Prerpints.org logo
Preprint
Article

Hydrogen Production by Methanol Steam Reforming over CuO/ZnO/Al2O3 Catalysts Based on Oxalate-Precursor Synthesis

Altmetrics

Downloads

110

Views

61

Comments

0

A peer-reviewed article of this preprint also exists.

This version is not peer-reviewed

Submitted:

07 September 2023

Posted:

08 September 2023

You are already at the latest version

Alerts
Abstract
CuO/ZnO/Al2O3 catalyst is a commonly used catalyst for rea methanol steam reforming reaction. Oxalic acid was as precipitant in preparing oxalate precursor of CuO/ZnO/Al2O3 catalyst by co-precipitation, deionized water and ethanol were as solvents, microwave irradiation and water bath were as aging heating manner respectively. It indicated that ethanol selected crystal phase composition of oxalate precursors and restricted their growth. Microwave irradiation prompted the isomorphous substitution between Cu2+ of CuC2O4 and Zn2+ of ZnC2O4 in mother liquid, forming the master phase (Cu,Zn)C2O4 in precursor, the solid solution Cu-O-Zn formed after calcination, which exhibited nano-fibriform morphology. It possessed small CuO grains, large surface area and strong synergy between CuO and ZnO, which is beneficial to improve the catalytic performance of methanol steam reforming, the STY of H2 reached 516.7 mL·g-1·h-1, and the selectivity of CO was only 0.29%.
Keywords: 
Subject: Chemistry and Materials Science  -   Physical Chemistry

1. Introduction

Hydrogen energy has been called "the ultimate energy of the 21st century", and there is a huge development space for hydrogen energy. Among various hydrogen production methods, hydrogen production via methanol is increasingly favored by researchers, methanol as a raw material is easy to store and transport [1]. Currently, there are four main ways to produce hydrogen from methanol: methanol decomposition, (MD, equation (1)), partial oxidative reforming of methanol (POM，equation (2)) methanol steam reforming (MSR, equation (3)), and oxidized methanol steam reforming (OSRM, equation (4)), respectively [2].
CH3OH → 2H2 + CO ΔH = +128.0 kJ·mol-1
CH3OH + 0.5O2 → 2H2 + CO2 ΔH = -192.2 kJ·mol-1
CH3OH + H2O → 3H2 + CO2 ΔH = +49.4 kJ·mol-1
CH3OH + (1-n)H2O + 0.5nO2 → (3-n)H2 + CO2 ΔH= +49(1-n)-192.2n kJ·mol-1
Among the four methods of hydrogen production, MSR is the most widely studied and the most in-depth method. MSR produce the highest amount of hydrogen per mole of methanol, and has the advantages of high purity of hydrogen and low content of CO [3]. Besides, MSR technology has low reaction temperature, low energy consumption and low investment [4].
At present, there are two types of catalysts used in MSR for hydrogen production [5,6]: one type is precious metal catalysts (such as Pd/ZnO, etc.); the other type is non-precious metal catalysts, including non-copper based catalysts (such as Zn-Cr, etc.) and copper based catalysts (such as CuO/ZnO/Al2O3, etc.).
Cu-based catalysts can produce H2 with high selectively at low temperatures and have low CO selectivity, so Cu-based catalysts are widely used. The Cu-based catalysts for MSR have been widely studied, the effect of synergy between CuO and ZnO and the surface structure of CuO/ZnO/Al2O3 catalysts on the catalytic activities are critical [7,8].
Co-precipitation is a common method for preparing CuO/ZnO/Al2O3 catalysts, the precipitation process have a profound impact on the structure and performance of the prepared catalysts. Inui et al. [9] studied the effects of pH and temperature on catalyst precursors in the precipitation process. It indicated that the formation of Cu2(NO3)(OH)3 is advantageous when pH ≤ 6, while (Cu,Zn)2CO3(OH)2 is dominant when pH ≥ 7. The effect of temperature on the precursor is mainly to change the reaction rate, it has almost no effect on its phase composition. Spencer et al. [10] studied the phase transition process in the mother liquor, it indicated that amorphous Cu2CO3(OH)2 first generated, which gradually transformed into (Cu,Zn)2CO3(OH)2 during the aging process. Fang et al. [11] studied the effects of different feeding methods. Cu2(NO3)(OH)3 mainly formed in the forward addition method, while amorphous Cu2CO3(OH)2 mainly formed in the concurrent flow method, which interacts with Zn5(CO3)2(OH)6 and transforms into (Cu,Zn)2CO3(OH)2 and (Cu,Zn)5(CO3)2(OH)6, respectively, a CuO-ZnO solid solution formed after decomposition, which is the active phase of MSR reaction.
The solvents and heating methods are the main factors in the precipitation process. Ma et al. [12] prepared CuO/ZnO/Al2O3 catalyst using ethanol and diethylene glycol as solvent, which possessed larger superficial area and exhibit higher catalytic performance. Zhang et al. [13,14] synthesized the smaller particle CuO/ZnO/Al2O3 catalyst by oxalate co-precipitation using ethanol as solvent, the catalyst showed better catalytic performance for MSR. Dai et al. [15] investigated the surface property of CuO/ZnO/Al2O3 catalysts prepared by oxalate co-precipitation, and explained that isomorphous substitution promoted synergy between CuO and ZnO and increased the superficial content of CuO.
Microwave irradiation heating was rapid and even in the preparation of catalysts, the active components was well-distributed on the support. Besides, microwave irradiation could control the micro structure of materials and enhance the selectivity of target product [16]. It is reported that microwave irradiation had obvious effects on preparation of ZnO and Al2O3 nanoparticles [17]. Zhang et al. [18] treated CuO/ZnO/Al2O3 catalysts with microwave irritation (200W) for 3 ~ 10 min, the catalyst micro structure was significantly improved and the catalytic activity of MSR increased by 7%. Fernández et al. [19] synthesized CuO/ZnO precursor mainly containing aurichalcite and CuO/ZnO/Al2O3 precursor only containing hydrotalcite-like, respectively, under microwave irradiation. The aurichalcite was burned into Cu-O-Zn solid-solution, which exhibited strong synergy and exhibited excellent activity and stability in MSR reaction.
At present, researchers generally believe that the strong synergy effect between Cu and Zn is beneficial for hydrogen production via MSR, many direct evidences for the evolution of the structure, morphology and coordination status of Cu-O-Zn solid solution were provided, which lay a foundation for identifying the active sites and studying the interface effect in the catalytic process [20,21,22].
In present work, the carbonate precursor is replaced by the oxalate precursor, and ethanol replaced water as a solvent, microwave replaced conventional heating as a heating method, the synergy effect between CuO and ZnO was further strengthened. The effects of solvents and heating methods on the composition of oxalate precursors, the structure, properties, and final MSR reaction performance of the calcined catalysts were studied from atomic to nano-scales.

2. Experimental

2.1. Catalyst preparation

The Cu-O-Zn/Al2O3 catalyst precursors were prepared by dropping simultaneously 1 mol/L Cu(NO3)2-Zn(NO3)2-Al(NO3)3 (Cu2+/Zn2+/Al3+ = 16/8/1 (molar ratio)) solution and 1 mol/L H2C2O4 solution into a beaker with stirring constantly and keeping in water bath at 70 °C. Then the suspension was aged in microwave oven or water bath with circulating cooling equipment after co-precipitation, the aging process was conducted at 80 °C for 1 h. The precipitate was filtered and washed with distilled water or ethanol, then the precursor was obtained after drying at 110 °C for 12 h, and the catalyst was obtained after calcining the corresponding precursor at 350 °C for 4 h in air atmosphere. The precursor was designated as XYP and the catalyst was designated as XYC. Table 1 shows the summary the preparation conditions of the catalysts.

2.2. Catalyst characterization

X-ray diffraction (XRD) patterns of solid samples were recorded using a Rigaku D/max 2500 power diffractometer with Cu Kα radiation at 40 kV and 100 mA with a scanning rate of 8°/min in the 2θ ranges from 10° to 40°.
Temperature-programmed reduction (H2-TPR) was performed in an Autochem Ⅱ 2920. About 20 mg catalyst sample was set in a U-mode quartz tube, pretreated in a Helium at 50 °C for 30 min, then heated to 300 °C at a rate of 10 °C /min, under a mixture of 10 vol% H2/Ar (50 ml/min), the sample was then heated to 600 °C at a rate of 10 °C /min, The consumption of hydrogen was monitored by a thermal conductivity detector.
Differential thermal gravity (DTG) measurement was executed in a STA409C thermal analyzer. 30 mg sample was heated to 600 °C at a rate of 8 °C/min in a gas mixture of 20 vol% O2/N2 (50 ml/min).
JSM-6700F cold-field scanning electron microscope (SEM) was used to characterize the size and morphology of the samples.
BET specific surface areas and pore distribution of catalyst was measured with a SORPTMATIC 1990 automatic adsorption instrument employing N2 as the adsorbent. BET specific surface areas were calculated by applying the Brunauer-Emmett-Teller (BET) method.
X-ray photoelectron spectroscopy (XPS) spectra of the samples were collected on an ESCAL-ab 220i-XL electron spectrometer using Al Kα radiation at 300 W. The samples were compressed into a pellet of 2 mm thickness and then mounted on a sample holder. The chamber was maintained at lower than 10−10 Torr. The binding energies were calibrated by C1s as the reference energy (C1s = 284.6 eV).

2.3. Catalytic performance of MSR

The performance evaluation of MSR was conducted on a continuous flow fixed bed device with a catalyst loading of 2 g, using industrial refined methanol as raw material. Evaluation conditions: raw material methanol aqueous solution (the molar ratio of water to methanol is 1.5), reaction temperature 260 °C, pressure 0.5 MPa, WHSV = 1.0 h-1. After cooling, gas and liquid samples were analyzed using chromatographs equipped with PorpakT columns and TDX-01 columns, respectively, and thermal conductivity cell detectors. The methanol conversion rate and product distribution were calculated.

3. Results and discussion

3.1. XRD characterization of precursors

Figure 1 shows the XRD patterns of all catalyst precursors. It is seen that the phases of CuC2O4·xH2O (2θ = 18.5°, 23.1°, 31.2°, 36°, 38.5°), α-ZnC2O4·2H2O (2θ = 18.9°, 35.1°), and β-ZnC2O4 (2θ = 24°, 25.1°, 29.1°, 34.1°, 36.9°) were observed in precursor of WWP prepared by water solvent and water bath heating. But only diffraction peaks of CuC2O4·xH2O (2θ = 23.1°, 36°, 38.5°) and weak peaks of β-ZnC2O4 (2θ = 24°, 36.9°) existed in precursor of EWP prepared by ethanol solvent and water bath heating, no α-ZnC2O4·2H2O phase was observed. It indicated that ethanol solvent restrained the formation of α-ZnC2O4·2H2O, and enhanced the phase selectivity of product. Microwave irradiation promoted the isomorphous substitution between Cu2+ of CuC2O4·xH2O and Zn2+ of ZnC2O4 in mother liquid, thus, WMP and EMP mainly contained (Cu,Zn)C2O4 and partial CuC2O4 failing to be substituted during aging, so diffraction peak of CuC2O4·xH2O (2θ = 23.1°, 36°) and β-ZnC2O4 (2θ = 24°, 36.9°) overlapped each other respectively and deviated original position. Compared with WWP and EWP, WMP and EMP didn’t contain diffraction peaks of α-ZnC2O4·2H2O and β-ZnC2O4, and the crystal degree declined and failed to be detected owning to isomorphous substitution, it indicated that microwave irradiation have strong selectivity on the formation of crystal phase [23,24].
CuC2O4·xH2O, α-ZnC2O4·2H2O and β-ZnC2O4 generated in mother liquid in co-precipitation, as equation (1), (2) and (3). The isomorphous substitution mainly occurred in the aging process, it means that the Cu2+ of CuC2O4 entered into ZnC2O4 and the Zn2+ of ZnC2O4 entered into CuC2O4 formed (Cu,Zn)C2O4, as equation (4) and (5). However, the concentration of Cu2+ was higher than that of Zn2+, it primarily produced CuC2O4 as equation (1) in mother liquid, and the ZnC2O4 was little. In other words, the reaction (4) and (5) were promoted simultaneously by microwave irradiation, while CuC2O4 was not substituted completely.
Cu2+ + C2O42- + xH2O → CuC2O4·xH2O
Zn2+ + C2O42- + 2H2O → α-ZnC2O4·2H2O
Zn2+ + C2O42- → β-ZnC2O4
CuC2O4 + xZn2+→ (Cu1-x,Znx)C2O4
ZnC2O4 + xCu2+→ (Cux,Zn1-x)C2O4

3.2. DTG characterization of precursors

DTG curves of different catalyst precursors are shown in Figure 2. Three weight loss peaks for WWP were observed at 118 °C, 308 °C and 343 °C respectively, as shown in equation (6) ~ (9), the peak at 118 °C was due to the desorption of physically absorbed water of α-ZnC2O4·2H2O, the peak around 308 °C was ascribed to the decomposition of CuC2O4·xH2O or (Cu,Zn)C2O4, and the peak at about 343 °C was attributed to decomposition of β-ZnC2O4 and further decomposition of α-ZnC2O4 [13]. The weight loss peak for CuC2O4·xH2O at 307 °C and weak peak for β-ZnC2O4 at 343 °C were observed from curve of EWP, which verified the XRD analysis of its precursor.
α-ZnC2O4·2H2O → α-ZnC2O4 + 2H2O t ≈ 118 °C
CuC2O4·xH2O → CuO + CO2 + H2O t ≈ 308 °C
α-ZnC2O4 → ZnO + CO2 t ≈ 343 °C
β-ZnC2O4 → ZnO + CO2 t ≈ 343 °C
(Cu,Zn)C2O4 →(Cu,Zn)O + CO2 t ≈ 296 °C
WMP and EMP prepared under microwave irradiation only included weight loss peak for (Cu,Zn)C2O4 or CuC2O4·xH2O at about 300 °C, it can be speculated that microwave irradiation accelerated the isomorphous substitution between Cu2+ and Zn2+, the lesser Zn2+ was incorporated into CuC2O4, so there is little content of α-ZnC2O4·2H2O or β-ZnC2O4 and there were no corresponding decomposition peaks. Especially, EMP had a large quantity of substitution and produced more (Cu,Zn)C2O4, the crystal phase trended to uniformity, therefore, the decomposition peak of EMP became narrower and the decomposition temperature decreased by 12 °C [23], the peak was mainly ascribe to (Cu,Zn)C2O4 and partial CuC2O4 unable to be substituted as equation (7) and (10).

3.3. SEM images of precursors and catalysts

SEM images of different precursors are shown in Figure 3, SEM images of different catalysts after calcining the corresponding precursors ar shown in Figure 4. The appearance of catalysts kept coherence with precursors in some extent by comparing Figure 3 and Figure 4. WWP presented as spherical particles, its diameter was 400 nm or so, it exhibited wafer-shaped and agglomerated each other after calcination, its particle size reduced to 300 nm about. EWC was consisted of irregular bar-shaped and block-shaped, 400 nm in size, it elucidated that ethanol solvent had effects on the shaping process of precursor in mother liquid. EWC didn’t change a lot on appearance or size compared with EWP, its size was about 300~400 nm, however, there were many minor porous channel in its superficial structure.
After introducing microwave irradiation, irregular uniwafer could be observed from morphology of WMP, its size was in the range of 300~500 nm. WMC was needle-like and flakiness owning to not be broke down completely, its diameter of section was about 50~100 nm; when ethanol was selected as solvent further, EMP mainly contained unidirectional ordered fibrous nanoparticles, its diameter of section was about 50 nm, which exhibited fine fibrous or flocculent and dispersed evenly after calcination [25].
After combining SEM photographies of precursors and catalysts, it can be concluded that precursors formed towards low dimensions under bulk heating effects of microwave. Precursors prepared by water bath exhibited spherical and massive, while precursors prepared by microwave irradiation presented single fibrous, which particle size was smaller than the former. The particle diameter of EMC was merely 50 nm, it dispersed well and the superficial activity sites distributed evenly, which benefited to improve the catalytic performance of MSR.

3.4. XRD characterization of catalysts

XRD patterns of different catalysts can be seen in Figure 5. The average grain size calculated by Scherrer formula at 2θ ≈ 35.5°, 38.7° and the texture parameters of different catalysts are listed in Table 2. There were no peaks assigned to Al2O3 in the four patterns, indicating that Al2O3 existed as amorphous or the content of Al2O3 was low. Diffraction peaks of CuO appeared in all the four catalysts at 2θ of 38.7°, CuO peaks of WWC were very sharp, the grain size of CuO was comparatively large, up to 18.8 nm as shown in Table 2. The CuO peaks of EWC became smoother when using ethanol as solvent, in which the ZnO peaks at 2θ＝34.4°, and 36.3° overlapped with CuO peak at 2θ＝35.5°. CuO grain size of EWC reduced to 12 nm, which indicated that viscous ethanol restricted the growth of precursor in mother liquid, resulting in a decrease in CuO grain size after calcination.
From patterns of WMC and EMC in Figure 5, it can be observed that the CuO peak becomes smoother, after introducing microwaves. Weak peaks of ZnO could still be seen in WMC, however, no peaks assigned to ZnO were detected in EMC. It indicated that isomorphous substitution took place in mother liquid when microwave irradiation was introduced, partial Cu2+ of CuC2O4 was incorporated into ZnC2O4 and almost all Zn2+ of ZnC2O4 was incorporated into CuC2O4, thereby, the original crystal structure were destroyed and the crystal degree declined after substitution. Cu-O-Zn solid solutions were obtained after calcining WMP and EMP, in which there existed strong synergy between CuO and ZnO. CuO crystal was surrounded averagely by ZnO crystal, which restricted the growth of CuO crystallites, so the grain size of CuO in WMC and EMC were merely 8.9 nm and 8.4 nm respectively [24].
As shown in Table 2, catalysts prepared under microwave irradiation possessed bigger surface area and pore volume than that prepared in water bath, surface area and pore volume of EMC were 77.2 m2/g and 0.36 cm3/g respectively. This is because there was much more (Cu,Zn)C2O4 in precursor prepared under microwave irradiation, the precursor were converted into (Cu,Zn)O (or Cu-O-Zn) solid solution after calcination, in which ZnO and CuO arrayed homogeneously and closely, restricting the agglomeration of CuO, therefore the catalysts were very fine and possessed large surface area. The mother liquid was sol-like after aging when ethanol was selected as solvent, the catalyst possessed large surface area after calcining corresponding precursor [26], so the pore volume of EWC and EMC was comparatively large as shown in Table 2.

3.5. H2-TPR characterization of catalysts

Figure 6 shows H2-TPR curves of different catalysts. Ethanol restricted the growth of precurs phase and favored forming fine catalysts which made the reduction process easy. It manifested that reduction temperature of catalysts prepared using ethanol as solvent was lower than that using water. The catalysts prepared by water bath heating were difficult to reduce, the reduction temperature of WWC and EWC was 240 °C approximately, while the reduction temperature of catalysts prepared by microwave irradiation was lower, it was 220 °C or so. It proved again that microwave irradiation selected the phase in the generation process of precursor, the catalyst arranged orderly in micro structure, which decreased the difficulty of reducing CuO by H2.
As shown in Figure 6, one low temperature reduction peak and one high emerged in curves of WWC, EWC, and WMC, however, three peaks emerged in curve of EMC, the first two were divided to low temperature reduction peaks, the third was divided to high temperature reduction peak. Low temperature reduction peaks were assigned to reduction of scattered phase CuO (Peak I), while the other was assigned to reduction of bulk phase CuO (Peak II). The amount of isomorphous substitution was little in mother liquids aging heated by water bath, thus, its synergy between CuO and ZnO was weak and there mainly existed bulk phase CuO in corresponding catalyst, so their Peak II was larger. The amount of substitution between Cu2+ and Zn2+ was great when aging under microwave irradiation, they mainly generated (Cu,Zn)C2O4 in precursors which were calcined into Cu-O-Zn solid solutions. The catalysts were homogeneous and dispersive, the synergy was strong, so the Peak I was larger. Especially, the amount of substitution for EMC was great, the reduction peak assigned to high temperature was much smaller than others [27,28].

3.6. XPS and AES characterization of catalysts

XPS spectra of catalysts are shown in Figure 7. As shown in Figure 7(a), all catalysts showed a distinctive BE (binding energy) of Cu 2p3/2 around 932~933 eV, companying a characteristic satellite peak between 940 ~ 945 eV due to the electron shakeup process, which indicated that Cu species were present as CuO. The BE of Cu 2p3/2 around 932 ~ 933 eV in spectra of WWC, EWC, WMC and EMC were 932.0 eV, 932.05 eV, 932.10 eV and 932.95 eV respectively, increasing gradually. The BE of Zn2p3/2 (Figure 7(b)) in corresponding spectra were 1021.45 eV, 1020.6 eV, 1020.35 eV and 1020.15 eV, decreasing gradually, which were lower than the BE (1022.2 eV) of pure ZnO [29].
It illustrated that isomorphous substitution took place when introducing microwave in aging process. The chemical environment and energy status of copper and zinc changed in the gotten Cu-O-Zn solid solution. Because the electronegativity of zinc was higher than copper, the outermost electron of copper shifted towards zinc, the electron density of copper decreased and its binding energy increased, while the electron density of zinc increased and its binding energy decreased [23].
Table 3 lists the data analysis based on XPS and AES spectra and the superficial elements concentration of different catalysts. EMC possessed higher superficial copper content and lower superficial zinc content, its ratio of XCu/XZn was up to 8.98, which exceeded all others, it can be verified by the intensity of spectra in Figure 7 and Figure 8. In Table 3, it also could be observed that ethanol solvent help to improve the content of superficial copper atoms. Besides, microwave irradiation raised the yield of (Cu,Zn)C2O4 in precursor, leading to lower KE (kinetic energy) of Cu LMM and higher KE of Zn LMM in final catalyst as shown in Figure 8. This was coincident with the research result of literature [15].

3.7. Catalytic performance test for MSR reaction

The catalytic performance of different catalysts for MSR is listed in Table 4. When comparing WWC and EWC, it can be concluded that ethanol solvent is conducive to reducing the CO selectivity of the catalyst. As can be seen from the XRD data, ethanol optimized precursor crystal phase composition, thereby reducing the CO selectivity. When comparing WWC and WMC, it can be concluded that microwave heating is conducive to improving the methanol conversion rate of the catalyst. As can be seen from the BET data and SEM images, microwave radiation increases the specific surface area of the catalyst, improves the dispersity of copper, increases more active sites, and thus improves the methanol conversion rate. Besides, as can be seen from the XRD data, microwave irradiation prompted the isomorphous substitution between cooper and zinc oxalate precursors, Cu-O-Zn solid solution formed after calcination, which possessed strong synergy and benefited the MSR reaction.
Thus, it illustrated that both ethanol and microwave irradiation benefited to improve the catalytic performance of MSR, the catalyst EMC prepared by ethanol solvent and microwave heating exhibited optimal catalytic performance, the conversion of methanol was 91.2%, the space time yield (STY) of H2 reached 516.7 mL·g-1·h-1, its selectivity of CO was only 0.29%; In stark contrast, the catalyst WWC prepared by water solvent and water bath heating showed the worst catalytic performance, its conversion of methanol was only 53.6%, and the STY of H2 was 300.0 mL·g-1·h-1, but its selectivity of CO was as high as 1.53%.

4. Conclusion

In the preparing process of CuO/ZnO/Al2O3 catalyst precursors, ethanol solvent selected the crystal phase composition in precursor and restricted its growth. Microwave irradiation promoted the isomorphous substitution between oxalate copper and oxalate zinc, the precursor mainly contain (Cu,Zn)C2O4 and exhibit nano-fibriform morphology. Either using ethanol as solvent or adopting microwave irradiation as aging heating manner benefited MSR reaction, the catalyst EMC prepared by ethanol solvent and microwave heating showed the optimal catalytic performance, the maximum STYH2 reached 516.7 mL·g-1·h-1, the conversion of CH3OH reached 91.2%, and the selectivity of CO was only 0.29%.

Acknowledgments

This study was supported by National Natural Science Foundation of China (21676158), and National Key Research and Development Program (2018A23).

References

  1. Kawamura Y, Ogura N, Igarashi A. Hydrogen production by methanol steam reforming using microreactor. J Jpn Petrol Inst 2013, 56, 288–297. [Google Scholar] [CrossRef]
  2. Yong ST, Ooi CW, Chai SP, Wu XS. Review of methanol reforming-Cu-based catalysts, surface reaction mechanisms, and reaction schemes. Int J Hydrogen Energ 2013, 38, 9541–9552. [Google Scholar] [CrossRef]
  3. Xu XH, Shuai KP, Xu B. Review on copper and palladium based catalysts for methanol steam reforming to produce hydrogen. Catalysts 2017, 7, 183. [Google Scholar] [CrossRef]
  4. Iulianelli A, Ribeirinha P, Mendes A, Basile A. Methanol steam reforming for hydrogen generation via conventional and membrane reactors: a review. Renew Sust Energ Rev 2014, 29, 355–368. [Google Scholar] [CrossRef]
  5. Iwasa N, Masuda S, Ogawa N, Takezawa N. Steam reforming of methanol over Pd/ZnO: effect of the formation of PdZn alloys upon the reaction. Appl Catal A: Gen 1995, 125, 145–157. [Google Scholar] [CrossRef]
  6. Shokrani R, Haghighi M, Jodeiri N, Ajamein H, Abdollahifar M. Fuel cell grade hydrogen production via methanol steam reforming over CuO/ZnO/Al2O3 nanocatalyst with various oxide ratios synthesized via urea-nitrates combustion method. Int J Hydrogen Energ 2014, 39, 13141–13155. [Google Scholar] [CrossRef]
  7. Shishido T, Yamamoto Y, Morioka H, Takehira K. Production of hydrogen from methanol over Cu/ZnO and Cu/ZnO/Al2O3 catalysts prepared by homogeneous precipitation: steam reforming and oxidative steam reforming. J Mol Catal A: Chem 2007, 268, 185–194. [Google Scholar] [CrossRef]
  8. Agrell J, Birgersson H, Boutonnet M, Melián-Cabrera I, Navarro RM, Fierro JLG. Production of hydrogen from methanol over Cu/ZnO catalysts promoted by ZrO2 and Al2O3. J Catal 2003, 219, 389–403. [Google Scholar] [CrossRef]
  9. Spencer, MS. Precursors of copper/zinc oxide catalysts. Catal Lett 2000, 66, 255–257. [Google Scholar] [CrossRef]
  10. Li JL, Inui T. Characterization of precursors of methanol synthesis catalysts copper/zinc/aluminum oxides precipitated at different pH and temperatures. Appl Catal A: Gen 1996, 137, 105–117. [Google Scholar] [CrossRef]
  11. Fang DR, Ren WZ, Liu ZM, Xu XF, Xu L, Lv HY, et al. Synthesis and applications of mesoporous Cu-Zn-Al2O3 catalyst for dehydrogenation of 2-butanol. J Nat Gas Chem 2009, 18, 179–182. [Google Scholar] [CrossRef]
  12. Ma Y, Sun Q, Wu D, Fan WH, Zhang YL, Deng JF. A practical approach for the preparation of high activity Cu/ZnO/ZrO2 catalyst for methanol synthesis from CO2 hydrogenation. Appl Catal A: Gen 1998, 171, 45–55. [Google Scholar] [CrossRef]
  13. Zhang YL, Sun Q, Deng JF, Wu D, Chen SY. A high activity Cu/ZnO/Al2O3 catalyst for methanol synthesis: Preparation and catalytic properties. Appl Catal A: Gen 1997, 158, 105–120. [Google Scholar] [CrossRef]
  14. Zhang XR, Wang LC, Yao CZ, Cao Y, Dai WL, He HY, et al. A highly efficient Cu/ZnO/Al2O3 catalyst via gel-coprecipitation of oxalate precursors for low-temperature steam reforming of methanol. Catal Lett 2005, 102, 183–190. [Google Scholar] [CrossRef]
  15. Dai WL, Sun Q, Deng JF, Wu D, Sun YH. XPS studies of Cu/ZnO/Al2O3 ultra-fine catalysts derived by a novel gel oxalate co-precipitation for methanol synthesis by CO2+H2. Appl Surf Sci 2001, 177, 172–179. [Google Scholar] [CrossRef]
  16. Wu ZJ, Ge SH, Zhang MH, Li W, Tao KY. Synthesis of a supported nickel boride catalyst under microwave irradiation. Catal Commun 2008, 9, 1432–1438. [Google Scholar] [CrossRef]
  17. Sule EE, Sadik C, Siddik I. Conventional and microwave-assisted synthesis of ZnO nanorods and effects of PEG400 as a surfactant on the morphology. Inorg Chim Acta 2009, 362, 1855–1858. [Google Scholar] [CrossRef]
  18. Zhang XR, Wang LC, Cao Y, Dai WL, He HY, K. N. Fan. A unique microwave effect on the microstructural modification of Cu/ZnO/Al2O3 catalysts for steam reforming of methanol. Chem Commun 2005, 102, 4104–4106. [Google Scholar]
  19. Fernández Y, Menéndez JA, Arenillas A, Fuente E, Peng JH, Zhang ZB, et al. Microwave-assisted synthesis of CuO/ZnO and CuO/ZnO/Al2O3 precursors using urea hydrolysis. Solid State Ionics 2009, 180, 1372–1378. [Google Scholar] [CrossRef]
  20. Nakamura J, Choi Y, Fujitani T. On the issue of the active site and the role of ZnO in Cu/ZnO methanol synthesis catalysts. Top Catal 2003, 22, 277–285. [Google Scholar] [CrossRef]
  21. Kasatkin I, Kurr P, Kniep B, Trunschke A, Schlögl R. Role of lattice strain and defects in copper particles on the activity of Cu/ZnO/Al2O3 catalysts for methanol synthesis. Angew Chem Int Edit 2007, 46, 7324–7327. [Google Scholar] [CrossRef] [PubMed]
  22. Behrens M, Studt F, Kasatkin I, Kühl S, Hävecker M, Abild-Pedersen F, et al. The active site of methanol synthesis over Cu/ZnO/Al2O3 industrial catalysts. Science 2012, 336, 893–897. [Google Scholar] [CrossRef] [PubMed]
  23. Wang LC, Liu YM, Chen M, Cao Y, He HY, Wu GS, et al. Production of hydrogen by steam reforming of methanol over Cu/ZnO catalysts prepared via a practical soft reactive grinding route based on dry oxalate-precursor synthesis. J Catal 2007, 246, 193–204. [Google Scholar] [CrossRef]
  24. Ning WS, Shen HY, Liu HZ. Study of the effect of preparation method on CuO-ZnO-Al2O3 Catalyst. Appl Catal A: Gen 2001, 211, 153–157. [Google Scholar] [CrossRef]
  25. An X, Li JL, Zuo YZ, Zhang Q, Wang DZ, Wang JF. A Cu/Zn/Al/Zr fibrous catalyst that is an improved CO2 hydrogenation to methanol catalyst. Catal Lett 2007, 118, 264–269. [Google Scholar] [CrossRef]
  26. Bao J, Liu ZL, Zhang Y, Tsubaki N. Preparation of mesoporous Cu/ZnO catalyst and its application in low-temperature methanol synthesis. Catal Commun 2008, 9, 913–918. [Google Scholar] [CrossRef]
  27. Yang RQ, Yu XC, Zhang Y, Li WZ, Tsubaki N. A new method of low-temperature methanol synthesis on Cu/ZnO/Al2O3 catalysts from CO/CO2/H2. Fuel 2008, 87, 443–450. [Google Scholar] [CrossRef]
  28. Bae JW, Kang SH, Lee YJ, Jun KW. Synthesis of DME from syngas on the bifunctional Cu–ZnO–Al2O3/Zr-modified ferrierite: Effect of Zr content. Appl Catal B: Environ 2009, 90, 426–435. [Google Scholar] [CrossRef]
  29. Baltes C, Vukojevi´c S, Schüth F. Correlations between synthesis, precursor, and catalyst structure and activity of a large set of CuO/ZnO/Al2O3 catalysts for methanol synthesis. J Catal 2008, 258, 334–344. [Google Scholar] [CrossRef]
Preprints 84495 g001
Figure 1. XRD patterns of the catalyst precursors.
Figure 1. XRD patterns of the catalyst precursors.
Preprints 84495 g001
Preprints 84495 g002
Figure 2. DTG curves of catalyst precursors.
Figure 2. DTG curves of catalyst precursors.
Preprints 84495 g002
Preprints 84495 g003
Figure 3. SEM images of catalyst precursors. (a) WWP; (b) EWP; (c) WMP; (d) EMP.
Figure 3. SEM images of catalyst precursors. (a) WWP; (b) EWP; (c) WMP; (d) EMP.
Preprints 84495 g003
Preprints 84495 g004
Figure 4. SEM images of catalysts. (a) WWC; (b) EWC; (c) WMC; (d) EMC.
Figure 4. SEM images of catalysts. (a) WWC; (b) EWC; (c) WMC; (d) EMC.
Preprints 84495 g004
Preprints 84495 g005
Figure 5. XRD patterns of catalysts.
Figure 5. XRD patterns of catalysts.
Preprints 84495 g005
Preprints 84495 g006
Figure 6. H2-TPR curves of catalysts.
Figure 6. H2-TPR curves of catalysts.
Preprints 84495 g006
Preprints 84495 g007
Figure 7. XPS spectra of catalysts.
Figure 7. XPS spectra of catalysts.
Preprints 84495 g007
Preprints 84495 g008
Figure 8. AES patterns of catalysts.
Figure 8. AES patterns of catalysts.
Preprints 84495 g008
Table 1. Summary of the preparation condition of catalysts.
Table 1. Summary of the preparation condition of catalysts.
Catalyst Precursor Solvent Heating manner
WWC WWP Water Water bath (WB)
EWC EWP Ethanol Water bath (WB)
WMC WMP Water Microwave irradiation (MI)
EMC EMP Ethanol Microwave irradiation (MI)
Table 2. Results of grain size and textural properties of catalysts.
Table 2. Results of grain size and textural properties of catalysts.
Catalyst Grain size /nm Textural properties
2θ≈35.5° 2θ≈38.7° Surface area (m2/g) Pore volume (cm3/g)
WWC 18.8 14.4 43.9 0.27
EWC 12.0 13.9 56.4 0.31
WMC 8.9 11.2 59.5 0.29
EMC 8.4 9.5 77.2 0.36
Table 3. XPS and AES data of different catalysts.
Table 3. XPS and AES data of different catalysts.
Catalyst Surface atom/% BE(Cu 2p3/2)
/eV		 BE(Zn 2p3/2)
/eV		 KE(Cu LMM)
/eV		 KE(Zn LMM)
/eV
Cu Zn XCu/XZn
WWC 6.56 15.61 0.42 932.00 1021.45 919.10 988.30
EWC 4.96 9.17 0.54 932.05 1020.60 919.05 988.35
WMC 5.49 8.7 0.63 932.10 1020.35 918.95 988.80
EMC 10.77 1.2 8.98 932.95 1020.15 918.20 988.85
Table 4. Catalytic performance of different catalysts for MSR reaction.
Table 4. Catalytic performance of different catalysts for MSR reaction.
Catalyst Solvent aHeating
Manner		 XMeOH
/%		 STYH2
/mL·g-1·h-1 		bSCO
/%
WWC Water WB 53.6 300.0 1.53
EWC Ethanol WB 59.1 333.9 0.39
WMC Water MI 85.0 479.5 0.82
EMC Ethanol MI 91.2 516.7 0.29
a Evaluation conditions: the molar ratio of water to methanol is 1.5 in the methanol aqueous solution, T = 260 °C, P =0.5 MPa, WHSV = 1.0 h-1. b WB represents water bath, MI represents microwave irradiation. c XMeOH：methanol conversion; SCO：CO selectivity.
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.
Copyright: This open access article is published under a Creative Commons CC BY 4.0 license, which permit the free download, distribution, and reuse, provided that the author and preprint are cited in any reuse.
Prerpints.org logo

Preprints.org is a free preprint server supported by MDPI in Basel, Switzerland.

facebook logotwitter logolinkedin logo
MDPI Initiatives
Important Links
Subscribe

Disclaimer

Terms of Use

Privacy Policy

© 2024 MDPI (Basel, Switzerland) unless otherwise stated