Urea Complete Conversion to Compound Fertilizer in Industrial‐Scale Tandem Reactors

A compound fertilizer with NH₄H₂PO₄ and KH₂PO₄ offer significant advantages in enhancing both crop yield and quality. Ammonia (NH₃) is essential for the synthesis of the compound fertilizer, which was produced by an energy intensive chemical process. Developing efficient and environmental friendly methods to produce ammonia-containing compound fertilizers is crucial and extremely challenging. Here, we present a tandem catalysis system capable of achieving complete conversion of abundant urea into compound fertilizer in industrial-scale reactors by combining electrochemical and subsequent chemical processes. In a typical cycle, with the use of 200 g urea, 1580 g of solid compound fertilizer (KH₂PO₄ and NH₄H₂PO₄) and 232 L of pure H₂ are produced without any further separation process. The key to the realization of this system is to precisely control the rate of urea consumption and NO₂ ^- formation in electrochemical process. By maintaining a precise molar concentration ratio of urea to NO₂ ^- at 1/2 in electrolyte, urea can completely react with NO₂ ^- to form N₂, while CNO^- can be converted into NH₄ ⁺ to form compound fertilizer in the second step of H₃PO₄ treatment, achieving complete conversion of urea without by-products formation. This method remarkably reduces H₂ production potential while allowing for extraction of ammonia from urea-containing wastewater or urine to create pure compound fertilizer at an anticipated lower price than that of current market.