Cool Catalysis

Almost every chemical reaction relies on a little help from a friend – a molecule which facilitates it without changing its own shape or composition. Without such catalysts life as we know it would be impossible and everything from the human body to large industrial processes would grind to a halt.

Despite its importance catalysis is still poorly understood in detail, particularly on the nano-scale, but this challenge just adds to the excitement for Vladimir Golovko, a chemist at the University of Canterbury and a principal investigator at the MacDiarmid Institute. “Catalysis is a very cool topic to be working in. There have been lots of Nobel prizes associated with catalysis and lots of important discoveries, including many things which enabled this civilisation to survive. The first major artificial booster in agriculture came from the synthesis of ammonia for fertiliser, and even though people later had their queries about it, it allowed civilisation to progress.”

Although catalysis has been used in industry for almost a century, Golovko says it was a bit like black magic and people are only now trying to understand the process in detail. “We know it works but how exactly it works is another question. The understanding of what happens during catalysis with nano-particles is still in its infancy.”

Golovko’s research focus is on improving this understanding, on developing methods to produce nano-sized catalysts in a controlled way and on making the catalytic process much greener. He likes to quote the 2007 Nobel laureate Gerhard Ertl, who received his prize in chemistry for elucidating what goes on, chemically speaking, on surfaces. Ertl described catalysis as “nanotechnology long before nanotechnology actually emerged” for the simple reason that industry has always tried to economise processes by decreasing the size – and thus increasing the reactive surface area – of catalytic ingredients.

Faced with the challenge of producing new nano-scale catalysts, Golovko says it is important to have as much control over the process as possible, from the input of synthetic precursors and components into the system to the detailed structure of the catalyst as it is being fabricated. “As a chemist I have the benefit of being able to control the process. We use inorganic materials and protocols which allow control over the fabrication of nano-particles in solution.”

One major advantage of working with solutions, or “wet chemistry”, rather than with gases is that the process can be scaled up, all the way to industrial proportions if needed. Golovko’s team uses heterogeneous catalysis processes (as opposed to working with biological enzymes) which means that the inorganic ingredients are often chemically more robust and cheaper. They are also easier to recycle, which is another goal for the team. Golovko says “there’s no point in making a funky cluster or colloid made of gold or something expensive if you lose it in one go. Preferably you want to be able to capture it back from the reaction mixture or to even have the continuous process going on, so that your reagents enter through one port and your products leave at the other port.”

To make the separation of the catalyst and products easier, Golovko’s team immobilises the nano-particles on various supports. “You start with small stuff, for example metal salts, and we control how they grow, how the salts are reduced to get the metal and how it is assembled together. Depending on the choice of conditions and ligands we can control the interactions. We have lots of degrees of control, from the size ofthe particle, the number of atoms, its shape and its crystalline phase or type of atom arrangement.”

“The principle is simple. A ligand or surfactant is something molecular in nature which binds to the surface of the metal nano-particle or any particle as it grows, but it’s not a catalyst because you can grow it without it. But without it you have no control whatsoever. Your particle will only be suspended in solution as long as it’s small and its weight is miniscule. As it grows bigger, gravity will outweigh the weak interactions between the particles and the solvent and it will crash out and form a bulk phase.”

This is another reason for the use of immobilization techniques. It allows you to place the particles in particular spots where they will stay even if the ligand is removed later or the whole system is heated. “And there’s more,” says Golovko. “Some supports can tune the catalytic activity of the metal nano-particle.”

For all these reasons, Golovko’s team has been exploring a range of key ingredients and support systems, blending them in a large matrix with the goal of producing many different catalysts that could be useful for many chemical reactions.

He says his background in wet chemistry has served him well. As an inorganic chemist he knows how to make things from scratch, and he has honed his skills in applying the products of his synthesis in nanofabrication. For several years, while still living in Kiev, things were difficult though. “I left Kiev in 1999. That period of history in the former Soviet Union wasn’t easy to live through. The old system had collapsed and the new system wasn’t in yet. It was like Chicago in the 1930s, a really rough time with gang wars, and science wasn’t supported well.”

Since arriving in New Zealand almost three years ago, he has already established collaborations with several other researchers at the MacDiarmid Institute and other science institutions, while maintaining research links overseas.

Golovko’s ultimate goal is to make catalysis greener. He says the chemical industry is a multi-billion dollar machine without which this civilisation would collapse, but it still relies heavily on oil and gas and often uses harsh chemicals to achieve its goals. Green catalysis is trying to use benign feed stocks and benign reaction conditions, minimizing waste at the same time. “The catalyst itself should be as selective as possible so that it produces what you want and nothing else, no waste, and the reaction should rely on renewable feed stocks or green building blocks as reagents, as well as good control of the process.”

His team has already had some success in this regard. “The production of epoxides – think epoxy resins – uses active chlorine compounds, but we have recently been able to use oxygen from the air. It’s as cheap as it gets, as green as it gets and as benign as it gets.”

 

Vladmir Golovko (centre back) and his research group