Abstract
Since the second half of the 20th century, various devices have been developed in order to reduce the emissions of harmful substances at the exhaust pipe of combustion engines. In the automotive field, the most diffuse and best known device of this kind is the “three way” catalytic converter for engines using the Otto cycle designed to abate the emissions of carbon monoxide, nitrogen oxides and unburnt hydrocarbons. These catalytic converters can function only by means of precious metals (mainly platinum, rhodium and palladium) which exist in a limited supply in economically exploitable ores. The recent increase in prices of all mineral commodities is already making these converters significantly expensive and it is not impossible that the progressive depletion of precious metals will make them too expensive for the market of private cars. The present paper examines how this potential scarcity could affect the technology of road transportation worldwide. We argue that the supply of precious metals for automotive converters is not at risk in the short term, but that in the future it will not be possible to continue using this technology as a result of increasing prices generated by progressive depletion. Mitigation methods such as reducing the amounts of precious metals in catalysts, or recycling them can help but cannot be considered as a definitive solution. We argue that precious metal scarcity is a critical factor that may determine the future development of road transportation in the world. As the problem is basically unsolvable in the long run, we must explore new technologies for road transportation and we conclude that it is likely that the clean engine of the future will be electric and powered by batteries.
Highlights
Road transportation today is mostly based on vehicles powered by internal combustion engines.These engines need fuels which can be gasified and which can provide a large amount of energy per unit weight and volume
The combustion of hydrocarbons in these engines creates a number of polluting substances, including unburnt hydrocarbons, particulate matter, and harmful chemicals such as carbon monoxide (CO) and nitrogen oxides (NOx)
The “lean” mixture of fuel and air reduces the problem of carbon monoxide and hydrocarbons, so that the main problem is to eliminate particulate matter and nitrogen oxides. The abatement of these pollutants is normally obtained by means of selective catalytic reactions (SCR), that is by a combination of an oxidation catalyst based on cerium oxide and by reaction with ammonia to remove nitrogen oxides
Summary
Road transportation today is mostly based on vehicles powered by internal combustion engines. That raises the question of whether there exist sufficient PGM mineral resources extractable at reasonable prices in order to satisfy the future demand This subject has been studied in previous papers and a popularized discussion of the platinum depletion problem was reported by Cohen in 2007 in “The New Scientist” [2]. That creates a critical problem for a large sector of the world’s road transportation system which cannot run without PGM-based catalysts, unless we were to return to unacceptable levels of pollution This situation is a strong incentive for developing radically different alternatives, in particular battery powered vehicles which are inherently cleaner and appear to suffer from less important depletion problems
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