The proliferation of plastic waste in the 21st century has serious environmental impacts on biodiversity and human health. Besides single-use plastic waste, there is mounting evidence that durable plastics, such as nitrogen-containing plastics, are being mismanaged and are accumulating in the environment. These plastics, such as polyamides and polyurethanes, are particularly challenging to biochemically degrade due to the added stability from hydrogen bonding within the polymer structure. However, current technologies for catalytic processing of nitrogen-containing plastics are underdeveloped compared to those for single-use plastics, such as the various recycling methods for polyethylene terephthalate bottles. In particular, there is a notable lack of examples in chemical recycling of nitrogen-containing plastics using highly robust and reusable heterogeneous catalysts. This thesis aims to explore the depolymerization of polyamide and polyurethane using ceria-based catalysts and to develop new solvent-free processes for the treatment of nitrogen-containing plastic waste. The results reveal that noble-metal nanoparticles supported on ceria can achieve high conversions of waste polyamide into ammonia and hydrocarbons, while pure ceria achieves complete depolymerization of polyurethane into the aniline monomers. Furthermore, new mechanistic insight of amide bond hydrogenation using these ceria-based catalysts was revealed by conducting experiments in operando. It was found that both the metal and the support play crucial roles in the activity and selectivity for amide conversions.