The direct conversion of methane to higher value products is of great interest to industry and academia. However, due to the inherent stability of methane, no commercial processes exist to date. Non-oxidative, co-processing of methane with methanol, ethanol and ethylene has been shown to improve methane conversion and product selectivity at moderate temperatures (less than 700K) and could be a route to direct methane valorisation. In particular, silver-exchanged zeolites show favourable catalytic properties for methane co-processing. This report studies the effect of the zeolite framework (MFI vs CHA) in silver-exchanged aluminosilicate and zincosilicate materials on the co-processing of methane with methanol. The aluminosilicate and zincosilicate CHA material, and zincosilicate MFI, were synthesized through reported methods and characterised by pXRD (Figure 1A), ssNMR, microporosimetry, and electron microscopy (SEM, TEM). Aluminosilicate MFI was supplied by Johnson Matthey. Methanol and methane-methanol conversion was carried out in a plug flow reactor (400 C, 0.015 mlMeOH/min, 40.0 mlN2/CH4/min) with online reaction monitoring (GC-MS-BID). Methanol conversion over Ag,K/CHA (16.5) was most selective towards propylene production over ethylene. For the zincosilicate Ag,Na/ZnCHA (21), product selectivity switched to ethylene over propylene (Figure 1B). In both cases, formaldehyde was detected as a minor product. Conversely, Ag,K/MFI (13.5) led to the production of BTX before loss of activity due to coking after 1 h. The zincosilicate Ag,K/ZnMFI (78) led to an identical product distribution to Ag,K/CHA (16.5), albeit at a lower conversion of around 35%. Hydrogen was observed during all reactions, which leads to silver reduction to form silver clusters and BAS. Zincosilicates have weak Brønsted acidity compared to zeolites, so BAS formation is less problematic, as MTG-like chemistry and carbonaceous deposition are not observed, highlighting the benefit of zeotype supports for silver promoted reactions. Initial methane-methanol coprocessing over Ag,K/ZnMFI (78) gave a similar product distribution to methanol only conversion, with a methane conversion of 0.6%. In contrast, Ag,Na/ZnCHA (21) led to changes in product selectivity with 5.1% methane conversion. Detailed studies using isotopically labelled methane are underway which will provide insight into the coprocessing reaction pathway and effects observed on the product selectivity.

Coprocessing of methane over silver-exchanged zeolites and zeotypes

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