Why does the reforming stage need a continuous supply of heat?

The reforming reaction is strongly endothermic. Extra natural gas is usually burned to heat the reformer, which releases more carbon dioxide.

What is the water-gas shift reaction, and why is it used after reforming?

The water-gas shift reaction is CO + H₂O → CO₂ + H₂. The reaction turns the carbon monoxide from reforming into extra hydrogen.

Write the overall equation for the steam reforming of methane.

The overall equation is CH₄ + 2H₂O → CO₂ + 4H₂. Each methane molecule gives four hydrogen molecules and one carbon dioxide molecule.

Using CH₄ + 2H₂O → CO₂ + 4H₂, what mass of carbon dioxide is released per kilogram of hydrogen? Take Mr of CO₂ as 44 and of H₂ as 2.

About 5.5 kg of carbon dioxide is released per kilogram of hydrogen. The working is 44 ÷ (4 × 2) = 5.5 kg. Burning gas to heat the reformer adds more.

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Hydrogen Fuel Cells

Hydrogen production: steam reforming, electrolysis and photocatalysis

3 things to know
A2 1

Overview

Steam methane reforming and the water-gas shift, reforming equations and carbon dioxide per kilogram, grey, blue and green hydrogen, electrolysis and its half-equations, electrolyser efficiency, and photocatalytic water splitting.

What you need to know

Answer each one before you reveal it.

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Key term

What is the difference between grey, blue and green hydrogen?

Key term

Why is photocatalytic water splitting not yet used for bulk hydrogen production?

Numbers

Give the equation for the reforming stage of steam methane reforming.

Questions from this subtopic

Each one with the model answer underneath.

1
Give the equation for the reforming stage of steam methane reforming.
Model answer
The reforming stage is CH₄ + H₂O → CO + 3H₂. The reaction runs over a nickel catalyst at roughly 700–1000°C.
2
Why does the reforming stage need a continuous supply of heat?
Model answer
The reforming reaction is strongly endothermic. Extra natural gas is usually burned to heat the reformer, which releases more carbon dioxide.
3
What is the water-gas shift reaction, and why is it used after reforming?
Model answer
The water-gas shift reaction is CO + H₂O → CO₂ + H₂. The reaction turns the carbon monoxide from reforming into extra hydrogen.
4
Write the overall equation for the steam reforming of methane.
Model answer
The overall equation is CH₄ + 2H₂O → CO₂ + 4H₂. Each methane molecule gives four hydrogen molecules and one carbon dioxide molecule.
5
Using CH₄ + 2H₂O → CO₂ + 4H₂, what mass of carbon dioxide is released per kilogram of hydrogen? Take Mr of CO₂ as 44 and of H₂ as 2.
Model answer
About 5.5 kg of carbon dioxide is released per kilogram of hydrogen. The working is 44 ÷ (4 × 2) = 5.5 kg. Burning gas to heat the reformer adds more.
6
What is the difference between grey, blue and green hydrogen?
Model answer
Grey hydrogen is made from natural gas with the carbon dioxide released to the air. Blue hydrogen is made the same way with the carbon dioxide captured and stored. Green hydrogen is made by electrolysis using renewable electricity.

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