The drive to reduce carbon dioxide from vehicles in recent years has lead to a number of different clean engine and fuel strategies. Currently biofuels are receiving a great deal of attention as cleaner alternatives to gasoline and diesel produced conventionally from crude oil, with most governments around the world setting percentage targets for future biofuel usage in transportation. Biofuel is a fuel made from biological materials: typical examples include alcohols made from the fermentation of sugar crops or wood chippings (usually bioethanol) and the production of biodiesel from animal fats and vegetable oils via transesterification.

There are many advantages to using biofuels: they provide a net reduction in carbon dioxide vehicle emissions when the amounts absorbed by the source during its growth are taken into account; they are free of sulphur and aromatics; they lower dependence on fossil fuels; can make use of organic waste from household and industrial sources as well as providing a market for locally grown crops. Trends in the type and amount of biofuel used globally vary, with Europe using mainly biodiesel and North and South America predominantly bioethanol for gasoline vehicles. Brazil has however, recently brought in legislation that all diesel fuel must contain 2 per cent biodiesel by 2008, rising to 5 per cent by 2013.

Use of biofuels, while greener in terms of CO2 emissions and lower in sulphur and aromatics, does not eliminate the need for catalytic converters. Cars running on biofuels will still produce pollutants with legislated maximum levels i.e. CO, HC and NOx and Particulate Matter (PM). Use of biodiesel blends, however, will assist diesel fuel in reaching the Ultra-Low Sulphur Diesel (ULSD) limits of 10-15 ppm, which are being enforced in Europe and North America. Since sulphur reduces the activity of the pgm, the lower sulphur levels will help improve catalyst performance. Cars running on bioethanol, may need a slightly different catalyst formulation, but in general the overall engine characteristics and legislated pollutant limits, in the country where the vehicle is sold, will play the largest part in deciding how much pgm is coated onto an autocatalyst'.