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Simon Cowell, platinum and catalysts

Q. What has Simon Cowell and a large, hot metal tube coated in precious metal got in common?

  • Both pass enormous amounts of hot gas
  • Both bring things together and make interesting things happen without ever being changed themselves
  • Both can go on doing exactly the same thing forever without changing

The answer is, of course, all of the above: both Simon and platinum can act as catalysts.

Simon Cowell a catalyst? What is one anyway?

  • A catalyst is a substance that causes or speeds up a chemical reaction.
  • Catalysts are not permanently changed as a result of the reaction.
Simon and the tube

So, in terms of Simon Cowell, you can say he gives hopefuls the chance to sign a record deal by providing a stage for stardom. At the end of the X Factor though, he’s still the same old Simon we all know and love. The difference is that biological catalysts, unlike Simon, are essential to life. Nearly all the chemical reactions that take place in the cells of your body need a type of catalyst, called an enzyme, to happen. So, we, humans, are essentially very complicated catalytic converters.

The most famous catalyst

The most famous catalyst in scientific history was used by Fritz Haber in the early 20th century to make ammonia. Ammonia is used to make nitric acid to produce ammonium nitrite. This is a very important fertiliser; without it millions of people would starve to death every year. Haber used magnetite, a form of iron oxide, as a catalyst to speed up the production of ammonia from nitrogen and hydrogen. Today, catalytic converters are fitted to virtually every car made.

Fritz Haber and Ammonia

A modern catalytic converter does three things at the same time:

  • Reduction of nitrogen oxides to nitrogen and oxygen
  • Oxidation of carbon monoxide to carbon dioxide
  • Oxidation of unburned hydrocarbons to carbon dioxide and water

This is really clever and produces a very clean exhaust gas. Precious metals such as platinum, palladium and rhodium are used as the catalysts. This is why catalytic converters can be very expensive.

Where would we be without catalysts!

Biological enzymes are perhaps the most important catalysts in nature. Without them we would not exist; they make the functioning of all the cells in our bodies possible.

How do enzymes work?

Enzymes have an active site. This is part of the molecule that has just the right shape to bind to one of the reacting molecules. The reacting molecule that binds to the enzyme is called the substrate.

The formation of an enzyme-substrate complex increases the possibility for chemical reaction by:

  • Reducing the element of chance in the collisions of molecules
  • Lowering the activation energy

But, how?

Part 1

The first part is fairly easy to understand: this is the simple ‘lock and key’ model. If two substrates are bound to a single active site then they can be lined up in the correct position so that they can come together.

Part 2

The second part is a bit more complicated: this is called the ‘induced fit’ model. What this means is that the lock and the key are not quite a perfect fit, so that when the substrate binds to the active site, both molecules are slightly distorted. This means that it is even easier for the substrate molecules to ‘snap’ together.

Lock and key

New developments

Bacteria are helping make even better catalysts for the chemical industry. The bacterium Bacillus sphaericus JG-A12 is a very strange little creature. It is an extremophile. It actually lives in piles of uranium mining waste. This is not an easy place to exist. It is one of the most toxic environments imaginable.

Extremophiles

All surface and no volume

To help it survive it has developed some amazing tricks. One of the things it does is to trap toxic metal ions in a protein layer. This layer contains a grid of identical nano pockets. Here palladium ions (very toxic stuff!) are trapped and turned into tiny balls of palladium metal and hydrogen (non-toxic stuff). The interesting bit from the point to view of the chemist is that these nano balls of palladium turn out to be fabulous catalysts. This is far better than anything that has been manufactured in a laboratory because they have such a huge surface area to volume ratio. In fact, they are so small they are nearly all surface and no volume!

Electricity as a by product!

Probably the most significant catalyst hasn’t quite been developed yet, but probably will be within the next year. This is the one that will make hydrogen fuel cells work cheaply and safely. Hydrogen fuel takes a source of hydrogen, reacts it with oxygen from the air and makes water. The nice bit about this reaction is that you get electricity as a by product! This will probably be the way electric cars finally become a commonplace reality.

Hydrogen Car

Hydrogen fuel cells have been commonplace on space craft for over forty years. They used liquid hydrogen and oxygen to make water for drinking and electricity to run the space craft. The problem with taking this technology and transferring to everyday cars is fundamentally about producing and storing super-cooled liquid hydrogen in large quantities (see the ‘Even the Greenies’ article).

A boozy solution

If we could use ethanol as the source of hydrogen all those problems would disappear. Ethanol (C2H5OH) contains lots of hydrogen and is easy to make. Its other name is drinking alcohol because it is the same chemical you get in booze! It would even be easy to change petrol stations and tankers over to being ethanol stations and tankers. The supply structure is already there. The trick is getting the hydrogen in the ethanol to react with the oxygen in the air to produce electricity.

Alcohol Station

This is where the catalyst comes in. If we could develop the catalyst that would do this trick, ethanol fuel-cell powered cars could become an economic reality in just a few years. We are right on the edge of sorting this problem out, and it may already have been done and be in the testing stage.

In reality, it is quite a tricky one to work out how well the research is going because billions of pounds will be at stake. So, final proof won’t be made public until the first ethanol fuel-cell powered cars are ready to roll. Watch this space!

Project

Meat tenderiser powder contains enzymes that break down the fibres in meat to make it tender. Can you devise and perform an experiment to find out what the enzyme is breaking down: the protein or the fat?

The same enzyme is present in papaya and pineapple juice. South American Indians used to wrap their meat in papaya leaves to help make it more succulent for hundreds of years; way before Europeans discovered the trick!

The big questions:

What is a catalyst?

Where can you find catalysts in nature?

Are catalysts used in technology?

How important are catalysts?