There are a couple of types of steam reformers, one reforming methanol and the other reforming natural gas.
The molecular formula for methanol is CH3OH. The goal of the reformer is to remove as much of the hydrogen (H) as possible from this molecule, while minimizing the emission of pollutants such as carbon monoxide (CO). The process starts with the vaporization of liquid methanol and water. Heat produced in the reforming process is used to accomplish this. This mixture of methanol and water vapor is passed through a heated chamber that contains a catalyst.
As the methanol molecules hit the catalyst, they split into carbon monoxide (CO) and hydrogen gas (H2):
The water vapor splits into hydrogen gas and oxygen; this oxygen combines with the CO to form CO2. In this way, very little CO is released, as most of it is converted to CO2.
Reforming Natural Gas
Natural gas, which is composed mostly of methane (CH4), is processed using a similar reaction. The methane in the natural gas reacts with water vapor to form carbon monoxide and hydrogen gases.
Just as it does when reforming methanol, the water vapor splits into hydrogen gas and oxygen, the oxygen combining with the CO to form CO2.
Neither of these reactions are perfect; some methanol or natural gas and carbon monoxide make it through without reacting. These are burned in the presence of a catalyst, with a little air to supply oxygen. This converts most of the remaining CO to CO2, and the remaining methanol to CO2 and water. Various other devices may be used to clean up any other pollutants, such as sulfur, that may be in the exhaust stream.
It is important to eliminate the carbon monoxide from the exhaust stream for two reasons: First, if the CO passes through the fuel cell, the performance and life of the fuel cell are reduced; second, it is a regulated pollutant, so cars are only allowed to produce small amounts of it.