Dependence of the catalytic activity of zeolite catalysts on the type of modification in the low-temperature cracking of polystyrene

The study focuses on the catalytic cracking of polystyrene in a hydrogen atmosphere in the presence of catalysts based on natural zeolite. The catalysts were synthesized through acid activation of zeolite, followed by its modification with nickel(II) oxide, cobalt(II) oxide, and titanium(IV) oxide. One of the most pressing issues is that, despite the rapid accumulation of plastic waste in the environment, particularly polystyrene, cost-effective and efficient industrial technologies for its conversion into valuable products remain largely unavailable. Modern plastic recycling methods often require high temperatures and significant energy inputs, which reduce their economic and environmental feasibility. Therefore, the development of technologies utilizing inexpensive natural materials for the production of plastic cracking catalysts remains relevant and highly demanded. Low-cost catalysts based on natural clinoptilolite from a Ukrainian deposit were obtained, with a significant increase in surface area following acid activation. However, this activation had no significant impact on the liquid-phase yield or styrene selectivity. Thus, natural clinoptilolite itself exhibited catalytic activity comparable to that of its acid-activated form. Further modification of the catalyst samples with metal oxides (NiO, CoO, TiO2) significantly enhanced their catalytic activity, as confirmed by gas chromatography analysis. The results indicate a liquid-phase yield ranging from 40 % to 80 %, with high styrene selectivity exceeding 80 % in some cases. This effect is attributed to specific features of the proposed catalyst synthesis method. Acid activation facilitates the removal of natural impurities and increases the surface area for reactant-phase contact, which is crucial in heterogeneous catalysis. Additionally, metal oxide modification introduces additional catalytic centers. Due to the reduced cost of the synthesized catalysts, achieved by utilizing inexpensive natural Ukrainian zeolites, and the significant decrease in the cracking temperature, the proposed polystyrene recycling method appears promising and economically viable for industrial implementation. Furthermore, the high styrene selectivity enables substantial reductions in energy and material costs compared to traditional technologies. In contrast to existing polymer recycling technologies, the use of natural clinoptilolite as a catalyst support offers an efficient and environmentally friendly approach to plastic waste utilization.