperature. The yield of LA and FA increased from 13.6% and 30.2% to 39.2% and 50.0%, respectively, after the temperature was increased from 140 °C to 180 °C. The yield of LA and FA decreased with further increase in temperature. As the temperature was further increased, the yields of LA and FA decreased. Fructose and HMF were not detected in the reaction solution when the temperature reached 200 °C. This indicated that fructose and HMF were further dehydrated to form LA in the presence of the Cu2/4@WIFA-S catalyst as the temperature increased [23].
As shown in Figure 7B, glucose conversion was maintained at about 94% (±1%) when the reaction was carried out at 180 °C for 1–5 h. The yields of LA and FA showed a tendency to increase and then decrease with the reaction time. When the reaction was carried out for 4 h, the yield of LA was 39.2% and FA was 50%. A significant decrease in LA and FA yields was observed with further extension of the reaction time. This may be due to the instability of LA in water, which generates humins through side reactions such as acetal cyclisation and aldol condensation [24]. The decrease in FA may be due to the easy decomposition in an acidic environment at a high temperature to produce CO and H2O.
The distribution of downstream products with catalyst dosage and substrate concentration during the conversion of glucose to LA is shown in Figure 7C,D. From Figure 7C, it can be observed that the HMF yield gradually decreased with the increase in catalyst dosage when the catalyst dosage was lower than 1.5 g. This may be due to the fact that enough H+ that dispersed on the structure of the reacting substrate can attack the hydroxyl group of the glucose α-terminal isomer to form hydrogen bonds during glucose hydrolysis [25]. The yield of LA decreased from 42.3% to 12.5% when the catalyst dosage further increased, which could be attributed to the side reaction of alcohol–formaldehyde condensation of LA [26,27]. When the glucose concentration increased from 10 g/L to 20 g/L, the LA yield increased from 14.7% to 42.3%. As the glucose concentration continued to increase, both LA yield and FA yield showed a slight trend of increasing and then decreasing. Shan et al. found that high concentrations of glucose solutions led to intense intermolecular motions and the formation of a large number of intermediates with furan rings. These also form unwanted by-products (humins, etc.) through intermolecular etherification and the electrophilic substitution reactions of furfuryl alcohols [28].

2.4. Optimization and Kinetic Analysis of Solvent Systems for LA Production

2.4.1. Effect of Different Solvent Systems and Percentages of GVL on LA Preparation from Glucose

Figure 8 shows the effect of different solvent systems and the percentages of GVL on the LA yield. Figure 8A shows that GVL/H2O and THF/H2O as solvent systems contributed to the LA yield. In the pure H2O system, the LA yield was 42.3%, while the LA yield increased to 50.7% and 45.9% with the addition of GVL and THF, respectively. This may be because GVL and THF, as polar nonprotonic solvents, can enhance the interaction with the reaction substrate, break the hydrogen bonding network of the reaction substrate, and thus favor the protonation reaction [29]. By contrast, the addition of acetonitrile/H2O as a solvent system decreased the yield of LA. When methanol/H2O and ethanol/H2O were used as typical polar proton solvent systems, they negatively affected the LA yield, which was separately reduced to 33.2% and 28.1%. This may be because polar proton solvents as the electron acceptors can form hydrogen bonds with the solute, forming stronger interaction effects, which also affected the selectivity of the target product [30,31]. The addition of alcohol solvents to the solvent system may contribute to the results that the fructose dehydration product HMF did not rehydrate to form LA but etherified to EMF [32]. In summary, GVL/H2O was selected as the best solvent system for further study.
Figure 8B shows the effect of different GVL contents in the GVL/H2O solvent system on LA yield. As the dosage of GVL increased, the conversion of glucose remained around 99% (±1%), while the yields of LA and FA increased and then decreased. This may be due to the cleavage ability of GVL, which could break the hydrogen bonds between glucose molecules [33]. Glucose is more soluble in water, so water as a co-solvent can increase the solubility of the reaction substrate and reduce the viscosity of the reaction medium (GVL/H2O), which is conducive to accelerating the mass transfer rate [34]. When the ratio of GVL/H2O was 20/80, the yield of the LA reached 51.4%, which was nearly 10% higher than that of the pure H2O system. It indicated that the side reaction of unwanted by-products such as humins could easily occur in the water, and the addition of GVL suppressed these side reactions. And further addition of GVL did not produce a boost to the LA yield, which may be due to the fact that the HMF was encapsulated by GVL and thus interrupted the rehydration reaction.

2.4.2. Reaction Kinetics of Glucose to LA

The conversion of glucose to LA as a secondary reaction involves the dehydration of glucose to produce HMF and the rehydration of HMF to produce LA [35]. This study evaluates the impact of various solvent systems on reaction energy barriers using reaction kinetics. The activation energy (Ea) and pre-exponential factor (A) were determined using the Arrhenius equation. According to Figure 8B, with LA yield as the screening basis, solvent systems composed of 15%, 20%, and 25% of GVL and H2O, respectively, were selected to calculate the reaction energy barriers from glucose to LA in different solvent systems.
Calculations have shown that the reaction energy barrier for the dehydration of glucose in a pure H2O solvent system is 54.95 kJ/mol and that for HMF rehydration it is 7.4 kJ/mol. This indicates that glucose dehydration is both energetically demanding and a rate-limiting step in the conversion of glucose to LA. The reaction kinetics were subsequently evaluated for different percentages of GVL in the reaction system. Under optimal conditions (temperature: 180 °C, time: 4 h, catalyst: 1.5 g, glucose concentration: 20 g/L, GVL content: 20%), the reaction energy barrier for glucose to LA was determined to be 51.33 kJ/mol, representing a reduction compared to that observed in the pure H2O solvent system. Table 2 shows that the reaction energy barriers showed a decreasing trend with the increase in the proportion of GVL. In the absence of added GVL, the reaction energy barrier was 54.95 kJ/mol, whereas it decreased to 18.37 kJ/mol, 30.38 kJ/mol, and 44.45 kJ/mol with the increase in the proportion of GVL, respectively. This indicates that the addition of GVL is favorable to promote the glucose dehydration reaction. The reaction energy barriers for the rehydration of HMF to form LA increased with the increase in GVL content. Specifically, the reaction energy barrier was 7.4 kJ/mol without the addition of GVL, whereas it increased to 25.05 kJ/mol, 20.95 kJ/mol, and 50.84 kJ/mol with the increase in GVL content, respectively. This is because GVL may surround the intermediate product (HMF), thereby hindering HMF rehydration. Studies have demonstrated that the addition of organic solvents (DMSO, etc.) acts as a shield against HMF and prevents HMF rehydration, thus effectively inhibiting by-product production [36]. Coupled with the distribution of downstream product yields of glucose shown in Figure 8B, it is evident that LA yield decreases slightly with the addition of GVL, whereas HMF yield increases gradually. It indicates that the addition of GVL will lead to difficulty in HMF dehydration.

2.4.3. Molecular Dynamics of Glucose to LA

As shown in Figure 9, in the GVL/H2O solvent system, as the proportion of GVL increased, more GVL tended to be distributed around the carbonyl, carboxyl, and hydroxyl groups of LA. This coordination helped to prevent the possibility of LA triggering side reactions, such as esterification and condensation, due to excess water. As reported, the water around LA was squeezed into the second solvation shell layer with the addition of co-solvents, so the occurrence of side reactions could be reduced by preferential solvation of solvents or by shielding certain functional groups [37]. The product yield graph in Figure 8B illustrates that HMF yield increases with additional GVL input, potentially because excess GVL forms a barrier around HMF, hindering its rehydration and creating a negative synergistic effect.
To elucidate the solvation shell layer more specifically, we simulated the solvation peaks across different solvent systems, as shown in Figure 10. Figure 10 analyzes the local arrangement of the surrounding solvent molecules of the LA in different solvent systems. Under the condition of pure aqueous solvent, the radius of the first solvation shell layer of water was 0.194 nm. With the addition of GVL in the solvent, the radius of the first solvation shell layer of water gradually decreased to 0.182 nm, and the radius of the first solvation shell layer of GVL stabilized at about 0.6 nm. This indicated that the attractive effects of LA on co-solvent GVL were enhanced compared to those on water. Combined with the spatial density distribution of the water around LA, it can be concluded that GVL provided a protective shell for LA and the addition of GVL as a co-solvent had a great potential for LA optimization.

2.5. Catalyst Environmental Risk Assessment

2.5.1. Analysis of Dioxin Compositions in WIFA and WIFA-S

In this study, WIFA was transformed into a WIFA-S catalyst through processes including calcination, nitric acid modification, and sulfonation. Figure 11 shows the variation of PCDD/Fs content in WIFA and WIFA-S catalysts. WIFA contained high levels of dioxin substances, whereas the dioxin levels in the WIFA-S catalyst were below the detection limit. The WIFA-S catalyst effectively removed PCDDs and PCDFs from WIFA, and the decomposition of dioxins in WIFA was up to 99.87% during calculation process. This indicated that the WIFA-S catalysts obtained after a series of pretreatments not only have a well-developed pore structure but also achieve detoxification and are more environmentally friendly.

2.5.2. Evaluation of the Risk of Leaching Heavy Metals from Reaction Solutions

The risk of heavy metal leaching was assessed for the LA reaction solution prepared from glucose under optimal preparation conditions. The heavy metal leaching contents of the Cu2/4@WIFA-S catalyst in the reaction solution after the completion of the reaction are listed in Table 3. The concentrations of the typical heavy metals Cu, Pb, and Cd of the catalyst in the reaction solution measured by ICP were 0.021, 0.442, and 0.100 mg/L, respectively. Zn was not detected in the leaching solution. The concentrations of the detected heavy metals were lower than the limits of “Integrated wastewater discharge standard GB 8978-1996 (Class I Standard)”, indicating a low environmental risk. Therefore, the use of WIFA for catalyst preparation and subsequent use poses little risk to the environment.

3. Materials and Experiments

3.1. Materials

Zinc chloride (ZnCl2, AR), iron (III) chloride (FeCl3, AR), aluminum chloride (AlCl3, AR), copper (II) chloride (CuCl2, AR), and glucose (C6H12O6, AR) were obtained from Biotest Technology, Tianjin, China. Fructose (C6H12O6, GR), 5-hydroxymethylfurfural (C6H6O3, GR), and levulinic acid (C5H7O3, GR) were obtained from Sigma-Aldrich, USA.
Since the fly ash in this paper is from the same waste treatment plant as reference [38], themain compositions of the crystalline phase of fly ash can be seen from the XRD graph in reference [38], including NaCl, KCl, CaCO3, etc. Due to the more complex crystalline phase structure of fly ash, the material phases corresponding to most of the peaks in its plots are more difficult to analyze because some of the material phases accounted for a very small proportion of the fly ash, or the component is not in the form of crystals.
WIFA was taken from a waste incineration plant in Tianjin, China, and the distribution and loss on ignition (LOI) of the components in the WIFA are analyzed in Table 4.

3.2. Preparation and Characterization of Catalysts

3.2.1. Preparation of WIFA-S

The WIFA was placed in a tube furnace, and nitrogen was introduced to maintain an inert atmosphere. The temperature was increased to 700 °C at a rate of 10 °C/min. Subsequently, CO2 was introduced for 30 min at 700 °C for opening the pore structure of carbon and decomposing the dioxins in the WIFA. After this process, the obtained catalyst precursors were pretreated by diluted nitric acid. The sulfuric acid and diluted nitric acid-treated catalyst precursor with a liquid–solid ratio of 20 mL/g were placed in a miniature magnetic autoclave with a PTFE liner and maintained at 140 °C for 14 h. After cooling to room temperature, the mixture was washed repeatedly with deionized water at 80 °C until the filtrate was neutral. After this process, the catalyst based on WIFA with sulfonic acid properties was obtained and named WIFA-S. Finally, the obtained WIFA-S was dried overnight at 80 °C under a vacuum, ground, and passed through 200-mesh sieves.

3.2.2. Preparation of Metalsx/4@WIFA-S

The WIFA-S was mixed and stirred with aqueous solutions of metal salts (ZnCl2, CuCl2, FeCl3, AlCl3) at different concentrations (the mass ratio of WIFA-S to metal salts was 4:1, 4:2, 4:3, 4:4) using the wet impregnation method, and then the mixtures were dried in an oven at 105 °C overnight. The mixture was then calcined in a tube furnace energized with nitrogen gas, and the temperature was raised to 200 °C for 6 h. The catalyst we obtained was named metalsx/4@WIFA-S. It was ground and passed through a 200-mesh sieve and kept in a dry dish for use. The produced metalsx/4@WIFA-S catalysts from different aqueous solution were designated as Znx/4@WIFA-S, Fex/4@WIFA-S, Alx/4@WIFA-S, and Cux/4@WIFA-S catalysts, respectively.

3.2.3. Metalsx/4@WIFA-S Characterization

The apparent structure and elemental composition of metalsx/4@WIFA-S catalysts were characterized by a high-resolution field emission scanning electron microscope (SEM, TESCAN MIRA LMS, Cranberry TWP, PA, USA) equipped with an energy-dispersive spectrometer (EDS, TESCAN MIRA LMS, Cranberry TWP, PA, USA). The equipment was acquired by TESCAN, Brno, Czech Republic. The crystal shape was analyzed by an X-ray diffractometer (XRD, Rigaku Smartlab 9KW, Neu-Isenburg, Germany) with a scanning range of 5~90° and a scanning speed of 10°/min. The facility was acquired by Nippon Rigaku Corporation, Akishima, Tokyo, Japan. The functional groups of samples were scanned by using a Fourier transform infrared spectrometer (FT-IR, Perkin Elmer Spectrum One, Shanghai, China) in the wave number range of 400–4000 cm−1. The facility was acquired by PerkinElmer AG, Waltham, MA, USA. Moreover, the pore characteristics were analyzed by using a specific surface area analyzer (Micromeritics ASAP 2460, Norcross, GA, USA), where the BJH method was used to determine the specific surface area and pore structure. The device was acquired by Mack Instruments of Norcross, GA, USA. The surface acidic sites of the samples were tested by using a temperature-programmed desorption of ammonia (NH3-TPD, VDSorb-91i, USA) instrument. The equipment is manufactured by Xi’an Wardens Instrument Co, Xi’an, China. The dioxin content was detected using a DFS-type high-resolution gas chromatograph–high-resolution mass spectrometer (SN03462M, USA). The device was acquired by Thermo Fisher Scientific, Waltham, MA, USA. The metal content in the reaction solution was determined using an inductively coupled plasma mass spectrometer (Thermo-Fisher iCAP Model 7400, Waltham, MA, USA). The device was acquired by Agilent Technologies, Santa Clara, CA, USA.

3.3. Catalytic Reactions of Metalsx/4@WIFA-S

In this paper, the conversion of glucose to LA was used as a reaction model and was carried out in a 250 mL batch reactor equipped with a magnetic stirrer. At the beginning of the experiment, 1 g of glucose, 1 g of Metalsx/4@WIFA-S catalyst, and 50 mL of solvent were added to the reactor. The optimal reaction conditions were then determined with the goal of LA yield. When the reaction was finished, the reactor was removed and placed in ice water for rapid cooling. Each set of experiments was repeated two times, and the results were averaged.
The product distribution in the reaction solution was detected by HPLC (LC-20A, Kyoto, Japan) with a column (BioRad Aminex HPX-87H, 300 nm × 7.8 nm) at 65 °C and 5 mM H2SO4 as the effluent at a flow rate of 0.6 mL/min. The equipment was acquired by Shimadzu Corporation, Kyoto, Japan. HPX-87H was acquired by BioRad, Hercules, CA, USA. A refractive detector was used, and an external standard method was used to determine the concentration of the product in the reaction solution and calculate the yield.

3.4. Molecular Dynamics Simulation

Molecular dynamics (MD) simulations were performed using the GROMACS 2021 software package. For simulation pre-processing, the structure files of FA and LA molecules were obtained from the PubChem database, and structure optimization and vibrational analysis of both were performed using Multiwfn and Gaussian, utilizing the Gaussian-based constrained electrostatic potential (RESP) protocol based on the Gaussian-generated electrostatic potential (ESP), via B3LYP-D2(BJ)/def2-. The partial atomic charges of FA and LA were calculated at the TZVP level of theory. Sobtop was used to obtain the relevant files of FA and LA molecules for subsequent molecular dynamics simulations in Gromacs. During the simulation, 13 molecules of LA and 16 molecules of FA were randomly placed inside a square box with a side length of 7 nm and filled with 10,000 water molecules. Periodic boundary conditions (PBCs) were used for all three dimensions of the system. FA and LA molecules were modeled with the Generalized Amber Force Field (GAFF) force field, and water molecules were modeled with TIP4P. After the construction of the system was complete, the energy minimization of the 5000-step steepest descent method and the 5000-step conjugate gradient method was carried out to ensure that the system was structurally normal, that the atoms were not too close to each other, and that the geometrical configuration was reasonable. Once the system was at the energy minimum, the real kinetic simulation could be started. NVT warming kinetics were first performed for 1 ns, followed by NPT equilibration for 1 ns, and finally, the NPT system was selected for simulation for 50 ns. The integral solution algorithm used in the simulation was the leap-frog method with a time step of 2 fs. The long-range electrostatic interactions were calculated according to the cut-off method, and the truncation distance for non-bonding interactions was 1.0 nm. The pressure coupling was isotropic Parrinello-Rahman pressure coupling with the pressure controlled at 1 Pa. Temperature coupling was performed using the velocity-rescale hot-bath method. The linear constraint solver (LINCS) algorithm was used to constrain all the bonds. The simulation trajectory data, with an interval of 2 ps, were analyzed using the GROMACS software package (gromacs 2021.6) and visualized using VMD software (VMD 1.9.3) [38].

4. Conclusions

In this study, a bifunctional catalyst (Metalsx/4@WIFA-S) was synthesized from WIFA to maximize its high-value utilization, and its catalytic performances, possible reaction mechanism, as well as environmental risks were evaluated. The main conclusions were as follows:
  • After screening, Cu2/4@WIFA-S was identified as the best catalyst, and under the pure water system—when the reaction temperature was 180 °C, the reaction time was 4 h, the catalyst dosage was 1 g, and the concentration of glucose was 20 g/L—the glucose conversion rate was 99%, and the highest LA yield was 42.3%.
  • It was shown that GVL has a facilitating effect on the reaction that turns glucose into LA. When 10 mL of GVL was added to 50 mL of solvent system, glucose conversion was maintained at 99% and LA yield was 50.7%, which is an increase of 8.4% in LA yield as compared to water as the solvent.
  • The reaction kinetic analysis showed that the reaction energy barrier of glucose to LA was 51.33 kJ/mol when 20% GVL was added in the solvent system and 62.35 kJ/mol in the pure water system. The addition of appropriate GVL in the solvent system was favorable for the generation of LA from glucose. Molecular dynamics simulations showed that the addition of GVL provided a protective shell for LA, which reduced the possibility of side reactions of LA and thus improved the yield of LA.
  • The dioxin decomposition rate reached 99.87% following the preparation processes of WIFA, effectively achieving catalyst detoxification. The concentrations of all detected heavy metals in the reaction solution were below the standard limits set by GB 8978-1996 for the leaching toxicity of hazardous wastes. That is, it should be a promising approach with low environmental risk for WIFA to prepare value-added bifunctional catalysts for upgrading glucose to levulinic acid.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15040402/s1, Figure S1: SEM and EDS spectra of Cu@WIFA-S catalysts in different ratios; Figure S2: NH3-TPD plots of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S and Cu2/4@WIFA-S; Figure S3: Adsorption isotherm plot of Metalsx/4@WIFA-S catalyst N2; Figure S4: XRD patterns of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S and Cu2/4@WIFA-S catalysts; Table S1: Standard curve equations for glucose and related products; Text S1: Kinetic study.

Author Contributions

Conceptualization, R.Z.; Data curation, J.L. and S.L.; Funding acquisition, R.Z., X.L. (Xiaoyun Li), J.X., Z.Y. and X.L. (Xuebin Lu); Investigation, S.L.; Methodology, J.C., J.X., Z.Y. and X.L. (Xuebin Lu); Resources, J.C.; Software, D.C.; Validation, H.W.; Visualization, X.L. (Xuebin Lu); Writing—original draft, H.W.; Writing—review and editing, R.Z., J.L. and X.L. (Xiaoyun Li). All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (Grant No. 51908400, 52066017, 51876180, 52206293; 22308253), Tianjin Natural Science Foundation key project (23JCZDJC00430), Central Financial Support Special Funds for Local Universities (Tibet University) ([2023] No. 1, [2024] No. 1), and Science and Technology Plan of Qinghai Province (2022-GX-C13).

Data Availability Statement

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

Acknowledgments

The authors thank the financial support from the funding sources mentioned above.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Pan, Y.; Wu, Z.; Zhou, J.; Zhao, J.; Ruan, X.; Liu, J.; Qian, G. Chemical characteristics and risk assessment of typical municipal solid waste incineration (MSWI) fly ash in China. J. Hazard. Mater. 2013, 261, 269–276. [Google Scholar] [CrossRef] [PubMed]
  2. Wang, Y.; Liang, Y.; Wang, X.; Zhu, X.; Liu, X. Chlorine removal technologies for resource utilization of municipal solid waste incineration fly ash. Environ. Res. 2025, 268, 120784. [Google Scholar] [CrossRef]
  3. Ma, X.D.; Da, Y.; He, T.S.; Su, F.Y.; Wan, Z.M. Improvement of harmlessness and resource utilization of incineration fly ash by high temperature sintering. J. Build. Eng. 2024, 84, 108589. [Google Scholar] [CrossRef]
  4. Xiao, Y.X.; Huang, Y.J.; Cheng, H.Q.; Zhu, Z.C.; Yu, M.Z.; Xu, W.T.; Li, Z.Y.; Zuo, W.; Zhou, H.Y.; Jin, B.S. Advances and Outlook of Heavy Metal Treatment Technology from Municipal Solid Waste Incineration Fly Ash: A Review. Energy Fuels 2023, 38, 895–918. [Google Scholar] [CrossRef]
  5. Lawagon, C.P.; Faungnawakij, K.; Srinives, S.; Thongratkaew, S.; Chaipojjana, K.; Smuthkochorn, A.; Srisrattha, P.; Charinpanitkul, T. Sulfonated graphene oxide from petrochemical waste oil for efficient conversion of fructose into levulinic acid. Cat. Today 2021, 375, 197–203. [Google Scholar] [CrossRef]
  6. Pan, X.; Yan, J.; Xie, Z. Detoxifying PCDD/Fs and heavy metals in fly ash from medical waste incinerators with a DC double arc plasma torch. J. Environ. Sci. 2013, 25, 1362–1367. [Google Scholar] [CrossRef]
  7. Wu, H.-L.; Lu, S.-Y.; Yan, J.-H.; Li, X.-D.; Chen, T. Thermal removal of PCDD/Fs from medical waste incineration fly ash–effect of temperature and nitrogen flow rate. Chemosphere 2011, 84, 361–367. [Google Scholar] [CrossRef]
  8. De Greef, J.; Villani, K.; Goethals, J.; Van Belle, H.; Van Caneghem, J.; Vandecasteele, C. Optimising energy recovery and use of chemicals, resources and materials in modern waste-to-energy plants. Waste Manag. 2013, 33, 2416–2424. [Google Scholar] [CrossRef] [PubMed]
  9. Ma, B.; Yang, H.; Wang, Y. Overview of resources reuse technologies and corresponding products for municipal solid waste incineration fly ash. Environ. Chem. 2023, 42, 2669–2687. [Google Scholar]
  10. Ma, W.; Chen, D.; Pan, M.; Gu, T.; Zhong, L.; Chen, G.; Yan, B.; Cheng, Z. Performance of chemical chelating agent stabilization and cement solidification on heavy metals in MSWI fly ash: A comparative study. J. Environ. Manag. 2019, 247, 169–177. [Google Scholar] [CrossRef]
  11. Yu, D.; Li, Z.; Li, J.; He, J.; Li, B.; Wang, Y. Enhancement of H2 and light oil production and CO2 emission mitigation during co-pyrolysis of oily sludge and incineration fly ash. J. Hazard. Mater. 2024, 462, 132618. [Google Scholar] [CrossRef]
  12. Chen, X.; Liu, Y.; Yang, Y.; Ren, T.; Pan, L.; Fang, P.; Chen, D.; Cen, C. Modified fly ash from municipal solid waste incineration as catalyst support for Mn-Ce composite oxides. IOP Conf. Ser. Earth Environ. Sci. 2017, 18, 012146. [Google Scholar] [CrossRef]
  13. Feng, W.; Lu, X.; Xiong, J.; Yu, Z.; Wang, Y.; Cui, J.; Zhang, R.; Weng, R. Solid–Waste–Derived Geopolymer–Type Zeolite–like High Functional Catalytic Materials Catalyze Efficient Hydrogenation of Levulinic Acid. Catalysts 2022, 12, 1361. [Google Scholar] [CrossRef]
  14. de Guzman, D.; de Leon, R. Preliminary Optimization and Kinetics of SnCl2-HCl Catalyzed Hydrothermal Conversion of Microcrystalline Cellulose to Levulinic Acid. J. Renew. Mater. 2021, 9, 145–162. [Google Scholar] [CrossRef]
  15. Iris, K.; Hanif, A.; Tsang, D.C.; Yip, A.C.; Lin, K.-Y.A.; Gao, B.; Ok, Y.S.; Poon, C.S.; Shang, J. Tailoring acidity and porosity of alumina catalysts via transition metal doping for glucose conversion in biorefinery. Sci. Total Environ. 2020, 704, 135414. [Google Scholar]
  16. Zhang, X.; Zhang, X.; Sun, N.; Wang, S.; Wang, X.; Jiang, Z. High production of levulinic acid from cellulosic feedstocks being catalyzed by temperature-responsive transition metal substituted heteropolyacids. Renew. Energy 2019, 141, 802–813. [Google Scholar] [CrossRef]
  17. Taghavi, S.; Ghedini, E.; Menegazzo, F.; Giordana, A.; Cerrato, G.; Cruciani, G.; Di Michele, A.; Zendehdel, M.; Signoretto, M. Balanced acidity by microwave-assisted ion-exchange of ZSM-5 zeolite as a catalyst for transformation of glucose to levulinic acid. Biomass Convers. Biorefin. 2022, 14, 8251–8269. [Google Scholar] [CrossRef]
  18. Wu, Q.; Zhang, G.Y.; Gao, M.M.; Cao, S.S.; Li, L.; Liu, S.W.; Xie, C.X.; Huang, L.; Yu, S.T.; Ragauskas, A.J. Clean production of 5-hydroxymethylfurfural from cellulose using a hydrothermal/biomass-based carbon catalyst. J. Clean. Prod. 2019, 213, 1096–1102. [Google Scholar] [CrossRef]
  19. Zeng, D.L.; Zhang, Q.; Chen, S.Y.; Liu, S.L.; Wang, G.H. Synthesis porous carbon-based solid acid from rice husk for esterification of fatty acids. Microporous Mesoporous Mater. 2016, 219, 54–58. [Google Scholar] [CrossRef]
  20. Qi, L.; Mui, Y.F.; Lo, S.W.; Lui, M.Y.; Akien, G.R.; Horváth, I.T. Catalytic Conversion of Fructose, Glucose, and Sucrose to 5-(Hydroxymethyl)furfural and Levulinic and Formic Acids in γ-Valerolactone As a Green Solvent. ACS Catal. 2014, 4, 1470–1477. [Google Scholar] [CrossRef]
  21. Thiyam, D.S.; Nongmeikapam, A.C.; Nandeibam, A.D.; Heikham, F.D.; Henam, P.S. Biosynthesized Quantum Dot Size Cu Nanocatalyst: Peroxidase Mimetic and Aqueous Phase Conversion of Fructose. Chem. Sel. 2018, 3, 12183–12191. [Google Scholar] [CrossRef]
  22. Hu, L.; Wu, Z.; Xu, J.; Sun, Y.; Lin, L.; Liu, S. Zeolite-promoted transformation of glucose into 5-hydroxymethylfurfural in ionic liquid. Chem. Eng. J. 2014, 244, 137–144. [Google Scholar] [CrossRef]
  23. Tyagi, U.; Anand, N.; Kumar, D. Synergistic effect of modified activated carbon and ionic liquid in the conversion of microcrystalline cellulose to 5-Hydroxymethyl Furfural. Bioresour. Technol. 2018, 267, 326–332. [Google Scholar] [CrossRef]
  24. Shi, N.; Liu, Q.; Ju, R.; He, X.; Zhang, Y.; Tang, S.; Ma, L. Condensation of α-carbonyl aldehydes leads to the formation of solid humins during the hydrothermal degradation of carbohydrates. ACS Omega 2019, 4, 7330–7343. [Google Scholar] [CrossRef]
  25. Kumar, K.; Parveen, F.; Patra, T.; Upadhyayula, S. Hydrothermal Conversion of Glucose to Levulinic acid using Multifunctional Ionic Liquids: Effect of metal ion co-catalysts on Product Yield. New J. Chem. 2017, 42, 228–236. [Google Scholar] [CrossRef]
  26. Wu, Y.; Song, X.; Cai, F.; Xiao, G. Synthesis of glycerol carbonate from glycerol and diethyl carbonate over Ce-NiO catalyst: The role of multiphase Ni. J. Alloys Compd. 2017, 720, 360–368. [Google Scholar] [CrossRef]
  27. Ramli, N.A.S.; Amin, N.A.S. A new functionalized ionic liquid for efficient glucose conversion to 5-hydroxymethyl furfural and levulinic acid. J. Mol. Catal. A Chem. 2015, 407, 113–121. [Google Scholar] [CrossRef]
  28. Shan, H.; Li, L.; Bai, W.; Liu, L. Evolution Process of Humins Derived from Glucose. Chem. Sel. 2022, 7, e202201237. [Google Scholar] [CrossRef]
  29. Guo, H.; Duereh, A.; Su, Y.; Hensen, E.J.; Qi, X.; Smith, R.L., Jr. Mechanistic role of protonated polar additives in ethanol for selective transformation of biomass-related compounds. Appl. Catal. B Environ. 2020, 264, 118509. [Google Scholar] [CrossRef]
  30. Zhang, T.; Tang, Y.; Guo, S.; Cao, X.; Pan, A.; Fang, G.; Zhou, J.; Liang, S. Fundamentals and perspectives in developing zinc-ion battery electrolytes: A comprehensive review. Energy Environ. Sci. 2020, 13, 4625–4665. [Google Scholar] [CrossRef]
  31. Yu, P.; Liu, X.; Lei, Y.; Gao, Y.; Peng, H. Study on Restart Safety of Waxy Crude Pipelines Based on Reliability Principle under Constant Flow. ACS Omega 2022, 7, 10687–10694. [Google Scholar] [CrossRef]
  32. Mellmer, M.A.; Sanpitakseree, C.; Demir, B.; Ma, K.; Elliott, W.A.; Bai, P.; Johnson, R.L.; Walker, T.W.; Shanks, B.H.; Rioux, R.M.; et al. Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents. Nat. Commun. 2019, 10, 1132. [Google Scholar] [CrossRef] [PubMed]
  33. Antonetti, C.; Fulignati, S.; Licursi, D.; Raspolli Galletti, A.M. Turning point toward the sustainable production of 5-hydroxymethyl-2-furaldehyde in water: Metal salts for its synthesis from fructose and inulin. ACS Sustain. Chem. Eng. 2019, 7, 6830–6838. [Google Scholar] [CrossRef]
  34. Wei, W.; Wu, S. Experimental and kinetic study of glucose conversion to levulinic acid in aqueous medium over Cr/HZSM-5 catalyst. Fuel 2018, 225, 311–321. [Google Scholar] [CrossRef]
  35. Mushrif, S.H.; Caratzoulas, S.; Vlachos, D.G. Understanding solvent effects in the selective conversion of fructose to 5-hydroxymethyl-furfural: A molecular dynamics investigation. Phys. Chem. Chem. Phys. 2012, 14, 2637–2644. [Google Scholar] [CrossRef]
  36. Vasudevan, V.; Mushrif, S.H. Insights into the solvation of glucose in water, dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) and its possible implications on the conversion of glucose to platform chemicals. R. Soc. Chem. 2015, 5, 20756–20763. [Google Scholar] [CrossRef]
  37. Lin, Y.; Wei, G.; Liu, H.; Liu, Z.; Li, Q. Innovative Technology for Secondary Fly Ash Full Resource Utilization: Industrial Testing and Life Cycle Assessment Research. ACS Sustain. Chem. Eng. 2024, 12, 17770–17782. [Google Scholar] [CrossRef]
  38. Abraham, M.J.; Murtola, T.; Schulz, R.; Páll, S.; Smith, J.C.; Hess, B.; Lindahl, E. GROMACS: High performance molecularsimulations through multi-level parallelism from laptops to supercomputers. SoftwareX 2015, 1, 19–25. [Google Scholar] [CrossRef]
Catalysts 15 00402 g001
Figure 1. Reaction pathway diagram of glucose to LA.
Figure 1. Reaction pathway diagram of glucose to LA.
Catalysts 15 00402 g001
Catalysts 15 00402 g002
Figure 2. Effect of metal chloride on glucose conversion and downstream product distribution. Other reaction conditions: glucose concentration of 20 g/L at 180 °C for 4 h and 1 g of catalyst (metalx/4@WIFA-S).
Figure 2. Effect of metal chloride on glucose conversion and downstream product distribution. Other reaction conditions: glucose concentration of 20 g/L at 180 °C for 4 h and 1 g of catalyst (metalx/4@WIFA-S).
Catalysts 15 00402 g002
Catalysts 15 00402 g003
Figure 3. Effect of the metal loading ratio on glucose conversion and downstream product distribution. Other reaction conditions: glucose concentration of 20 g/L at 180 °C for 4 h and 1 g of Cux/4@WIFA-S.
Figure 3. Effect of the metal loading ratio on glucose conversion and downstream product distribution. Other reaction conditions: glucose concentration of 20 g/L at 180 °C for 4 h and 1 g of Cux/4@WIFA-S.
Catalysts 15 00402 g003
Catalysts 15 00402 g004
Figure 4. SEM images (A) and EDS distribution of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts ((B) metal elements, (C) S elements).
Figure 4. SEM images (A) and EDS distribution of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts ((B) metal elements, (C) S elements).
Catalysts 15 00402 g004
Catalysts 15 00402 g005
Figure 5. SEM images (A) and EDS (B) distribution of WIFA-S catalysts.
Figure 5. SEM images (A) and EDS (B) distribution of WIFA-S catalysts.
Catalysts 15 00402 g005
Catalysts 15 00402 g006
Figure 6. FT-IR curves of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts.
Figure 6. FT-IR curves of Zn2/4@WIFA-S, Fe2/4@WIFA-S, Al2/4@WIFA-S, and Cu2/4@WIFA-S catalysts.
Catalysts 15 00402 g006
Catalysts 15 00402 g007
Figure 7. (A) Effect of reaction temperature on the yield of LA from glucose. Other reaction conditions: the glucose concentration was 20 g/L, the time was 4 h, and Cu2/4@WIFA-S was 1 g. (B) Effect of reaction time on the yield of LA from glucose. Other reaction conditions: the glucose concentration was 20 g/L, the temperature was 180 °C, and Cu2/4@WIFA-S was 1 g. (C) Effect of catalyst dosage on the yield of LA from glucose. Other reaction conditions: reacted at 180 °C for 5 h with 1.5 g of Cu2/4@WIFA-S. (D) Effect of substrate concentration on the yield of LA from glucose. Other reaction conditions: reacted for 5 h at 180 °C with a glucose concentration of 20 g/L.
Figure 7. (A) Effect of reaction temperature on the yield of LA from glucose. Other reaction conditions: the glucose concentration was 20 g/L, the time was 4 h, and Cu2/4@WIFA-S was 1 g. (B) Effect of reaction time on the yield of LA from glucose. Other reaction conditions: the glucose concentration was 20 g/L, the temperature was 180 °C, and Cu2/4@WIFA-S was 1 g. (C) Effect of catalyst dosage on the yield of LA from glucose. Other reaction conditions: reacted at 180 °C for 5 h with 1.5 g of Cu2/4@WIFA-S. (D) Effect of substrate concentration on the yield of LA from glucose. Other reaction conditions: reacted for 5 h at 180 °C with a glucose concentration of 20 g/L.
Catalysts 15 00402 g007
Catalysts 15 00402 g008
Figure 8. Effect of different solvent systems (A) and percentages of GVL (B) on the yield of LA generated from glucose.
Figure 8. Effect of different solvent systems (A) and percentages of GVL (B) on the yield of LA generated from glucose.
Catalysts 15 00402 g008
Catalysts 15 00402 g009
Figure 9. (A) Spatial density distribution of water (blue) around LA. (B–E) Spatial density distribution of GVL (red) and H2O (blue) around LA.
Figure 9. (A) Spatial density distribution of water (blue) around LA. (B–E) Spatial density distribution of GVL (red) and H2O (blue) around LA.
Catalysts 15 00402 g009
Catalysts 15 00402 g010
Figure 10. Radial distribution function of the center of mass of solvent molecules with respect to LA.
Figure 10. Radial distribution function of the center of mass of solvent molecules with respect to LA.
Catalysts 15 00402 g010
Catalysts 15 00402 g011
Figure 11. Changes in dioxins substance content between WIFA-S and WIFA. Note: (A) Toxic equivalent (TEQ): converted to a mass concentration equivalent to 2,3,7,8-T4CDD. TEQ = ρ×i − TEF. (B) “N.D.” indicates that the measured mass concentration is below the limit of detection (LOD), and the TEQ mass concentration is calculated as 1/2 LOD.
Figure 11. Changes in dioxins substance content between WIFA-S and WIFA. Note: (A) Toxic equivalent (TEQ): converted to a mass concentration equivalent to 2,3,7,8-T4CDD. TEQ = ρ×i − TEF. (B) “N.D.” indicates that the measured mass concentration is below the limit of detection (LOD), and the TEQ mass concentration is calculated as 1/2 LOD.
Catalysts 15 00402 g011
Table 1. Physicochemical properties of different catalysts.
Table 1. Physicochemical properties of different catalysts.
No.CatalystSpecific Surface Area
(m2/g)		Pore Size
(nm)		Pore Volume
(cm3/g)		Amount of Weak Acid
(mmol/g)		Amount of Strong Acid
(mmol/g)		Total Acid Quantity
(mmol/g)
1Zn2/4@WIFA-S2383.034.380.6211.6812.302
2Fe2/4@WIFA-S2673.075.610.1582.1662.324
3Al2/4@WIFA-S846.750.160.152.1172.267
4Cu2/4@WIFA-S1903.780.508.27316.06924.342
5WIFA-S3995.158.33———
Table 2. Kinetic parameters of glucose dehydration and HMF rehydration in H2O and different ratios of GVL/H2O solvent systems.
Table 2. Kinetic parameters of glucose dehydration and HMF rehydration in H2O and different ratios of GVL/H2O solvent systems.
Solvent SystemsTem.
(°C)		Glucose Dehydration
KG		Ea
(kJ/mol)		HMF Rehydration
KH		Ea
(kJ/mol)
H2O1600.0676954.950.110137.4
1800.08810.12427
2000.249560.13086
15% GVL1600.1020918.370.340825.05
1800.127090.3985
2000.157270.617
20% GVL1600.382930.380.0815120.95
1800.463880.14557
2000.628010.16549
25% GVL1600.0896144.450.393250.84
1800.162110.7683
2000.254511.2985
Table 3. Evaluation of heavy metal leaching.
Table 3. Evaluation of heavy metal leaching.
Test ElementsReaction Solution
(mg/L)		Standard Limit Value
(Class I Standard of GB8978–1996)
(mg/L)
Cu0.021≤0.5
ZnN.A.≤2
Pb0.442≤1
Cd0.100≤0.1
Table 4. Composition of raw materials.
Table 4. Composition of raw materials.
NameCaOSO3SiO2ClFe2O3MgOAl2O3K2OTiO2ZaOLOI
WIFA57.2710.735.554.53.572.451.472.931.11.7219.8
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhang, R.; Wu, H.; Li, J.; Chen, D.; Li, S.; Chen, J.; Li, X.; Xiong, J.; Yu, Z.; Lu, X. Waste Incineration Fly Ash-Based Bifunctional Catalyst for Upgrading Glucose to Levulinic Acid. Catalysts 2025, 15, 402. https://doi.org/10.3390/catal15040402

AMA Style

Zhang R, Wu H, Li J, Chen D, Li S, Chen J, Li X, Xiong J, Yu Z, Lu X. Waste Incineration Fly Ash-Based Bifunctional Catalyst for Upgrading Glucose to Levulinic Acid. Catalysts. 2025; 15(4):402. https://doi.org/10.3390/catal15040402

Chicago/Turabian Style

Zhang, Rui, Han Wu, Jiantao Li, Dezhi Chen, Shimin Li, Jiale Chen, Xiaoyun Li, Jian Xiong, Zhihao Yu, and Xuebin Lu. 2025. "Waste Incineration Fly Ash-Based Bifunctional Catalyst for Upgrading Glucose to Levulinic Acid" Catalysts 15, no. 4: 402. https://doi.org/10.3390/catal15040402

APA Style

Zhang, R., Wu, H., Li, J., Chen, D., Li, S., Chen, J., Li, X., Xiong, J., Yu, Z., & Lu, X. (2025). Waste Incineration Fly Ash-Based Bifunctional Catalyst for Upgrading Glucose to Levulinic Acid. Catalysts, 15(4), 402. https://doi.org/10.3390/catal15040402

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop