Catalytic Chemistry for Methane Dehydroaromatization (MDA) on a Bifunctional Mo/HZSM-5 Catalyst in a Packed Bed

Abstract

This paper presents an experimental and modeling study of methane dehydroaromatization (MDA) chemistry using a bifunctional 6 wt % Mo/HZSM-5 catalyst in an isothermal laboratory-scale packed-bed configuration. The reported measurements include methane conversion and product yields and selectivities as a function of temperature and flow rates (space velocity). The modeling is particularly concerned with developing and validating a microscopically reversible 54-step detailed reaction mechanism. The reaction mechanism is validated via direct comparison with the measured packed-bed performance. Although the operating conditions for the measurements are relatively limited, the detailed reaction mechanism is expected to have much wider predictive capability.

Nonoxidative methane activation, coupling, and conversion to ethane, ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

“…The induction period over Mo/HZSM‐5 usually lasts about 1 hour, depending on the reaction conditions. The conversion of methane in this period increases until it reaches the maximum, and then, it starts slowly decreasing with TOS due to catalyst deactivation, which is a consequence of carbon deposits formation . In Figure , the conversion of methane and concentration of ethylene at the outlet from the packed bed reactor for monometallic and bimetallic catalysts are presented.…”

In Situ Formation of Metal Carbide Catalysts

“…The main products of MDA are benzene and hydrogen; naphthalene is an undesired side product and ethylene and ethane can be formed at very low levels. Typical reaction conditions are 1 bar, 948–1073 K and 750–4500 WHSV (mL g catalyst −1 h −1 ) . The general reaction for MDA is shown in Eq.…”

“…Only about 60–80 % of the Mo 6+ is incorporated into the Mo‐carbide structure, at which point a quasi‐steady state of methane conversion and benzene yield is reached. Molybdenum oxide species still coexist after carburization, especially within the narrow pores of the zeolite due to mass transport limitations . After carburization initiation, molybdenum carbide sites begin to convert CH 4 into ethylene and hydrogen, which then react on the acid sites to form aromatics .…”

“…Typical reaction conditions are 1bar, 9 48-1073 Ka nd 750-4500 WHSV (mL g catalyst À1 h À1 ). [24] The general reaction for MDA is shown in Eq. (3):…”

“…Molybdenum oxide species still coexist after carburization, especially within the narrow pores of the zeolite due to mass transport limitations. [24] After carburization initiation, molybdenum carbides ites begin to convert CH 4 into ethylene and hydrogen, which then react on the acid sites to form aromatics. [32] Additionally,c oke forms within the pores throughout the process.…”