Natural Gas to Ehylene Conversion over Mn-Na-W/SiO2 Catalyst

Naseem Hayek, Chemical Engineering, Technion, Haifa, Israel
Oz Gazit, Chemical Engineering, Technion, Haifa, Israel

Oxidative coupling of methane to ethylene (OCM) has attracted a lot of attention since 1982 (Eq. 1). Unfortunately, this process is still industrially inapplicable due to the lack of active and stable catalyst that overcomes the formation of COx (Eq. 2), the thermodynamically favorable products.

1. CH4 + 1/2O2  ==> 1/2C2H4 + H2O

2. CH4 + 2O2 ==> CO2 + 2H2O

Mn-Na-W/SiO2 is one of the most promising catalysts for OCM. Its high stability and selectivity makes it a good candidate for practical applications. However, besides that the C2 yield achieved so far is insufficient for an economically feasible process, the identity of the active site and the surface properties that govern this catalyst its activity and selectivity are still not completely understood.

The work here presents a thorough evaluation of the effect of the Mn-Na-W/SiO2 surface parameters on its catalytic performance. To do so, a set of catalysts with different properties were synthesized by the incipient-wetness impregnation of various silica types with different Mn precursors. The catalysts were characterized by ICP-OES, N2-physisorption, XRD, HR-SEM-EDS and XPS. Finally, the performance of each catalyst was evaluated in the catalysis of OCM in a fixed-bed reactor. The combination of the characterization and the catalysis results showed that surface porosity, Mn2O3 dispersion and Na2WO4 particle size are key factors in the catalysis of OCM. Cross-referencing our results with prior studies lead us to single out that the active center is composed of two adjacent Mn2O3 and Na2WO4 species that participates in a redox reaction mechanism. In the presentation, interesting results from synthesis, characterization and catalysis will be discussed. 

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