Hydrogen Diffusion on a Solid Surface Accelerated by Water


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Molecular hydrogen. Chemical bond breaking originates atomic hydrogen. Photo by Clara Piccirillo

How much difference does a little H2O make? According to new research published in Science, when it comes to hydrogen diffusion, a tiny amount of water can make a big difference. The water causes an immense increase in the speed of diffusion of atomic hydrogen on the surface of solid iron oxide – This finding could have important applications in industrial reactions where hydrogen is used or produced.

About Hydrogen: H2

Hydrogen (H) is the first and simplest element of the periodic table; in standard pressure and temperature conditions, hydrogen is stable as a diatomic gaseous molecule H2.

Despite its simplicity, H2 is a very important molecule, as it is used in many industrial processes.

  • H2 as a Reactant: Hydrogen is employed, for instance, in the Fisher-Tropsch reaction; here, carbon monoxide (CO) and hydrogen react to form hydrocarbons. Hydrocarbons, besides being fuels themselves, are successively used in a series of applications, i.e. to produce pharmaceutical compounds, plastics, etc. The petrochemical industry also uses hydrogen for many processes. Some petrochemical-derived molecules, for instance, can be converted into others with better properties by adding hydrogen to them (hydrogenation).
  • H2 as Product: Hydrogen is also a reaction product formed in other industrial processes; catalytic reforming, in the petrochemical industry, is an example of this. In catalytic reforming, some molecules are converted into others with higher octane numbers, and hence having better performances as fuels. This conversion generates H2 as the main by-product.

Hydrogen has potential for use as a clean fuel. Photo by Suzan Black.

Hydrogen Fuel: No CO2 Emissions

Further to its applications in industry, H2 is considered very valuable as potential clean fuel. Its combustion takes place according to the reaction:

H2 + ½ O2 → H2O

Unlike fossil fuels, the reaction only generates water, and not carbon dioxide (CO2). For this reason, H2 is considered a promising fuel for the future; it could help to reduce CO2 emissions, as required by the Kyoto protocol.

Hydrogen and the Catalyst

The majority of the reactions mentioned above are performed at the industrial level using reaction catalysts. These catalysts are chemical compounds which can increase the rate of a reaction; they are not consumed or produced during the reaction itself.

The use of catalysts in industrial processes is of extreme importance; in fact, performing a reaction in a quicker and more efficient manner can reduce the cost of the process itself and, at the same time, increase the productivity.

Many catalysts employed in reactions with hydrogen are solid compounds. Their nature depends on the process considered; often metals or metal oxides are employed.

The Catalyst Mechanism – Diffusion

Understanding the mechanisms of catalysis is very important to improve its efficiency and develop better catalysts. For reactions in which hydrogen is involved, one of the key elements is the diffusion of atomic hydrogen (H) on the surface of the catalysts; a faster diffusion can obviously mean a faster reaction.

It is therefore important to understand which parameters can affect the formation of atomic H (from the molecular H2) and its diffusion.

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