17. Recycling of Platinum Group Metals and Alternative Catalysts for Catalytic Converters

Platinum group metals (PGM) are used as a catalyst in the automotive catalytic converters to curb engine emissions. The modern catalytic converter (three-way) executes oxidation of CO and unburnt HC, and reduction of NO using its large active surfaces containing PGM, which are precious metals with high cost all over the world. Due to the high cost of the PGM, researchers are working on efficient methods for extracting and reusing these valuable metals from catalytic converters. Pyrometallurgy and hydrometallurgy are the most common ways for the extraction of the PGMs among other methods. Alternative to platinum, materials like titanium dioxide and other metal-based oxides can be used for carrying out redox reactions of toxic vehicular emissions. The use of such alternative catalysts can help in reducing the increasing demands and cost of PGMs. This chapter focuses on the possibilities of recycling the PGMs from catalytic converters and also of reducing the ever-increasing requirement of PGMs in the manufacturing of autocatalysts in the catalytic converters. The chapter reports the recent global trends of PGM recycling and its demand for use as autocatalysts, alternative materials of to PGMs in catalytic converters and alternative methods for emission reduction. Further, the engine-related challenges and research on future directions of replacing PGM’s as autocatalysts has been performed; it includes some experimental results of direct decomposition of NOx using non-noble metal catalysts such as Cu-COK12, Cu-Nb₂O₅, Cu-YZeolite, and Cu-ZSM5. The article should also provide a quicker understanding of research on development of low-cost non-noble metal-based alternative autocatalysts.