Selective Oxidation of Methane to Methanol in Oleum over Pd/ C Catalyst. WEI Xin, YE Linmin, ZHU Mingxia, YUAN Youzhu 3

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1 Vol. 29 No. 8 Chi nese Jou rnal of Catalysis August 2008 : (2008) : Pd/ C,,, (,, ) : PdCl 2, Pd/ C,, X X CO., 5 %Pd/ C Pd 30 mol MPa 4 h SO 3 50 %, 2316 %, 6915 % 1614 %,. Pd/ C, Pd Pd. : ; ; ; ; ; ; : O643/ TQ54 : A Selective Oxidation of Methane to Methanol in Oleum over Pd/ C Catalyst WEI Xin, YE Linmin, ZHU Mingxia, YUAN Youzhu 3 ( S tate Key L aboratory of Physical Chemist ry of Solid S urf aces, Depart ment of Chemist ry, College of Chemist ry and Chemical Engineering, Xiamen U niversity, Xiamen , Fujian, China) Abstract : The selective oxidation of methane to methanol over Pd/ C catalysts generated from a PdCl 2 precursor was investigated in oleum. Characterization of t he catalyst s was performed by X2ray diff raction, X2ray photo2 elect ron spect roscopy, high2resolution t ransmission elect ron microscopy, and CO adsorption. The major product in the oxidation reaction was methyl bisulfate, which was then hydrolyzed into methanol. Methane conversion of 2316 % with methanol selectivity of 6915 % and yield of 1614 % was achieved under the optimum conditions of 5 %Pd/ C, 30 mol Pd, reaction temperature 180, methane pressure 410 MPa, reaction time 4 h, and 50 % sulfur trioxide concentration. After facile separation with the reactants and pretreatment, the catalyst could be reused several times wit h considerable stability. The selective oxidation of met hane catalyzed by Pd/ C catalyst s in oleum possibly involved an elect rophilic substit ute mechanism. The catalytic performance was related to t he Pd loading, dispersion, and particle size. Key words : palladium ; activated carbon ; supported catalyst ; methane ; selective oxidation ; methanol ; oleum,.,, Gol dshleger [1 ], [2 8 ],. 1987, Shilov [9 ] : :. Tel : (0592) ; E2mail : edu. cn. : ( ) ; (2005HZ0123).

2 8 : Pd/ C 721 Pd / Pd. Kao [10 ] Shilov, 1 %. 1994, Lin [11 ] RhCl 3,. Yuan [12 ], OsCl 3 ( TOF) 12 h , Catalytica Periana [13 ],, 43 %., 81 %, 90 % [14 ],. [15 20 ],, Pd [15 ] PdSO 4 [15 ] [21 ] [22 ] [23 ] [24 ].,. Pd/ C,,, X ( XRD) X ( XPS) CO ( HRTEM), Pd/ C, : (, ) 6 h,, ; PdCl 2 (, ),, p H = 4,, 100., 5 %H 2 / Ar h, 3 / min. x Pd/ C( x ) ml, 50 % ( ),, 5 %Ne/ CH 4 ( 9919 %, ), 4 MPa,., ;, 20, 90 3 h,. Bruker AVANCE 400 MHz. GC2 8A, TCD, 5A (3 m) Porapak2Q (3 m) ; GC2920, FID, SE254 ( 50 m 0125 mm 0125 m). Ne XRD Philips PANalytical X pert PRO X, : Cu K ( = nm), 40 kv, 30 ma., /, 10 90, 10 s. HRTEM Philips FEI Tecnai 30, 300 kv, 011 nm, 012 nm, 0114 nm. IRIS IN2 TREPID II XSP RADIAL (ICP2AES), W, 28 psi, 5 s, 10 s. CO ASAP 2010M + C, h, 011 g, h, CO, 30 Pd. XPS Physical Elect ronics Quant um22000 Scanning ESCA Micro2 probe, Mg K X ( ev), 50 ev, C 1s ( E b = ev) Pd/ C,,

3 Ne, CO 2 ; 1 H NMR ( = 3190), C NMR,,, H 2 C(OSO 3 H) 2. Michalkiewicz [15 ],,, H 2 C(OSO 3 H) 2., H 2 C(OSO 3 H) 2,,,,. 1 (, )., 5 %Pd/ C 2,, Pd/ C,,.,, 5 %,. :,,,,,,, ;,,,, 1 Pd/ C 13 C NMR Fig 1 13 C NMR spectrum of the crude reaction mixture of selec2 tive oxidation of methane in oleum over Pd/ C catalyst,, 5 %. TOF,, TOF,,., 915 %, CO %, 7210 % 618 %,,., 5 %Pd/ BaSO 4 (, ),,,., Pd/ C. 1 Table 1 Results of selective oxidation of methane catalyzed by supported Pd catalysts Catalyst Pd dispersion ( %) CH 4 conversion ( %) Selectivity ( %) CH 3 OH CO 2 CH 3 OH yield ( %) TOF (h - 1 ) Blank Activated carbon Pd black %Pd/ C %Pd/ C %Pd/ C %PdCl 2 / C %Pd/ BaSO %Pd/ C Reaction conditions : catalyst = 6415 mg ( Pd black = 312 mg, 30 mol), 50 % SO 3 oleum = 5 ml, reaction time = 4 h, reaction temperature = 180, methane pressure = 410 MPa. TOF : turnover frequency, in mole of methanol yield per mole of Pd per hour.

4 8 : Pd/ C 723 Pd/ C, 5 %Pd/ C, 2.,,,,,, %Pd/ C Table 2 Effects of reduction temperature on Pd particle size and catalytic performance of 5 %Pd/ C catalyst Reduction temperature ( ) Particle size (nm) CH 4 conversion ( %) Selectivity ( %) CH 3 OH CO 2 CH 3 OH yield ( %) Reaction conditions are the same as in Table %Pd/ C,, 2. 2 (a),,,. 2 (b),,, 60 %., [4 ],, ;,. 2 (c),,,, 5 h, 4711 %.,,., 50 %SO 3, : 5 %, 4 MPa, 180, 4 h., 2316 %, 6915 %, 1614 % ( 1). 2. 3, Pd/ C,,. 3 5 %Pd/ C., 5 %Pd/ C, mg, 4 5 mg, 3,,,., ICP- AES., 1, 111 % (01035 mg Pd), % 012 %., 1 mg PdSO 4 2H 2 O ( 13 ), 1, 2 5 %Pd/ C Fig 2 Effects of reaction temperature (a), methane pressure (b), and reaction time (c) on selective oxidation of methane over 5 %Pd/ C catalyst (1) Conversion, (2) Methanol selectivity, (3) CO 2 selectivity (Reaction conditions are the same as in Table 1. )

5 %Pd/ C Fig 3 Recycle of 5 %Pd/ C catalyst in selective oxidation of methane to methanol in oleum (Reaction conditions are the same as in Table 1. ) : 314 %, CO % 6110 %, 211 %. 5 %Pd/ C,, %Pd/ C 4 XRD., 4, 4,. 5 5 %Pd/ C 4 HRTEM., 4 7 nm, ; 4,, nm. 4 5 %Pd/ C XRD Fig 4 XRD patterns of 5 %Pd/ C catalyst before and after reaction (1) Before reaction, (2) After four recycles,,,., Pd/ C. 6 5 %Pd/ C XPS., ev Pd 0 3 d 5/ 2 3 d 3/ 2, ev Pd d 5/ 2 3 d 3/ 2., Pd 2 +, ;, Pd 0 3 d 5/ 2, Pd 2 +, Pd 0 / Pd %Pd/ C Fig 5 HRTEM images of 5 %Pd/ C catalyst before and after reaction (a) Before reaction, (b) After four recycles

6 8 : Pd/ C Pd/ C. 5 % Pd/ C, 2316 %, 1614 %. Pd/ C.,, %Pd/ C Pd 3 d XPS Fig 6 Pd 3 d XPS spectra of 5 %Pd/ C catalyst before and after reaction (1) Before reaction, (2) After four recycles 2. 5, Shilov [2 ] Michalkiewicz [15 ] Pd/ C Pd 0 SO 3 Pd 2 +,, CH Pd 2 +. H 2 SO 4, CH 3 OSO 3 H, Pd 2 + Pd 0., Pd/ C, 1., Pd 0 SO 3 Pd 2 +, Pd/ C SO 3,. 1 Pd/ C Scheme 1 A possible mechanism for selective oxidation of methane catalyzed by Pd/ C in oleum 1 Gol dshleger N F, Tyabin M B, Shilov A E, Shteinman A A. Zh Fiz Khim, 1969, 43 (8) : Shilov A E, Shul pin G B. Chem Rev, 1997, 97 ( 8) : Sen A. Acc Chem Res, 1998, 31 (9) : Labinger J A, Bercaw J E. N ature, 2002, 417 (6888) : Michalkiewicz B, Kalucki K. Chem Pap, 2003, 57 (6) : Periana R A, Bhalla G, Tenn W J, Young KJ H, Liu X Y, Mironov O, Jones C J, Ziatdinov V R. J Mol Catal A, 2004, 220 (1) : 7 7 Michalkiewicz B. Chem Pap, 2006, 60 (5) : Conley B L, Tenn W J, Young K J H, Ganesh S K, Meier S K, Ziatdinov V R, Mironov O, Oxgaard J, Gonza2 les J, Goddard W A, Periana R A. J Mol Catal A, 2006, 251 (122) : 8 9 Shilov A E, Shul pin GB. R uss Chem Rev, 1987, 56 (5) : Kao L C, Hutson A C, Sen A. J A m Chem Soc, 1991, 113 (2) : Lin M R, Sen A. N ature, 1994, 368 (6472) : Yuan Q, Deng W P, Zhang Q H, Wang Y. A dv S ynth Catal, 2007, 349 (7) : Periana R A, Taube D J, Evitt E R, Loffler D G, Wen2 trcek P R, Voss G, Masuda T. Science, 1993, 259 : Periana R A, Taube D J, Gamble S, Taube H, Satoh T, Fuji H. Science, 1998, 280 : Michalkiewicz B, Kalucki K, Sosnicki J G. J Catal, 2003, 215 (1) : Jones C J, Taube D, Ziatdinov V R, Periana R A, Nielsen R J, Oxgaard J, Goddard W A. A ngew Chem Int Ed, 2004, 43 (35) : 4626

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