Anti-sintering and High-activity Ni Catalyst Supported on Mesoporous

Subscriber access provided by University of Sunderland

Kinetics, Catalysis, and Reaction Engineering

Anti-sintering and High-activity Ni Catalyst Supported on Mesoporous Silica Incorporated by Ce/Zr for CO Methanation Chenxu Liu, Jingyu Zhou, Hongfang Ma, Weixin Qian, Haitao Zhang, and Weiyong Ying Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03254 • Publication Date (Web): 15 Oct 2018 Downloaded from http://pubs.acs.org on October 20, 2018

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 52 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

Anti-sintering and High-activity Ni Catalyst Supported on Mesoporous Silica Incorporated by Ce/Zr for CO Methanation Chenxu Liu,1 Jingyu Zhou,1 Hongfang Ma,1 Weixin Qian,1 Haitao Zhang,1 and Weiyong Ying1*

1Engineering

Research Center of Large Scale Reactor Engineering and Technology,

Ministry of Education, State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

1

ACS Paragon Plus Environment

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 52

Keywords: methanation, composite support, anti-sintering, nickel

Abstract Mesoporous Silica (MS) and a series of completely new MS incorporated by Ce/Zr (CZMS) supports were synthesized by hydrothermal synthesis method. 30wt.% Ni were impregnated in the supports. N2 adsorption-desorption, FTIR, XRD, TEM, H2-TPR, CO-TPD and XPS were used to characterize the catalysts. And results showed Ce and Zr were successfully incorporated into the structure of MS. The CZ-MS supports provided an appropriate interaction with Ni active metal to promote the dispersibility of Ni and restrain catalysts from sintering. Compared with Ni/MS, Ni/1CZ-1MS showed better ability of anti-sintering and kept high catalytic activity after calcination at 700 °C for 3 h. The series of Ni/CZ-MS exhibited more excellent catalytic activity than Ni/MS at 200-450 °C. Ni/1CZ-1MS exhibited the best catalytic property at low temperature of 200 °C. CO conversion and CH4 selectivity reached 91.12% and 84.40%, respectively. Ni/1CZ1MS also showed excellent catalytic stability in harsh reaction conditions.

2


Page 3 of 52 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 With the development of the society, natural gas, a kind of high efficient clean energy, has gained more and more application both in industrial production and academic research.1 China maintains the energy structure of “sufficient coal, scarce oil and gas”, as a result, the demands for natural gas promote the research in process of coal to synthetic natural gas(SNG).2 Since CO methanation was first discovered in 1902 by Sabatier and Senderens, the reaction has attracted widespread attention among researchers.3 Catalysts are the key point to accelerate the methanation reaction. Absolutely, how to develop highly efficient catalysts is the most important procedure in the syngas methanation. The active components of methanation catalysts are distributed in the Ⅷ B and Ⅵ B group. Ru-based catalysts are found as the most active catalysts. However, the exorbitant price of metal Ru limits its application in large-scale industrial production.4 Through plenty of research, Ni-based catalysts are generally accepted using in methanation reaction for its appropriate catalytic activity and low price. Whereas the conventional Ni-based catalysts can’t exhibit excellent catalytic performance at low temperature (200 °C). High activity at lower temperature can reduce energy consumption for heating methanation reaction. The supports play an important role in catalysts. It can determine the number and dispersion of active site on the surface of catalysts, which act as the reactive center of methanation.5 Supports 3



Page 4 of 52

is not only involved in the activity and selectivity of catalysts, but also relevant to the stability, mechanical strength and transmission characteristics of catalysts. Thus, synthesizing suitable support is pivotal to the excellent catalysts. Oxides and zeolites supports were mostly investigated.6-8 Al2O3 support has been widely applied in industrial production due to its relatively low price and good catalytic performance. However, Al2O3 and NiO will generate NiAl2O4 spinel species which are hardly to be reduced while nickel supported on alumina catalysts are prepared, leading to unfavorable catalytic performance.9 Ocampo et al. synthesized a series of Ni-CexZr1xO2

catalysts by sol-gel method and the Ni-based catalysts having CeO2/ZrO2=60/40 displayed the

most excellent catalytic performance for CO2 conversion, due to an optimal Ni0/Ni2+ ratio.10 Except oxides, molecular sieves such as MCM-41 serving as support of catalysts attract more and more attention of researchers owing to the relatively high specific surface areas and ordered pore structures. M.C. Bacariza et al.

compared the influence of supports on CO2 methanation. MCM-

41, SBA-15 and USY zeolite were studied.11 MCM-41 presented the highest TOF values among the catalysts studied and superior catalytic performances. J. Zhang et al. prepared several antisintering Ni-incorporated MCM-41 methanation catalysts with various nickel content and investigated their performances for CO methanation. Among these catalysts, the one with 10% nickel incorporated showed the highest activity with CO conversion and CH4 yield reaching almost 100% and 95.7% at 350 °C.12 However, they didn’t investigate the catalytic activity at lower temperature. Investigations on the Ni-based catalysts supported by mesoporous silica(MS) incorporated 4


Page 5 of 52 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


by Ce/Zr have barely been conducted. In this paper, the catalytic properties of Ni impregnation on MS (mesoporous silica) incorporated by Ce/Zr catalysts with different ratio of CZ and MS for CO methanation were explored and discussed. XRD, FTIR, nitrogen-physical adsorption instruments, H2-TPR, CO-TPD, TEM and XPS were used to characterize the prepared catalysts to analyze the structures and properties. The catalytic performance of the catalysts from 150 °C to 450 °C was studied, especially compared at low temperature (200 °C).

2. EXPERIMENTAL SECTION 2.1. Synthesis of supports. The support was synthesized by the hydrothermal synthesis method based on previous reported method.13 TEOS (Tetraethylorthosilicate, C8H20O4Si, 99%) and CTAB (Cetyltrimethylammonium bromide, AR 99.0%) were supplied by Shanghai Lingfeng chemical reagent Co. Ltd. Ammonium ceric nitrate (Ce(NH4)2(NO3)6 AR99.0%) and Zirconium(IV) oxynitrate hydrate (ZrO(NO3)2∙xH2O AR99.5%) were supplied by Shanghai Macklin Biochemical Co. Ltd. TEOS and CTAB were used as silicon sources and templates separately for the synthesis of mesoporous silica(MS). The mole ratio of materials was guided by TEOS: CTAB: NaOH: H2O=1:0.12:0.2:100. First of all, the certain amount of CATB and NaOH were dissolved in deionized water at 40 °C. Then the TEOS was slowly dropped into the solution in the condition of continuously and vigorously stirring. The solution was aged at 40 °C for 2 h under stirring then transferred into PTFE-lined reaction kettles which kept rotating at 35 r/min. 5



Page 6 of 52

The systems were kept at 120 °C for 24 h in order to proceed dynamic crystallization. After the crystallization, when the systems were cooled down to the room temperature, the obtained solid was centrifuged and washed by deionized water until the pH of suspension approached to 7. The solid was dried at 110 °C for 12 h and calcinated in air at 550 °C for 6 h (heating rate = 2 °C /min) to remove the template. Finally, the MS support was acquired. For the MS incorporated by Ce/Zr, the Ammonium ceric nitrate and Zirconium (IV) oxynitrate hydrate were added in the solution after the TEOS was dropped, meanwhile the mole ratio of Ce and Zr was fixed at 1:3. Following the procedure, the Ce/Zr incorporated MS supports, named as 1CZ-xMS in which x represent the molar ratios of Si/CZ ranging from 0.8 to 1.6, were synthesized.

2.2. Preparation of Ni impregnated catalysts. 30wt.%Ni impregnated MS and CZ-MS catalysts were synthesized by wetness impregnation method. Certain amount of supports prepared before was impregnated in the solution of Nickel(II) nitrate hexahydrate (Ni(NO3)2∙6H2O AR 99.0% Shanghai Lingfeng chemical reagent Co. Ltd.) at room temperature overnight then dried at 110 °C for 12 h and calcined in air at 550 °C for 4 h (heating rate = 2 °C /min). The catalysts were designated as Ni/MS, Ni/1CZ-0.8MS, Ni/1CZ-1MS, Ni/1CZ-1.2MS, Ni/1CZ-1.4MS and Ni/1CZ1.6MS.

6


Page 7 of 52 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


2.3. Catalysts characterization. N2 physical adsorption at low temperature was carried out in ASAP 2020 instrument of American Micrometeritics Instrument Corporation Company to measure the surface areas of samples. 0.2 g samples were pretreated at 350 °C, 1333 Pa for 4 h in order to remove moisture adsorbed in the catalysts. Then N2 adsorption and desorption were proceeded at the temperature of liquid nitrogen. The surface areas and the distribution of pore size were calculated by Brunauer Emmett Teller (BET) and Barrett Joyner Halenda (BJH) based on Kelvin equation respectively. The FTIR spectra were obtained in the range of 400-4000 cm-1 on a Nicolet 6700 equipment to explore the structure of catalysts. The sample was pretreated by KBr disk technique. 0.0015 g samples were milled and mixed with 0.1 g KBr. Then the mixture was compressed in the mold for testing at 20 °C and vacuum environment. To investigate the reducibility of catalysts, H2-TPR were performed on AutoChem 2920 of American Micrometeritics Instrument Corporation Company. 0.2 g fresh samples were loaded in U-shaped quartz tube and out-gassed in He gas at 300 °C for 1 h to remove moisture and impurities. After the samples were cooled down to 50 °C, 10%H2-Ar gas was introduced to the system. Meanwhile, the samples were heated from 50 °C to 800 °C (heating rate=10 °C /min). The content of H2 varying with reduce temperature was detected by thermal conductivity detector (TCD). CO-TPD was proceeded to characterize the adsorptive property of CO on catalysts using AutoChem 2920 of American Micrometeritics Instrument Corporation Company. 0.2 g fresh samples were put into U-shaped quartz tube. The samples were preprocessed at 500 °C for 2 h in 7



Page 8 of 52

the atmosphere of H2 gas to reduce the catalyst. Then the H2 gas was changed to He gas to purge the sample for removing the adsorbed H2 and impurities. 5%CO-He gas mixture was inlet in the U-shaped quartz tube after the system was cooled down to 50 °C. Then the system was kept in the circumstance for 0.5 h so that CO was adequately adsorbed on the catalyst. Next, the gas steam was changed to He gas to purge the catalyst meanwhile the catalyst was heated from 50 °C to 800 °C. During the temperature-rise period, desorption volume of CO was detected by TCD. XRD instrument (D/Max 2550 of Japanese Rigaku Company) was used to characterize the samples with Cu Kα radiation. The scanning voltage was 40 KV while the electric current was 100mA. The range of scanning was from 5° to 80° with the scanning step of 0.02°. The samples were preprocessed at 500 °C for 2 h in the atmosphere of H2 gas to reduce the catalyst. TEM (JEM-2100) was conducted at 200 KV for the purpose of observing the pattern of Ni active particles loading on the supports. Before measurement, the sample was added into ethanol and treated by ultrasonic for 0.5 h to disperse the sample. Then the sample was put on copper grid and dried by IR dryer. CO pulse chemisorption was carried out by AutoChem 2920 of American Micrometeritics Instrument Corporation Company. The catalyst (0.1 g) was first reduced at 500 °C for 2 h under 10% H2/Ar. Then the sample was cooled down to room temperature. Pulses of 5% CO/He were injected through the catalysts. XPS was carried out to investigate the state of metals on the catalysts. The test was performed on American Thermo ESCALAB 250 with Al Ka (hv = 1486.6 eV), 150 W and 500 μm beam 8


Page 9 of 52 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


spot. The binding energies (BEs) were reference to the C 1s line at 284.8 eV from the adventitious carbon.

2.4. Catalytic evaluation. CO methanation reaction was performed in a fixed-bed tube reactor (Φ14×2×500 mm). Quartz sands were firstly added into the end of reactor to load 0.5 g catalysts. Before each test, the catalysts were reduced in the atmosphere of H2 at 500 °C for 2 h. After the catalysts were cooled down to reaction temperature, syngas (15.5vol.%CO, 11.5vol.%CO2, 68.0vol.%H2 and 5.0vol.%N2) was introduced into the reactor along with a WHSV of 30000 ml/g/h to study the catalytic activity at 150-450 °C and 2 MPa. The tail gas was analyzed by the gas chromatography Agilent 7890A online after the reaction came to stability. The XCO (CO conversion) and SCH4 (CH4 selectivity) were calculated as follow: XCO =

NCO,in - NCO,out NCO,in

NCH4,out

SCH4 = NCO + CO ,in 2

(1)

× 100%

- NCO + CO2,out

× 100%

(2)

Ni represents the molar flow of different component.

3. RESULTS AND DISCUSSION 3.1. Characterization of catalysts. The N2 adsorption-desorption isotherms and the pore diameter distribution curves of the fresh catalysts were shown in Figure 1. All series of catalysts generally produced the type Ⅳ isotherms, indicating that all the samples contain structure of 9



Page 10 of 52

mesoporous. Ni/MS belonged to H1-type hysteresis loop, which demonstrated the catalyst consist of uniform pore. With the incorporation of Ce/Zr, the hysteresis loops transformed to H2-type hysteresis loop which Ni/CZ-MS produced. The existence of H2-type hysteresis loop meant that the formation of “ink bottle” pore structure and slit type pore structures composed of irregularly shaped and interconnected pores.14,15 It attested that excessive ratio of Ce/Zr and MS will cause the collapse of ordered pore structure. Moreover, for the catalysts other than Ni/MS, the inflection point on the curve occurs at higher relative pressure (p/p0=0.43), indicating the existence of mesopores with greater pore size verified by the pore diameter distribution in Figure 1 b.16 The distribution of pore size for Ni/MS is mainly within the range of 2.0-3.0 nm while that for other catalysts is approximately situated in the range of 3.0-5.5 nm. Comparatively, the pore size of Ni/1CZ-1MS mainly concentrate in the range of 3.0-4.0 nm with the sharpest peak according to the pore size distribution curve, proving that the pore size of Ni/1CZ-1MS is more uniformed. The surface area, pore volume and pore size of catalysts were shown in Table 1, it could be found that the surface area and pore volume of samples diminished after the incorporation of Ce/Zr compared to the sample without Ce/Zr. For the series of catalysts containing Ce/Zr, the surface area, pore volume and pore size increased with the ratio of Ce/Zr and MS decreased. With the ratio of CZ and MS decreased, the content of CZ increased. The radius of Ce4+ and Zr4+ are larger than Si4+, thus, with the Si4+ was replaced by Ce4+ and Zr4+, the thickness of pore wall increased and the pore volume and pore size of Ni/CZ-MS catalysts decreased. Ce4+ and Zr4+ were proved as the main existence form in support CZ-MS by XPS characterization. The situation strongly 10


Page 11 of 52 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


demonstrated that Ce/Zr were successfully incorporated into the pore structure of MS, corresponding to the following FTIR results. The addition of Ce/Zr will lead to partial breakdown of ordered pore structure, influencing the formation of ordered pore structure. However, the mesoporous size will expand on account of the collapse of the ordered channel framework, indicating more NiO species could be impregnated into the internal of mesopore and imbedded in the pores surface of MS. The behavior would promote stability and activity of catalysts.17

11



Page 12 of 52

Figure 1. a) N2 adsorption-desorption isotherms of catalysts; b) Pore size distribution of catalysts.

Table 1. Physical properties of samples. Surface areaa

Pore volumeb

Pore Sizec

(m2∙g-1)

(cm3∙g-1)

(nm)

Ni/MS

571.6

0.45

2.67

Ni/1CZ-0.8MS

341.4

0.29

3.27

Ni/1CZ-1MS

361.8

0.31

3.30

Ni/1CZ-1.2MS

393.9

0.38

3.56

Ni/1CZ-1.4MS

395.3

0.43

4.06

Ni/1CZ-1.6MS

420.4

0.44

4.16

Catalysts

12


Page 13 of 52 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


a

Calculated by the BET equation. b BJH desorption pore volume. c BJH desorption average pore size.

The IR spectra is considered as an important method for the investigation of the molecular structure. The FT-IR spectra for MS, 1CZ-0.8MS, 1CZ-1MS and 1CZ-1.2MS supports and Ni/MS catalyst were shown in Figure 2. The peak at 3435 cm-1 attributed to the vibration of the Si-OH and stretching vibration of H2O; the peak at 1638 cm-1 was from bending vibration of H2O.18 The peaks at 1084 cm-1 and 802 cm-1 were reflected by the stretching vibration of Si-O-Si while the peak at 465 cm-1 was ascribed to scissoring vibration of Si-O-Si; and the peak at 968 cm-1 was due to vibration of the Si-OH.20 Contrastively, for 1CZ-0.8MS, 1CZ-1MS and 1CZ-1.2MS supports, the vibration of Si-OH was observed at 3423 cm-1, which was shifted toward the lower wavenumber (12 cm-1) compared with that in MS (3435 cm-1). The band was designated by silanol groups interacting through hydrogen bonding. The band shift between MS (3435 cm-1) and CZ-MS (3423 cm-1) could be attributed to more hydrogen bonding in CZ-MS owing to the existence of more vacancy (Si-OH groups), which suggested the Si-O-Ce partially replaced the Si-OH groups. For CZ-MS, the bands decreased from 1084 cm-1 to 1077 cm-1 compared with MS. Generally, the shift could be considered as an attestation of Ce incorporating into the frame structure of MS, proving the formation of Si-O-Ce. For the band at 802 cm-1 of MS, shift to lower wavenumber for CZ-MS (794 cm-1) and weaker peak intensity were observed. These are strong evidences for the existence of SiO-Ce. 21 For the band at 968 cm-1, an obvious attenuation of the vibration for CZ-MS was observed and the peak almost disappeared, which was due to the Si-OH bond was consumed by the Zr-OH 13



Page 14 of 52

bond. That meant Si-OH bonds were partially replaced by (Si-O)nZr=O for CZ-MS. Z. Zhan, HC. Zeng,22 SW.Lee, RAC. Sr,23 and Y. Wang, R. Wu,24 also observed the similar situation in their investigation. It could be deduced that Zr species were highly incorporated into the framework of MS and Si-O-Zr presented in the CZ-MS supports. Compared with MS, the peaks showed shift to lower wavenumber at 3435 cm-1 and 1638 cm-1 for Ni/MS, indicating that Ni2+ had been inserted into the structure of MS during the impregnation. And the change of peak intension could be found at 968 cm-1, which could demonstrate the formation of Si-O-Ni.12

Figure 2. FTIR spectra for 1CZ-0.8MS, 1CZ-1MS, 1CZ-1.2MS, MS and Ni/MS

Figure 3 reported the XRD patterns for Ni/MS and Ni/CZ-MS after reduction. All the samples 14


Page 15 of 52 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


generated sensible XRD peaks at 2θ=44.51°, 51.85° and 76.37°, corresponding to Ni (110), Ni (200) and Ni (220) crystal planes.25 The appearance of diffraction peaks due to Ni proved nickel active metal was successfully impregnated into the supports of CZ-MS systems. There were no characteristic peaks for Ce and Zr detected in X-ray diffraction, suggesting the homogenous species of CZ was incorporated into MS uniformly combined with the results of FTIR.10 In addition, according to the peaks of Ni species, the intensity of peaks for Ni/CZ-MS series were obviously weaker than that for Ni/MS, indicating the dispersibility of nickel active metal was promoted since the incorporation of Ce and Zr. Especially, Ni/1CZ-1MS revealed the weakest peak intensity among all the samples, speculating the most favorable dispersibility of Ni, which promoted catalytic performance for the catalysts. 26

Figure 3. XRD patterns for Ni/MS and Ni/CZ-MS. 15



Page 16 of 52

For the further investigation of dispersion for Ni species on the reduced catalysts, TEM and CO pulse chemisorption were employed. TEM and the statistical data of Ni particle size were shown in Figure 4. It could be observed that conspicuous aggregation appeared and the Ni particle size was quite nonuniform on the Ni/MS. Comparatively, Ni particle size of Ni/CZ-MS was more uniform, mainly located in 5-20 nm according to Figure 4 e. However, a slight aggregation of Ni still appeared on the Ni/1CZ-0.8MS, indicating that the ratio of CZ and MS would influence the properties of supports. Quite decent dispersion of Ni particles on Ni/1CZ-1MS and Ni/1CZ-1.2MS presaged high catalytic activity. The results well corresponded to the investigation in XRD. Apparently, Ni metal in the Ni/CZ-MS possess higher dispersion degree owing to the interaction between Ni and Ce/Zr incorporated into the structure of MS. The dispersion of active metal Ni and average Ni particle size for all the reduced catalysts measured by CO pulse chemisorption were shown in Figure 5. It could be observed that Ni/CZ-MS series catalysts contained better Ni dispersion and smaller Ni particle size compared with Ni/MS, especially for Ni/1CZ-1MS.

16


Page 17 of 52 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


Figure 4. TEM images of reduced catalysts. a)Ni/MS; b)Ni/1CZ-0.8MS; c)Ni/1CZ-1MS; d)Ni/1CZ-1.2MS;e) Ni particle size distribution.

17



Page 18 of 52

Figure 5. Active metal dispersion and Ni particle size for catalysts obtained from CO chemisorption.

In order to investigate the metal-support interaction and the reducibility of NiO loading on CZ-MS series supports, H2-TPR was carried out. TPR figures of catalysts were reported in Figure 6. For all the catalysts, the reduction peaks can be classified into 3 types: α, β and γ.27 Low temperature α-type peaks represent the reduction of NiO dipping in the pore of supports. Mid temperature β-type peaks are attributed to NiO in the stronger interaction with supports. And the α- and β-NiO were loaded on the pore surface of support, which were available for CO methanation. And the high-temperature (480-620 °C) γ-peak was assigned to the reduction of Ni2+ species infiltrating into supports’ structure during the process of impregnation, which were useless for CO methanation and difficult to be reduced owing to the strong bonding force between Ni2+ and silica 18


Page 19 of 52 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


matrix.12,28 For the series of Ni/CZ-MS catalysts, the α-type peaks shifted to low temperature region. In general, the addition of Zr would enhance the catalytic activity at low temperature. Further, the position of these α-type peaks shifting to the low temperature region showed that some loaded NiO was easily reduced, which demonstrated the existence of Ni active sites at low reaction temperature.29 Especially for Ni/1CZ-1MS and Ni/1CZ-1.2MS, the α-type peaks of them appear at lower temperature (210 °C) compared with that (275-280 °C) of other Ni/CZ-MS catalysts. The behavior indicated that the catalysts would have better catalytic performance in low temperature. Comparing Ni/MS and the series of Ni/CZ-MS, the β-type peaks at 325-450 °C for the series of Ni/CZ-MS shifted to higher temperature region than that at 250-350 °C for Ni/MS. The situation suggested stronger interaction between Ni species and CZ-MS supports, which promoted the dispersion and anti-sintering of Ni particles,21 coinciding with the analysis of XRD and TEM. In addition, the total quantity of absorbed H2 and proportion for the three kinds of peaks were shown in Table 2. It can be concluded that the quantity of absorbed H2 had no much difference. However, the proportion of different types peaks area showed much difference. The area of β-type reduction peaks for all the Ni/CZ-MS were larger than that for Ni/MS, confirming more amount of available NiO particles were reduced to Ni as the active sites of catalysts. The status of more reducible NiO species were also verified in XPS analysis. The area of γ-type peaks for Ni/CZ-MS decreased distinctly compared with Ni/MS, indicating Si-O-Ce and Si-O-Zr inhibited the useless Ni2+ species from infiltrating into the structure of MS. All the factors above were helpful to enhance the activity 19



Page 20 of 52

and stability of the catalysts.

Table 2. H2-TPR quantitative data of samples. Catalysts

Quantity of absorbed H2 (μmol∙g-1)

α-type peak

β-type peak

γ-type peak

Ni/MS

3684.65

14.44

13.05

72.51

Ni/1CZ-0.8MS

3669.90

1.95

79.68

18.37

Ni/1CZ-1MS

3622.85

3.81

85.42

10.77

Ni/1CZ-1.2MS

3711.27

3.13

81.23

15.64

Ni/1CZ-1.4MS

3768.21

3.08

75.71

21.21

Ni/1CZ-1.6MS

3725.07

1.70

64.56

33.74

Fraction of total peaks area / %

Figure 6. H2-TPR profiles for Ni/MS and Ni/CZ-MS.

20


Page 21 of 52 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


The behavior of CO plays vital role in methanation reaction, thus CO-TPD was performed to explore the adsorptive property of CO in catalysts, shown in Figure 7. The peaks of CO desorption arising at different temperature regions illustrated different CO adsorbed states corresponding to different reaction performance. The low-temperature peaks below 160 °C could result from the CO molecular adsorption on the Ni particles, being useless for methanation, whereas the midtemperature peaks accompanied by several shoulder peaks between 160 °C and 400 °C arose from the CO dissociative adsorption on the Ni species, which mainly contributed to methanation. For the series of Ni/CZ-MS, the low-temperature peaks area decreased distinctly compared with Ni/MS, which deduced the higher utilization of Ni active sites due to the influence of Ce and Zr incorporating into the supports. Furthermore, the increase of mid-temperature peaks area for dissociative adsorption in the series of Ni/CZ-MS demonstrated that there were more active sites for CO adsorption contrasting to Ni/MS. Especially for Ni/1CZ-1MS, the maximal peak area was detected in mid-temperature region, indicating Ni/1CZ-1MS contained more active sites for CO adsorption, supporting better catalytic performance.

21



Page 22 of 52

Figure 7. CO-TPD profiles for Ni/MS and Ni/CZ-MS.

The Ni 2p3/2 XPS spectra of reduced catalysts were shown in Figure 8. Two different chemical states of Ni were found in the Ni 2p3/2 XPS spectra as Ni0 and Ni2+ based on their binding energy (BE). The binding energy (BE) of Ni0 in Ni 2p3/2 XPS spectra for reduced Ni/MS was situated at 853.2 eV, and the peak at 856.0 eV was allocated to the Ni2+ species，accompanied with satellite peak at 861.1 eV.17,30,31 With the support incorporated with Ce/Zr, distinct increase of Ni0 species was observed in the Ni 2p3/2 XPS spectra, which could illustrate that Ce/Zr were advantageous to the reducibility of loaded NiO species in CZ-MS support. Additionally, through calculating the peak area of Ni0 and Ni2+, the ratio of Ni0/(Ni2++ Ni0) was obtained. The content of the Ni0 species 22


Page 23 of 52 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


on the catalysts was shown in Table 3. Comparing the series of catalysts, the relative amounts of Ni0 species in Ce/Zr-incorporating MS supports were higher than that in pure MS support. Extraordinary, the reduced Ni/1CZ-1MS showed the highest relative amounts of Ni0 species, as high as 58.77%. Ce/Zr-incorporating MS supports provided more Ni active sites attributing to excellent catalytic activity.

Table 3. Ni, Ce, Zr compositions of the catalysts for XPS spectra

Catalysts

Ni2p /%

Ce3d /%

Ni0/(Ni0+Ni2+)

Ce4+/(Ce3++Ce4+)

Zr3d /% ZrⅡ/(ZrⅠ+ZrⅡ )

Ni/MS

30.66

Ni/1CZ-0.8MS

51.11

52.38

34.86

Ni/1CZ-1MS

58.77

56.90

45.36

Ni/1CZ-1.2MS

54.12

56.70

44.75

Ni/1CZ-1.4MS

50.19

50.25

42.68

Ni/1CZ-1.6MS

49.69

23



Page 24 of 52

Figure 8. The Ni2p3/2 XPS spectrum of reduced Ni/MS and Ni/CZ-MS

Figure 9 showed the XPS spectra of Ce3d of catalysts. The elemental oxidation states of Ce on the surface of the catalysts were investigated by XPS. The XPS spectra of Ce3d3/2 and Ce3d5/2 could be divided into ten Gaussian distributions due to different ionization states.30,32 Peaks at 880.1 and 884.6 eV originated from Ce3+ 3d5/2. Peaks at 882.2, 886.5 and 898.4 eV were ascribed to Ce4+ 3d5/2. Analogously, the peaks at 899.8 and 904.5 eV corresponded to Ce3+ 3d3/2 and the peaks at 901.8, 907.1 and 916.0 eV were attributable to Ce4+ 3d3/2. Through the calculation of peak area for Ce4+ and Ce3+ respectively, the ratio of Ce4+/(Ce3++ Ce4+) was obtained.33 For the catalysts Ni/1CZ-0.8MS, Ni/1CZ-1MS, Ni/1CZ-1.2MS and Ni/1CZ-1.4MS, the ratios 24


Page 25 of 52 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


of Ce4+/(Ce3++ Ce4+) for these samples were shown in Table. 3. It could be concluded that the proportion of Ce4+ firstly increased and then decreased with the ratio of Ce/Zr and MS decreasing. The Ni/1CZ-1MS and Ni/1CZ-1.2MS contained higher amounts of Ce4+, indicating more Ce4+ oxidation states could interconvert into Ce3+ oxidation states due to the catalytic action of Ni and H2 spillover. The process of interconversion of Ce (Ce4+ to Ce3+) would motivate the oxygen vacancies to form and release free electrons. Thus more electrons would concentrate on Ni species. More oxygen vacancies and denser electron cloud of Ni species would promote adsorption and dissociation of CO, respectively. These phenomena primarily improved the catalytic performance of the catalysts.

25



Page 26 of 52

26


Page 27 of 52 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


Figure 9. The Ce3d XPS spectrum of reduced catalysts. a)Ni/1CZ-0.8MS; b)Ni/1CZ-1MS; c) Ni/1CZ-1.2MS; d)Ni/1CZ-1.4MS.

Figure 10 reports Zr3d XPS spectra of the four catalysts. From the spectra, it could be concluded that all the four catalysts revealed a spin-orbit doublet of the Zr 3d5/2 and Zr 3d3/2 levels in Zr3d core level. The peaks in Figure 10 best corresponded to assuming the existence of two kinds of Zr4+ components. The Binding Energy of the lower energy component (182.2-182.5 eV) is in agreement with Zr4+ in pure zirconia (ZrⅠ), whereas the BE of Zr4+ in these samples slightly moved to lower BE compared with that of Zr4+ criterion(182.6 eV) in stoichiometric zirconia, distinctively for Ni/1CZ-1MS sample(182.2 eV), presumably owing to the oxygen vacancies in the ZrO2 framework,34 which contribute to CO dissociation and further improve the catalytic performance. 27



Page 28 of 52

The Binding Energy of the higher energy component(183.0-183.3 eV) match the formation of a more electron attractive specie of Zr and “less oxidized” Zrδ+ sites(ZrⅡ).35,36 Moreover, the peak area proportions of ZrⅡ/(ZrⅠ+ZrⅡ) for different catalysts were reported in Table.2. The relatively higher proportion of ZrⅡ/(ZrⅠ+ZrⅡ) for Ni/1CZ-1MS (0.45) and Ni/1CZ-1.2MS (0.44) revealed the enhancement of oxygen vacancies, compared with other catalysts.17

Figure 10. The Zr3d XPS spectrum of reduced Ni/CZ-MS catalysts.

In the catalyst supports, valence of Ce and Zr was characterized by XPS, shown in Figure 11. Figure 11a showed the spectra of Ce 3d of supports MS and 1CZ-1MS. It could be observed that the intensity of peaks of Ce4+ was greatly stronger than that of Ce3+, indicating that most of Ce existed in support in the form of Ce4+. Figure 11b showed the spectra of Zr3d of supports MS and 28


Page 29 of 52 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


1CZ-1MS. From spectrum of 1CZ-1MS, compared the intensity of peaks for ZrⅠ (Zr4+) and ZrⅡ (Zrδ+), it could be concluded that most of Zr existed in support in the form of ZrⅠ, proving that Zr4+ was the main state in supports. The result provided evidence for Ce4+ and Zr4+ were main existence state in N2 adsorption-desorption characterization part.

29



Page 30 of 52

Figure 11. The XPS spectrum of support MS and 1CZ-1MS

3.2. Catalytic performance. The catalytic performance of the catalysts was shown in Figure 12. All the catalysts were studied at 2.0 MPa with WHSV of 30000 ml/g/h at 150-450 °C. The CO conversion and CH4 selectivity for the series of Ni/CZ-MS catalysts were noticeably more excellent than those for the Ni/MS, indicating that the incorporation of Ce and Zr into supports could greatly improve the catalytic activity of catalysts. The results benefited from better dispersibility of Ni and more active sites according to the characterization of catalysts. According to Figure 12, the temperature for maximum CO conversion of Ni/CZ-MS transferred to a lower temperature compared with that of Ni/MS. The series of Ni/CZ-MS kept high catalytic activity at 250-450 °C while the CO conversion and CH4 selectivity were close to 100% and above 90%, respectively. Extraordinarily, the CO conversion and CH4 selectivity for 30


Page 31 of 52 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


Ni/1CZ-1MS reached 100% and 98.94% at 350 °C respectively. Moreover, at 200 °C, the series of Ni/CZ-MS catalysts also showed greater catalytic performance than Ni/MS. Meanwhile, the CO conversion and CH4 selectivity of Ni/CZ-MS series catalysts firstly increased then decreased with the increase of silicon sources, shown in Figure 13. It could be observed that the Ni/1CZ-1MS showed the most active catalytic performance at low temperature of 200 °C, while the CO conversion and CH4 selectivity reached 91.12% and 84.40%. The performance was highly consistent with the previous analysis of characterization for catalysts.

31



Page 32 of 52

Figure 12. The catalytic performance for Ni/MS and Ni/CZ-MS a) CO conversion; b) CH4 selectivity

32


Page 33 of 52 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


Figure 13. The catalytic performance at 200 °C for Ni/CZ-MS.

3.3. The resistance for sintering of Ni/1CZ-1MS. CO methanation is a strong exothermic reaction, so the resistance for high-temperature sintering is important for methanation catalysts. To investigate the anti-sintering property of catalysts, catalytic performance of Ni/1CZ-1MS and Ni/MS after calcination at 700 °C was studied. The catalysts firstly were reduced at 500 °C for 2 h in H2 atmosphere. Catalytic performance was studied at 350 °C and 2 MPa, then the catalysts were calcined at 700 °C for 3 h in N2 atmosphere. After that, the catalysts were cooled down to 350 °C for catalytic performance study. Comparing the catalytic activity before and after calcination, the ability of anti-sintering could be 33



Page 34 of 52

evaluated. The results were shown in Table 4. It could be found that the catalytic activity of Ni/MS decreased distinctly after calcination. The CO conversion decreased from 89.97% to 65.76% and the CH4 selectivity reduced from 96.24% to 76.35%. On the contrary, Ni/1CZ-1MS still kept high catalytic activity after calcination. The CO conversion maintained 100% before and after calcination. The CH4 selectivity slightly decreased from 98.94% to 97.88%. Comparatively, Ni/1CZ-1MS showed better ability of anti-sintering due to the stronger metal-support interaction proved by H2-TPR.

Table 4. Catalytic activity of the catalysts. Before calcination Catalysts

After calcination

Conversion of

Selectivity

Conversion

Selectivity

CO/%

of CH4/%

of CO/%

of CH4 /%

Ni/MS

89.97

96.24

65.76

76.35

Ni/1CZ-1MS

100

98.94

100

97.88

3.4. The catalytic stability of Ni/1CZ-1MS catalyst. The stability plays an important role in catalytic performance of catalysts, especially for industrial application. The Ni/1CZ-1MS was firstly calcinated at 700 °C for 3 h. Then catalytic stability was tested at 550 °C and 2 MPa for 100 h with WHSV of 30000 ml/g/h. The results were reported in Figure 14. It could be seen that Ni/1CZ-1MS maintained high catalytic activity during 100 h test. There was no obvious decline for CO conversion and CH4 selectivity. The investigation strongly indicated the excellent antisintering and catalytic stability of Ni/1CZ-1MS. 34


Page 35 of 52 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


Figure 14. The catalytic stability test of Ni/1CZ-1MS.

4. CONCLUSIONS Ni/MS (Mesoporous Silica) and a series of completely new Ni/CZ-MS (MS incorporated by Ce/Zr) catalysts with 30wt.% Ni impregnated were synthesized by hydrothermal synthesis method. The FTIR detection proved that Ce and Zr (CZ) were successfully incorporated into the structure of mesoporous silica (MS). The incorporation of CZ into MS would greatly promote the catalytic performance since the growth of active sites certified by CO-TPD, H2-TPR and XPS and the excellent dispersion of Ni proved by XRD, TEM and H2-TPR. The incorporated Ce species would interconvert from Ce4+ to Ce3+ during CO methanation, which would motivate oxygen vacancies 35



Page 36 of 52

to form and release free electrons tending to concentrate on Ni. More oxygen vacancies and denser electron cloud of Ni species would promote adsorption and dissociation of CO respectively. The state changes of incorporated Zr also promoted oxygen vacancies to form. The incorporated Zr species would enhance the catalytic activity at low temperature attested by H2-TPR. The catalytic performance of all the catalysts were examined at 2.0 MPa at a WHSV of 30000 ml/g/h at 150-450 °C. Obviously, the series of catalysts with CZ-MS supports showed superior catalytic activity than the catalyst with MS support. Among the catalysts, Ni/1CZ-1MS exhibited the best catalytic property at low temperature of 200 °C, which CO conversion and CH4 selectivity reached 91.12% and 84.40% respectively. Meanwhile, at 250-450 °C, the CO conversion and CH4 selectivity for Ni/1CZ-1MS maintained 100% and exceeded 95% respectively. The catalytic activity of Ni/1CZ-1MS showed no obvious decline after calcination at 700 °C for 3 h, indicating the high anti-sintering. It also showed excellent catalytic stability at 550 °C in 100 h test after calcination at 700 °C for 3 h.

Corresponding Author *Weiyong Ying; E-mail: [email protected]

ACKNOWLEDGMENT This work is financially supported by the National Science and Technology Supporting Plan (No. 2012AA050102) and the Fundamental Research Funds for the Central Universities (No. 36


Page 37 of 52 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


22201817013).

REFERENCE (1) Le, T.A.; Kim, M.S.; Lee, S.H.; Kim, T.W.; Park, E.D. CO and CO2 Methanation over supported Ni catalysts. Catal. Today. 2016, 293, 89. (2) Liu, Q.; Qiao, Y.; Tian, Y.; Gu, F.; Zhong, Z.; Su, F. Ordered Mesoporous Ni-Fe-Al Catalysts for CO Methanation with Enhanced Activity and Resistance to Deactivation. Ind. Eng. Chem. Res. 2017, 56, 9809. (3) Alexmills, G.; Steffgen, F. Catalytic Methanation. Catal. Rev. 1974, 8, 159. (4) Lu, Z.; Zhang, H.; Tang, S.; Liu, C.; Yue, H. Molybdenum Disulfide–Alumina/Nickel‐Foam Catalyst with Enhanced Heat Transfer for Syngas Sulfur‐Resistant Methanation. Chemcatchem. 2018, 10, 720. (5) Nithinart, C.; Praserthdam, P.; Jongsoijit, B. A Study on Characteristics and Catalytic Properties of Co/ZrO 2 -B Catalysts Towards Methanation. Catal. Lett. 2009, 128, 119 (6) Bacariza, M.C.; Graca, I. Lopes, J.M.; Henriques, C. Ni‐Ce/Zeolites for CO2 Hydrogenation to CH4: Effect of the Metal Incorporation Order. Chemcatchem. 2018, 10, 1. (7) Kamboils, A.; Ferri, D.; Lu, Y.; Yannopoulos, SN.; Pokrant, S.; Structural Modification of Ni/γ‐Al2O3 with Boron for Enhanced Carbon Resistance during CO Methanation. Chemcatchem. 2015, 7, 3261. 37



Page 38 of 52

(8) Li, Y.; Zhang, Q.; Chai, R.; Zhao, G.; Liu, Y. Structured Ni‐CeO2‐Al2O3/Ni‐Foam Catalyst with Enhanced Heat Transfer for Substitute Natural Gas Production by Syngas Methanation. Chemcatchem. 2015, 7, 1427. (9) Cai, M.; Wen, J.; Chu, W.; Cheng, X.; Li, Z. Methanation of carbon dioxide on Ni/ZrO2Al2O3 catalysts: Effects of ZrO2 promoter and preparation method of novel ZrO2-Al2O3 carrier. Nat. Gas Chem. 2011, 20, 318. (10) Ocampo, F.; Louis, B.; Kiwi-Minsker, L. Effect of Ce/Zr composition and noble metal promotion on nickel based CexZr1−xO2, catalysts for carbon dioxide methanation. Appl. Catal. AGen. 2011, 392, 36. (11) Bacariza, M.C.; Graça, I.; Bebiano, S.S.; Lopes, J.M.; Henriques, C. Micro- and mesoporous supports for CO2 methanation catalysts: a comparison between SBA-15, MCM-41 and USY zeolite. Chem. Eng. Sci. 2018, 175, 72. (12) Zhang, J.; Xin, Z.; Meng, X.; Tao, M. Synthesis, characterization and properties of antisintering nickel incorporated MCM-41 methanation catalysts. Fuel. 2013, 109, 693. (13) Zhang, J.; Xin, Z.; Meng, X. Activity and stability of nickel based MCM-41 methanation catalysts for the production of synthetic natural gas. Ciesc Journal. 2014, 65, 160. (14) Yang, X.; Wendurima, Gao, G.; Shi, Q.; Wang, X.; Zhang, J.; Han, C. Impact of mesoporous structure of acid-treated clay on nickel dispersion and carbon deposition for CO methanation. Int. J. Hydrogen Energy. 2014, 39, 3231. (15) Bian, Z.; Xin, Z.; Meng, X.; Tiao, M.; Lv, Y.; Gu, J. Effect of Citric Acid on the Synthesis 38


Page 39 of 52 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


of CO Methanation Catalysts with High Activity and Excellent Stability. Ind. Eng. Chem. Res. 2017, 56, 2383. (16) Sun, L.; Gu, F.; Chun, Y.; Zhu, J. Attempt to Generate Strong Basicity on Silica and Titania. J. Phys. Chem. C. 2008, 112, 4978. (17) Li, H.; Ren, J.; Qin, X.; Qin, Z.; Lin, J.; Li, Z. Ni/SBA-15 catalysts for CO methanation: effects of V, Ce, and Zr promoters. Rsc. Advances. 2015, 5, 96504. (18) Jiang, T.; Tang, Y.; Zhao, Q,; Yin, H. Effect of Ni-doping on the pore structure of pure silica MCM-41 mesoporous molecular sieve under microwave irradiation. Colloids Surf. A Physicochem. Eng. Asp. 2008, 315, 299. (19) Ying, Z.; Li, Z.; Yong, Z.; Xiao, S. Synthesis and characterization of Fe–Ce–MCM-41. Mater. Lett. 2006, 60, 3221. (20) Khalil, KMS. Cerium modified MCM-41 nanocomposite materials via a nonhydrothermal direct method at room temperature. J. Colloid. Interf. Sci. 2007, 315, 562. (21) Laha, SC.; Mukherjee, P.; Sainkar, SR.; Kumar, R. Cerium Containing MCM-41-Type Mesoporous Materials and their Acidic and Redox Catalytic Properties. J. Catal, 2002, 207, 213223. (22) Zhan, Z.; Zeng, HC. A catalyst-free approach for sol–gel synthesis of highly mixed ZrO2 – SiO2, oxides. J. Non-Cryst. Solids. 1999, 243, 26. (23) Lee, SW.; Sr, RAC. The infrared and Raman spectra of ZrO2 -SiO2, glasses prepared by a sol-gel process. J. Mater. Sci. 1988, 23, 2951. 39



Page 40 of 52

(24) Wang, Y.; Wu, R.; Zhao, Y. Effect of ZrO2 promoter on structure and catalytic activity of the Ni/SiO2 catalyst for CO methanation in hydrogen-rich gases. Catal. Today. 2010, 158, 470. (25) Ren, J.; Li, H.; Jin, Y.; Liu, S. Silica/titania composite-supported Ni catalysts for CO methanation: Effects of Ti species on the activity, anti-sintering, and anti-coking properties. Appl. Catal. B-Environ. 2017, 201, 561. (26) Zeng, Y.; Ma, H.; Zhang, H.; Ying, W.; Fang, D. Highly efficient NiAl2O4-free Ni/γ-Al2O3, catalysts prepared by solution combustion method for CO methanation. Fuel. 2014, 137,155. (27) Meng, F.; Li, X.; Shaw, G. M.; Smith, P. J.; Morgan, D. J.; Perdjon, M.; Li, Z. Sacrificial Carbon Strategy toward Enhancement of Slurry Methanation Activity and Stability over NiZr/SiO2 Catalyst. Ind. Eng. Chem. Res. 2018, 57, 4798. (28) Takahashi, R.; Sato, S.; Sodesawa, T.; Yoshida, M.; Tomiyama, S. Addition of zirconia in Ni/SiO2, catalyst for improvement of steam resistance. Appl. Catal. A-Gen. 2004, 273, 211. (29) Ashok, J.; Ang, M.L.; Kawi , S. Enhanced activity of CO2, methanation over Ni/CeO2 -ZrO2, catalysts: Influence of preparation methods. Catal. Today. 2017, 281, 304. (30) Liu, Q.; Gu, F.; Lu, X. Enhanced catalytic performances of Ni/Al2O3, catalyst via, addition of V2O3, for CO methanation. Appl. Catal. A-Gen. 2014, 488, 37. (31) Gao, J.; Jia, C.; Li, J.; Gu, F.; Xu, G. Nickel Catalysts Supported on Barium Hexaaluminate for Enhanced CO Methanation. Ind. Eng. Chem. Res. 2012, 31, 10345. (32) Bêche, E.; Charvin, P.; Perarnau, D.; Abanades, S. Ce 3d XPS investigation of cerium oxides and mixed cerium oxide (CexTiyOz). Surf. Interface Anal. 2008, 40, 264. 40


Page 41 of 52 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


(33) Razzaq, R.; Zhu, H.; Jiang, L.; Muhammad, U.; Li, C. Catalytic Methanation of CO and CO2 in Coke Oven Gas over Ni-Co/ZrO2-CeO2. Ind. Eng. Chem. Res. 2013, 52, 2247. (34) Sato, AG.; Volanti, DP.; Meira, DM.; Damyanova, S.; Longo, E. Effect of the ZrO2 phase on the structure and behavior of supported Cu catalysts for ethanol conversion. J. Catal. 2013, 307, 1. (35) Ardizzone, S.; Bianchi, CL.; Signoretto, M. Zr(IV) surface chemical state and acid features of sulphated-zirconia samples. Appl. Surf. Sci. 1998, 136, 213. (36) Ardizzone, S.; Bianchi, CL. XPS characterization of sulphated zirconia catalysts: the role of iron. Appl. Surf. Sci. 2015, 30, 77.

TOC

41



Figure 1. a) N2 adsorption-desorption isotherms of catalysts; b) Pore size distribution of catalysts.


Page 42 of 52

Page 43 of 52 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


Figure 2. FTIR spectra for 1CZ-0.8MS, 1CZ-1MS, 1CZ-1.2MS, MS and Ni/MS

Figure 3. XRD patterns for Ni/MS and Ni/CZ-MS.



Figure 4. TEM images of reduced catalysts. a)Ni/MS; b)Ni/1CZ-0.8MS; c)Ni/1CZ1MS; d)Ni/1CZ-1.2MS;e) Ni particle size distribution.


Page 44 of 52

Page 45 of 52 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


Figure 5. Active metal dispersion and Ni particle size for catalysts obtained from CO chemisorption.

Figure 6. H2-TPR profiles for Ni/MS and Ni/CZ-MS.



Figure 7. CO-TPD profiles for Ni/MS and Ni/CZ-MS.

Figure 8. The Ni2p3/2 XPS spectrum of reduced Ni/MS and Ni/CZ-MS


Page 46 of 52

Page 47 of 52


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



Figure 9. The Ce3d XPS spectrum of reduced catalysts. a)Ni/1CZ-0.8MS; b)Ni/1CZ1MS; c) Ni/1CZ-1.2MS; d)Ni/1CZ-1.4MS.


Page 48 of 52

Page 49 of 52 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


Figure 10. The Zr3d XPS spectrum of reduced Ni/CZ-MS catalysts.



Figure 11. The XPS spectrum of support MS and 1CZ-1MS


Page 50 of 52

Page 51 of 52 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


Figure 12. The catalytic performance for Ni/MS and Ni/CZ-MS a)CO conversion; b)CH4 selectivity

Figure 13. The catalytic performance at 200℃ for Ni/CZ-MS.



Figure 14. The catalytic stability test of Ni/1CZ-1MS. TOC:


Page 52 of 52

Anti-sintering and High-activity Ni Catalyst Supported on Mesoporous

Recommend Documents