Water–gas shift reaction

Scientists can change gas to make more fuel.

They mix water vapor with a special gas. This gas is called carbon monoxide. The mix turns into two new things. One is the air we breathe. The other is hydrogen gas.

Hydrogen is very useful. It helps make things like fuel. It can also help power fuel cells. This process is a big help to the world. It makes making fuel much easier.

Scientists use a special way to make fuel. This is called the water-gas shift reaction.

It was found by Felice Fontana in 1780. In this reaction, carbon monoxide and water vapor mix together. This mix makes two new things. One is carbon dioxide. The other is hydrogen.

Hydrogen is very important for many jobs. It helps make ammonia. It also helps make things like methanol.

This reaction can also help fuel cells work better. Fuel cells use hydrogen for power. This reaction can help make more hydrogen for them.

To make the reaction work well, workers use a catalyst. A catalyst is a material that helps a change happen. In big plants, they use two stages. The first stage is the high temperature shift. It uses iron and chromium. This part is very fast. The second stage is the low temperature shift. It uses copper. This part makes sure the carbon monoxide is mostly gone. This helps make very pure hydrogen.

The water-gas shift reaction is a very important way to make hydrogen.

This process happens when carbon monoxide and water vapor mix together. When they react, they turn into carbon dioxide and hydrogen. This reaction is useful because hydrogen is needed for many things. It helps make ammonia, which is used in farming. It also helps make methanol and other hydrocarbons.

Scientists use this to change the mix of gases in water gas. This is why the process is called a "shift."

This reaction works in a few different ways depending on the heat. One way is called the redox mechanism. In this way, carbon monoxide takes an oxygen atom from the catalyst. This turns the carbon monoxide into carbon dioxide. Then, a water molecule lands on the spot where the oxygen used to be. This water splits apart to make hydrogen and help the catalyst reset.

Another way is the associative mechanism. In this way, the gases stick to the surface of the catalyst first. They form a middle step called an intermediate before turning into the final gases.

An Italian physicist named Felice Fontana discovered this reaction in 1780. For a long time, people did not know how useful it could be. Before the 1900s, people made hydrogen by using steam and iron under high pressure. This was a slow and difficult way to work. Later, people needed a better way to make hydrogen for the Haber-Bosch process. This process is used to make ammonia. Using the water-gas shift reaction with coal became a much better solution.

In big factories, workers use two different stages to get the best results. The first stage is the high temperature shift, or HTS. This stage uses a catalyst made of iron oxide and chromium oxide. It works very fast between 310 degrees Celsius and 450 degrees Celsius.

The second stage is the low temperature shift, or LTS. This stage uses a copper-based catalyst to finish the job. It works at a lower heat between 200 and 250 degrees Celsius. This second step lowers the carbon monoxide to less than 1 percent.

You can think of a catalyst like a helper that makes a job easier. In this reaction, the catalyst helps the gases change without being used up itself. This reaction is also very important for the future of clean energy. It can help fuel cells work better by making more hydrogen.

It also helps by removing carbon monoxide, which can poison some fuel cells. Scientists are still researching new catalysts that work well at low temperatures. This could help create a "hydrogen economy" for the whole world.

The water–gas shift reaction (WGSR) is a vital chemical process used to produce hydrogen. It occurs when carbon monoxide (CO) and water vapor (H2O) react together. This reaction transforms the starting gases into carbon dioxide (CO2) and hydrogen (H2). In industry, this process is essential for creating many important substances. It helps manufacture ammonia, methanol, and various hydrocarbons. The term "shift" refers to how the reaction changes the ratio of gases in a mixture. By adding steam, scientists can reduce the amount of carbon monoxide and increase the hydrogen content.

Understanding how this reaction works requires looking at its thermodynamics. The WGSR is an exothermic reaction, meaning it releases heat as it proceeds. Because of this, the reaction's equilibrium is highly dependent on temperature. As the temperature increases, the reaction rate becomes faster. However, higher temperatures actually make hydrogen production less favorable. According to Le Chatelier's principle, the chemical equilibrium shifts away from hydrogen production when heat is added. Therefore, lower temperatures are better for maximizing the amount of hydrogen created.

There are two main ways scientists describe how the molecules move during this reaction. These are known as the redox mechanism and the associative mechanism. The redox mechanism is usually the primary pathway during high-temperature shifts above 350 °C. In this process, carbon monoxide takes an oxygen atom directly from the catalyst. This turns the CO into CO2. Then, a water molecule attaches to the empty spot on the catalyst and splits apart. This step releases hydrogen and returns the catalyst to its original state.

The associative mechanism is the main pathway used at lower temperatures. This method was first proposed by Armstrong and Hilditch in 1920. In this version, both the CO and the water vapor stick to the surface of the catalyst first. They form a middle step called an intermediate. One common intermediate is a carboxyl or formate group. The carboxyl pathway is especially important because it accounts for about 90% of the reaction rate on certain catalysts. This happens because the active site forms at the interface where the metal meets the metal-oxide support.

Industrial plants often use two distinct stages to get the best results from the WGSR. The first is the High Temperature Shift (HTS). This stage uses a catalyst made of 74.2% iron oxide and 10.0% chromium oxide. The chromium helps stabilize the iron and prevents it from breaking down. HTS operates between 310 °C and 450 °C to take advantage of fast reaction rates. However, HTS alone does not convert all the carbon monoxide. To finish the job, the gas moves to a Low Temperature Shift (LTS) reactor.

The LTS stage uses a copper-based catalyst to reach higher efficiency. A typical commercial LTS catalyst contains 32-33% copper oxide (CuO) and 34-53% zinc oxide (ZnO). The zinc oxide provides structural support and protects the copper from sulfur poisoning. The LTS reactor operates at a much cooler 200–250 °C. This lower temperature allows the process to reduce carbon monoxide levels to less than 1%. Scientists must be careful with LTS because copper can suffer from thermal sintering if it gets too hot.

The history of this reaction shows how much technology has changed. Italian physicist Felice Fontana discovered the WGSR in 1780. For a long time, its industrial value was not fully understood. Before the early 20th century, hydrogen was made by reacting steam with iron under high pressure. This was an expensive and inefficient method. The need for hydrogen for the Haber–Bosch ammonia synthesis process changed everything. Engineers realized that combining the WGSR with coal gasification was a much better way to produce hydrogen at scale.

Today, the WGSR is a cornerstone of modern energy research. It is particularly important for the development of fuel cells. Some fuel cells, like proton-exchange membrane (PEM) cells, can be poisoned by carbon monoxide. The WGSR helps by removing the CO and increasing the hydrogen supply. Researchers are currently working to develop new catalysts that work at low temperatures. This is necessary because current industrial catalysts are too large or too dangerous for consumer use. Solving these challenges is a key step toward a global hydrogen economy.