A Solution Novel Catalysts in the Car Industry Using Fragments to Probe

Autumn 2009 New materials for better batteries Novel catalysts in the car industry Electron correlation: a solution Using fragments to probe biology As I see it... Martyn Twigg started life in academia, but has spent most of his career in the chemical industry. He tells Sarah Houlton how he ended up there, and the importance of catalysts in the motor industry How did you come to work in industry? What do the autocatalysts do? ishing. It is rewarding that chemists together with After a junior faculty position at the University of In a petrol engine, partially oxidised hydrocarbons engineers are able to produce things like this that Toronto, I came to Cambridge to work with Jack such as aldehydes and carbon monoxide are pro - have such a major benefit to society. Lewis and Brian Johnson – the only kineticist work - duced, as well as the expected combustion prod - ing in a preparative group! It was one of the most ucts water, carbon dioxide, and nitrogen. Because What’s the next challenge for catalysts in exciting times of my life – working almost every the temperature is so high at the flame front, oxy - the car industry? day until midnight, and it was a very stimulating gen and nitrogen combine through a complex This is already being addressed. The composition environment with eminent visitors from all over the series of free radical reactions to form nitric oxide. of diesel exhaust is very different from petrol world, many of whom I am still in contact with. This is a fascinating molecule – at room tempera - engines that operate around the stiochiometric One of my colleagues was an ICI employee, vis - ture it is thermodynamically unstable, it is a free point with no excess oxygen. Diesel engines also iting the lab for six months, and he invited me to radical, and it should fall apart, but it does not! contain CO, hydrocarbons and NOx, but because visit ICI’s corporate laboratory in Runcorn to see Instead, its only facile reaction is oxidation to of the higher thermodynamic efficiency of the what they did there. When I first arrived, I was nitrogen dioxide and because this is a third order diesel engine, its exhaust temperature is consider - introduced to one of their senior people who told process (second order in NO) at low nitric oxide ably lower. As if this was not a significant challenge me there were ‘no jobs’. I reassured him I was not concentrations the homogeneous oxidation in air itself, diesel engines run lean, so excess oxygen is after a job – to which his response was that there is extremely slow. present, making it impossible to reduce the NOx. were no short-term contracts either! I went on to However, in combination with hydrocarbons We have developed two solutions. One is to trap meet several of scientists, including one senior and sunlight, NO 2 is more readily formed, and and store NOx as nitrate so it does not enter the researcher whom I interrogated about what they photolytically this can form oxygen atoms that environment through the tailpipe, and then peri - actually made. He pulled a jar of little polythene react with oxygen to form ozone. This is a lachry - odically enrich the exhaust gas to reduce the beads out of his desk drawer, and I must have mator – and in particularly sunny locations like stored nitrate to nitrogen. While this is effective, asked some good questions as later on I was inter - Los Angeles, Tokyo and even Rome, other photo - there is an alternative strategy – selective catalytic cepted and offered a job. So I ended up in indus - chemical reactions can lead to very potent lachry - reduction using ammonia as the reductant. Since it try very much by accident! mators like peroxyacetylnitrate . This can make you is not practical to store the necessary ammonia on cry at levels of parts per trillion. These secondary the vehicle, an aqueous solution of urea is used, So what did you do at ICI? pollutants are only formed if the primary pollu - that readily decomposes to give the desired I started off, bizarrely, managing the accounts of a tants are present, and as legislation has brought ammonia. The urea tank needs to be refilled at research group of more than 100 people who these levels down, catalyst technology has devel - service intervals, but this is straightforward, and were spending huge amounts of money develop - oped to meet the increasingly stringent demands. we are well on the way to making a success of this ing an organometallic catalysed ethylene poly - Today, tailpipe emissions have been lowered to lev - approach – already there are several tens of thou - merisation process for low-density polythene. But els that can be below those present in the natural sands of cars on the roads in Europe using this I still had time to work on several of my chemical environment, so this is really a tremendous success new technology! hobbies such as phthalocyanines and low-spin story of what can be achieved at the chem - iron(II) complexes. I also got involved with the istry/engineering interface. CV Martyn Twigg development of phosphate non-misting glasses. After a couple of years I moved to the agricul - What about diesel engines? tural division in Billingham, where I first became One of our big success stories at Johnson Matthey Born: Wolverhampton involved with heterogeneous catalysis, with involves particulates – soot from diesel engines – Status: He and his wife responsibility for developing and manufacturing and while modifications to engines have reduced Sarah have a six-year-old catalysts for producing hydrogen, ammonia, the levels that are produced, the particulate matter daughter, Isabella methanol and so on. It was very exciting as it was remains very worrying in terms of health effects. Education: Studied a completely new field for me, and there were sev - Initially, very expensive multicomponent filter sys - ‘special chemistry’ at eral significant successes. After 12 years, I moved tems were used, comprising one or more usually Hull. His PhD was in to the US to manage a research group investigating two oxidation catalysts, a large ceramic soot filter kinetics and reaction new polymerisation routes to PVC with facilities and a small tank of fuel additive that mediated the mechanisms of inorganic in America, England and Italy, and an office in periodic combustion of retained soot in the filter. complexes at the Univer - Brussels. I did an enormous amount of travelling! They were heavy and both material and energy sity of Kent at Canterbury. In 1992, I was headhunted by Johnson Matthey as intensive to produce, and they also consumed a technology director in the automotive catalyst busi - considerable amount of energy in use. Career: He spent two years at the University of ness, a very important area for the company that was Recently we introduced a new filter design that Toronto as an NRC Fellow, before returning to the being severely pressed by the competition who, can remove the particulates from diesel exhaust, as UK and Cambridge on a personal ‘Bring-Back basically, had better technology. The challenge was to well as control gaseous tailpipe emissions. The Fellowship’ with Jack Lewis and Brian Johnson. improve the commercial situation by enhancing the new single units are only six-inch long so they can After two years he moved to ICI, and then to technical performance of our catalysts. be mounted directly in the engine compartment, Johnson Matthey, where he is now chief scientist. preventing heat loss and thus adding to overall Interests: Applications of chemistry, including Why are catalysts used in the car industry? efficiency. Periodically, perhaps every 1000 km pyrotechnics. He is a Class A licensed radio Catalysts have been fitted in cars sold in the US depending on driving conditions, the temperature amateur, and in the past was a member of the since 1975 to control tailpipe exhaust emissions in the filter is increased to above 600°C to initiate British Rocketry Association of hydrocarbons, carbon monoxide and nitrogen combustion of the retained particulate in the filter. Did you know? He did not study any science at oxides (NOx), but it was not until the early 1990s This is done by putting additional fuel through school, and owes his chemical career to his that it became mandatory to fit them in Europe. I the engine, which is oxidised over catalyst at the mother’s decision to arrange for him to sit came into the industry just as the European mar - front of the filter. The particulate oxidation is a entrance exams at a college of further education ket started, and we focused on the development of very exothermic process that is carefully con - to do science O-levels. His chemical interest was fundamental chemistry required to make better trolled to prevent a meltdown! The car does this ignited by an exceptional chemistry teacher called catalysts. One of the key features is durability – computer-controlled process automatically, and Ivan Nutter who, Martyn says, lived up to his these hi-tech products must meet minimum per - the emissions generated during this process are name. In the evenings he and several other formance criteria and effectively last the life of the controlled as well. This design has won several students stayed in the laboratory to do all sorts of car. The better the catalyst technology the less awards, most notably two Queen’s Awards this fascinating experiments – he remembers amount of costly platinum, palladium or rhodium summer – one for innovation and one for interna - preparing a series of mixed salts, while other that is required, so making it overall more cost- tional trade.

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