Scientists involved in chemical catalysis research should devise means to improve the quality of petroleum products, and reduce the pollution caused by production processes and emissions, the Union Petroleum Secretary, Mr. T. S. Vijayaraghavan, said on Wednesday. The country had spent nearly Rs. 6,000 crores in nine refineries in the last few years for bringing down the sulphur content in diesel from 0.5 per cent to 0.25 per cent in metro cities.