Researchers in Japan have developed a "crystal-shaped" sponge that can trap pollutants in vehicle emissions before a catalytic converter starts to work.

Up to 80 per cent of hydrocarbons released into the atmosphere are emitted from vehicles before the converter reaches its operating temperature, the Hindustan Times has reported.

But scientists at the University of Tokyo believe zeolite, a crystalline aluminosilicate, could act as a good hydrocarbon trap.

The atoms in zeolites are linked into rings and form a three-dimensional framework which helps them clean up exhaust emissions by trapping pollutants for the few minutes after the engine has been started, the newspaper reported.

Zeolite beta had previously been used for the job but it fell apart in moist air at high temperatures and lost its grip on the hydrocarbons as a result.

Writing in the Journal of Physical Chemistry B , however, the Tokyo team found that another form of zeolite, known as SSZ-33, could hold up to 30 per cent more hydrocarbons than zeolite beta without breaking down under heat.