In situ Exsolution of Bimetallic Rh-Ni Nano-alloys: Highly. Efficient Catalyst for CO 2 Methanation

Transcription

1 Supporting Information In situ Exsolution of Bimetallic Rh-Ni Nano-alloys: Highly Efficient Catalyst for CO 2 Methanation Hamidreza Arandiyan,* a Yuan Wang, a Jason Scott,* a Sara Mesgari, b Hongxing Dai, c and Rose Amal* a Dr. Hamidreza Arandiyan, Yuan Wang, Dr. Jason Scott, and Prof. Rose Amal a Particles and Catalysis Research Group, School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia Dr. Sara Mesgari b School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW 2052, Australia Prof. Hongxing Dai c Beijing Key Laboratory for Green Catalysis and Separation, and Laboratory of Catalysis Chemistry and Nanoscience, Beijing University of Technology, Beijing , China Corresponding Author ID: * h.arandiyan@unsw.edu.au (H. A.) * jason.scott@unsw.edu.au (J. S.) * r.amal@unsw.edu.au (R. A.) S-1

2 Item Contents Page Catalyst characterisation procedures S-2 Catalyst preparation S-4 Fig. S1 S-5 Fig. S2 S-6 Fig. S3 S-8 Fig. S4 S-9 Fig. S5 S-10 Fig. S6 S-10 Fig. S7 S-11 Fig. S8 S-11 Fig. S9 S-12 Fig. S10 S-13 Fig. S11 S-14 Table S1 S-14 Table S2 S Catalyst characterisation procedures 1.1. X-ray diffraction (XRD) X-ray diffraction (XRD) analyses were performed on a PANalytical Empyrean II diffractometer with Cu Kα radiation (λ = nm) at 45 kv and 40 ma to identify the crystal phases and to analyze lattice parameters. Scattering intensity was recorded in the range of 8 o < 2θ < 90 o for all of the samples with a 2θ step of 0.03 o and a count time of 2 s per step. The diffraction patterns were indexed by the JCPDS (Joint Committee on Powder Diffraction Standards) files Field-emission scanning electron microscope (FE-SEM) Morphologies of the as-prepared samples were observed by scanning electron microscopy S-2

3 (SEM) and field-emission high resolution scanning electron microscopy (FE-HRSEM) using an FEI Nova NanoSEM 450 FE-SEM microscope at an accelerating voltage of 5 kv, with a work distance (WD) between 5 and 8 mm and magnifications in the range of HRSEM images of the samples were obtained using the back-scattered electron detector (BSED). The secondary electron detector (SED) modes showed morphologies of the surface structures. For determining chemical compositions of the crystal phases, energy-dispersive spectroscopy (SDD-EDS) was used to obtain the EDS spectra by means of an EDS DX-4 analysis system. A very thin Cr film was used to provide a better conductivity of the sample, for example, for the PMMA microspheres Field-emission high resolution transmission electron microscopy (FE-HRTEM) Field-emission high resolution transmission electron microscopic (FE-HRTEM) images, as well as the selected-area electron diffraction (SAED) patterns, were obtained on a Philips CM200 apparatus. To determine the detailed surface structure, high-angle annular dark-field - scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (HAADF- STEM-EDS) images were taken on a JEOL JEM-ARM200F STEM BET surface area and N 2 adsorption desorption isotherm The surface areas and pore size distributions of the samples were obtained using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. The N 2 adsorption-desorption isotherms, surface areas, and pore parameters of the samples were determined via N 2 adsorption at 196 o C on a Micrometric Tristar 3030 adsorption analyser. Before the measurement, the samples are degassed at 150 o C for 3 h H 2 temperature-programmed reduction (H 2 -TPR) Hydrogen temperature-programmed reduction (H 2 -TPR) experiments were performed on a Micromeritics Autochem II apparatus equipped with a TCD detector. The experiments were conducted with the use of approximately 50 mg of sample. The samples were initially flushed with an argon flow of 40 ml/min as the temperature was increased to 150 o C at a ramp rate of S-3

4 10 o C/min. The samples were kept at this temperature for 30 min to remove water after which they were cooled to 50 o C. Then, the reducing gas (10% H 2 in Ar) was introduced at a flow rate of 40 ml/min and the sample was heated at a ramp rate of 10 o C/min to 900 o C. The variation in H 2 concentration of the effluent was monitored online by the TCD X-ray photoelectron spectroscopy (XPS) The X-ray photoelectron spectroscopic (XPS) technique was used to determine the Ce 3d, La 3d, Ni 2p, O 1s, and C 1s binding energies (BEs) of surface species. The analyses were performed on a Thermo Scientific, UK (model ESCALAB250Xi) using Mg Kα (hν = ev) as the excitation source with 150W power (13 kv x 12 ma). Before the XPS measurement, the sample was treated in an O 2 flow of 20 ml/min at 200 o C for 1 h. After being cooled to room temperature (RT), the pretreated sample was transferred to a holder in a Glove Bag (Instruments for Research and Industry, USA) that was filled with helium, and then the holder was transferred into the spectrometer chamber under helium. The sample was outgassed (0.5 h) in the preparation chamber before being analyzed in the analysis chamber. The BE values of Ce 3d, La 3d, Ni 2p, O 1s, and C 1s were calibrated against the C 1s signal (BE = ev for adventitious hydrocarbon) of contaminant carbon with spectrometer calibration of Au 4f7 = ev, Ag 3d5 = ev, Cu2p3 = ev. 2. Catalyst preparation 2.1. Materials The methyl methacrylate (MMA), potassium peroxydisulfate (K 2 S 2 O 8, >99.0%), Pluronic P- 123 (M n ~ 5,800), aluminum nitrate nanohydrate (Al(NO 3 ) 3 9H 2 O, >98.0%), lanthanum nitrate hexahydrate (La(NO 3 ) 3 6H 2 O, >99.99%), nickel nitrate hexahydrate (Ni(NO 3 ) 2 6H 2 O, >98.5%), Rhodium (III) chloride trihydrate (RhCl 3 3H 2 O, >99.98%) used in the follow preparation are purchased from Sigma Aldrich without further purification. S-4

5 2.2. Synthesis of monodisperse PMMA microspheres Monodisperse poly(methyl methacrylate) (PMMA) microspheres with an average diameter of ca. 200 nm (Fig. S1) were synthesized by adopting the procedures described in the literature g (3.00 mmol) of K 2 S 2 O 8 and 1500 ml of deionized water were mixed under stirring at 400 rpm, heated at 70 C, and degassed with a flow of N 2 in a separable four-necked 2000-mL round-bottom flask. After equilibrating at 70 C, 115 ml of methyl methacrylate was poured into the flask, and the resulting suspension was stirred at 70 C for 60 min. The PMMA colloidal crystal template was prepared with 120 ml of the colloidal suspension (ca g) in a 25-mL centrifugation tube for 75 min. Fig. S1. FE-HRSEM images of well-aligned PMMA microspheres. The diameter of the PMMA microspheres can be controlled by adjusting either the N 2 flow or the initiator (K 2 S 2 O 8 ) during synthesis. When the amount of K 2 S 2 O 8 was kept constant, the microsphere diameter decreases with increasing N 2 flow. When the flow rate of the N 2 was kept constant, the microsphere diameter increased with an increasing amount of K 2 S 2 O 8. Additionally, the PMMA microsphere diameter can be increased by increasing the amount of monomer or by changing the temperature of the polymerization reaction (increasing S-5

6 temperature decreases PMMA microsphere diameter). By optimizing the synthesis conditions, PMMA microspheres with diameters 200 nm can be synthesized. After the deionized water was evaporated in a water bath at 80 C, the obtained wet dense material was first dried at RT for two days and then well grounded. During polymerisation, several factors such as monomer, temperature, initiators, and the stirring rate can influence the size of the PMMA microspheres. The average diameter of macropores in the 3DOM materials is 145 ± 10 nm, indicating a 25 35% shrinkage compared with the initial size of PMMA microspheres (200 nm). This shrinkage is caused by the melting of the polymer template and the growth of crystal size of perovskite structure along with the increasing of calcination temperature. Fig. S2. Three dimensional environmental atomic force microscopy (3D-eAFM) images (1 µm 1 µm) of the free surface of monodisperse PMMA microspheres. S-6

7 2.3. Synthesis of 3DOM LNAO The 3DOM LNAO perovskite was prepared by infiltration of the appropriate perovskite precursors into the interstitial void spaces of the three-dimensionally aligned PMMA. They were fabricated by adopting the Pluronic P 123-assisted method. Under magnetic stirring and at room temperature, stoichiometric amounts of Al(NO 3 ) 3 9H 2 O, La(NO 3 ) 3 6H 2 O, Ni(NO 3 ) 2 6H 2 O, 1.20 g of Pluronic P123, and 3.00 ml of methanol were dissolved in 5 ml of deionized water. After being well mixed, 200 mmol of urea was added dropwise to the above mixed solution under stirring for 2 h and the ph value was carefully regulated to 11 for the generation of yellowish co-precipitates. Then, after obtaining a uniform precursor solution, ca g of highly ordered PMMA colloidal crystal microspheres was added and soaked with the above mixed solution. After the PMMA microspheres were thoroughly wetted, the excessive liquid was filtered via a Buchner funnel connected to vacuum (0.07 MPa). Finally, after filtration and drying at RT for 24 h, the solid was transferred to a ceramic boat and thermally treated in a tubular furnace. Treatment involved: (i) initially heating at a ramp rate of 1 C/min from RT to 300 C for 3 h in a 50 ml/min N 2 flow after which it was cooled in the same atmosphere to RT; (ii) heating in a 50 ml/min air flow at a ramp rate of 1 C/min from RT to 850 C where it was kept at this temperature for 4 h. 1DDN LNAO was prepared by a sol-gel method as a control sample and possessed a much lower surface area compared to 3DOM LNAO. The synthesis process involved dissolving equal moles of the metal precursors with citric acid in distilled water. After drying at 120 C for 24 h, the formed gel was calcined in an air flow at 850 C for 4 h Synthesis of Rh/3DOM LNAO, Rh/1DDN LNAO and Ni-Rh LAO The Rh/3DOM LNAO and Rh/1DDN LNAO were synthesized by an impregnation method. A desired amount of Rhodium (III) chloride trihydrate was added to the 1g 3DOM or 1DDN S-7

8 LNAO support in 5 ml water and stirred for 2 h. After drying at 85 C for 12 h, the sample was calcined in air at 450 C for 3 h. In-situ Ni exsolution and Ni-Rh alloy formation were performed by a reduction process. The Rh/3DOM LNAO was calcined in 5% H 2 /Ar atmosphere at 900 C for 20 h. Fig. S3. (a-d) FE-HRTEM images of different magnifications of 3DOM LNAO. S-8

9 Fig. S4. HAADF-STEM images of Rh-Ni/3DOM LAO (a) bright field (BF), (b) bright field secondary electrons (BF-SE), and (c) high-angle annular dark-field imaging (HAADF). S-9

10 Fig. S5. XRD pattern of the 3DOM LNAO sample. Volume adsorbed (cm 3 /g, STP) Rh-Ni/3DOM LAO Rh/3DOM LNAO 3DOM LNAO 1DDN LNAO Relative Pressure (P/P 0 ) Fig. S6. Nitrogen adsorption desorption isotherms of the as-prepared samples. S-10

11 Rh 3d Blue shift 0.2 ev Intensity (a.u.) Rh-Ni/3DOM LAO Rh/3DOM LNAO Binding energy (ev) Fig. S7. XPS profile of Rh 3d for Rh/3DOM LNAO and Rh-Ni/3DOM LAO samples. La 3d and Ni 2P Rh-Ni/3DOM LAO La 3d3/2 Ni 2p 3/2 Intensity (a.u.) Rh/3DOM LNAO 3DOM LNAO Shifted 0.4 ev Ni 2p 1 1DDN LNAO Binding energy (ev) Fig. S8. La 3d and Ni 2p XPS spectra of the samples. S-11

12 2.5. Catalytic activity measurement Catalytic activity for the CO 2 methanation reaction was conducted in a fixed-bed quartz tubular microreactor (i.d. = 6.0 mm) at atmospheric pressure, as shown in Fig. S1. Initially 50 mg of catalyst was packed in the glass reactor and reduced in a flow of H 2 (30 ml/min)at 450 C for 2 h, after which it was cooled to 150 C under an N 2 flow (30 ml/min). Following catalyst pre-treatment, the reaction gas (5% CO 2 : 20% H 2 : 75% N 2 ) with a total flow rate of 40 ml/min was introduced into the reactor, giving a gas hourly space velocity (GHSV) of ca. 48,000 ml/(g h). CO 2 conversion was measured over the temperature range of C using a gas chromatograph (Young Lin 6500) equipped with a TCD detector and a Carboxen PLOT column. The catalytic activities of the samples were evaluated using the temperatures required for methane conversions of 10, 50, and 90% (T 10%, T 50%, and T 90%, respectively). Fig. S9. Photograph of the experimental set-up used for catalyst activity assessment. S-12

13 CO 2 conversion and CH 4 selectivity are calculated with the formula below: Conversion of (%) = [ ] /[ ] [ ] /[ ] [ ] /[ ] 100% Selectivity of (%)= [ ] [ ] +[ ] +[ ] 100% where [ ] and [ ] are the concentrations of CO 2 at the inlet and outlet, respectively, [ ] and [ ] are the concentrations of N 2 at the inlet and outlet, respectively. [ ] and [ ] are the concentrations of CH 4 and CO at the outlet, respectively. In order to examine the catalytic stability, we carried out the lifetime experiment over the Rh- Ni/3DOM LAO catalyst within 3000 min of on-stream reaction (Fig. S10) and recorded the TEM image of the used Rh-Ni/3DOM LAO catalyst after activity test as shown in Fig. S11. The stability test indicated that over 3000 min of on stream reaction, no significant decrease in catalytic activity was observed. The TEM image showed that there was no obvious metal nanoparticle agglomeration after stability test, indicating the as-obtained perovskite material is thermally stable under the reaction conditions. 100 Linear Fit CO 2 Conversion (%) Rh-Ni/3DOM LAO on-stream reaction time (h) Fig. S10. CO 2 conversion versus on-stream reaction time over the Rh-Ni/3DOM LAO catalyst under the conditions: reaction temperature = 300 C; 5% CO 2 : 20% H 2 : 75% N 2 at a total flow rate of 40 ml/min and GHSV of ca. 48,000 ml/(g h). S-13

14 Fig. S11. TEM image of used Rh-Ni/3DOM LAO catalyst after 3000 min of on-stream reaction under the conditions; reaction temperature = 300 C; 5% CO 2 : 20% H 2 : 75% N 2 at a total flow rate of 40 ml/min and GHSV of ca. 48,000 ml/(g h). Table S1. Preparation parameters and calcination conditions for the Rh-Ni/3DOM LAO, Rh/3DOM LNAO, 3DOM LNAO, and 1DNN LNAO samples. Catalyst Hard template/soft template Calcination condition XRD result Crystal phase 1DNN LNAO 850 C 4 h (in air) Rhombohedral 3DOM LNAO PMMA/P C 3 h (in N 2 ) 300 C 1 h (in air) 800 C 4 h (in air ) Rhombohedral Rh/3DOM LNAO PMMA/P C 3 h (in N 2 ) 300 C 1 h (in air) 800 C 4 h (in air ) Rhombohedral Rh-Ni/3DOM LAO PMMA/P C 3 h (in N 2 ) 300 C 1 h (in air) 800 C 4 h (in air ) (5% H 2 /Ar) at 900 C for 20 h Rhombohedral S-14

15 Table S2. Catalytic activities of various catalysts for CO 2 methanation as reported in the literature. Catalyst Preparation method Reaction condition ( C) (%) (%) Ref. 12 wt% Ni/ZrO 2 -Al 2 O 3 Impregnation-precipitation CO 2 /H 2 = 1/3.5, GHSV = 8,100 ml/(g h) wt% Ni/ceria-zirconia Co-impregnating boehmite CO 2 /H 2 = 1/4, GHSV = 15,000 ml/(g h) with metal solutions 5 wt% Ni-Ce x Zr 1-x O 2 Pseudo sol-gel CO 2 /H 2 = 1/4, GHSV = 43,000 ml/(g h) wt% Ni-La/SiC Impregnation CO 2 /H 2 = 1/4, GHSV = 12,000 ml/(g h) wt% Ni/CeO 2 Impregnation CO 2 /H 2 = 1/4, GHSV = 10,000 ml/(g h) Ni/SiO 2 Impregnation CO 2 /H 2 = 1/4, GHSV = 7,200 ml/(g h) Co/KIT-6 Impregnation CO 2 /H 2 = 1/4, GHSV = 22,000 ml/(g h) Co/meso-SiO 2 Impregnation CO 2 /H 2 = 1/4, GHSV = 22,000 ml/(g h) Co 4 N/γ-Al 2 O 3 NH 3 -temperature CO/CO 2 /N 2 /CH 4 /H 2 = 7/3/4/27/58, GHSV = programmed reaction 5,000 h -1 Co/γ-Al 2 O 3 Impregnation CO/CO 2 /N 2 /CH 4 /H 2 = 7/3/4/27/58, GHSV = ,000 h -1 Rh/ZrO 2 Impregnation S-15

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