March 8, 2021. By Kolemann Lutz
Researchers from the University of Illinois Chicago discovered a new way to electrochemically oxidize methane on transition metal oxides, via the catalytic direct conversion of methane to methanol, to reduce the reaction by more than 200 degrees Celsius to room temperatures.
Liquid methane (CH4) for rocket propellant on Mars enables many chemical reactions, products, and a variety of industrial uses including propellant for other vehicles, to make heat and electricity, and to manufacture organic chemicals such as methanol, formaldehyde, and formic acid.
As industry transitions away from conventional two-step process, the partial oxidation of CH4 offers a single step reaction to methanol, which significantly reduces the cost and energy. The conversion of hydrocarbons usually requires a lot of energy and CO2 pollution to break C-H bonds. CH4 to liquid fuel such as methanol (CH3OH) also offers a sustainable and environmentally benign route to utilise shale gas on Earth.
Additionally, the storage of liquid hydrogen requires cryogenic temperatures because the boiling point of hydrogen at one atmosphere pressure is -252.8°C (-421.6°F), which requires high energy and pressures and demonstrates a need to find alternative means of storing liquid hydrogen.
As the intended rocket propellant on Mars, methane (CH4) can store large volumes of hydrogen safely in regular containers under average temperatures around −40 °F, considering average surface temperature on Mars is -81°F, which makes CH4 storage less expensive and energy intensive.
Researchers at the University of Illinois Chicago (UIC) conducted an experiment to convert methane, H2O, and CO2 into liquid methanol at room temperature. The electrochemical oxidation of CH4 on transition metal oxides (TMO’s) such as titanium and copper electrocatalysts facilitate the breaking of the strong hydrocarbon bonds in CH4 with a high faradaic efficiency of 6%.
Out of the 12 catalysts tested, TiO2, IrO2, PbO2, and PtO2 satisfy the methane oxidation reaction (MOR) catalyst and activity criteria of higher binding energy and lower Madelung potentials. A previously unrecognised effect of electrostatic or Madelung potential of metal atoms on TMOs has a direct effect on the binding energy of CH4 and other hydrocarbons. To minimise the overoxidation of CH3OH, a bimetallic Cu2O3 on TiO2 catalysts is developed, in which Cu reduces the barrier for the reaction of *CH3 and *OH and facilitates the desorption of *CH3OH.
"We have been able to reduce the temperature of the industrial process from more than 200 degrees Celsius to room temperature, which is around 20 degrees Celsius," said Aditya Prajapati, a graduate student University of Illinois Chicago.
Methanol is an easy-to-transport liquid fuel and feedstock that can be converted to olefins such as ethylene (C2H4) and propylene to make plastics, alcohol, food packaging, antifreeze, and many other products. Alternatively, CH4 feedstocks synthesize acetic acid and formaldehyde as a base in acrylic plastic, synthetic fabrics, fibers, adhesives, paint, and plywood.
Considering transition metal oxides (TMO’s) are widely present on Mars, the more accessible TMO’s can be used to electrochemically oxidize hydrocarbons for in-situ resource utilisation.
Although the conversion of liquid CH4 to gaseous CH4 to methanol and then again to other chemicals is a multistep reaction, more research is required to understand the most efficient means of creating a variety of products, feedstocks, and commodities on Mars.
And storing most hydrogen for manufacturing and water electrolysis as CH4 may be preferred
"Our process doesn't need to be centralised," Singh said. "It can be implemented in a space as small as a van and is portable for distributed utilisation of natural gas and manufacturing of methanol."
“Alternatively, it is also possible to directly convert CO2 from Martian atmosphere and water to methanol through a different electrocatalytic reaction mechanism”, mentioned by Meenesh R. Singh, Assistant Professor of Chemical Engineering, at the University of Illinois at Chicago. A synthesis gas reactor and a CO2 capture compressor could be the preferred avenue to enable the situ production of CO2 and H2O to CH3OH later on in settlement development.
This research provides much deeper in-sights into the binding energy, breakage and formation of C–H and C–O bonds, and greatly advances the scientific understanding of hydrocarbon electrochemistry.
Aditya Prajapati, et al. Fundamental insight into electrochemical oxidation of methane towards methanol on transition metal oxides. Proceedings of the National academy of sciences. February 23, 2021.
