Direct Catalytic Conversion of Methane

Transcription

1 Direct Catalytic Conversion of Methane Xiulian Pan, Zengjian An, Ding Ma, Yide Xu, Xinhe Bao State Key Laboratory of Catlaysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences

2 Methane is a highly symmetrical molecule and is very difficult to activate C-H bond strength: 438.8kJ mol -1 Ionization potential: 12.5eV Proton affinity: 4.4eV Acidity (pka): 48

3 Introduction Catal. Rev.-Sci. Eng., 2003,45, 151

4 Example 1 CH 4 + 1/2O 2 CH 3 OH Example 2 6CH 4 C 6 H 6 +9H 2

5 Example 1 Low Temperature Catalytic Oxidation of Methane

6 Examples Electrophiles and superacids, G. Olah, ACC. Chem. Res. 1987, 20, 422.

7 Work of Periana et al.? HgSO4 CH4 + H2SO4 + SO3 CH3OSO3H + H2O + SO2 180 CH3OSO3H + H2O CH3OH + H2SO4 SO2 + 1/2O2 SO3 Net reaction: CH 4 + 1/2O 2 HgSO4 180 CH 3 OH CH 4 conversion 50%, yield 43% Periana et al. Science, 1993, 340

8 Work of Periana et al.? A more effective catalyst---- Pt-complex was developed, methane conversion was 72%. Conv. 90%, Sel. 81% 220 C, 35 bar CH4 Methyl bisulfate on the Pt-complex catalyst in fuming sulfuric acid. Periana et al. 1998, Science, 280, 560.

9 Work of Fujiwara et al.? Catal. Solvent Oxidant Reagent T ( ) TON (h -1 ) CaCl 2 CF 3 CO 2 H /(CF 3 CO 2 ) 2 O K 2 S 2 O 8 CO Angew. Chem. Int. Ed. 2000, 39, 2475 Pd (OAc) 2 /Cu(OAc) 2 CF 3 CO 2 H acid K 2 S 2 O 8 CO 80 < 1 J. Organometal. Chem. 1994, 473: 329 Mg C F 3 CO 2 H K 2 S 2 O 8 CO 80 < 0.1 Appl. Organometal. Chem. 1999, 13: 539 Carboxylation to acetic

10 Work of Bell et al.? CH 4 + SO 2 + K 2 S 2 O 8 CF 3 SO 3 H, CaCl 2 65 C CH 3 SO 3 H 69 atm CH4 (268 mmol); 2.4 atm SO2 (13.14 mmol); 5 mmol K2S2O8; 5 ml triflic acid; 10 h. J. AM. CHEM. SOC. 2003, 125,

11 Work of Sen et al.? 0 CF CH 4 Pd H + 3 COOH C CF 3 COOCH Pd 2+ CF 3 COOH + CH 3 OH H 2 O 2 + CH 4 (CF 3 CO) 2 O PdCl2, 90 C CF 3 COOCH 3 adamantane arene ethane methane E. Gretz, et al. J. Am. Chem. Soc. 109 (1987) 8109; L. Kao, et al. J Am Chem Soc 113 (1991) 700

12 We want To make a catalytic process; To avoid HCl, H 2 SO 4, SO 3, SO 2, H 2 O 2 ; To use O 2 as oxidant.

13 ? Redox couples forming electron transfer chain in biological oxidation processes High efficiency O 2 as oxidant

14 ? Redox couples forming electron transfer chain in nature Gretz, E.; et al. J. Am. Chem. Soc. 1987, 109, CF CH 4 Pd H + 3 COOH C CF 3 COOCH (1) Pd 2+ Stoichiometric CF 3 COOH + CH 3 OH?

15 Pd 0 Pd 2+? Wacker process: CuCl 2 /CuCl/O 2

16 The Wacker Process Developed simultaneously by Wacker-Chemie and by the group of Moiseev. It involves the reaction of ethylene with PdCl 2 in HCl (reaction 1). Pd(II) is reduced to Pd black. To make the reaction catalytic, Pd(0) is reoxidized by CuCl 2 and O 2 (reactions 2 and 3). 2- C 2 H 4 + Pd Cl + 3H 2 O CH 3 CHO+Pd 0 +2H 3 O+4Cl - 4 (1) Pd 0 +2CuCl 2 +2Cl - 2- Pd Cl 4 + 2CuCl (2) CuCl+ 4H 3 O + + 4Cl - + O 4CuCl 2 + 6H 2 O (3) 2

17 Quinone / Hydroquinone O OH O OH Backvall et al. J. Am. Chem. Soc. 1990, 112, 5160

18 Search for active oxidants for regeneration of Pd 0 Pd 2+ Run oxidant CF 3 COOCH 3 TONa (μmol) 1 b Cu(oAc) FeCl K 2 S 2 O Q LiNO H 2 O c Conditions: 50 μmol Pd(oAc) 2, 500 μmol oxidant, 3 ml (39 mmol) CF 3 COOH, 80, 10 h, CH 4 : 55 atm. a: molar ratio of CF 3 COOCH 3 / Pd(oAc) 2. b: Pd(oAc) 2: 100 μmol. c: 880 μmol.

19 Combination of Pd 2+ and Q Run Pd 2+ Q O 2 CF 3 COOCH 3 Pd2+a (μmol) (μmol) (atm) (μmol) (%) Conditions: CF 3 COOH: 3 ml (39 mmol), CH 4 : 54 atm (114 mmol), O 2 : 1 atm (2 mmol), 80 ºC, 10 h; a: Remaining Pd 2+ after the reaction. OH 2+ O CF + Pd + 2 H + + Pd 0 3 COOH CH 4 + CF 3 COOCH 3 O OH + 1/2O 2 + H 2 O OH + Pd0 + 2H + + Pd 2+ O

20 Determination of remaining Pd 2+ in the solution by Gravimetric method Evaporation of solvent Addition of water Addition of dimethylglyoxime/ethanol solution H 2 Q + Pd 0 + Pd(CFCOOH) 2 H 2 Q + Pd 0 + Pd(dmg) 2 washed with anhydrous alcohol Addition of HNO 3 acid H 2 Q Q (water soluble) Pd 0 Pd 2+ Centrifugal separation Pd(dmg)2 Weight

21 Scheme of methane oxidation O H CH + CF COOH 4 3 Pd 2+ 1/2O 2 OH O CF 3 COOCH 3 Pd 0 + 2H + O

22 Search for active oxidants to speed up: OH O + 1/2O 2 + H 2 O OH metal macrocycles: O Backvall et al. J. Am. Chem. Soc. 1990, 112, 5160 Co(salophen), Co(TPP), iron phthalocyanine (Fe(Pc)) nitrogen oxide /CH 2 Cl 2 Feasibility test in CF 3 COOH Unstability OH O + NO 2 + NO + H 2 O OH O

23 Combination of Pd 2+ and Q for aerobic oxidation of CH 4 Run Pd 2+ Q NaNO 2 O 2 CF 3 COOCH 3 Pd2+a (μmol) (μmol) (μmol) (atm) (μmol) (%) CF 3 COOH: 3 ml (39 mmol), CH 4 : 54 atm (114 mmol), O 2 : 1 atm (2 mmol), 80 ºC, 10 h; a: Remaining Pd 2+ after the reaction.

24 CF 3 COOCH 3 (umol) reaction time (h) A catalytic process Q and NaNO2 key to prevent the precipitation of Pd Pd key, determining the TON The yield to CF 3 COOCH 3 versus the reaction time. TON: 0.7 h -1

25 Additional experiments for further confirmation Run Pd 2+ Q NaNO 2 O 2 CF 3 COOCH 3 Pd2+a (μmol) (μmol) (μmol) (atm) (μmol) (%) Conditions: CF3COOH: 3 ml (39 mmol), CH4: 54 atm (114 mmol), O2: 1 atm (2 mmol), 80 ºC, 10 h; a: Remaining Pd 2+ after the reaction.

26 Additional experiments for further confirmation isotope experiments GC-MS 14 atm 13 CH 4 40 atm 12 CH 4 O 2 CF 3 COOH -COO 13 CH 3 (m/e = 60) -COO 12 CH 3 (m/e = 59) 1 3 CF3COOCH3

27 Features OH CH + CF COOH 4 3 Pd 2+ NO 2 OH O CF 3 COOCH 3 Pd 0 + 2H + H 2 O + NO 1/2O 2 CF 3 COOH + CH 4 + 1/2O 2 CF 3 COOCH 3 + H 2 O CH 4 + 1/2O 2 CH 3 OH CF 3 COOCH 3 + H 2 O CF 3 COOH + CH 3 OH O Catalytic process in one pot at 80 C HCl, H 2 SO 4 avoided O 2 as oxidant

28 Example 2 High Temperature Conversion of Methane to Aromatics

29 Typical HT Direct Conversion Process Selective Oxidation CH 4 + O 2 CH 3 OH+CO 2 +H 2 O Oxidative Coupling CH 4 + O 2 C 2 H x +CO 2 +H 2 O

30 A New Route To higher hydrocarbons, without forming CO 2? CH 4 + O 2 6CH 4 Mo/HZSM-5 Higher HC C 6 H 6 + 9H 2 Y. Xu,, et al.,catal. Lett.. 21 (1993) 35-41

31 Conversion of methane to aromatics H CH 3 C M H CH 3 C M nch 3 n/2c 2 H x Catalysts Mo, W, Re HZSM-5, MCM-22

32 Bifunctionality of Mo/HZSM-5 Acidity and catalytically active sites

33 Loadings of Mo in Mo/HZSM-5 10 %Mo/HZSM %Mo/HZSM-5 E o? 2 %Mo/HZSM-5 HZSM-5 HZSM-5 with Al irradiation ppm D. Ma, X. Bao et al., Angew. Chem-Inter Edit. 39 (2000); Chem. Eur.. J., 8 (2002).

34 Aromatization over different Mo species 30 Mo species related to B acid sites(moc x O y ) Mo species in the form of Mo 2 C Mo species supported on SiO 2 n Highly active and stable MoC x O y ; TOF 20 n Low activity and stability of Mo 2 C; 10 n 0.5 acidic sites per unit cell required for 0 30min 240min 600min aromatization. D. Ma, X. Bao et al., Chem. Eur. J. 8 (2002), Y. Xu, X. Bao, et al., J. Catal (2003)

35 Bifunctionality of Mo/HZSM-5 Acidic sites MoC x O y active species

36 Pore Morphology of Catalyst Carriers

37 Pore morphology of zeolite supports MCM-22 ZRP-1 Percentage (%) ESR-7 ZSM-5 ZSM-11 JQX-1 SBA-15 Conv.of CH 4 Sel.of BTX Sel.of Nap. Sel.of coke 0 8 ring 0.4nm 10ring 0.55nm 10\12 12ring 0.75nm meso >1nm Applied Catalysis A-general A 188 (1-2) 2),J. Catal (2003)

38 Morphology of Zeolites ZSM-23 ZSM-22 Conversion or Yield(%) b 4.5x4.7 CH 4 conversion Benzene yield Coke yield H 2 concentration Time on stream(h) Conversion or Yield(%) a 4.5x Time on stream(h) CH 4 conversion Benzene yield Coke yield H 2 concentration

39 Morphology of zeolites ZSM-22 ZSM-23 MCM-22

40 Mo/MCM-22

41 Comparison between Mo/ZSM-5 and Mo/MCM-22 Open Mo/HMCM-22 Solid Mo/HZSM-5 Y. Shu,, X. Bao et al., Catal. Lett.. 70 (2000) 67.

42 200 H Z S M -5 (P ) H Z S M -5 (A T 1 ) H Z S M -5 (A T 2 ) 3 N2 adsorbed/cm (STP)/g Modification of HZSM -5 with HZSM-5 alkali treatment P /P

43 Modification of zeolite carrier Methane conversion% o C, 1500ml/g.h, 1atm After treatment Aromatics yield% Before treatment Reaction time (min) Catal. Lett.. 91 (2003)

44 Pore morphology of carriers Shape selectivity size (dynamic( diameter of benzene (0.59 nm) crossing with two-dimensional structure micro-mesoporous mesoporous composite

45 A Coupled Process Aromatization + Oxidative Coupling

46 Why to couple? Aromatization: CH + H Coke

47 Effect of co-feeding CO, CO 2, H 2, CO/H 2, H 2 O CH 4 Conv., aromat.y. /% CH4 Conv Mo/HZ aromatics yield +1.3%H 2 O Time on stream / h +0.6%CO 2 Aromatics yield/% % CO+CH 4 5% H 2 +CH 4 CH 4 5% H % CO+CH Time on stream /h Improved yield and stability

48 Why to couple? OCM:CH CH 4 +O 2 C 2 H 4 + CO 2 CO 2 + Aromatization: CH + H Coke Coke 2CO

49 Aromatization of methane by coupling oxidative coupling aromatics CH 4 + O 2 Aromatization Oxidative coupling

50 Aromatization + Oxidative Coupling Conversion or Yield/% T im e on S trea m /m in at 1010K CH 4 conversion ( ) on SLC-6Mo/HZ a, ( ) on SLC-6Mo/HZ b, Yield to aromatics ( ) on SLC-6Mo/HZ a, ( ) on SLC-6Mo/HZ b, J. Catal (2003), Catal. Lett.. 89 (2003)

51 Achievements over the years Convers before < 10% 18% (Coupled) Yield 10 to Benzene ~6-8% ~12% Life time 6 6~8 h ~50 h 4 yield C, 1atm with a flow rate of 1500mL/gcat. h

52 Thank you