Two Pathways for Near Room Temperature Electrochemical Conversion of Methane to Methanol

Methane is one of the most important industrial gases.  Not only is it directly used for heat generation, it is the primary feedstock for several of the most widely produced commodity chemicals including hydrogen, ammonia, methanol and formaldehyde.  Methane activation and conversion is typically accomplished though syngas production by steam reforming which requires high pressure (typically above 10 bar) and high temperature (above 650 ^oC).^1-3 The syngas product is an over oxidized product, necessitating reduction back to methanol or other desired oxygenates.  This process involves excessive intermediate reaction steps and has a large energy requirement

Since they allow for control of the catalyst surface free energy, electrochemical methods have the potential to reduce the thermal and overall energy barrier to convert methane to oxygenates.^{1, 4, 5}  Processing conditions for electrosynthesis can also be tailored to selectively and dynamically change the reaction selectivity, meaning that the several unit operations that are currently required for the conversion of methane to methanol or formaldehyde might be reduced to a single step.  Methanol is a particularly high value target; it is used to synthesize numerous products, and has been touted as an important energy carrier of the future.  Its high energy density and liquid state in atmospheric conditions make it ideal for stable transportation and storage that is compatible with existing petroleum infrastructure.^{6, 7}

In this study, we will present a new system that is able to directly convert methane to methanol at low temperatures (T < 100^oC) in alkaline mediate.  Electrochemical experiments, including cyclic voltammetry, linear sweep voltammetry, and chronoamperometry, were conducted on several catalyst systems and electrode formulations to assess their effectiveness, selectivity, and faradaic efficiency.  Physical characterization methods, including XRD, XPS, SEM, TEM, BET, GC and MS were used to understand the catalyst structure and quantify products.  An important goal of this research is to identify the controlling factors for catalyst selectivity, mechanism, and the faradaic efficiency of the reactions. 

In this presentations, variations in performance and the product profile will be presented over several cell operation conditions.  Trends from this promising technology will help to guide future cell design with the prospect of improving the applications for methane and natural gas resources.

References:

1. N. Spinner and W. E. Mustain, J. Electrochem. Soc., 160, 11 (2013).

2. R. G. Bergman, Nature (London, U. K.)., 446, 7134 (2007).

3. T. V. Choudhary and V. R. Choudhary, Angew. Chem., Int. Ed., 47, 10 (2008).

4. N. Spinner and W. E. Mustain, J. Electrochem. Soc., 159, 12 (2012).

5. N. Spinner and W. E. Mustain, Electrochim. Acta., 56, 16 (2011).

6. G. A. Olah, A. Goeppert and S. K. Surya-Prakash, Beyond oil and gas: the methanol economy, Wiley-VCH (2009).

7. G. A. Olah, Angew Chem Int Ed Engl., 44, 18 (2005).