Reverse Water-Gas Shift Reaction
The synthesis of carbon monoxide is readily achieved using the Reverse Water-Gas Shift Reaction.
Metal Oxide Reduction
The reduction of metal oxides, with carbon produces carbon monoxide as a byproduct. Iron oxide is used in the following example:
FeO + C → Fe + CO
Liquid carbon monoxide and liquid oxygen can be burned as a fuel producing only carbon dioxide and unreacted oxygen and carbon monoxide in the exhaust. This is especially suitable for utility vehicles on Mars because carbon monoxide and oxygen and can be readily produced from the Martian atmosphere. Carbon monoxide and oxygen can readily be produced anywhere on Mars while fuels containing hydrogen need water as a raw material which is scarce in tropical Mars.
The lower energy density per unit weight of this fuel compared to liquid methane and liquid oxygen should not be a problem in Mars' low gravity unless the requirement is for a long range vehicle. A disadvantage of this fuel is that carbon monoxide is a poison. For safety reasons the engine of such a vehicle must be isolated from the passenger compartment. Repair and maintenance en route would require the driver to put on a Mars suit and exit the vehicle.
Carbon monoxide can be used to fill rocket launching silos on Mars. This would prevent Carbon dioxide (which has a much higher freezing point) from condensing as a frost on cryogenic tanks and piping.
Carbon monoxide is toxic to humans and many other species. It bonds redily to hemoglobin molecules in blood, preventing the transfer of oxygen within the body. Symptoms begin at concentrations as low as 100ppm. The potential release of incidental amounts of carbon monoxide outside need not be a worry on Mars because carbon monoxide is already a component of the atmosphere, and that atmosphere is already 100% fatal for short term exposures of people whether carbon monoxide has been released or not. Release of carbon monoxide in the sealed environment of a Mars colony must be avoided rigorously.