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Article

Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

by
Xiaoguang San
1,
Xiaohui Gong
1,
Yiming Lu
1,
Juhua Xu
2,
Liming He
2,
Dan Meng
1,*,
Guosheng Wang
1,
Jian Qi
3,4,* and
Quan Jin
2,*
1
College of Chemical Engineering, Shenyang University of Chemical Technology, Shenyang 110142, China
2
Key Laboratory of Automobile Materials (Ministry of Education), School of Materials Science and Engineering, Jilin University, Changchun 130022, China
3
State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, 1 North 2nd Street, Zhongguancun, Haidian District, Beijing 100190, China
4
School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
*
Authors to whom correspondence should be addressed.
Catalysts 2022, 12(11), 1326; https://doi.org/10.3390/catal12111326
Submission received: 19 September 2022 / Revised: 18 October 2022 / Accepted: 25 October 2022 / Published: 28 October 2022
(This article belongs to the Special Issue Hollow and Porous Micro-/Nanostructured Materials in Catalysis)
Browse Figures
Review Reports Versions Notes

Abstract

:
Recently, the Cu-based catalyst has attracted wide attention for the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) due to its high catalytic activity and it is low cost. However, its poor stability, ease of agglomeration, and the short life of the catalyst restrict its further development in industrial applications. Here, we constructed a novel MOF-derived Cu/SiO2 catalyst (MOF-CmS for short) with a controllable distribution of Cu active sites for the hydrogenation of the DMO to EG reaction. The catalyst was prepared by a hydrothermal method with the HKUST-1 uniformly coated on the surface of the silica microspheres. After the calcination, the highly dispersed and uniform Cu species were loaded on the surface of the silica. The resulted MOF-CmS catalyst showed a 100% conversion of DMO and over 98% selectivity of EG at 200 °C and 2 MPa while a traditional Cu/SiO2 catalyst exhibited serious agglomeration of Cu active sites and low catalytic activity (DMO conversion of 86.9% and EG selectivity of 46.6%). It is believed that the highly dispersed active metal center and the interaction between the active metal and carrier were the main reasons for higher catalytic activity of the MOF-CmS catalyst. Therefore, the developed method opened another avenue to synthesize highly dispersed and stable Cu-based catalysts.

Graphical Abstract

1. Introduction

Ethylene glycol (EG) is mainly used in the production of polyester, antifreeze, adhesives, paint solvents, cold-resistant lubricants, surfactants, and polyester polyols [1,2]. The hydrogenation of dimethyl oxalate to ethylene glycol (DMO-to-EG reaction) is recognized as a promising synthetic route, and the synthesis of a high-efficiency catalyst is the key and has always been a research hotspot [3,4,5].
Considering the cost of Ru [6], Ag [7], and other precious metals, Cu-based catalysts have attracted wide attention from researchers. Among them, Cu/SiO2 catalysts show excellent catalytic activity and selectivity in a DMO-to-EG reaction owing to the hydrogenation action of the C–O bonds and relative inaction for the hydrogenation of the C–C bonds [8,9,10,11,12]. However, the weak interaction between the catalyst carrier and the active sites leads to aggregation of the Cu particles, which decreases the lifetime and activity of the catalyst [13]. Therefore, controlling the dispersion of Cu active sites on the support is one of the key factors to improving the catalytic performance [14].
At present, the structure of metal-organic frameworks (MOFs) for controllable pyrolysis has become a new strategy [15,16]. Due to the regular framework structure formed by oxygen or nitrogen-containing organic ligands with the inorganic metals, the arrangement of metal nanoparticles within the pores/cages or crystal defects can be controlled [17,18,19]. Moreover, pyrolysis can transform unstable MOFs’ structures into stable metal oxides and promote the formation of ultrafine metal particles or oxides [20,21]. Among the reported MOF materials, HKUST-1 was widely used for the relatively inexpensive reactants, facile preparation methods, and excellent performance [22,23,24,25]. Ye et al. [22] reported the preparation of a Cu/SiO2-MOF catalyst by the sol−gel method; the highly dispersed Cu nanoparticles that formed after calcination have good activity for the DMO-to-EG reaction. However, it is difficult to adjust the metal loading of the catalyst due to the limited space in the MOF cavity in the presence of SiO2.
In this work, we utilized the advantages of uniformity, stability, and the controllable size of microspheres to guide the growth of the MOF around SiO2 microspheres by surface modification (Scheme 1). The prepared Cu/SiO2 catalyst had remarkable catalytic activity for the DMO-to-EG reaction after being calcined in air and reduced in the H2 atmosphere.

2. Results

2.1. Catalyst Structure Design and Characterization

The synthesis of the MOF-CmS catalyst is exhibited in Figure S1. First, silica microspheres were prepared by the Stöber method and modified. Subsequently, the synthesis of the HKUST-1 was performed on its surface. Last, the Cu species were exposed on the surface of the silica microspheres after removing the MOF skeleton via calcination. The TEM images of the MOF-CmS and MOF-CS precursors are shown in Figure 1A,B, which clearly reveals that the cladding integrity of the HKUST-1 is quite different. The crumpled film in Figure 1A shows that the HKUST-1 has a better and more complete coating effect on silica microspheres, which proves that the modified microspheres play a crucial role in the integrity of the HKUST-1 coating and affect the structure of the Cu species after subsequent calcination. The Cu species’ dispersion of the catalyst was also exhibited by TEM. After calcination at 450 °C for 4 h, a MOF-CmS catalyst was formed; it can be observed that the silica microspheres are densely covered by Cu species < 5 nm in size (Figure 1D and Figure S2). However, only a few nanoparticles are supported on the silica microspheres in Figure 1E, and no nanoparticles were loaded in Figure 1F. Because of the spatial structure of the HKUST-1, the Cu species were still arranged in regular order after removing the organic framework, which fully reflects its advantage as a precursor. At the same time, the silica microspheres can support and fix the surrounding Cu species to inhibit their sintering during the heat treatment [18]. This has been confirmed by the high distribution of the Cu species on the surface of the microspheres in the TEM image (Figure 1D and Figure S2). This proved that the density skeleton of the HKUST-1 did not change much after calcination even if the load mode of the carrier was changed.
Figure 2 shows the XRD pattern of MOF-CmS, MOF-CS, CS, and SiO2 samples as well as their precursors. The diffraction peaks of the HKUST-1 and SiO2 crystallites were observed on the MOF-CmS and MOF-CS precursors, indicating that HKUST-1 crystalline phases were successfully synthesized. The diffraction peaks’ intensities of the HKUST-1 crystalline phases in the MOF-CmS precursor were much sharper than those of MOF-CS, which should be attributed to the decoration of the surfactant APTES and succinic anhydride to make the SiO2 better coated by the HKUST-1. The calcined HKUST-1 exhibited four evident diffraction peaks at 2θ = 35.5°, 38.7°, 48.8°, and 61.6°, which is characteristic of CuO (Joint Committee on Powder Diffraction Standards, JCPDS 48-1548). It is worth nothing that the MOF-CS shows a sharper characteristic peak of CuO than MOF-CmS, which may be caused by the aggregation of active centers to produce larger CuO particles after calcination. No characteristic peaks of CuO were found in the CS sample, which indicated that the low content of CuO or Cu species exists in the amorphous state.
As shown in Figure 3, the FT-IR spectra of HKUST-1, CS, MOF-CS, MOF-CmS, and their precursors were studied. The HKUST-1 shows a carboxyl absorption band at 1710 cm−l and symmetric and asymmetric stretching vibrations of carboxyl groups at 1645/1560 cm−1 and 1445/1374 cm−1, respectively [26]. The bands at 1220 and 1100 cm−1 are assigned to the stretching vibrations of Si–O bonds; the bands at 958 cm−1 correspond to the existence of non-bonded oxygen Si–OH bonds [27]. The bands at 802 and 471 cm−1 are attributed to the bending vibrations of Si–O bonds and –O–Si–O– bonds, respectively [28]. The infrared characteristic peaks of the HKUST-1 can be observed on the MOF-CmS and MOF-CS precursors. It is worth noting that the MOF-CmS shows a sharper characteristic FT-IR peak of HKUST-1 than MOF-CS, which can be ascribed to the large number of carboxylic acid sites provided by the modified silica microspheres. The absorption bands of the HKUST-1 disappeared after the calcination in air, which proves that organic linkers have been completely removed. There are mainly two kinds of Cu species left on the silicon. One of them is the Cu–O–Si units; the 960 cm−1 band is covered by a 958 cm−1 band of silicon [29]. The other is the CuO, which cannot be clearly observed from the bands at 580, 500, and 460 cm−1 due to the existence of a broad band at 471 cm−1 [30].
The XPS and XPAES measurements were illustrated to investigate the electronic interactions of Cu in Figure 4 and Table S1. Over the reduced MOF-CmS, MOF-CS, and CS catalysts, the Cu2p1/2 and Cu2p3/2 peaks appear at 953.1 and 933.3 eV, respectively (Figure 4A). A shakeup satellite peak appeared near 938.7~945.8 eV. The peaks’ intensities of the reduced MOF-CmS catalyst are much stronger than those of the reduced MOF-CS and CS catalysts, which can be ascribed to the relatively abundant types of surface Cu species in this catalyst [31]. Meanwhile, a asymmetric Auger peak, ranging from 905 to 925 eV, was displayed in the Cu LMM XAES spectrogram for the reduced MOF-CmS, MOF-CS, and CS catalysts (Figure 4B), which was deconvoluted into two symmetric peaks at 913.6 and 918.3 eV, indicating that both Cu0 and Cu+ appeared on those catalysts. As the results show in Table S1, the proportion of the Cu+ species increases significantly with HKUST-1 as the copper precursor. The MOF-CmS shows an obviously higher Cu+ content (74.8%) than MOF-CS (63.3%) and CS (61.6%). This result further supports our hypothesis that there are more Cu–O–Si units and Cu+ species in the MOF-CmS catalysts.

2.2. Catalytic Performance

As shown in Table S3, the MOF-CmS catalyst exhibited a surface area of 154 m2 g−1, a copper concentration of 13%, and a Cu dispersion of 49.4%. It showed better structural advantages and a more active center content than the other two catalysts. The catalytic performances of the Cu/SiO2 catalysts of three different preparation methods were presented in Figure 5 and Table S2. Figure 5A displays that the DMO conversion and EG selectivity of the MOF-CmS catalyst were only 37.59% and 8.08% at 170 °C, respectively. With the increase of reaction temperature, the DMO conversion and EG selectivity changed significantly. The conversion of the DMO can reach 100%, and the selectivity of the EG can reach a maximum of 98.81% at 200 °C. As a contrast, the catalytic performance of the MOF-CS and CS was poor (Table S2). On the one hand, different preparation methods lead to a different dispersion (Figure 1) and size of the Cu species. On the other hand, due to the weak interaction between the Cu species and silica, the Cu species tend to aggregate into large particles, which, in turn, exhibits poor activity and stability [14,32,33,34]. Additionally, a negligible changing of Conv. DMO and Selec. EG with the EG selectivity of more than 98.0% was observed over the MOF-CmS catalyst after performance for 100 h (Figure S3). This indicated that the MOF-CmS catalyst exhibited not only good activity but also superior stability.

3. Discussion

In this work, silica microspheres and modified silica microspheres were used as the carrier to synthesize Cu-based catalysts (Scheme 1 and Figure S2). It can be seen from the data summarized in Table S3 that the Brunauer-Emmett-Teller surface area is 154 m2g−1 for the MOF-CmS, which is lower than HKUST-1 (336 m2g−1) but much higher than SiO2 (89 m2g−1). The materials present the typical type IV N2 sorption isotherms with a H3 hysteresis loop, which is usually considered to be indicative of gas adsorption in the mesopores’ materials. The pore size was 4.2 nm. The physicochemical properties of the MOF-CmS catalyst are significantly different from those of the MOF-CS and CS catalysts. A uniform and ordered dispersion of the Cu species was achieved in the modified silica microspheres over the MOF-CmS catalyst, and the high dispersion of the MOF-CmS exposed more active sites for the DMO hydrogenation to EG. From the previous reports [35,36,37], the dispersibility of the Cu, specific surface area, and size of the Cu particles were confirmed to be the key factors affecting the performance of the Cu-based catalysts, which makes huge differences in the catalytic performance of different catalysts. Furthermore, the HKUST-1 was distributed in the outer layer of the silica microspheres, then calcined to form well-dispersed CuO, and, finally, reduced. In the CS catalyst, a pair of copper species was covered by silica matrix and difficult to reduce. Using HKUST-1 as a precursor can obtain different types of copper from conventional impregnation methods. The FT-IR and XPS results (Figure 3 and Figure 4B) prove that there were some well-dispersed CuO and Cu–O–Si units on the MOF-CmS and MOF-CS samples. It is generally believed that reducing copper sintering to maintain good dispersibility is an important factor in maintaining high activity of Cu-based catalysts. The superiority of the MOF-CmS catalyst could be attributed to two reasons. One was the high dispersion of copper nanoparticles. The second was that the ultrafine copper particles (5 nm) contain a large amount of Cu+ species. In addition, after fixing HKUST-1 on the silica microspheres with a surfactant and further calcining to remove the organic framework, there was a strong interaction between the copper species and the carrier, which was helpful in preventing the active center from sintering and maintaining high dispersion. We believe that Cu+ can be used as an electrophile or Lewis’s acid site to polarize the C=O bond in the DMO molecule, and methoxy and acyl species are formed during the reaction, while Cu0 and Cu+ have a synergistic catalytic effect in the DMO hydrogenation reaction. In other words, the Cu+ species can be used as a Lewis acid to adsorb and activate the C=O/C–O bond by using the lone pair of electrons on the surrounding oxygen atoms, while Cu0 is used to dissociate and adsorb hydrogen, and its synergistic catalytic mechanism is consistent with the literature reports [38]; the reaction mechanism is shown in Figure 6. As shown in Table 1, we compared the methanol activity in our work with other catalysts in the literature. It shows excellent catalytic performance.

4. Materials and Methods

4.1. Synthesis of HKUST-1

Briefly, 10.0 g of Cu (CH3COO)2·H2O and 5.0 g of 1,3,5-benzenetricarboxylic acid (BTC) were ultrasonically dissolved for 30 min in a mixture of N, N-dimethylformamide (DMF), deionized (DI) water, and ethanol (300 mL, v/v/v, 1/1/1). Then, the mixture was placed in an oven at 85 °C for 20 h. The blue product was obtained via centrifugation and subsequently washed with DMF and ethanol several times. The HKUST-1 powder was acquired at 170 °C for 6 h in a vacuum drying oven.

4.2. Synthesis of MOF-CmS Catalyst

4.2.1. Synthesis of Silica Microspheres

The silica microspheres were synthesized using the Stöber method. Firstly, 13.5 mL ethyl orthosilicate and 136.5 mL ethanol were mixed under stirring for 30 min to obtain solution A. Secondly, 27 mL strong ammonia, 49 mL ethanol, and 74 mL DI water were placed in a flask under magnetic stirring for 30 min; the above solution was denoted as solution B. Solution A was slowly dripped into solution B at 40 rpm, and then the mixed solution was sealed with a plastic wrap and reacted for 2 h. All the above operations were performed at room temperature (~25 ± 3 °C). The synthesis solution underwent ammonia removal at 70 °C until solution pH ~7. After the above experimental process, uniform silica microspheres were obtained.

4.2.2. Synthesis of Modified Silica Microspheres

A total of 250 μL APTES (3-ammonia propyl triethoxy silane) was dripped into the silica microspheres obtained in the previous step and stirred at 60 °C for 12 h; then, 3.000 g of succinic anhydride was added into the above solution and stirred overnight.

4.2.3. Synthesis of MOF-CmS Catalyst

A total of 1.256 g of BTC and 2.574 g of Cu(CH3COO)2·H2O were dissolved in a 150 mL solution with a DMF, ethanol, and DI water volume ratio of 1:1:1 and ultrasonically mixed for 20 min. Then, the above solution was added into a solution of modified silica microspheres under stirring for 20 min and transferred to a sealed Teflon-lined autoclave at 60 °C for 20 h. After that, the precipitate was obtained via centrifugation and washing with DMF and ethanol several times and then vacuum dried at 170 °C for 24 h to yield precursor. Finally, the MOF-CmS catalyst was acquired after calcination for 4 h at 450 °C under air.

4.3. Synthesis of MOF-CS Catalyst

For comparison, the MOF-CS catalyst was also synthesized in the same way as the MOF-CmS catalyst except that modified silica microspheres were replaced by silica microspheres. The MOF-CS catalyst was obtained.

4.4. Synthesis of CS Catalyst

In addition, the CS catalyst was also prepared under the same conditions as the MOF-CmS catalyst, but only the silica microspheres and Cu(CH3COO)2·H2O were used as the reagents.

4.5. Characterization

The powder X-ray diffraction (XRD) was performed on a Shimadzu XRD-6100 (Shimadzu Corp., Kyoto, Japan) using Cu Kα radiation with a scanning angle (2θ) range of 5° to 80°. The transmission electron microscope (TEM) was collected on a Tecnai G2 F20 (FEI Company., Hillsboro, OR, USA). The X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (XAES) were carried out on a Thermo ESCALAB 250Xi spectrometer (Thermo Fisher Scientific., Waltham, MA, USA) with an Al Kα X-ray radiation source (hν = 1486.6 eV). The Fourier-transform infrared (FT-IR) spectra were measured on a Varian 6400 FT-IR spectrometer (Agilent Technologies., Palo Alto, CA, USA).

4.6. Catalytic Test

The catalyst performance was evaluated on a fixed-bed reactor (Figure S4). A total of 1.0 g of catalyst (20~40 meshes) was loaded in the center of the reaction tube (9.5 mm OD and 250 mm length), and both ends of the catalyst bed were packed with ample quartz sand (40 to 60 meshes). Each catalyst was reduced and activated in a flow of pure H2 (99.99%) atmosphere (100 mL·min−1) at 300 °C for 4 h under atmospheric pressure. The cooling reached the target reaction temperature (170–220 °C), and the pressure was controlled to 2.0 MPa. The feed flow of the H2 was controlled by a mass flowmeter (H2/DMO molar ratio = 50), and the flow of the DMO methanol solution (10 wt% DMO) was pumped into the reactor on a Shimadzu LC-10AT pump (Shimadzu Corp., Kyoto, Japan) (WLHSVDMO = 0.82 h−1, 0.82 g DMO/1 g catalyst h−1). The DMO methanol solution was gasified at a high temperature in the reactor, fully mixed, and preheated in the quartz sand bed. The temperature of the reaction section was measured by a thermocouple, which can move along the axis in the casing. The condensed products were collected for qualitative and quantitative analysis by an online gas chromatograph (Shimadzu GC-2014) with a flame ionization detector (FID). All the above data were measured after the reaction conditions reached the requirements and stabilized for one hour.

5. Conclusions

Highly dispersed Cu/SiO2-MOF catalysts were successfully prepared in this study. It is worth noting that the surface modification of the SiO2 microspheres played an important role in the coating of the HKUST-1. It was found that both the specific surface area and metal loading of the modified silica spheres and MOF were increased, and the growth coating was more uniform. Even when the catalyst of the same element is hydrogenated on dimethyl oxalate, the influence of different dispersity and load on the activity is very important. Compared with ordinary MOF and SiO2 microspheres, ordinary microspheres were doped with copper. The results showed that their binding was not as tightly dispersed as the catalyst, and the copper was often agglomerated together, resulting in lower activity. With SiO2 microspheres as the carrier, MOF as the coated catalyst with high dispersion and high efficiency provides a good application prospect for other MOF catalysts.

Supplementary Materials

The following supporting information can be downloaded at the following: https://www.mdpi.com/article/10.3390/catal12111326/s1. Figure S1: Diagram of catalyst preparation process; Table S1: Kinetic energy and Cu+ ratio in different catalysts; Table S2: Catalytic performance of MOF-CmS, CS, and MOF-CS samples at 220 °C with WLHSVDMO = 0.82 h−1; Table S3: Physicochemical properties of different catalysts; Figure S2: TEM images of the MOF-CmS catalyst. Figure S3: Long-term stability test of the MOF-CmS sample at a reaction temperature of 200 °C and WLHSVDMO of 0.82 h−1. Figure S4: Reaction tube diagram; Reference [40] is cited in the supplementary materials.

Author Contributions

Conceptualization, X.S. and X.G.; methodology, X.S., X.G. and Y.L.; software, X.G.; validation, X.S., X.G. and Y.L.; formal analysis, X.S., X.G., Y.L. and J.X.; investigation, X.S., X.G., Y.L., J.X., L.H. and G.W.; resources, D.M.; data curation, D.M.; writing—original draft preparation, D.M.; writing—review and editing, J.Q. and Q.J.; visualization, D.M. and Q.J.; supervision, D.M., J.Q. and Q.J.; project administration, D.M. and Q.J.; funding acquisition, D.M., J.Q. and Q.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (No. 61973223, 51972306), Education Department Foundation of Jilin Province (JJKH20220997KJ), Fundamental Research Funds for the Central Universities (415010200032), Innovative Talents in Colleges and Universities in Liaoning Province (No. 2020389), Interdisciplinary Integration and Innovation Project of JLU (JLUXKJC2020204), Liaoning Educational Department Foundation (No. LJ2020001), Liao Ning Revitalization Talents Program (No. XLYC2007051), Natural Science Foundation of Liaoning Province (No. 2019-ZD-0072, 2021-MS-257), and Young and Middle-Aged Scientific and Technological Innovation Talents of Shenyang Science and Technology Bureau (No. RC200352).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 12 01326 sch001 550
Scheme 1. The preparation process of Cu/SiO2-MOF(MOF-CmS).
Scheme 1. The preparation process of Cu/SiO2-MOF(MOF-CmS).
Catalysts 12 01326 sch001
Catalysts 12 01326 g001 550
Figure 1. TEM images with size distributions of the precursor and MOF-CmS (A,D, respectively); precursor and MOF-CS (B,E, respectively); CS (C,F, respectively); among them, (D–F) are the enlarged pictures of (A–C), respectively.
Figure 1. TEM images with size distributions of the precursor and MOF-CmS (A,D, respectively); precursor and MOF-CS (B,E, respectively); CS (C,F, respectively); among them, (D–F) are the enlarged pictures of (A–C), respectively.
Catalysts 12 01326 g001
Catalysts 12 01326 g002 550
Figure 2. XRD patterns of pure HKUST-1, SiO2, and Cu/SiO2 samples and their precursors.
Figure 2. XRD patterns of pure HKUST-1, SiO2, and Cu/SiO2 samples and their precursors.
Catalysts 12 01326 g002
Catalysts 12 01326 g003 550
Figure 3. FT-IR spectra of HKUST-1, CS, and Cu/SiO2 samples and their precursors.
Figure 3. FT-IR spectra of HKUST-1, CS, and Cu/SiO2 samples and their precursors.
Catalysts 12 01326 g003
Catalysts 12 01326 g004 550
Figure 4. (A) Cu 2p XPS spectra and (B) Cu LMM XAES spectra of reduced MOF-CS, CS, and MOF-CmS samples.
Figure 4. (A) Cu 2p XPS spectra and (B) Cu LMM XAES spectra of reduced MOF-CS, CS, and MOF-CmS samples.
Catalysts 12 01326 g004
Catalysts 12 01326 g005 550
Figure 5. Catalytic performance of MOF-CmS (A), MOF-CS (B), and CS (C) samples in different reaction temperatures (170–220 °C) with WLHSVDMO = 0.82 h−1. WLHSV means weight liquid hourly space velocity.
Figure 5. Catalytic performance of MOF-CmS (A), MOF-CS (B), and CS (C) samples in different reaction temperatures (170–220 °C) with WLHSVDMO = 0.82 h−1. WLHSV means weight liquid hourly space velocity.
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Catalysts 12 01326 g006 550
Figure 6. Schematic model of the reaction mechanisms over MOF-CmS catalyst for the hydrogenation of DMO.
Figure 6. Schematic model of the reaction mechanisms over MOF-CmS catalyst for the hydrogenation of DMO.
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Table
Table 1. Comparison of catalysts’ properties in the present work and other literature.
Table 1. Comparison of catalysts’ properties in the present work and other literature.
CatalystsTemperature/°CConv.DMO/%Selec.EG/%
MOF-CmS20010098.1
T-869 [10]21099.8-
Cu/HMS [12]2208886
Cu3Ni1/HMS [12]2208940
20Cu/SiO2 [39]22097.986.8
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MDPI and ACS Style

San, X.; Gong, X.; Lu, Y.; Xu, J.; He, L.; Meng, D.; Wang, G.; Qi, J.; Jin, Q. Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol. Catalysts 2022, 12, 1326. https://doi.org/10.3390/catal12111326

AMA Style

San X, Gong X, Lu Y, Xu J, He L, Meng D, Wang G, Qi J, Jin Q. Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol. Catalysts. 2022; 12(11):1326. https://doi.org/10.3390/catal12111326

Chicago/Turabian Style

San, Xiaoguang, Xiaohui Gong, Yiming Lu, Juhua Xu, Liming He, Dan Meng, Guosheng Wang, Jian Qi, and Quan Jin. 2022. "Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol" Catalysts 12, no. 11: 1326. https://doi.org/10.3390/catal12111326

APA Style

San, X., Gong, X., Lu, Y., Xu, J., He, L., Meng, D., Wang, G., Qi, J., & Jin, Q. (2022). Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol. Catalysts, 12(11), 1326. https://doi.org/10.3390/catal12111326

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