545614 Direct Methane Conversion to Value-Added Products over Fe-FER Catalysts

Monday, June 3, 2019: 3:21 PM
Texas Ballroom D (Grand Hyatt San Antonio)
Guangyu Zhao1, Michael Stockenhuber1, Eric M. Kennedy1, Adesina Adesoji A.2, Meng-Jung Li1 and Matthew Drewery3, (1)Chemical Engineering, The University of Newcastle, Newcastle, Australia, (2)ATODATECH LLC, Pasadena, CA, (3)University of Newcastle, Callaghan, Australia

Direct methane conversion to value-added products over Fe-FER catalysts

G. Zhao1, E. Kennedy1, M. Stockenhube1*, Adesoji A. Adesina2, Meng-Jung Li1

1. Chemical Engineering, School of Engineering, The University of Newcastle, Callaghan, NSW, 2308
2. Atodatech LLC, 23586 Calabasas Road, CA 91302 

Keywords: Direct methane conversion, active sites, incipient wetness impregnation, solid state ion exchange <>1. Introduction

Direct oxidation of methane to value-added products, such as methanol and formaldehyde, has received extensive attention in the field of chemical engineering and catalysis 1. However, current direct methane oxidation processes at high temperature (normally 600¡ãC¨C900¡ãC) suffer from poor selectivity of C1-oxygenates 2. Conversely, a relatively high selectivity to desired products was observed at low temperature (lower than 200¡ãC), but these routes are not regarded as truly catalytic processes because an additional extraction step is necessary to obtain the desired products 3. Therefore, the current study on methane oxidation under moderate temperatures (350¡ãC) has been conducted, aiming to synthesize methanol, formaldehyde and dimethyl ether (DME) over heterogeneous catalysts with the need for an extract step 4.

In this study, methane oxidation over Fe-FER catalysts prepared by incipient wetness impregnation (IWI) and solid state ion exchange (SSIE) techniques at 350¡ãC was investigated. The catalysts were characterised with in situ IR spectroscopy, XAS, XPS and microreactor studies. The aims of the research were to determine the effect of preparation methods on transition metal site structure and in turn methane conversion to value products generation, and infer the involved mechanisms of the reactions. <>2. Results and discussion

TEM micrographs of IWI and SSIE prepared Fe-FER catalysts are compared in Fig. 1. Large iron oxide aggregates are observed in both samples, and the size of the aggregates is generally larger in IWI catalyst than in SSIE catalyst.

The EDS mapping images of two catalysts are presented in Fig. 2. It is shown that particles over 100 nm were detected in IWI Fe-FER catalyst, and the particles size in SSIE sample are much smaller, which indicated better metal dispersion of SSIE sample.

  

a                                                                                 b

Fig. 1 TEM micrographs of (a) IWI and (b) SSIE Fe-FER  

a                                                                                        b

Fig. 2 EDS mapping images of (a) IWI and (b) SSIE Fe-FER

Fig. 3 compares the H2-TPR profiles of IWI and SSIE catalysts that were activated in a stream of air with or without extra N2O pre-treatment (at 250¡ãC). The results show that the N2O pre-treatment leads to a new reduction peak at around 230¡ãC, and the area of the peak observed correlates with the number of active sites for the N2O decomposition 5. In comparison to IWI Fe-FER, this peak is larger for SSIE Fe-FER.

a                                                                                        b

Fig. 3 TPR profiles of (a) IWI and (b) SSIE catalysts

The activity test results show that the SSIE Fe-FER obtained higher methane conversion, N2O decomposition and more amount of methanol, formaldehyde and DME, as shown in Table 1.

Table 1. Activity rest results of IWI and SSIE prepared Fe-FER catalysts

Conversion or decomposition (%)

Concentration (µmol)

methane conversion

N₂O decomposition

methanol

formaldehyde

DME

IWI

2.0

13.7

13.4

3.8

11.0

SSIE

2.8

20.6

24.7

6.4

25.6

<>3. Conclusion

The experimental results demonstrated that methane can be converted to methanol, formaldehyde and DME over Fe-FER catalysts using N2O as the oxidant. Additionally, in comparison to catalyst prepared by IWI technique, the Fe-FER catalyst prepared by SSIE method displayed better iron dispersion on zeolites, more active sites for N2O decomposition, and consequently provided more significant performance, in terms of methane conversion, N2O decomposition, and the amount of value-added products. In this paper, details of the site structure and its correlation with activity are discussed. <>4. Reference

1.        Z. C. Wang, N. Dietl, R. Kretschmer, J. B. Ma, T.Weiske, M. Schlangen, H. Schwarz, Angew. Chem. Int. Ed. Engl. 2012, 51, 3703-37077.

2.        R.G. Herman, Q. Sun, C. Shi,  C. Shi, K. Klier, C.B Wang, H. Hu, I. E. Wachs, M. M. Bhasin, Cataly. Today 1997, 37, 1¨C14.

3.        E.V. Starokon, M. V. Parfenov, L.V.Pirutko,  S.I. Abornev, G.I. Panov, J. Phys. Chem. C 2011, 115, 2155-2161.

4.        B. Michalkiewwicz, Appl. Catal. A. Gen. 2004, 277, 147-153

5.        K. J¨ªša, J. Nov¨¢kov¨¢, M. Schwarze, A. Vondrov¨¢, S. Sklen¨¢k, Z. Sobalik, J. Cataly. 2009, 262, 27¨C34.


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