Al2O3 Catalyst for CO2

Subscriber access provided by UNIV OF LOUISIANA

Kinetics, Catalysis, and Reaction Engineering

Investigation on Deactivation of Cu/ZnO/Al2O3 Catalyst for CO2 Hydrogenation to Methanol Binglian Liang, Junguo Ma, Xiong Su, Chongya Yang, Hongmin Duan, Huanwen Zhou, Shaoliang Deng, Lin Li, and Yanqiang Huang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b01546 • Publication Date (Web): 30 Apr 2019 Downloaded from http://pubs.acs.org on April 30, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Investigation on Deactivation of Cu/ZnO/Al2O3 Catalyst for CO2 Hydrogenation to Methanol Binglian Liang,†,‡ Junguo Ma,† Xiong Su,† Chongya Yang,†,‡ Hongmin Duan,† Huanwen Zhou,§ Shaoliang Deng,§ Lin Li,† Yanqiang Huang*,†,⊥ †Dalian

Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road,

Dalian, 116023, China. ‡University

§Dalian

of Chinese Academy of Sciences, 19A Yuquan Road, Beijing, 100049, China.

Reak Science & Technology Co., Ltd., 327 Shunle Street, Lvshun Economic

Development Zone, Dalian 116023, China. ⊥Dalian

National Laboratory for Clean Energy, Dalian, 116023, China.

Corresponding Author

Fax: (+) 86-411-84685940; Tel: (+) 86-411-84379416; E-mail: [email protected]

ACS Paragon Plus Environment

1

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

ABSTRACT: The catalytic performance of Cu/ZnO/Al2O3 (CuZnAl) catalyst for CO2 hydrogenation to methanol was investigated over a period of 720 h time-on-stream, which showed that the space time yield of CH3OH was decreased by 34.5% during the long-term testing. Different characterization techniques including X-ray diffraction (XRD), scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and N2O adsorption experiments, were applied to study the deactivation reasons. XRD and N2O adsorption experiments indicated that there were no obvious changes in Cu particle size after the CuZnAl catalyst was exposed to reaction atmosphere for 720 h, while agglomeration took place on ZnO particles. XPS results revealed that part of the metallic Cu was oxidized to Cu2+. The CuZnAl catalyst deactivation was proved to be due to the comprehensive effect of Cu oxidation and ZnO species agglomeration during CO2 hydrogenation to methanol.

KEY WORDS: CO2 hydrogenation; Methanol synthesis; Cu/ZnO/Al2O3 catalyst; Deactivation.


2

Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION The gradual increase in atmospheric CO2 concentration poses a grand challenge to the global environment.1-2 There was an ongoing research upsurge in finding ways to stabilize the atmospheric CO2 levels by reducing CO2 production, effective transforming or storing of CO2.3-8 CO2 utilization through catalytic converting CO2 to liquid fuels or other valuable chemicals has received considerable attention from the viewpoint of environmental protection and energy conservation issues.9-15 In particular, the hydrogenation of CO2 to methanol was considered as one of the most promising ways for CO2 utilization in a large scale.16-24 As a kind of liquid fuel with high energy density, methanol can act as an additive being directly added into gasoline, and also a key platform chemical to manufacture several important chemicals such as formaldehyde, dimethyl ether, light olefins, acetic acid, and a wide variety of other products.25 The synthesis of CH3OH by CO2 and H2 originated from renewable energy (wind, solar, or biomass energy), can realize not only the utilization of CO2, but also the storage of renewable energy into methanol.26 This process fits in the vision of the powerful “liquid sunshine” strategy which combines the renewable energy with CO2 and water to produce green liquid fuel.27 Catalysts possessing good stability and longer lifetime have a significant value for developing industrial processes. However, the industrial application is always accompanied by a deactivation behavior of catalysts. Recognition and exploration of the reasons for catalyst deactivation and then developing catalysts with better stability appears to be an extremely important task. Previously, the reasons for deactivation on CuZnAl catalyst in methanol synthesis from syngas have been widely studied, which can be summarized as following: (1) catalyst poisoning resulted from the trace impurity in feed gas;28-29 (2) Cu particles sintering


3


Page 4 of 27

caused by the high reaction temperature;30 (3) carbon deposition.31 Recently, benefitting from the development of modern characterization techniques, there were some new observations for CuZnAl catalyst deactivation in CO hydrogenation to methanol. Lunkenbein et al. investigated the deactivation behavior of CuZnAl catalyst for the synthesis of methanol over a time-on-stream (TOS) period of 148 days. It was suggested that the deactivation was mainly resulted from the changes in ZnO moiety because ZnO acted as the most dynamic species, and only slight changes took place on the Cu nanoparticles.32 It is noteworthy that there are differences for methanol synthesis between CO hydrogenation and CO2 hydrogenation. During CO2 hydrogenation to methanol, the in situ water generation may accelerate the crystallization of Cu and ZnO components in Cu/ZnO-based catalysts, which leads to the catalyst deactivation.33 However, it still lacks systematic understanding on the details of dynamic structural changes of catalyst during the deactivation period, and the real deactivation reasons need to be further investigated. In this study, CuZnAl catalyst was evaluated for as long as 720 h in the catalytic hydrogenation of CO2 to methanol. The change of catalyst structure during the operation was explored in detail with the help of various characterization techniques and the reasons for catalyst deactivation were systematically analyzed.

2. EXPERIMENTAL SECTION 2.1 Catalyst evaluation. The CuZnAl catalyst was provided by Dalian Reak science & technology Co., Ltd. The activity evaluation of methanol synthesis from CO2 hydrogenation was carried out in a fixed-bed continuous-flow reactor at high pressure. Typically, the catalyst (0.2 mL, 20 - 40 mesh) diluted with quartz sand (0.8 mL, 20 - 40 mesh) was placed in a stainless steel tubular flow reactor (i.d. 10 mm). Prior to reaction, the catalyst was reduced at 250 oC for 1 h in


4

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pure hydrogen with a flow rate of 20 mL min-1 under atmospheric pressure. After cooling down, the feed gas with a H2/CO2 ratio of 3/1 was introduced into the reactor and adjusted to the setting pressure (typically 3 MPa), followed by elevating the temperature to the desired value (typically 200 oC) to initiate the reaction. The reaction temperature was controlled by a thermocouple which was located at the central position of the catalyst bed. The reaction conditions were controlled as following except for special labelled: H2/CO2 = 3; pressure, 3 MPa; temperature, 200 oC; gas hourly space velocity, 9000 h-1. The catalytic reaction data were collected after at least 10 hours on stream. The effluent gas products were kept at 120 oC to prevent any condensation. The products were analyzed by two online Agilent 7890B gas chromatograph equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID), respectively. Carbon molecular sieve (TDX-01) packed column was connected to TCD for H2, CO2, CO and Ar analysis, while the FFAP capillary column was connected to FID for CH4 and CH3OH analysis. The selectivity to CH4 would not be mentioned in the following study since it was below 1%. The activity of methanol synthesis was evaluated by space time yield (STY) of the methanol product, and the detailed calculation formulas was as flowing.34

𝑋𝐶𝑂2(%) =

𝐶𝑂2(in) ― 𝐶𝑂2(out) 𝐶𝑂2(in)

× 100%；

𝐶𝐻3𝑂𝐻(out)

S𝐶𝐻3𝑂𝐻(%) = 𝐶𝑂2(in) ― 𝐶𝑂2(out) × 100%； STY(gCH3OH kgcat·h) =

𝐹𝐶𝑂2(in) × 𝑋𝐶𝑂2 × S𝐶𝐻3𝑂𝐻 × 𝑀𝐶𝐻3𝑂𝐻 𝑊𝑐𝑎𝑡

× 100%.

where 𝑋𝐶𝑂2is CO2 conversion, S𝐶𝐻3𝑂𝐻is CO2 conversion, 𝐶𝑂2(in) and 𝐶𝑂2(out) are the amount of CO2 at the inlet and outlet of the reactor, 𝐶𝐻3𝑂𝐻(out) is the amount of CH3OH at the outlet of the reactor, 𝐹𝐶𝑂2(in) is the molar flow rate of CO2 at the inlet of the reactor, 𝑀𝐶𝐻3𝑂𝐻 is the molecular weight of methanol (32 g mol-1) and Wcat is the used catalyst weight.


5


Page 6 of 27

2.2 Catalyst characterization. X-ray diffraction (XRD) patterns were carried out on a PANalytical X’Pert-Pro powder X-ray diffractometer, using Cu Kα monochromatized radiation (λ = 0.1541 nm) with a scanning angle (2θ) of 10 - 80o at a scan speed of 6o min-1. The voltage and current were operated at 40 kV and 40 mA, respectively. The high resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images were measured on a JEM-2000EX (JEOL) microscope. Scanning electron microscopy (SEM) images were recorded on a JSM-7800F microscope. X-ray photoelectron spectroscopy (XPS) experiments were recorded on an ESCALAB 250Xi spectrometer using Al Kα (hυ = 1486.6 eV) X-ray source with pass energy of 20 eV, and base pressure of analysis chamber was less than 1 × 10-8 Pa. The binding energy was corrected for surface charging by C1s peak at 284.6 eV as the charge calibration reference. For XPS experiments, all samples were passivated in 1%O2/Ar to avoid the severe oxidation in air. Chemisorption of N2O experiment was carried out by dissociative N2O adsorption at 50 oC following a procedure described by Van Der Grift et al,35-36 and the detailed experiment process was shown in Supporting Information.

3. RESULTS AND DISCUSSIONS The STY of CH3OH for CuZnAl catalyst under certain reaction conditions during CO2 hydrogenation to CH3OH with a TOS of 720 h is displayed in Figure 1a. During the initial period of 24 h, the STY of CH3OH almost kept stable with 181.2 gCH3OH kgcat·h, which was shown in the region A of Figure 1a. This result is basically consistent with the catalyst activity that has reacted for 10 h, shown in Figure 1b. However, with the increase of TOS, catalyst deactivation took place (region B). The STY of CH3OH showed a rapid decrease by 25.1% from 181.2 to


6

Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


135.8 gCH3OH kgcat·h with the reaction time prolonged to 350 h, indicating that the catalyst deactivated severely at this stage. With the TOS further prolonged to 720 h (region C), the STY of CH3OH altered with only a slight decreasing tendency from 135.8 to 118.7 gCH3OH kgcat·h. From the overall experiment result of 720 h TOS, the STY of CH3OH experienced a significant decline by 34.5% from 181.2 to 118.7 𝑔𝐶𝐻3𝑂𝐻 𝑘𝑔cat·h indicating that a deactivation occurred during the 720 h TOS. Furthermore, the rate of deactivation in the first 350 h was obviously higher than the latter period.

Figure 1. The STY of CH3OH over CuZnAl catalyst with the TOS of 720 h (a) and 10 h (b) in CO2 hydrogenation. Reaction conditions: H2/CO2 = 3:1; 200 oC; 3.0 MPa; 9000 h-1.


7


Page 8 of 27

In order to study the deactivation reason of CuZnAl catalyst on CO2 hydrogenation to methanol, the catalyst structure at different reaction stages was systematically analyzed. Figure 2 shows the XRD patterns of CuZnAl catalyst at different stages (after H2 reduction, after reaction for 10 h and 720 h). For the different stages of CuZnAl catalysts, there were no diffraction peaks of Al2O3, which was possibly due to the low content (less than 9%) of Al species and its high dispersion in the catalyst. The peak at 26.5o was attributed to (002) plane of the graphite, which usually acts as the binder in the forming process of catalyst.37 Graphite will not be considered in the following discussions since it is commonly considered as an inert component with no contribution to catalytic activity.38 In the case of CuZnAl components, three major diffraction peaks could be observed with 2θ values of 43.3o, 50.4o and 74.1o, belonging to (111), (200), and (220) planes of metallic Cu (PDF # 01-085-1326), respectively.39 It is important to highlight that the peak intensity of metallic Cu was markedly reduced after reaction, which may reflect the change of Cu species. The average particle size of Cu0 particles over the CuZnAl catalyst calculated by the Scherrer equation are showed in Table 1. It has been reported that the aggregation of Cu particles is the main reason for the deactivation on Cu-based catalyst in methanol synthesis.30-31 High temperature often led to the increase in metal size because of sintering, Ostwald ripening or otherwise. However, for our case, it is interesting to note that the average size of Cu particles was decreased from 11.7 nm to 7.9 nm after a reaction period of 10 h. This change was possibly due to the reconstruction of Cu species during the initial reaction stage. The size of Cu particles was basically kept at 7.8 nm with the reaction prolonged from 10 h to 720 h, indicating that the dispersion of Cu was not changed obviously. In other words, there was no obvious agglomeration of Cu particles during the entire reaction process of CO2 hydrogenation. On this basis, it is proposed that the sintering of Cu particles may not be the main


8

Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


deactivation reason of CuZnAl catalyst for CO2 hydrogenation to methanol. In addition, the 2θ values for other diffraction peaks at 31.9o, 34.6o, 36.4o, 47.7o, 56.8o, 63.1o and 68.2o were attributed to ZnO species.40-41 The peak with the highest intensity at 36.4o was ascribed to the (101) plane of ZnO (PDF # 01-079-0205), the intensity of which was slightly increased after reaction compared to the reduced sample. As calculated by the Scherrer equation (Table 1), the particle size of ZnO was 7.2 nm for the reduced sample, which was slightly increased to 7.7 nm after a reaction time of 10 h and further grew up to 10.7 nm with reaction time extending to 720 h. This observation indicated that ZnO species was aggregated during the reaction process, consistent with the previous report that the generated water during CO2 hydrogenation may cause the crystallization of ZnO.33 Therefore, the agglomeration of ZnO species may be the main reason for the catalyst deactivation.

Figure 2. XRD patterns of CuZnAl catalyst at different stages: (a) after H2 reduction; (b) after reaction for 10 h; (c) after reaction for 720 h.


9


Page 10 of 27

Table 1 Physicochemical properties of CuZnAl catalyst at different stages.

ad

Cu and

Catalyst

dCu (nm) a

dZnO (nm) a

N2O-SA (m2 g-1)

H2-reduction

11.7

7.2

45.4

10 h

7.9

7.7

54.2

720 h

7.8

10.7

16.7

dZnO was calculated by Scherrer equation.

Recently, it was reported that chemisorption of N2O experiment is powerful for measuring the Cu surface area and redox active sites on ZnO.32,

42

Figure 3 shows the reduction proﬁles of

CuZnAl catalysts at different reaction stages after N2O oxidation treatment at 50 oC. According to the calculated hydrogen consumption in the second TPR of the CuZnAl catalysts at different stages after N2O oxidation, the N2O-SA values could be calculated and summarized in Table 1. The N2O-SA of H2 reduced CuZnAl catalyst was 45.4 m2 g-1 and it was slightly increased to 54.2 m2 g-1 after reaction for 10 h, which was likely to be due to the reconstruction of Cu species consistent with the XRD results. More importantly, it should be mentioned that the N2O-SA value was remarkably decreased to only 16.7 m2 g-1 with increasing the TOS to 720 h. Generally, the decrease of N2O-SA may be due to the agglomeration of Cu particles for a long reaction time at high temperatures. Nevertheless, the XRD results have revealed that no significant changes happened on the Cu particles after reaction for 10 h and 720 h (Table 1). Therefore, other factors may exist affecting the N2O-SA value. Since N2O-SA can quantify the Cu surface area and redox active sites on ZnO,32, 42 the decrease of N2O-SA was possibly due to the reduction in the amount of partially reduced ZnO1-x sites. Combined with the XRD results, the particle size of ZnO was enlarged over the used catalyst after 720 h of TOS, being likely to lead to the reduction of the


10

Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


amount of ZnO1-x sites and the decrease in the N2O-SA value. Therefore, the decrease of N2OSA further proved the agglomeration of ZnO particles.

Figure 3. H2-TPR profiles of the CuZnAl at different stages after N2O oxidation. In order to explore the effect of morphology on catalytic activity, SEM images of the CuZnAl catalyst at different reaction stages were observed, as shown in Figure 4. The sample after H2 reduction showed a granular morphology with a particle size of approximately 40 nm. After reaction for 10 h and 720 h, the catalyst nanoparticles maintained a granular morphology, but the size decreased to approximately 25 nm, which may be due to the reconstruction of the catalyst under the atmosphere of CO2 and H2O, consistent with the changes in the Cu particle size obtained from the XRD result. SEM images show that there were no obvious changes in morphology during the reaction period from 10 h to 720 h. Consequently, the morphology and the particle size of the catalyst may be a spectator on the deactivation of catalyst.


11


Page 12 of 27

Figure 4. SEM images of the CuZnAl catalyst after: (a) H2-reduction; (b) reaction for 10 h; (c) reaction for 720 h.


12

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


HAADF-STEM, TEM and HRTEM characterizations further illustrated the morphology of the CuZnAl catalyst at different stages (Figure 5). The HAADF-STEM images showed that Cu particles displayed similar morphology as the bright spot region (Figure 5a-c). TEM images showed that the particles in CuZnAl catalyst displayed good dispersion. The crystal size was in a range of 4 to 15 nm after H2 reduction treatment. Even after reacted for 10 and 720 h, the catalyst still kept as nanoparticles and the size showed a wide distribution which was similar to the situation of catalyst after H2 pretreatment. From the HRTEM images, the H2-reduced catalyst was consisted of aggregated nanoparticles with the features of Cu, ZnO, and Al2O3 species (Figure 5g). The sample showed characteristic spacing of 2.56 and 2.38 Å, representing the (104) and (110) lattice planes of Al2O3.43 Although Al2O3 was not detected in the XRD pattern, it could be observed in HRTEM images, further indicating that Al2O3 possessed high dispersion. Figure 5g shows the expected spacing of 2.08 Å for the metallic Cu lattice planes of (111)44 and 2.47 Å for the ZnO planes of (101).45 The sample after reaction also kept similar state in the Cu lattice fringes, which suggested that the reaction condition of 10 h had almost no influence on the Cu species, consistent with the XRD result that only the intensity was changed with no position shift. When the catalyst was evaluated for 720 h, the Cu and ZnO spacing also maintained, but the margin of Cu particles became indistinct, which was possibly due to the oxidation of Cu species. Besides, the overview image of the catalyst after 720 h TOS showed a large region of crystalline ZnO particle, indicating the agglomeration of ZnO during the reaction, which is consistent with the results obtained from XRD patterns.


13


Page 14 of 27

Figure 5. HAADF-STEM, TEM and HRTEM images of the CuZnAl catalyst after: (a, d, g) H2 reduction; (b, e, h) reaction for 10 h; (c, f, i) reaction for 720 h. The chemical state of Cu species and surface composition of CuZnAl catalyst at different stages were investigated by XPS measurements (see Figure 6). The calculated and deconvoluted results are shown in Table 2. Figure 6a shows the energy region of Cu 2p3/2 core level in the fresh CuZnAl catalyst. The higher binding energy peak at 934.4 eV was assigned to Cu2+ in the CuO, indicating that Cu species mainly existed in the form of CuO for fresh CuZnAl catalyst.4647

The shakeup satellite peak at the high binding energy of 941-945 eV was obviously observed,

which was an additional characteristic of Cu2+ compounds.48 For the CuZnAl catalyst after H2 reduction, the binding energy of 932.5 eV and 934.5 eV were assigned to Cu0 and Cu2+, respectively.48 Besides, the satellite peak further indicated the existence of Cu2+ in the sample.


14

Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Compared with the fresh CuZnAl catalyst, the content of surface Cu2+ was reduced to a great extent. There were no significant changes in the peak position of Cu0 and Cu2+ in the catalyst after reaction for 10 h and 720 h. However, the fraction of surface Cu2+ increased from 17.4% to 22.6% after reaction for 10 h, and further significantly increased to 31.6% after 720 h TOS, indicating that part of surface Cu0 was oxidized to Cu2+ species during the process of CO2 hydrogenation to methanol. In addition, the surface Cu/Zn ratio was decreased from 1.42 to 0.76 when the fresh catalyst was reduced by H2, and it was increased to 1.54 after reaction for 10 h, further remaining at 1.43 with prolonging the reaction time to 720 h. The results are in good consistence with the observation that the surface Cu/Zn ratio would be decreased in reductive atmosphere and increased in oxidative atmosphere.49 The changes in Cu/Zn ratio suggested that the catalyst treated in CO2 hydrogenation condition was similar to that with the treatment condition of an oxidizing atmosphere, further indicating that the Cu species can be oxidized in a CO2 hydrogenation atmosphere. CO2 hydrogenation to methanol reaction contained high concentration of in situ produced water. Thus, the oxidation of Cu species was likely due to the existence of CO2 and water.37, 50 With prolonging the reaction time, the oxidation degree of Cu species was increased. Consequently, the oxidation of Cu species was possibly another reason for the deactivation in CO2 hydrogenation to methanol.


15


Page 16 of 27

Table 2 Binding energies (eV) of core electrons of Cu 2p3/2 and surface composition in CuZnAl catalyst at different stages. Binding energy (eV) Cu2+(%) Cu(%) Zn(%) Cu/Zn

Catalyst Satellite1 Satellite2

Cu2+

Cu0 -

Fresh

944.3

941.9

934.4

100

58.7

41.3

1.42

H2-reduction

944.2

941.6

934.5 932.5

17.4

43.2

56.8

0.76

10 h

944.2

942.2

934.5 932.6

22.6

60.6

39.4

1.54

720 h

944.1

941.6

934.4 932.5

31.6

58.9

41.1

1.43

Figure 6. The Cu2p3/2 core-level spectra of: (a) fresh CuZnAl; (b) CuZnAl after H2 reduction; (c) CuZnAl after reaction for 10 h; (d) CuZnAl after reaction for 720 h.


16

Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


As determined from all the characterization results, the structural changes of CuZnAl catalyst at different stages are showed in Scheme 1. From the H2 reduction stage to the stage after reaction for 10 h, the size of Cu particle was decreased with a redispersion effect and ZnO species experienced a slight agglomeration. Besides, the surface metallic Cu showed a certain degree of oxidation. Further extending the reaction time from 10 h to 720 h, the size of Cu particles remained almost unchanged while the size of ZnO particles was enlarged by 38.9% to 10.7 nm and further aggregated. It was also indicated that the agglomeration of ZnO species has no significant effect on the dispersion of Cu. Due to the lower Tammann temperature of the Cu (405 oC), the agglomeration of Cu species was mainly due to the high temperature. However, the reaction temperature of CO2 hydrogenation is relatively low (200 oC), and therefore the temperature-triggered aggregation of Cu does not occur. Another interesting finding is that the oxidation degree of metallic Cu was prominently increased. Overall, ZnO species has showed agglomeration, and part of the surface metallic Cu was oxidized after a long period of reaction, resulting in the loss of interfacial sites between ZnO and Cu, which are considered as the active sites for methanol synthesis from CO2 hydrogenation.20 Therefore, it can be inferred that the oxidation of Cu species and the aggregation of ZnO during reaction contribute to the deactivation of CuZnAl catalyst.

Scheme 1. The schematic representation of the structure changes of CuZnAl catalyst at different stages.


17


Page 18 of 27

4. CONCLUSIONS The deactivation behavior of a CuZnAl catalyst in CO2 hydrogenation to methanol during 720 h TOS was systematically investigated, where the agglomeration of ZnO species and the oxidation of metallic Cu were certified to be the main reasons for catalyst deactivation. The particle size of Cu was not changed obviously after 720 h TOS, which may be due to the low reaction temperature during CO2 hydrogenation to methanol, inferring that the Cu particle size can be recognized as a spectator in deactivation. Therefore, it is crucial to stabilize the structure of ZnO species and metallic Cu to improve the catalyst lifetime for CO2 hydrogenation to methanol. It is proposed that the regulation of the structural promoter and the addition of hydrophobic promoter can help realize the stabilization of ZnO species and the inhibition of metallic Cu oxidation for further improving the stability of the catalyst.


18

Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/xxxxxxxxx. The detailed process of N2O chemisorption experiment. (PDF)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Fax: (+) 86-411-84685940; Tel: (+) 86-411-84379416 ORCID Yanqiang Huang: 0000-0002-7556-317X Notes The authors declare no competing ﬁnancial interest. ACKNOWLEDGMENTS This work was supported by the National Key R&D Program of China (2016YFB0600902), Dalian Science Foundation for Distinguished Young Scholars (2016RJ04), Dalian National Laboratory for Clean Energy (DNL180401), the Youth Innovation Promotion Association CAS.


19


Page 20 of 27

REFERENCES (1) Jackson, R. B.; Quéré, C. L.; Andrew, R. M.; Canadell, J. G.; Peters, G. P.; Roy, J.; Wu, L. Warning signs for stabilizing global CO2 emissions. Environ. Res. Lett. 2017, 12, 110202. (2) Aresta, M.; Dibenedetto, A.; Angelini, A. Catalysis for the valorization of exhaust carbon: From CO2 to chemicals, materials, and fuels. Technological use of CO2. Chem. Rev. 2014, 114, 1709. (3) De Falco, M.; Iaquaniello, G.; Centi, G. CO2: A valuable source of carbon; SpringerVerlag: London, 2013. (4) Song, C. Global challenges and strategies for control, conversion and utilization of CO2 for sustainable development involving energy, catalysis, adsorption and chemical processing. Catal. Today. 2006, 115, 2. (5) Wang, W.; Wang, S.; Ma, X.; Gong, J. Recent advances in catalytic hydrogenation of carbon dioxide. Chem. Soc. Rev. 2011, 40, 3703. (6) Liang, B.; Duan, H.; Su, X.; Chen, X.; Huang, Y.; Chen, X.; Delgado, J. J.; Zhang, T. Promoting role of potassium in the reverse water gas shift reaction on Pt/mullite catalyst. Catal. Today. 2017, 281, 319. (7) Centi, G.; Perathoner, S. Green carbon dioxide: Advances in CO2 utilization. John Wiley & Sons, Inc: Hoboken, New Jersey, 2014. (8) Stangeland, K.; Li, H.; Yu, Z. Thermodynamic Analysis of Chemical and Phase Equilibria in CO2 Hydrogenation to Methanol, Dimethyl Ether, and Higher Alcohols. Ind. Eng. Chem. Res.


20

Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2018, 57, 4081. (9) Gao, P.; Li, S.; Bu, X.; Dang, S.; Liu, Z.; Wang, H.; Zhong, L.; Qiu, M.; Yang, C.; Cai, J.; Wei, W.; Sun, Y. Direct conversion of CO2 into liquid fuels with high selectivity over a bifunctional catalyst. Nat. Chem. 2017, 9, 1019. (10) Wei, J.; Ge, Q.; Yao, R.; Wen, Z.; Fang, C.; Guo, L.; Xu, H.; Sun, J. Directly converting CO2 into a gasoline fuel. Nat. Commun. 2017, 8, 15174. (11) Li, Z.; Qu, Y.; Wang, J.; Liu, H.; Li, M.; Miao, S.; Li, C. Highly Selective conversion of carbon dioxide to aromatics over tandem catalysts. Joule. 2019, 3, 570. (12) Ni, Y.; Chen, Z.; Fu, Y.; Liu, Y.; Zhu, W.; Liu, Z. Selective conversion of CO2 and H2 into aromatics. Nat. Commun. 2018, 9, 3457. (13) Li, Z.; Wang, J.; Qu, Y.; Liu, H.; Tang, C.; Miao, S.; Feng, Z.; An, H.; Li, C. Highly selective conversion of carbon dioxide to lower olefins. ACS Catal. 2017, 7, 8544. (14) Saeidi, S.; Amin, N. A. S.; Rahimpour, M. R. Hydrogenation of CO2 to value-added products—A review and potential future developments. J. CO2. Util. 2014, 5, 66. (15) Tan, Q.; Shi, Z.; Wu, D. CO2 Hydrogenation to Methanol over a Highly Active Cu– Ni/CeO2–Nanotube Catalyst. Ind. Eng. Chem. Res. 2018, 57, 10148. (16) Bhanage, B. M. Transformation and utilization of carbon dioxide. Springer: Berlin Heidelberg, 2014. (17) Olah, G. A. Beyond oil and gas: the methanol economy. Wiley-VCH: Weinheim, 2005.


21


Page 22 of 27

(18) Yu, K. M. K.; Curcic, I.; Gabriel, J.; Tsang, S. C. E. Recent advances in CO2 capture and utilization. ChemSusChem. 2008, 1, 893. (19) Wang, J.; Li, G.; Li, Z.; Tang, C.; Feng, Z.; An, H.; Liu, H.; Liu, T.; Li, C. A highly selective and stable ZnO-ZrO2 solid solution catalyst for CO2 hydrogenation to methanol. Science Advances. 2017, 3, 1. (20) Kattel, S.; Ramírez, P. J.; Chen, J. G.; Rodriguez, J. A.; Liu, P. Active sites for CO2 hydrogenation to methanol on Cu/ZnO catalysts. Science. 2017, 355, 1296. (21) Rui, N.; Wang, Z.; Sun, K.; Ye, J.; Ge, Q.; Liu, C.-j. CO2 hydrogenation to methanol over Pd/In2O3: effects of Pd and oxygen vacancy. Appl. Catal. B: Environ. 2017, 218, 488. (22) Zhang, C.; Yang, H.; Gao, P.; Zhu, H.; Zhong, L.; Wang, H.; Wei, W.; Sun, Y. Preparation and CO2 hydrogenation catalytic properties of alumina microsphere supported Cubased catalyst by deposition-precipitation method. J. CO2. Util. 2017, 17, 263. (23) Martin, O.; Martín, A. J.; Mondelli, C.; Mitchell, S.; Segawa, T. F.; Hauert, R.; Drouilly, C.; Curulla-Ferré, D.; Pérez-Ramírez, J. Indium Oxide as a Superior Catalyst for Methanol Synthesis by CO2 Hydrogenation. Angew. Chem. Int. Ed. 2016, 55, 6261. (24) Díez-Ramírez, J.; Dorado, F.; de la Osa, A. R.; Valverde, J. L.; Sánchez, P. Hydrogenation of CO2 to Methanol at Atmospheric Pressure over Cu/ZnO Catalysts: Influence of the Calcination, Reduction, and Metal Loading. Ind. Eng. Chem. Res. 2017, 56, 1979. (25) Ertl, G.; Knozinger, H.; Schüth, F.; Weitkamp, J. Handbook of heterogeneous catalysis. Wiley-VCH: Weinheim, 1997.


22

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(26) Turner, J.; Sverdrup, G.; Mann, M. K.; Maness, P.-C.; Kroposki, B.; Ghirardi, M.; Evans, R. J.; Blake, D. Renewable hydrogen production. Int. J. Energy Res. 2008, 32, 379. (27) Shih, C. F.; Zhang, T.; Li, J.; Bai, C. Powering the Future with Liquid Sunshine. Joule. 2018, 2, 1925. (28) Radovic, L. R.; Vannice, M. A. Sulfur tolerance of methanol synthesis catalysts: Modelling of catalyst deactivation. Appl. Catal. 1987, 29, 1. (29) Ma, Y.; Ge, Q.; Li, W.; Xu, H. Study on the sulfur tolerance of catalysts for syngas to methanol. Catal. Commun. 2008, 10, 6. (30) Sun, J. T.; Metcalfe, I. S.; Sahibzada, M. Deactivation of Cu/ZnO/Al2O3 methanol synthesis catalyst by sintering. Ind. Eng. Chem. Res. 1999, 38, 3868. (31) Zhai, X.; Shamoto, J.; Xie, H.; Tan, Y.; Han, Y.; Tsubaki, N. Study on the deactivation phenomena of Cu-based catalyst for methanol synthesis in slurry phase. Fuel. 2008, 87, 430. (32) Lunkenbein, T.; Girgsdies, F.; Kandemir, T.; Thomas, N.; Behrens, M.; Schlögl, R.; Frei, E. Bridging the Time Gap: A Copper/Zinc Oxide/Aluminum Oxide Catalyst for Methanol Synthesis Studied under Industrially Relevant Conditions and Time Scales. Angew. Chem. Int. Ed. 2016, 55, 12708. (33) Wu, J. G.; Saito, M.; Takeuchi, M.; Watanabe, T. The stability of Cu/ZnO-based catalysts in methanol synthesis from a CO2-rich feed and from a CO-rich feed. Appl. Catal. A: Gen. 2001, 218, 235. (34) Xu, J.; Su, X.; Liu, X.; Pan, X.; Pei, G.; Huang, Y.; Wang, X.; Zhang, T.; Geng, H.


23


Page 24 of 27

Methanol synthesis from CO2 and H2 over Pd/ZnO/Al2O3: Catalyst structure dependence of methanol selectivity. Appl. Catal. A: Gen. 2016, 514, 51. (35) Van Der Grift, C. J. G.; Wielers, A. F. H.; Jogh, B. P. J.; Van Beunum, J.; De Boer, M.; Versluijs-Helder, M.; Geus, J. W. Effect of the reduction treatment on the structure and reactivity of silica-supported copper particles. J. Catal. 1991, 131, 178. (36) Gervasini, A.; Bennici, S. Dispersion and surface states of copper catalysts by temperature-programmed-reduction of oxidized surfaces (s-TPR). Appl. Catal. A: Gen. 2005, 281, 199. (37) Sahibzada, M.; Chadwick, D.; Metcalfe, I. S. Hydrogenation of carbon dioxide to methanol over palladium-promoted Cu/ZnO/A12O3 catalysts. Catal. Today. 1996, 29, 367. (38) Hansen, T. W.; DeLaRiva, A. T.; Challa, S. R.; Datye, A. K. Sintering of catalytic nanoparticles: Particle migration or ostwald ripening? Acc. Chem. Res. 2013, 46, 1720. (39) Salavati-Niasari, M.; Davar, F. Synthesis of copper and copper(I) oxide nanoparticles by thermal decomposition of a new precursor. Mater. Lett. 2009, 63, 441. (40) Guo, L.; Yang, S.; Yang, C.; Yu, P.; Wang, J.; Ge, W.; Wong, G. K. L. Synthesis and characterization of poly(vinylpyrrolidone)-modified zinc oxide nanoparticles. Chem. Mater. 2000, 12, 2268. (41) Zhang, Y.; Yang, Y.; Han, H.; Yang, M.; Wang, L.; Zhang, Y.; Jiang, Z.; Li, C. Ultradeep desulfurization via reactive adsorption on Ni/ZnO: The effect of ZnO particle size on the adsorption performance. Appl. Catal. B: Environ. 2012, 119-120, 13.


24

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(42) Kuld, S.; Conradsen, C.; Moses, P. G.; Chorkendorff, I.; Sehested, J. Quantification of Zinc Atoms in a Surface Alloy on Copper in an Industrial-Type Methanol Synthesis Catalyst. Angew. Chem. Int. Ed. 2014, 53, 5941. (43) Hanawalt, J. D.; Rinn, H. W.; Frevel, L. K. Chemical analysis by X-Ray diffraction. Ind. Eng. Chem., Anal. Ed. 1938, 10, 457. (44) van den Berg, R.; Prieto, G.; Korpershoek, G.; van der Wal, L. I.; van Bunningen, A. J.; Lægsgaard-Jørgensen, S.; de Jongh, P. E.; de Jong, K. P. Structure sensitivity of Cu and CuZn catalysts relevant to industrial methanol synthesis. Nat. Commun. 2016, 7, 13057. (45) McLaren, A.; Valdes-Solis, T.; Li, G.; Tsang, S. C. Shape and size effects of ZnO nanocrystals on photocatalytic activity. J. Am. Chem. Soc. 2009, 131, 12540. (46) Zhu, Y.; Kong, X.; Zhu, S.; Dong, F.; Zheng, H.; Zhu, Y.; Li, Y.-W. Construction of Cu/ZrO2/Al2O3 composites for ethanol synthesis: Synergies of ternary sites for cascade reaction. Appl. Catal. B: Environ. 2015, 166–167, 551. (47) Dai, W.-L.; Sun, Q.; Deng, J.-F.; Wu, D.; Sun, Y.-H. XPS studies of Cu/ZnO/Al2O3 ultrafine catalysts derived by a novel gel oxalate co-precipitation for methanol synthesis by CO2+H2. Appl. Surf. Sci. 2001, 177, 172. (48) Sepúlveda, A.; Márquez, C.; Rodríguez-Ramos, I.; Guerrero-Ruíz, A.; Fierro, J. L. G. Spectroscopic studies of surface copper spinels. Influence of pretreatments on chemical state of copper. Surf. Interface Anal. 1993, 20, 1067. (49) Behrens, M.; Studt, F.; Kasatkin, I.; Kuhl, S.; Havecker, M.; Abild-Pedersen, F.; Zander,


25


Page 26 of 27

S.; Girgsdies, F.; Kurr, P.; Kniep, B. L.; Tovar, M.; Fischer, R. W.; Norskov, J. K.; Schlogl, R. The active site of methanol synthesis over Cu/ZnO/Al2O3 industrial catalysts. Science. 2012, 336, 893. (50) Fichtl, M. B.; Schlereth, D.; Jacobsen, N.; Kasatkin, I.; Schumann, J.; Behrens, M.; Schlögl, R.; Hinrichsen, O. Kinetics of deactivation on Cu/ZnO/Al2O3 methanol synthesis catalysts. Appl. Catal. A: Gen. 2015, 502, 262.


26

Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents


27

Al2O3 Catalyst for CO2

Recommend Documents