545162 The Hierarchical Porous W-Mn/SiO2 Catalyst for Oxidative Coupling of Methane

Monday, June 3, 2019: 5:24 PM
Texas Ballroom EF (Grand Hyatt San Antonio)
Ning Zhang1, Jian Yang2, Huahua Zhao2, Liang Yan2, Huanling Song2 and Lingjun Chou2, (1)State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Lanzhou, China, (2)Lanzhou Institute of Chemical Physics, Lanzhou, China

The hierarchical porous W-Mn/SiO2 catalyst for oxidative coupling of methane

 

Ning Zhangab, Jian Yanga, Huahua Zhaoa, Liang Yana, Huanling Songa, Lingjun Choua*

 

a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China.

b University of Chinese Academy of Sciences, Beijing 100049, P. R. China.

*Corresponding author, Tel: +86 931 4968136; Fax: +86 931 4968129

Email: ljchou@licp.cas.cn

 

Introduction

Recently, three-dimensionally ordered macroporous and mesoporous (3OM)[1] materials, have captured the interest of scientists and engineers owing to their potential applications in the realms of catalysis, separations and photonic crystals. The macropores could provide interconnected framework and this was beneficial to gas reaction. The reactant molecule could enter into and pass through the channels quickly. The reaction heat could be released by macroporous channels. Until now, few researches investigate about 3OM SiO2 materials as catalyst support in oxidative coupling of methane (OCM)[2], which has attracted renewed interest. However, it still has great challenges: first, the selectivity of C2 is low; second, reaction has hot spots at high temperature. Therefore, development of an efficient catalyst for OCM reaction remains to be the most crucial step in the commercialization of this process.

Now, we prepared 3OM SiO2 as catalyst support to improve OCM catalyst activity. By the comparison of the different support catalysts SBA-15, KIT-6, Tianjin- SiO2, the 3OM SiO2 catalyst owns the excellent catalytic performance at 850oC.

Experimental

The 3OM SiO2 was prepared using a method reported previously. PMMA crystal as macroporous template was synthesized via a soap-free-emulsion polymerization[3]. In a typical synthesis, 15mL monomer MMA was washed three times with a NaOH solution (100mL, 10 wt %) and distilled water respectively to remove any trace of the fire retardant. Then, 11.3g of the washed MMA and 150g of distilled water were added to a 500mL round bottom flask and stirred for an hour. Then, 12mL (0.0005g mL-1) K2S2O8 was added to the solution and the mixture was constantly reacted at 70 oC for 7h under a nitrogen atmosphere with mild stirring until a milky solution appeared. The milky solution was centrifuged and dried at 80oC to obtain PMMA. 4g HCl (0.2M) and 6.4g F127 were added into EtOH (30mL) at 40oC for an hour. Then, 8.32g TEOS was added into the above solution to stir 1h to obtain a homogeneous precursor of silicon. The PMMA template was added into Si precursor to soak five day at 40oC. Then, excess solution was removed by filtration. The resulting sample was dried at 120oC overnight and calcined at a heating rate of 1 oC min-1 to 600 oC for 5h.

Results and Discussion

Fig.1 shows the typical TEM image of the W-Mn-SiO2. Fig.2 shows the HAADF image of the W-Mn-SiO2. It was clearly observed that the catalysts exhibited well developed interconnected networks of the ordered macroporous and mesoporous structures.

Fig.1 TEM of W-Mn-SiO2 calcined in 600oC   Fig.2 HAADF of W-M-SiO2 calcined in 600oC

The catalytic performance was listed in table.1. At 850oC, 3OM SiO2 catalyst showed the optimum catalytic activity. The CO2-TPD indicated that 3OM SiO2 catalyst enhanced the moderate-strong basic sites at 566oC. The O2-TPD revealed the 3OM SiO2 catalyst owned the highest quantity of lattice oxygen.

Table.1 Catalytic performance of the different support catalysts in 850oC

Catalyst

Conv. (%)

Selectivity (%)

Yield (%)

CH4

C2

C2H4

C2

SBA-15

24.70

61.71

45.19

15.24

3OM SiO2

27.65

60.37

43.43

16.69

Tianjin SiO2

24.93

62.57

43.13

15.60

KIT-6

24.49

61.33

41.66

15.02

 

Fig. 3 CO2-TPD of the catalysts          Fig. 4 O2-TPD of the catalysts       Fig. 5 XRD patterns of the catalysts

Conclusion

3OM W-Mn-SiO2 materials own interconnect macroporous structure and mesopores in macroporous wall, which could make W and Mn more dispersed in channels. The hierarchical porous structure also could enhance the moderate-strong basic sites and O2- quantity of catalyst. This was favourable for OCM reaction. These results indicated that the 3OM SiO2 catalyst was a promising class of catalysts for the OCM reaction.

REFERENCES

[1]    H. M¨ªguez, F. Meseguer, C. L¨®pez, A. Mifsud, J.S. Moya, L. V¨¢zquez, Langmuir : the ACS journal of surfaces and colloids 13 (1997) 6009-6011.

[2]    G.E. Keller, M.M. Bhasin, Journal of Catalysis 73 (1982) 9-19.

[3]    Z. Wang, A. Stein, Chemistry of Materials 20 (2007) 1029-1040.

 


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