Currently more and more countries around the globe are legislating controls aimed at achieving safe concentrations of these pollutants by regulating their level of emissions from combustion sources, notably those discharged from the exhausts of automobiles. The maximum allowable levels of emissions from automobiles are already regulated by many governments using measures in grams per kilometre or grams per mile.
Emission control standards were initially established in the major centres of Japan, the United States, and the European Union. These regions have similar approaches to emission reduction, although each set of regulations is tailored to specific requirements. The most stringent emissions standards in the world are to be found in California which has become the benchmark for worldwide environmental legislation. The legislation refers to LEV (Low Emission Vehicle), ULEV (Ultra LEV), SULEV (Super Ultra LEV), and ZEV (Zero Emission Vehicle). The US system, based on groups of regulations called Tiers, has decreasing emissions limits and increasing durability requirements. The European regulations also define increasing restrictions through regulations called Euro (Euro 1 to Euro 6) and have continued to get tighter over the past two decades cutting emissions by 83%.
Euro Emission Regulations
Emerging markets are increasingly adopting emissions regulations but are hampered by fuel quality and as such lag mature markets by on average 6 years.
Emission Standards (Source: BASF)
Catalytic Converters have been instrumental in reducing emissions of harmful gases from vehicles since their inception in response to the US Clean Air Act of 1970. Platinum, palladium and rhodium are essential components in automobile catalytic converters reducing emissions by well over 90%, and in some cases by over 99%. Catalytic converters oxidize hydrocarbon exhaust into carbon dioxide and water. The Environmental Protection Agency estimates that fuels burned by transportation accounts for 13% of global carbon dioxide emissions. Therefore, different governments are implementing regulations to decrease carbon dioxide emissions from cars. For example, the United States plans to decrease carbon dioxide emissions from the current 220 g/km to 109 g/km by year 2025.
Carbon Dioxide Emissions (Source: International Council on Clean Transportation)
This has meant automobile manufactures have had to come up with strategies to downsize engines, include turbo-chargers, use lighter bodies and start-stop devices to save fuel and decrease carbon dioxide emissions. The downsizing of engines alone has meant more platinum group metals are required in the overall auto catalyst systems. As an example, an inline four cylinder turbo charged engine with less carbon dioxide emissions requires on average 50% more platinum group metals than a comparable V6 non-turbo engine which uses more fuel and has higher carbon dioxide emissions.
In gasoline vehicles, reduction catalysts are used to decrease NOx by transforming it into Nitrogen and Oxygen. A Three Way Catalyst (TWC) converts NOx, HC, and CO simultaneously.
Example of a Three Way Catalyst (Source: Johnson Matthey)
This technology can only be used in gasoline engines because of its exhaust composition. NOx abatement in diesel engines is trickier, but is currently being met using NOx absorbers, which utilise platinum as the primary catalytic agent.
The legislated levels of PM reduction require the use of catalysed particulate filters which contain platinum. The platinum converts NO to NO2 which generates heat allowing the filter to self-clean. Although some manufacturers have found an alternative to costly particulate filters to meet Euro standards, Euro 6 will force the installation of particulate filters on all diesel vehicles. Furthermore, Euro 6 will extend to all vehicles by September 2015, meaning even gasoline engines will require particulate filters. In the US, particulate filters are required on most diesel vehicles to meet current standards. As the limits decrease in 2015 and 2017 due to CAL LEV III and US Tier 3 regulations, all vehicles will need to use particulate filters to meet the new standards. However, this is complicated by high backpressure in the catalyst system affecting engine efficiency. To maximise engine efficiency, while minimising backpressure, automakers are looking at incorporating a gasoline particle filter with a three way catalyst. This will inadvertently increase platinum group metals loadings as the particulate filter needs to be larger than the three way catalyst in order to have sufficiently high catalytic activity.