The Mauritian who Helped Us Breathe Cleaner Air: Dr Raj Rao Rajaram
A Quiet Hero for Clean Air
Every single day, millions of cars, buses and lorries line our streets and highways. While we rely on them to get around and for the transportation of goods, the gases coming out of exhaust pipes can pollute the air and harm our health. For 35 years at the Johnson Matthey Technology Centre in the UK, chemist Dr. Raj Rao Rajaram quietly dedicated his life to solving this problem. He didn't just study air pollution—he designed practical solutions that turn these noxious fumes into harmless gases before they ever reach our lungs.
Dr. Rajaram’s career was a journey of continuous innovation, adapting to new challenges as petrol and diesel engines evolved over the decades. He was born in Curepipe Mauritius into a humble family.
1980s – 1990s: Contributed to the development of the three way catalytic converter (TWC) for application to petrol vehicles.
2000s: Cleaning Up Diesel – Involved in the design of Catalytic processes for the removal of soot particles and nitric oxides (NOX) fumes from diesel exhaust.
2010s: Solving Cold-Start Pollution – Creating "sponges" to catch dangerous gases before the engine gets hot enough to burn them off.
Today: All-in-One Cleaners – Combining multiple cleaning steps into a single compact device fitted under the car.
With over 30 patents to his name, Dr. Rajaram provided the crucial technology that car, lorry and bus makers needed to satisfy strict global clean-air emission laws. His work serves as an invisible shield for public health, helping prevent respiratory illnesses for millions of people worldwide.
Development of TWC for Petrol Vehicles
Petrol engines require a delicate balance of fuel and air near stoichiometric to run efficiently. Catalytic converters—the devices attached to car exhaust systems—need that exact balance to turn toxic gases into harmless vapours. A TWC simultaneously removes three harmful exhaust gases using reduction and oxidation reactions. The reduction of nitrogen oxides (NOX) which creates smog and acid rain to nitrogen. The oxidation of carbon monoxide which can be lethal if inhaled into carbon dioxide. The oxidation of hydrocarbons which is harmful and creates smog into carbon dioxide and water. Dr Rajaram and his team of scientists at Johnson Matthey studied a series of precious metal catalysts containing palladium, rhodium and platinum to improve the performance and durability of the TWC. These catalysts are coated on the surface of a flow through honeycomb.
A major issue caused by driving conditions is whenever you accelerate or brake, that delicate stoichiometric condition of the exhaust is temporarily perturbed, allowing raw pollutants to slip out into the environment. Dr. Rajaram and his team studied the mixed oxides of cerium and zirconium to fix this issue. They found that these mixed oxides can act like a chemical lung: it absorbs extra oxygen when there's too much air at high air to fuel ratio and releases it when there's too much fuel at low air to fuel ratio. By acting as a buffer, it keeps the catalytic converter working steadily no matter how unpredictably someone drives. A TWC can reduce CO, HC and NOx by over 99% and is fitted to most petrol vehicles.
Tackling the Diesel Challenge
When diesel vehicles became popular due to their fuel efficiency, they presented a new environmental problem. Diesel engines not only produce high amounts of harmful toxic gases such as nitrogen oxides but also black diesel particulate mostly fine carbon particles which have been shown to cause respiratory problems.
The diesel exhaust, unlike petrol exhaust, has a much higher concentration of oxygen due to their mode of operation. However, the oxidation of the carbon particles by oxygen requires a temperature much higher than that of the diesel exhaust temperature. To solve the problem Dr Rajaram and his team discovered a new reaction that enable the oxidation of the carbon particles to occur at normal exhaust temperatures. It involves the oxidation of nitric oxide (NO) present in the diesel exhaust over a platinum catalyst to nitrogen dioxide (NO2) which then oxidise the carbon particles. It led to the discovery of the continuous regenerating trap (CRT) which is also known as diesel particulate filter (DPF). The CRT works by passing the exhaust gas first over a diesel oxidation catalyst (DOC) which oxidises CO and HC to CO2 and H2O and turns NO to NO2. The exhaust gas then flows into a filter that traps up to 99% of the fine soot and particulate matter. The NO2 generated upstream over the oxidation catalyst then reacts with the trapped soot particles at normal exhaust temperature. Today most diesel vehicles are fitted with a CRT or DPF.
The reduction of nitric oxide to harmless nitrogen poses a real challenge in a diesel exhaust as it contains high concentration of oxygen making reduction reactions difficult. To solve this, scientists had to find a reductant that will selectively react with the nitric oxide rather than oxygen. The selective catalytic reduction (SCR) uses ammonia (NH3) to reduce the nitric oxide (NO). Its application in a diesel exhaust requires catalysts which are thermally durable and resistant to exhaust gases. Dr. Rajaram and his team turned to special microscopic mineral structures called zeolites. By adding metals like copper and iron into these frameworks, they built durable catalysts that could withstand extreme conditions of the diesel exhaust and could last over hundreds of thousands of miles. Today the SCR is an advanced emission control technology fitted to most diesel vehicles. A liquid reductant agent typically urea also known as AdBlue is sprayed onto the exhaust stream. The exhaust heat vaporises the urea to ammonia which then passes over the metal zeolite catalyst to reduce the nitric oxide. It is the most common route used on diesel vehicles including cars, lorries and buses for the control of NOx emissions.
The Cold-Start Problem: Cleaning the First Few Minutes
Even with advanced catalysts, a major challenge remained: when you first start your car on a cold morning, the exhaust system takes a few minutes to warm up. During these first few minutes, standard converters are too cold to clean the air, allowing a surge of unfiltered pollution to escape.
To bridge this gap, Dr. Rajaram helped to invent Passive Nitrogen Oxide Adsorbers (PNA) Using palladium inside zeolite filters, these devices temporarily trap pollutants like a sponge while the engine is cold, and then safely release them to be destroyed once the system warms up.
Why This Cold-Start Solution Works
Smart Timing: Holds onto fumes when cold and releases them only when the rest of the catalytic converter is hot and ready.
High Capacity: Traps harmful gases securely, even when mixed with humid or complex exhaust flows.
Long Lifespan: Continues to perform reliably year after year, even after many thousands of miles.
Maximizing Impact in Limited Spaces
As clean-air standards became stricter, cars required more exhaust-cleaning equipment, but exhaust manifold had limited physical room. Dr. Rajaram and his team shifted their attention to multi-tasking technology—combining several separate cleaning steps into single, compact units under the car.
Today the oxidation catalyst (DOC) and selective catalytic reduction catalyst (SCR) can be incorporated on the diesel particulate filter (DPF) to make a more compact system that can trap and oxidise soot, trap cold-start gases, and eliminate toxic fumes (CO, HC and NOx) all at once.
Benefits of All-in-One Systems:
Saves Fuel: Fewer individual parts mean exhaust flows more easily, helping the engine run smoother and use less fuel.
Warms Up Faster: Smaller, lighter components reach working temperatures much faster, reducing overall emissions.
Cleaner Air: Ensures harmful compounds are completely broken down without accidentally creating unwanted byproducts.
Conclusion: A Lasting Legacy
Dr. Rajaram’s 35-year career made a lasting impact on global health. By bridging research laboratories in the UK and manufacturing centers in the US, Europe, Asia and South Africa he and his team helped transform lab discoveries into real-world tools used in millions of vehicles every day.
Alongside key academic and industry collaborators, Dr. Rajaram made clean-air technology practical and affordable for widespread use.
His 30+ patents are more than academic achievements—they protect our communities. Thanks to his work, the air we breathe near busy roads today is significantly cleaner and safer for everyone.
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