Cu2In alloy-embedded ZrO2 catalysts for efficient CO2 hydrogenation to methanol: promotion of plasma modification

Cu₁In₂Zr₄-O-C catalysts with Cu₂In alloy structure were prepared by using the sol–gel method. Cu₁In₂Zr₄-O-PC and Cu₁In₂Zr₄-O-CP catalysts were obtained from plasma-modified Cu₁In₂Zr₄-O-C before and after calcination, respectively. Under the conditions of reaction temperature 270°C, reaction pressure 2 MPa, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g h), Cu₁In₂Zr₄-O-PC catalyst has a high CO₂ conversion of 13.3%, methanol selectivity of 74.3%, and CH₃OH space-time yield of 3.26 mmol/gcat/h. The characterization results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction chemisorption (H₂-TPR) showed that the plasma-modified catalyst had a low crystallinity, small particle size, good dispersion, and excellent reduction performance, leading to a better activity and selectivity. Through plasma modification, the strong interaction between Cu and In in Cu₁In₂Zr₄-O-CP catalyst, the shift of Cu 2p orbital binding energy to a lower position, and the decrease in reduction temperature all indicate that the reduction ability of Cu₁In₂Zr₄-O-CP catalyst is enhanced, and the CO₂ hydrogenation activity is improved.

1 Introduction

The catalysts for CO₂ hydrogenation to methanol mainly include Cu-based catalysts and other metal oxide catalysts (Bowker et al., 2022; Yan et al., 2022). Cu-based catalysts have been most widely studied. Among the other metal oxide catalysts, the In₂O₃ and ZrO₂ catalysts show high activity and selectivity, due to their good CO₂ adsorption and activation performance (Wu et al., 2021; Tada et al., 2022). Inspired by this, we prepared Cu₁In₂Zr₄-O catalyst with Cu₂In alloy structure by using the sol–gel method, which exhibited an excellent performance for CO₂ hydrogenation to CH₃OH. The CO₂ conversion and methanol selectivity were 12.8% and 72.8%, respectively at 270°C, 2 MPa, and 12,000 mL·(g·h)⁻¹. The special structure of Cu₂In alloy strengthened the interaction between In and Cu species, further readjusted good dispersion, high surface area, and the adsorption and reduction properties of the catalyst. Briefly, Cu₂In alloy is a key factor for improving catalytic performance (Gao et al., 2020).

On the basis of the Cu₁In₂Zr₄-O catalyst, how can we further improve the catalytic performance? The preparation and modification methods of catalysts are worthy of special consideration. Different preparation and modification methods lead to changes in the particle size of metal particles, the dispersion of active components, the crystallinity of the catalyst, and the interaction between each component, which ultimately leads to differences in catalytic activity (Cg et al., 2021; Lasobras et al., 2021). Plasma modification of the catalyst results in better dispersion, larger specific surface area, and more lattice defects (Liu et al., 2016; Bagherzadeh and Haghighi, 2017).

Zeng et al. (2022) prepared NiMnAl-LDO (layered double oxides) catalysts for CO₂ methanation. Solution plasma treatment was used to improve the dispersion, generate oxygen defects, and enhance the adsorption sites, improving the low-temperature activity and stability of the catalyst. Kierzkowska-Pawlak et al. (2017) investigated CO₂ methanation on nanoscale metal oxides carried out on wire gauzes (FeCrAl). The catalysts were synthetized by plasma-assisted chemical vapor deposition. The plasma deposition promoted the generation of the specific nanostructure of metal oxides, which was responsible for ascendant catalytic activity. Han et al. (2020) prepared CuZnO-ZrO₂ by using a co-precipitation method. The catalyst was pretreated by the glow discharge plasma before and after calcination. After treated with plasma, the catalyst showed a lower crystallinity and a better dispersion, and CO₂ conversion increased by 38.9%.

In this work, the plasma-improved sol–gel method was used to prepare the Cu₁In₂Zr₄-O catalyst with Cu₂In alloy structure. Because the Cu₁In₂Zr₄-O catalyst with Cu₂In alloy structure prepared using the sol–gel method had exhibited good dispersion and excellent catalytic performance, the promotion of plasma modification may not be particularly significant. However, it still makes sense for the catalyst. The structure, chemical property, and catalytic activity of the catalysts before and after plasma treatment were systematically studied. In addition, the process parameters of the catalytic hydrogenation reaction were also optimized.

2 Experimental methods

2.1 Materials

Cu(NO₃)₂·3H₂O, In(NO₃)₃·4.5H₂O, Zr(NO₃)₄·5H₂O, and C₆H₈O₇·H₂O were purchased from Sinopharm Chemical Reagent Co., Ltd.

2.2 Preparation of catalysts

Cu₁In₂Zr₄-O-C catalysts with Cu₂In alloy structure were prepared by using the sol–gel method, as described in our previous research (Gao et al., 2020). Cu₁In₂Zr₄-O-CP and Cu-In/ZrO₂-PC catalysts with Cu₂In alloy structure were prepared by using the plasma-improved sol–gel method. The specific operation steps are as follows: first, the catalyst precursor was prepared by using the sol–gel method, which was divided into two parts after grinding (labeled as sample 1 and sample 2, respectively). Next, the No. 1 sample was roasted at 350°C for 4 h in a tubular furnace and then treated by plasma for 15 min. The obtained catalyst was recorded as Cu-In/ZrO₂-CP. Finally, the No. 2 sample was first treated by plasma and then calcined, and other conditions remained the same to obtain the Cu-In/ZrO₂-PC catalyst.

2.3 Characterization techniques

The XRD patterns were obtained on a PANalytical X’Pert3 Powder with Cu K α (λ = 0.154 nm). The working voltage, current, and scanning speed were 40 kV, 100 mA, and 8°/min, respectively. The specific surface area, pore volume, and pore size of catalytic materials were measured using Beckman Coulter SA3100. The composition of catalysts was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES, Agilent 730). The morphology was observed using a Nova NanoSEM 450. The field emission operating voltage and current were 5 kV and 10 mA, respectively. The XPS atlas was analyzed using an ESCALAB 250Xi X-ray spectrometer. The H₂-TPR and H₂-TPD curves were collected using AutoChem II 2920, and the test temperature range was 50–800°C and 50–600°C, respectively. The plasma instrument used was the MVP-401 glow discharge plasma instrument produced by Kunshan Sokunlai Electromechanical Technology Co., Ltd.

2.4 Catalytic activity evaluation

The catalytic activity test was carried out on an HP-WF51 fixed bed reactor (stainless steel reactor with 10 mm inner diameter), and the catalyst loading amount was the mixture of 0.5 g of the catalyst (20–40 mesh) and 0.5 g of quartz sand (20–40 mesh). The reaction was carried out at 270°C, pressure 2 MPa, feed gas component ratio V (H₂): V (CO₂): V (N₂) = 69:23:8, and space velocity 12,000 mL/(h · g). Before the reaction, the catalyst was reduced in a V (H₂): V (N₂) = 10:40 mixture in advance. The temperature was 350°C, and the pressure was 0.1 MPa. Afterward, when the temperature dropped to 270°C, the gas was switched to the feed gas component to start the reaction. The reaction products were analyzed by gas chromatography, and the concentration of CO₂ and CO was detected using a TCD detector (TDX-01 was used for filling the column). The FID detector was used to detect hydrocarbon gases such as methanol (Porapak Q was used for the capillary column), and the corrected area normalization method was used to quantitatively analyze the gas concentration in tail gas.

3 Results and discussion

3.1 XRD analysis

Figure 1 shows the XRD spectra of Cu₁In₂Zr₄-O-PC, Cu₁In₂Zr₄-O-C, and Cu₁In₂Zr₄-O-CP catalysts before and after reduction. The diffraction peaks at 2θ of 30.3°, 35.3°, 50.4°, and 60.2° belong to (011), (110), (112), and (121) crystal planes of t-ZrO₂, respectively (Jcpds-050-1089) (Pei et al., 2022), and the diffraction peaks of In₂O₃ are located at 2θ of 21.5°, 35.5°, 51.0°, and 60.7° belong to the (211), (400), (440), and (622) crystal planes of the In₂O₃, respectively (Jcpds-06-0416) (Zafar et al., 2022). The diffraction peak intensity of Cu₁In₂Zr₄-O-PC and Cu₁In₂Zr₄-O-CP catalysts before reduction is significantly lower than that of Cu₁In₂Zr₄-O-C catalysts, indicating that plasma modification reduces the crystallinity of the catalyst (Zhang et al., 2010). No CuO diffraction peak is found in all samples before reduction, indicating that CuO in all catalysts is mainly dispersed on the support surface in the highly dispersed or amorphous form (Azenha et al., 2017). In the reduced Cu₁In₂Zr₄-O-PC, Cu₁In₂Zr₄-O-C, and Cu₁In₂Zr₄-O-CP catalysts, the t-ZrO₂ diffraction peaks of the catalyst after plasma modification have no obvious change, while the diffraction peak intensity of Cu₂In has decreased significantly, and the diffraction peak has widened. The reduced sample has no diffraction peak of metal Cu and In, indicating that the reduced Cu and In combine to form the Cu₂In alloy phase. The XRD results show that the crystallinity of the catalyst after plasma modification is generally lower than that after direct calcination, and the particle size of the catalyst is reduced, thus improving the dispersion of the catalyst.

FIGURE 1

FIGURE 1. XRD patterns of the catalysts.

3.2 BET and ICP analysis

Figure 2 shows the N₂ adsorption and desorption curves and pore size distribution of three catalyst samples. As shown in Figure 2A, according to the IUPAC classification, all catalysts show type IV isotherms with a H₂ hysteresis loop, indicating that all catalysts have the characteristics of mesoporous materials (Witoon et al., 2018a). As shown in Figure 2B, all samples have a maximum pore size distribution of about 3.8 nm, indicating that the pore size of the catalyst sample is mainly mesoporous, with fewer micropores and macropores (Li et al., 2019). The N₂ adsorption–desorption curves and the most probable pore size distribution of Cu₁In₂Zr₄-O-PC, Cu₁In₂Zr₄-O-C, and Cu₁In₂Zr₄-O-CP catalysts are basically consistent, indicating that plasma modification has little effect on the physical properties of the catalysts. Table 1 shows the physicochemical properties of the catalysts. The specific surface area of the Cu₁In₂Zr₄-O-CP catalyst (115.89 m²/g) is lower than that of the untreated catalyst (122.38 m²/g). The reason may be that the duration of plasma treatment is too long or the temperature is too high, which leads to the increase of the crystallinity of the catalyst, the aggregation of the catalyst, and the reduction of the specific surface area. The specific surface area of Cu₁In₂Zr₄-O-PC catalyst (119.49 m²/g) has little change from that of the untreated catalyst (122.38 m²/g); that is, plasma modification has little effect on the specific surface area of the catalyst, and the pore volume of the catalyst after plasma modification and that of the untreated catalyst have no change basically. The molar percentage of Cu, In, and Zr in the three samples is in the range of 14.26%–14.29%, 28.49%–28.61%, and 57.11%–57.24%, respectively. The Cu/In/Zr molar ratio is very close to the theoretical value of 1:2:4.

FIGURE 2

FIGURE 2. N₂ adsorption–desorption isotherms (A) and pore size distributions (B) of the catalysts.

TABLE 1

TABLE 1. Physicochemical properties of the catalysts.

3.3 XPS analysis

The XPS spectra of Cu 2p orbitals of different catalysts are shown in Figure 3A. The binding energies of Cu 2p_3/2 and Cu 2p_1/2 orbitals are approximately 932.8 and 952.8 eV, respectively, indicating that the Cu element in the three reduced catalysts exists in the Cu⁰ form, while the catalyst without plasma treatment has a shoulder peak at 934.5 eV, indicating that the Cu element in the untreated catalyst also exists in the Cu²⁺ form (Jiang et al., 2015). However, the catalyst after plasma treatment does not have a Cu²⁺ peak, and the binding energy at the Cu 2p orbit of the Cu₁In₂Zr₄-O-CP catalyst is approximately 0.3 eV which is lower than that of the catalyst Cu 2p without plasma treatment, indicating that the density of the electron cloud around the Cu 2p orbit of the catalyst after plasma modification changed, thus causing chemical changes in elements and enhancing the interaction between Cu and In. Therefore, the Cu₁In₂Zr₄-O-CP catalyst shows a good catalytic activity (Zhang et al., 2010). As shown in Figure 3B, the binding energies at 443.8 eV and 451.4 eV in the XPS spectrum of the In 3d orbit correspond to the binding energies at In 3d_5/2 and In 3d_3/2, respectively. The binding energies at the In 3d orbit of the Cu₁In₂Zr₄-O-CP catalyst shift to the lower binding energies, indicating that the chemical environment and energy state around the In 3d orbit of the catalyst after plasma treatment have changed compared with those of the untreated catalyst sample. Figure 3C shows the XPS spectrum of the Zr element on the 3d orbit. The Zr 3d_5/2 and Zr 3d_3/2 orbital binding energies of the three catalysts are 181.6 and 184.0 eV, respectively. There is no significant difference in the binding energies of the three catalysts on the Zr 3d orbit, indicating that Zr elements of all the catalysts exist in the Zr⁴⁺ form, and the chemical environment and energy state around the Zr 3d orbit have not changed. Figure 4D shows the O1s spectra of the three catalysts. The fitted O1s spectra are composed of two asymmetric peaks, proving that there are two different O types on the catalyst surface. Among them, 529.5 eV at low binding energy belongs to lattice oxygen, and 531.0 eV at high binding energy belongs to adsorbed oxygen. As can be seen from the figure, the content of adsorbed oxygen is lower than that of lattice oxygen.

FIGURE 3

FIGURE 3. XPS patterns of the catalysts after reduction. (A) Cu 2p, (B) In 3d, (C) Zr 3d and (D) O1s.

FIGURE 4

FIGURE 4. SEM diagram of catalysts after reduction. (A,C) Cu₁In₂Zr₄-O-C and (B,D) Cu₁In₂Zr₄-O-PC.

3.4 SEM analysis

The SEM diagrams of Cu₁In₂Zr₄-O-C and Cu₁In₂Zr₄-O-CP catalysts after reduction are shown in Figure 4. Figures 4A, C show the catalyst morphology at 30 μm scale. The morphology of both catalysts belongs to an irregular blocky structure. Figures 4B, D correspond to the enlarged view of Figures 4A, C, respectively. From Figures 4A, C, it is observed that the Cu₂In structure of the catalyst after reduction is composed of spherical particles of different sizes. The particle size of Cu₂In particles in the Cu₁In₂Zr₄-O-C catalyst after reduction is large, and Cu₂In particles are unevenly dispersed on the support. After reduction, the particle size of Cu₂In alloy in the Cu₁In₂Zr₄-O-CP catalyst decreases, and the dispersion on the carrier is uniform. The catalyst modified by plasma can reduce the particle size of the active component, improve the dispersion of the active component, and therefore improve the catalytic activity of the catalyst (Sajjadi and Haghighi, 2018).

3.5 H₂-TPR analysis

H₂-TPR was used to explore the reduction ability of the catalyst after plasma modification, and the results are shown in Figure 5. All three catalysts have a strong H₂ consumption peak in the range of 150°C–300°C, which is attributed to the consumption of CuO to H₂. The multiple peaks in the range of 300°C–800°C correspond to the H₂ consumption of dispersed and lattice In₂O₃, respectively (Li et al., 2022). It can be clearly observed that the H₂ consumption peaks of the three catalysts CuO are asymmetric, which can be fitted into α and β peaks. The α peak belongs to the reduction of highly dispersed CuO on the surface of the catalyst carrier, while the β peak belongs to the reduction peak of CuO embedded in ZrO₂ or In₂O₃ lattice (Ezeh et al., 2018). The calculated amount of H₂ consumption of three catalysts listed in Table 2 is within the range of 76.4–76.6 mL, which slightly differs from each other. However, the peak shapes of the three samples are significantly different. There are two distinct peaks in the H₂-TPR spectrum of Cu₁In₂Zr₄-O-C, which overlap with each other but do not overlap at the top of the peaks. The top of the two peaks of Cu₁In₂Zr₄-O-CP overlaps, while those of Cu₁In₂Zr₄-O-PC almost completely overlap, appearing to have only one peak. The α peak difference of Cu₁In₂Zr₄-O-PC and Cu₁In₂Zr₄-O-CP is not significant (1°C), but there is a significant difference (5.3°C) in the β peaks. The reduction peak of bulk CuO has not been found, indicating that CuO in the three catalysts mainly exists in highly dispersed and lattice forms, which is consistent with the XRD results. Compared with the reduction temperature of Cu₁In₂Zr₄-O-PC and Cu₁In₂Zr₄-O-CP, the reduction temperature of Cu₁In₂Zr₄-O-PC is the lowest, meaning that the catalyst treated by plasma reduces the reduction temperature of CuO, enhances the reduction ability of the catalyst, and shows good catalytic activity (Chen et al., 2019).

FIGURE 5

FIGURE 5. H₂-TPR patterns of the catalysts.

TABLE 2

TABLE 2. Amount of H₂ consumption calculated from H₂-TPR and desorbed H₂ calculated from H₂-TPD.

3.6 H₂-TPD analysis

The H₂-TPD spectra of the three catalysts are shown in Figure 6. There is an asymmetric H₂ desorption peak composed of α and β peaks in the range of 50°C–600°C. The peak at lower temperature (α peak) belongs to highly dispersed metal copper, and the peak at higher temperature (β peak) is attributed to massive metal copper and lattice metal oxides (In₂O₃ and ZrO₂) (Witoon et al., 2018b). After plasma treatment, both α and β peaks shift to lower temperature, and the α and β peak shift of Cu₁In₂Zr₄-O-PC is the largest, indicating that the catalyst can desorb more H₂ at lower temperature (Lu et al., 2020). As listed in Table 2, the amount of desorbed H₂ of Cu₁In₂Zr₄-O-PC is 114.7 mL, which is significantly higher than that of Cu₁In₂Zr₄-O-C (91.5 mL). It further explains that plasma modification can produce more defect sites, increase the adsorption active sites of hydrogen on the surface of the catalyst, and enhance the adsorption capacity of H₂, which can activate more H₂ in the reactant and enhance the catalytic performance of CO₂ hydrogenation to methanol. Therefore, the Cu₁In₂Zr₄-O-PC catalyst with lower desorption temperature and higher hydrogen desorption peak area showed better CO₂ hydrogenation performance.

FIGURE 6

FIGURE 6. H₂-TPD patterns of the catalysts.

3.7 Effect of plasma modification on catalytic performance

Table 3 shows the activity test results of Cu₁In₂Zr₄-O-PC, Cu₁In₂Zr₄-O-C, and Cu₁In₂Zr₄-O-CP catalysts under the conditions of reaction temperature at 270°C, reaction pressure of 2 MPa, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g·h). The Cu₁In₂Zr₄-O-C catalyst has a CO₂ conversion of 12.8%, CH₃OH selectivity of 72.8%, and CH₃OH yield of 9.3%. Compared with the unmodified catalyst, the conversion of CO₂ and the selectivity of methanol on the catalyst modified by plasma have been improved, and the Cu₁In₂Zr₄-O-PC catalyst shows the best performance of CO₂ hydrogenation (a CO₂ conversion of 13.3%, methanol selectivity of 74.3%, CH₃OH yield of 9.8%, and a space-time yield of 3.26 mmol/gcat/h). The dispersion and reduction abilities of the catalyst modified by plasma are improved, thus improving the performance of CO₂ hydrogenation to methanol. The carbon balance of Cu₁In₂Zr₄-O-C was approximately 91.3%, while that of Cu₁In₂Zr₄-O-CP and Cu₁In₂Zr₄-O-PC achieved 94.1% and 96.7%, respectively. It is consistent with the changes in methanol selectivity and yield, indicating that the carbon balance is influenced by the dispersion of active components in the catalyst. The carbon balance of all three samples is below 100%, which may be attributed to carbon deposition on the catalyst, residues of products in chromatographic columns, and systematic errors in chromatographic analysis.

TABLE 3

TABLE 3. Activity test results of the catalysts.

3.8 Effect of reaction temperature on catalytic performance

Under the conditions of reaction pressure 2 MPa, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g · h), the effect of reaction temperature on CO₂ conversion and methanol selectivity of the catalyst was investigated. The activity test results are shown in Figure7. Figures 7A, B, D show that the CO₂ conversion, methanol selectivity, and methanol yield of Cu₁In₂Zr₄-O-PC and Cu₁In₂Zr₄-O-CP catalysts after plasma treatment are higher than those of Cu₁In₂Zr₄-O-C catalysts, indicating that the catalysts after plasma treatment show good catalytic activity, and the CO₂ conversion of Cu₁In₂Zr₄-O-C, Cu₁In₂Zr₄-O-PC, and Cu₁In₂Zr₄-O-CP catalysts increases with the increase in reaction temperature. The selectivity of methanol decreased with the increase in reaction temperature. It is observed from Figure 7C that the selectivity of CO increases with the increase in temperature because the formation of CO is an endothermic reaction, and the increase in temperature causes the chemical equilibrium to move toward the positive reaction direction. The selectivity of methanol of Cu₁In₂Zr₄-O-C and Cu₁In₂Zr₄-O-PC catalysts decreased from 72.8% to 63.1% and 74.3% to 67.0%, respectively, at the reaction temperature of 270°C and 290°C. The Cu₁In₂Zr₄-O-PC catalyst after plasma treatment has good methanol selectivity at higher temperatures.

FIGURE 7

FIGURE 7. (A) CO₂ conversion, methanol selectivity (B), CO selectivity (C), and methanol yield (D) of the catalysts at different temperatures. Reaction conditions: P = 2 MPa, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g h).

3.9 Effect of reaction pressure on catalytic performance

Under the conditions of reaction temperature 270°C, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g · h), the effect of reaction pressure on the CO₂ conversion and methanol selectivity of the catalyst was investigated. The activity test results are shown in Figure 8. It is observed in Figures 8A, D that the CO₂ conversion and methanol yield increase significantly with pressure. It is observed in Figure 8B that the selectivity of methanol slightly increases with pressure. In Figure 8C, the selectivity of CO continues to decrease with the increase in pressure. These results are consistent with the laws of thermodynamics. The CO₂ conversion and methanol selectivity of Cu₁In₂Zr₄-O-PC are higher than those of Cu₁In₂Zr₄-O-CP under the same pressure, which corresponds to the better catalytic activity of the Cu₁In₂Zr₄-O-PC catalyst. When the pressure increases to 4 MPa, the CO₂ conversion rate of the Cu₁In₂Zr₄-O-PC catalyst reaches 19.1%, the selectivity of methanol reaches 75.4%, and the yield of methanol reaches 14.4%. In other words, with the increase in pressure, the CO₂ conversion rate, methanol selectivity, and methanol yield of the catalyst are significantly improved. Therefore, increasing the reaction pressure can effectively improve the catalytic activity and methanol selectivity of the catalyst.

FIGURE 8

FIGURE 8. (A) CO₂ conversion, methanol selectivity (B), CO selectivity (C), and methanol yield (D) of the catalysts at different pressures. Reaction conditions: T = 270°C, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g h).

3.10 Catalytic performance comparisons

The recently reported catalysts closely related to our paper are listed in Table 4 for catalytic performance comparisons with our work. As shown in Table 4, the CO₂ conversion, CH₃OH selectivity, and yield of the reported catalysts are 10%–25%, 26%–86.2%, and 3.6%–18.3%, respectively, at 2–8 MPa, 170°C–350°C, and H₂: CO₂ molar ratio of 3. In our study, the CO₂ conversion, CH₃OH selectivity, and yield of CuInZr catalyst are 13.3%, 74.3%, and 9.8%, respectively, at 2 MPa, 270°C, and H₂: CO₂ molar ratio of 3, while those of CuInZr catalyst are 19.1%, 75.4%, and 14.4%, respectively, at 4 MPa, 270°C, and H₂: CO₂ molar ratio of 3. Therefore, the catalytic activity level in our work is upper middle above average under similar conditions. Considering that the testing conditions cannot be completely identical, this comparison of catalytic performance can only be used as a reference and cannot be blindly believed.

TABLE 4

TABLE 4. Catalytic performance comparisons of catalysts in our work and literatures.

4 Conclusion

Cu₁In₂Zr₄-O-C catalysts with Cu₂In alloy structure were prepared for CO₂ hydrogenation to methanol. Cu₁In₂Zr₄-O-PC and Cu₁In₂Zr₄-O-CP were obtained from plasma-modified Cu₁In₂Zr₄-O-C before and after calcination, respectively. The characterization analysis showed that the precalcination plasma treatment can improve the dispersion, reduce the crystallinity, reduce the particle size, and enhance the reduction performance of the catalyst. Under the conditions of reaction temperature 270°C, reaction pressure 2 MPa, CO₂/H₂ = 1/3, and GHSV = 12,000 mL/(g·h), the Cu₁In₂Zr₄-O-PC catalyst has a CO₂ conversion of 13.3%, a methanol selectivity of 74.3%, and a CH₃OH space-time yield of 3.26 mmol/gcat/h and also shows good stability. Compared with the Cu₁In₂Zr₄-O-C catalyst, the CO₂ conversion and methanol selectivity of the Cu₁In₂Zr₄-O-PC catalyst were significantly improved.

Data availability statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

Author contributions

YC and JG prepared the catalysts; BY and HL performed the performance test and data analysis; FS and QX wrote the manuscript. All authors contributed to the article and approved the submitted version.

Funding

This work was supported by the Funding for School-level Research Projects of Yancheng Institute of Technology. This work was also supported by the Joint Open Fund of the Key Laboratory under Construction for Volatile Organic Compounds Controlling of Jiangsu Province and Natural Science Research Project of Jiangsu Universities (18KJB610020).

Acknowledgments

The authors also acknowledge support from the Analysis and Test Center, Yancheng Institute of Technology, and appreciate the help provided by D. Zheng.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fchem.2023.1187762/full#supplementary-material

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