Modulating oxygen vacancies in Pt-WOx-decorated MOF-74(Co) catalysts for the efficient conversion of glucose to 1,2-propanediol under mild conditions
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Abstract
Selective conversion of glucose to valuable 1,2-propanediol (1,2-PDO) has been a research priority, but the process often suffers from problems such as harsh reaction conditions. Therefore, the development of efficient catalysts for the efficient synthesis of 1,2-PDO from glucose under mild conditions is essential. Herein, we prepared Pt-WOx-metal-organic framework (MOF)-74(Co) catalysts by a simple two-step method, achieving a high yield of 52.9% of 1,2-PDO under milder conditions (160 °C, 0.2 MPa H2, 4 h), surpassing the majority of recent studies in this field. High-resolution transmission electron microscopy (HRTEM) revealed that Pt nanoparticles (~2.1 nm) and WOx species were uniformly dispersed within the structure of MOF-74(Co). The experimental results confirmed that MOF-74(Co) facilitated the isomerization of glucose into fructose, which then underwent further conversion to yield 1,2-PDO. In addition, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and NH3 temperature-programmed desorption (NH3-TPD) results revealed that Pt-WOx-MOF-74(Co) has more oxygen vacancies to act as acidic sites. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) further confirmed the efficient conversion of glucose to intermediate and final products over Pt-WOx-MOF-74(Co). Furthermore, cycling experiments confirmed that Pt-WOx-MOF-74(Co) can be reused several times. This is the first report that MOFs can be employed as the catalyst support in facilitating glucose conversion to diols, which provides important guidance for using MOFs in biomass utilization in the future.
Keywords
INTRODUCTION
With the depletion of traditional fossil resources, the efficient conversion of renewable biomass into liquid fuels and high-value-added chemicals has attracted widespread attention[1-4]. Among them, 1,2-propanediol (1,2-PDO) is a critical raw material for the synthesis of useful chemicals, such as surfactants, plasticizers, and surfactants, as well as a final product for applications in the pharmaceutical, food, and refrigeration industries[5,6]. Typical production methods for 1,2-PDO include petroleum product conversion, glycerol hydrogenolysis, and direct biomass hydrogenolysis[7,8]. Comparatively, the hydrogenolysis of biomass is considered to be green-friendly with sufficient bio-feedstocks such as polysaccharides (e.g., stalks and cellulose)[9] and monosaccharides (e.g., glucose and fructose)[10]. Among them, it is significant to attack the glucose conversion pathway because glucose is not only the starting material for the production of 1,2-PDO but also an important intermediate for the conversion of polysaccharide biomass to 1,2-PDO.
However, during the preparation of 1,2-PDO, glucose undergoes multiple reaction pathways
Since metal oxide carriers can act as electronic modulators for noble metal nanoparticles, a variety of metal oxides have been used to support noble metal nanoparticles (e.g., Ru, Pt, Pd) for selective hydrogenolysis of glucose in the aqueous phase[15,17-21]. For example, Lv et al. synthesized Pd@Al-MSiO2 yolk-shell structured nanospheres for the catalytic preparation of 1,2-PDO from glucose, which showed a 1,2-PDO yield of 22.7% after a reaction at 200 °C, 5 MPa, for 3 h[18]. The Pd@Al-MSiO2 utilized its unique core-shell structure to provide an active site for the RAC reaction of fructose. In a previous study, Gu et al. constructed a
In our prior research[22], we observed that the Ru-WOx-MgOy efficiently facilitated the conversion of fructose into 1,2-PDO under moderate experimental conditions. However, when glucose was used as the substrate, the resulting yield of 1,2-PDO was disappointing. Therefore, we prepared Pt-WOx-metal-organic framework (MOF)-74(Co) catalysts with MOF-74(Co) as a carrier by in situ synthesis for the selective hydrogenolysis of glucose to 1,2-PDO. MOFs are a novel class of materials that have attracted much attention due to their distinctive structural and functional properties. They have been applied in a wide range of fields, especially in environmental management and energy applications[23-25]. Recently, many studies have designed MOFs-supported noble metal catalysts and shown excellent catalytic performance for biomass conversion[26,27]. However, these noble metal particles are usually dispersed on the outer surface of MOFs and can easily aggregate to some extent.
Herein, Pt-WOx-MOF-74(Co) catalysts were facilely constructed and Pt nanoparticles (Pt NPs) (~2.1 nm) along with WOx species were observed to be highly uniformly dispersed on the surface of MOF-74(Co) by high-resolution transmission electron microscopy (HRTEM). Employing milder reaction parameters, specifically a temperature of 160 °C, a H2 pressure of 0.2 MPa, and a reaction time of 4 h, Pt-WOx-MOF-74(Co) was able to fully convert glucose with a yield of 1,2-PDO as high as 52.9%. The experimental results revealed that the MOF-74(Co) catalyst enhanced the isomerization of glucose into fructose, thereby subsequently boosting the generation of 1,2-PDO. Moreover, a series of characterizations such as X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and NH3 temperature-programmed desorption (NH3-TPD) suggested that WOx modulated the oxygen vacancies of MOF-74(Co), thereby generating additional acidic sites, which was beneficial for glucose isomerization and RAC reactions. According to in situ diffuse reflectance infrared Fourier transform (DRIFT), the Pt-WOx-MOF-74(Co) facilitated the conversion of glucose into intermediate and final products, which was dynamically detected. In conclusion, a certain synergy exists between Pt NPs, WOxand MOF-74(Co), contributing to the high yield of 1,2-PDO. This work reports for the first time that MOFs can be used to convert glucose to lower diols in aqueous systems without structural damage and can be recycled many times. It breaks the spell that the structure of MOF materials will collapse in an aqueous solution environment with higher temperatures.
EXPERIMENTAL
Catalyst preparation
Synthesis of MOF-74(Co)
MOF-74(Co) was synthesized according to the previous work[28]. First, 273 mg of Co(NO3)2·6H2O and
Synthesis of WOx and Pt-WOx
WOx was synthesized according to the previously reported method[29]. A solution was prepared by dissolving 600 mg of WCl6 in anhydrous ethanol (25 mL), which yielded a yellow solution. This solution was subsequently poured into a 50 mL Teflon-coated autoclave, which was then subjected to heating at a temperature of 160 °C for a period of 24 h. Once the heating process was complete, the autoclave was allowed to cool down to ambient temperature. The blue-colored WOx precipitate, which had formed on the interior lining, was isolated by means of centrifugation. The precipitate was subsequently rinsed with deionized water and then dried under vacuum conditions in an oven set at 80 °C for the duration of one night. Pt-WOx was synthesized in a similar way as WOx, except that Na2PtCl6·6H2O was added to the precursor. The actual Pt content in Pt-WOx was 1.2 wt% measured by inductively coupled plasma optical emission spectroscopy (ICP-OES).
Synthesis of WOx-MOF-74(Co)
A mixture consisting of 200 mg of MOF-74(Co) and 30 mg of WCl6 was prepared by dissolving it in anhydrous ethanol (25 mL). This mixture was then poured into a 50 mL autoclave that was Teflon-lined, and the autoclave was heated to a temperature of 160 °C for 24 h. Following this, the autoclave was allowed to cool down to ambient temperature. The resulting solid product was subsequently washed with ethanol and then subjected to drying in a vacuum oven at a temperature of 80 °C for an entire night.
Synthesis of Pt-MOF-74(Co)
A mixture consisting of 200 mg of MOF-74(Co) and 10 mg of Na2PtCl6·6H2O was prepared by dissolving it in anhydrous ethanol (25 mL). This mixture was then poured into the 50 mL autoclave that was Teflon-lined, and the autoclave was heated to a temperature of 160 °C for 24 h. Following this, the autoclave was allowed to cool down to ambient temperature. The resulting solid product was subsequently washed with ethanol and then subjected to drying in a vacuum oven at a temperature of 80 °C for an entire night. The actual Pt content in Pt-MOF-74(Co) was 1.2 wt%.
Synthesis of Pt-WOx-MOF-74(Co) and Pt/WOx-MOF-74(Co)
A mixture consisting of 200 mg of MOF-74(Co), 30 mg of WCl6 and 10 mg of Na2PtCl6·6H2O was prepared by dissolving it in anhydrous ethanol (25 mL). This mixture was then poured into a 50 mL autoclave that was Teflon-lined, and the autoclave was heated to a temperature of 160 °C for 24 h. Following this, the autoclave was allowed to cool down to ambient temperature. The resulting solid product was subsequently washed with ethanol and then subjected to drying in a vacuum oven at a temperature of 80 °C for an entire night. The actual Pt content in Pt-WOx-MOF-74(Co) was 1.4 wt%. The Pt/WOx-MOF-74(Co) catalyst was prepared by impregnating WOx-MOF-74(Co) with Na2PtCl6·6H2O, followed by a reduction process using hydrogen gas at a temperature of 200 °C for 4 h, resulting in the formation of Pt/WOx-MOF-74(Co). The actual Pt content in Pt/WOx-MOF-74(Co) was 1.2 wt%.
Catalytic reaction
The glucose catalytic conversion experiment was carried out in a 25 mL homemade stainless autoclave, and the results were analyzed by high-performance liquid chromatography (HPLC). The glucose conversion and product yield were calculated using glucose conversion (%) = 100% × (carbon atoms in the converted glucose) / (carbon atoms in the initial glucose); yield of product (%) = 100% × (carbon atoms in the product) / (carbon atoms in the initial glucose). Some by-products (such as aldehydes, carboxylic acids, furan compounds, humins, etc.) were not individually quantified, and no gaseous product was generated confirmed by gas chromatography (GC) analysis. The specific operation steps and analytic method were shown in the Supplementary Materials.
RESULTS AND DISCUSSION
Characterization of the prepared catalysts
MOF-74(Co) was synthesized according to the previously reported methods[28,30] with slight modifications and then reacted with WCl6 and Na2PtCl6·6H2O to obtain Pt-WOx-MOF-74(Co) [Figure 1A]. The morphology of the synthesized product was described by transmission electron microscopy (TEM). As shown in Supplementary Figure 2A and B, MOF-74(Co) exhibited an irregular morphology, while WOx presented a blooming flower-like structure. After modification with WOx, WOx-MOF-74(Co) still displayed irregular morphology [Supplementary Figure 2C]. Figure 1B reveals that the incorporation of Pt did not change the flower-like morphology of WOx. Notably, Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) surfaces exhibited distinct metal nanoparticles [Supplementary Figure 3], with particle size distribution plots showing an average nanoparticle size of approximately 2.1 nm [Figure 1C and D]. High-angle annular dark field scanning TEM (HAADF-STEM) images along the [001] crystal axis of Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) are presented in Figure 1E and F. The MOF-74(Co) and WOx-MOF-74(Co) frameworks remained crystalline post Pt loading, as confirmed by the Fourier transform in the inset images. The bright contrast features (examples marked with circles) in the HAADF-STEM images correspond to Pt NPs. These nanoparticles exhibited a relatively uniform size, larger than the pore size, indicating the presence of highly dispersed metal nanoparticles on the surface of Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co). The predominant fraction of the nanoparticles was crystallized Pt NPs, as evidenced by the HRTEM images
Figure 1. (A) Diagram of the preparation process of Pt-WOx-MOF-74(Co); (B-D) TEM pictures of Pt-WOx, Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co); (E and F) HAADF-STEM images from the [110] projection of Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co); (G) HAADF-STEM image of Pt-WOx; (H-J) EDS elemental mappings of Pt-WOx, Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co). MOF: Metal-organic framework; TEM: transmission electron microscopy; HAADF-STEM: high-angle annular dark field scanning TEM; EDS: energy-dispersive X-ray spectroscopy.
The crystal structure of the catalysts was determined by X-ray powder diffractometry (XRD). As displayed in Figure 2A and Supplementary Figure 6A, the positions of the first two peaks of WOx-MOF-74(Co), Pt-MOF-74(Co), and Pt-WOx-MOF-74(Co) matched well with the MOF-74(Co), indicating the Pt NPs and WOx did not disrupt the crystal structure of MOF-74(Co). As a comparison, the XRD patterns of WOx and Pt-WOx were also measured and the results were identical to the literature[29]. There were no diffraction peaks belonging to WOx and Pt NPs (PDF#04-0802) in Pt-WOx-MOF-74(Co), probably due to the low content [Supplementary Table 1] and high dispersion of WOx and Pt NPs. Thus, it was illustrated by XRD, ICP and TEM that Pt NPs were highly distributed on the MOF-74(Co) surface.
Figure 2. (A) XRD patterns, (B) FTIR spectra, (C) N2 adsorption-desorption isotherms and (D) pore size distribution plots of the synthesized samples. XRD: X-ray powder diffractometry; FTIR: Fourier transform infrared.
In addition, the Fourier transform infrared (FTIR) spectroscopy of the samples was performed [Figure 2B and Supplementary Figure 6B] to further validate the composition of the catalysts. The peaks were assigned as follows: 1,555 cm-1 represented the stretching vibration of C=O; 1,409 cm-1 represented the framework vibration of benzene ring; 1,243 and 1,193 cm-1 represented the stretching vibration of C–O; 883 and
The N2 adsorption/desorption isotherms of the catalyst were shown in Figure 2C and Supplementary Figure 6C. Depending on the International Union of Pure and Applied Chemistry (IUPAC) classification of isotherm profiles[35], the isotherms of MOF-74(Co), WOx-MOF-74(Co), Pt-MOF-74(Co), and Pt-WOx-MOF-74(Co) were of type I, showing their microporous structures. MOF-74(Co), WOx-MOF-74(Co), Pt-MOF-74(Co), and Pt-WOx-MOF-74(Co) had large specific surface areas of 818, 699, 790, and 180 m2·g-1, respectively, which favored their catalytic activities. The decreased specific surface area of Pt-WOx-MOF-74(Co) compared to MOF-74(Co) may be related to the occupation of MOF pores by Pt NPs and WOx, which could also be seen from their pore volumes [Figure 2D, Supplementary Figure 6D and Supplementary Table 1], which were 0.7 and 0.2 cm3·g-1 for MOF-74(Co) and Pt-WOx-MOF-74(Co), respectively.
The transformation of glucose into diols catalyzed by the synthesized catalysts
In aqueous-based reaction solutions, the reaction activity and product yields are significantly affected by the reaction parameters, including temperature and time. Consequently, an in-depth analysis was conducted to examine the impact of various reaction parameters, such as temperature, time, and catalyst dosage, on both the conversion of glucose and the yield of 1,2-PDO. The temperature dependence of glucose conversion was shown in Figure 3A. At a temperature of 140 °C, the conversion of glucose and the yield of 1,2-PDO were found to be 68.1% and 27.2%, respectively, which indicated a lower hydrogenolysis rate. When the reaction temperature was increased from 140 to 160 °C, the conversion increased to 100% and the yield of 1,2-PDO increased to 52.9%, the phenomenon suggesting that high temperature was an important factor in facilitating the reaction. However, a sustained increased in temperature to 180 °C resulted in a decreased in 1,2-PDO yield to 45.6%, which may be because high temperature promoted the dehydration reaction, resulting in cyclization and partial polycondensation of 1,2-PDO; thus, the production of 1,2-PDO was reduced. As displayed in Figure 3B, the reaction time was also an important factor affecting the conversion and product yield. For reaction durations shorter than 4 h, the glucose conversion did not exceed 80%, and the yield of 1,2-PDO remained below 25%. Extending the reaction time to 4 h, both the conversion and 1,2-PDO yield peaked at 100% and 52.9%, respectively. Prolonged reaction durations led to a reduction in the yield of 1,2-PDO. Consequently, a reaction duration of 4 h was identified as the most effective for maximizing 1,2-PDO production. As depicted in Figure 3C, the catalyst dosage significantly influences the yield of 1,2-PDO. Experimental results indicated that when the catalyst dosage is increased to 25 mg, the yield of 1,2-PDO reaches 33.4%. Further increasing the catalyst dosage to 100 mg elevated the 1,2-PDO yield to 45.6%. However, compared with the 52.6% yield of 1,2-PDO obtained with 50 mg of catalyst, additional increments in catalyst amount did not further enhance the yield. Consequently, it can be concluded that an optimal amount of catalyst is sufficient to effectively facilitate the conversion of glucose to 1,2-PDO, and excess catalyst does not contribute to increased yields. These findings provide empirical evidence for optimizing catalyst usage, contributing to the economic and efficient nature of the catalytic process.
Figure 3. The influence of various reaction parameters on the conversion of glucose and the yield of diols using the Pt-WOx-MOF-74(Co), (A) temperature, (B) reaction time, and (C) Pt-WOx-MOF-74(Co) dosage; (D) The catalytic conversion of glucose to 1,2-PDO across a range of catalysts. Reaction conditions: glucose (100 mg), catalyst (50 mg) and water (10 mL), conducted at 160 °C, 0.2 MPa of H2, for a period of 4 h. MOF: Metal-organic framework; 1,2-PDO: 1,2-propanediol.
In order to interpret more rigorously the effect of Pt-WOx-MOF-74(Co) on glucose hydrogenolysis, the catalytic performance of Pt-WOx-MOF-74(Co) was tested and compared with other catalysts [Figure 3D]. When no catalyst was present, glucose conversion was as low as 62.7% and 1,2-PDO was almost absent from the liquid phase product. When MOF-74(Co) or WOx was used as a catalyst, glucose conversion was increased to 87.2% and 99.8%, respectively, but 1,2-PDO yields were lower than 10% for both. WOx-MOF-74(Co) increased the yield of 1,2-PDO to 11.4%, indicating that WOx favored the generation of 1,2-PDO. Considering the effect of the carriers, the activities of Pt-MOF-74(Co) and Pt-WOx were compared, and their conversions were 86.1% and 99.6%, while the 1,2-PDO yields were 21.5% and 6.7%, respectively, suggesting that MOF-74(Co) was the main reason to the great selectivity of 1,2-PDO. We physically mixed the samples [Pt-WOx mixed with MOF-74(Co) or Pt-MOF-74(Co)] and found that mixing Pt-WOx with Pt-MOF-74(Co) improved the conversion and 1,2-PDO yield to 99.8% and 21.7%, respectively. Under identical reaction parameters, the Pt-WOx-MOF-74(Co) achieved a 1,2-PDO yield of up to 52.9%, surpassing numerous outcomes documented in the existing literature, as detailed in Supplementary Table 2. Wang
The 1,2-PDO yield of Pt/WOx-MOF-74(Co) synthesized by the impregnation method was 37.7%, which was much lower than that of Pt-WOx-MOF-74(Co). On the one hand, the specific surface area of Pt/WOx-MOF-74(Co) was known to be 90 m2·g-1 through Supplementary Table 1, indicating that the active site of Pt/WOx-MOF-74(Co) was lower than that of Pt-WOx-MOF-74(Co). XRD [Supplementary Figure 7A] tests showed that Pt/WOx-MOF-74(Co) presented a similar structure to that of Pt-WOx-MOF-74(Co). A TEM image
We compared the glucose conversion, fructose yield and 1,2-PDO yield of Pt-WOx, Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) at 140 °C [Figure 4]. The glucose conversion of Pt-WOx, Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) showed an upward trend with increasing reaction time, suggesting that glucose was continuously converted to the target products (e.g., fructose and 1,2-PDO). When the reaction time was 2 h, we found that more fructose was produced when MOF-74(Co) was present, and as the time increased, the fructose decreased, implying that the fructose was further converted to some product (probably 1,2-PDO). For Pt-WOx, the decrease of fructose did not promote the generation of 1,2-PDO [Figure 4A], whereas, for Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) [Figure 4B and C], the increment in 1,2-PDO corresponded to a reduction in fructose, further confirming that 1,2-PDO was the primary conversion product derived from fructose. The 1,2-PDO yield of Pt-WOx-MOF-74(Co) decreased when the reaction time was extended to
Figure 4. The glucose conversion, fructose yield and 1,2-PDO yield of Pt-WOx, Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co). Reaction conditions: glucose (100 mg), catalyst (50 mg) and water (10 mL), 140 °C, 0.2 Mpa of H2. 1,2-PDO: 1,2-Propanediol; MOF: metal-organic framework.
An in-depth study on the superior catalytic performance of Pt-WOx-MOF-74(Co)
To reveal the reason for the excellent activity of Pt-WOx-MOF-74(Co) at a deeper level, we next performed a series of characterization analyses. XPS was utilized to analyze the surface components and chemical states of the catalysts. Figure 5A showed the W 4f XPS spectrum of Pt-WOx and Pt-WOx-MOF-74(Co); the peaks located at 35.5 and 37.7 eV could be attributed to W 4f7/2 and W 4f5/2 of the W5+ species, whereas the other double peaks located at 36.1 and 38.3 eV could be attributed to W 4f7/2 and W 4f5/2 of the W6+ species, respectively[37]. The W5+/W6+ of Pt-WOx and Pt-WOx-MOF-74(Co) were 0.4 and 0.6 [Supplementary Table 3], respectively, suggesting that more W6+ species in Pt-WOx-MOF-74(Co) were reduced to W5+ species, subsequently creating a higher concentration of oxygen vacancies[38-40]. Oxygen vacancies could be used as Lewis acid sites[41,42], suggesting that Pt-WOx-MOF-74(Co) had higher acid content.
Figure 5. (A) W 4f XPS, (B) EPR of these three catalysts. XPS: X-ray photoelectron spectroscopy; EPR: electron paramagnetic resonance.
In the analysis of XPS, the O1s peak of the Pt-WOx catalyst [Supplementary Figure 9] could be resolved into a triplet structure. These peaks were attributed to lattice oxygen (Olat), hydroxyl oxygen (O–H), and adsorbed oxygen atoms on the surface (Oads)[43,49]. Similarly, the O1s XPS peak of the Pt-WOx-MOF-74 (Co) catalyst [Supplementary Figure 9] also exhibited a triplet feature, corresponding to C=O, O–H, and Co–O bonds[43-45,50]. The existence of oxygen vacancies was confirmed by EPR, as illustrated in Figure 5B. The EPR signal observed at g = 2.002 is indicative of electrons being trapped within oxygen vacancy sites[51-53]; it is reasonable to infer that Pt-WOx-MOF-74(Co) had significant oxygen vacancies.
Considering that suitable acid sites played a key role in facilitating the biomass conversion process, the acid sites of the catalyst were detected using pyridine-adsorbed DRIFT spectroscopy (DRIFTS) [Figure 6A-C]. The absorption bands at 1,451 and 1,600 cm-1 in the spectrum were assigned to Lewis acid sites, whereas the bands at 1,538 and 1,664 cm-1 were indicative of Brönsted acid sites. Additionally, the band observed at 1,488 cm-1 represented a combined feature of both Lewis and Brönsted acid sites[54,55]. Pyridine desorption was noted to occur from Pt-WOx at a temperature of 300 °C. In contrast, the pyridine molecules adsorbed onto both Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) exhibited negligible desorption at the same temperature, maintaining their stability. The aforementioned results revealed that MOF-74(Co) was favorable to maintaining the acid strength stable, but the better activity of Pt-WOx-MOF-74(Co) compared with Pt-MOF-74(Co) deserved to be further explored.
Figure 6. Pyridine-adsorbed DRIFTS spectra of (A) Pt-WOx, (B) Pt-MOF-74(Co) and (C) Pt-WOx-MOF-74(Co); (D) NH3-TPD-MS curve of Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co). DRIFTS: Diffuse reflectance infrared Fourier transform spectroscopy; MOF: metal-organic framework; NH3-TPD: NH3 temperature-programmed desorption.
The intensity and total acid amount of the acidic sites of Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) were determined using NH3-TPD curves. Figure 6D illustrated that the Pt-MOF-74(Co) and Pt-WOx-MOF-74(Co) exhibited two significant peaks within the temperature region of approximately 500 °C, indicative of the presence of strong acid sites within their structures. The total acid amount was 5.9 mmol·g-1 in Pt-WOx-MOF-74(Co) and 3.3 mmol·g-1 in Pt-MOF-74(Co) [Supplementary Table 1], suggesting that the incorporation of WOx into the Pt-WOx-MOF-74(Co) enhanced the creation of acidic sites, which was consistent with the EPR.
Further investigation of the conversion of glucose to 1,2-PDO by in situ DRIFTS
The in situ DRIFTS spectra of chemoselective transformation process of glucose were shown in Figure 7. Single Pt-WOx-MOF-74(Co) and glucose-impregnated Pt-WOx-MOF-74(Co) [Pt-WOx-MOF-74(Co)-G] were kept at room temperature for 30 min (black line). As the temperature increased, a series of distinct bands appeared in Pt-WOx-MOF-74(Co), in which the bands near 1,000-1,500 cm-1 and at 1,608 cm-1 were from the C–O and C=O bonds of the catalyst, respectively[56,57]. The bands of Pt-WOx-MOF-74(Co)-G located around 1,000-1,500 cm-1 were different from those of Pt-WOx-MOF-74(Co), suggesting that these were C–O belonging to glucose, and as the temperature increased, the bands around 1,000-1,150 cm-1 receded significantly due to the glycosidic bonds and pyran rings cleavaged into volatiles[57]. Furthermore, the carbonyl group (C=O) absorption band at 1,777 cm-1[56] began to manifest around 100 °C, with its intensity escalating as the temperature rose, peaking at approximately 200 °C. The increase in the C=O signal corresponds to the primary phase of glucose conversion[58], indicating that the C–O and C–C bonds in the glucose molecule were cleaved to form intermediates[57,59]. The aforementioned findings confirm the effective transformation of glucose into intermediate compounds facilitated by the Pt-WOx-MOF-74(Co) catalyst, subsequently leading to the production of 1,2-PDO.
Figure 7. DRIFTS spectroscopy of (A) single Pt-WOx-MOF-74(Co) and (B) glucose-impregnated Pt-WOx-MOF-74(Co) at varying temperatures. DRIFTS: Diffuse reflectance infrared Fourier transform spectroscopy; MOF: metal-organic framework.
Stability experiments of Pt-WOx-MOF-74(Co) and the generalization in raw biomass conversion
The recycling experiment of Pt-WOx-MOF-74(Co) was shown in Supplementary Figure 10A. The catalyst, after the reaction, was recovered by centrifugation, rinsed extensively with ethanol, and then vacuum-dried overnight in an oven before proceeding to the next reaction cycle. It can be seen that such catalyst activity decreased slightly during six consecutive cycles. XRD pattern of the recycled catalyst [Supplementary Figure 10B] maintained its crystallinity during the recycling tests. Although thermal filtration tests showed that the yield of 1,2-PDO maintained around 20% after removing Pt-WOx-MOF-74(Co) from the reaction mixture
In order to investigate the generalization of Pt-WOx-MOF-74(Co) in the reaction of raw biomass conversion for the preparation of diols, several different biomasses were selected as reactants. As shown in Supplementary Table 4, Pt-WOx-MOF-74(Co) could rapidly prepare 1,2-PDO from corncob, xylan, and starch, whose yields were 26.5%, 30.4%, and 27.9%, respectively, confirming the generalizability of Pt-WOx-MOF-74(Co) in the preparation of 1,2-PDO-derived biomass. However, the yield of 1,2-PDO derived from these substrates was much lower than that from glucose, which was mainly due to the difficulty of hydrolysis of these substrates to active mono-carbohydrates over Pt-WOx-MOF-74(Co) catalyst. Future work to improve 1,2-PDO yield from raw biomass is still ongoing.
CONCLUSIONS
The synergistic interaction of Pt NPs, WOx and MOF-74(Co) was realized by a facile and efficient two-step method. The synthesized Pt-WOx-MOF-74(Co) demonstrated superior catalytic activity for the conversion of biomass into 1,2-PDO. When glucose was used as the substrate, the yield of 1,2-PDO was as high as 52.9% under milder reaction conditions (160 °C, 0.2 MPa H2, 4 h), which outperformed most of other reported catalysts. Moreover, the catalyst was able to be reused several times. The reason for the efficient catalytic activity of Pt-WOx-MOF-74(Co) was explained in detail by various characterization results including XPS, EPR, NH3-TPD, etc. This work contributed to the design of efficient MOF catalysts for the production of high-value-added chemicals from biomass.
DECLARATIONS
Authors’ contributions
Manuscript design, preparation, and revision: Luo, S.; Wang, J.
Manuscript discussion and preparation: Luo, S.; Mao, M.; Yu, H.; Zheng, Y.; Liu, Z.; Liu, L.; Wang, J.
Availability of data and materials
The detailed materials and methods in the experiment were listed in the Supplementary Materials. Other raw data that support the findings of this study are available from the corresponding author upon reasonable request.
Financial support and sponsorship
Wang, J. is grateful for the financial support from Chongqing Human Resources and Social Security Bureau Project (cx2024049), State Key Laboratory of Coal Mine Disaster Dynamics and Control (2011DA105287- MS202203), Natural Science Foundation of Chongqing (CSTB2022NSCQ-MSX0458), and Joint Fund for Innovation and Development of Chongqing (CSTB2022NSCQ-LZX0030). Liu, L. acknowledges the financial support from the National Natural Science Foundation of China (22105028) and the Natural Science Foundation of Chongqing (cstc2021jcyj-msxmX0572). Liu, Z. appreciates the financial support from the National Natural Science Foundation of China (22102013). This research used resources from the Analytical and Testing Center of Chongqing University.
Conflicts of interest
All authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2025.
Supplementary Materials
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Luo, S.; Mao, M.; Yu, H.; Zheng, Y.; Liu, Z.; Liu, L.; Wang, J. Modulating oxygen vacancies in Pt-WOx-decorated MOF-74(Co) catalysts for the efficient conversion of glucose to 1,2-propanediol under mild conditions. Chem. Synth. 2025, 5, 35. http://dx.doi.org/10.20517/cs.2024.197
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