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

Abstract A compound fertilizer with NH 4 H 2 PO 4 and KH 2 PO 4 offer significant advantages in enhancing both crop yield and quality. Ammonia (NH 3 ) 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 (KH 2 PO 4 and NH 4 H 2 PO 4 ) and 232 L of pure H 2 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 NO 2 − formation in electrochemical process. By maintaining a precise molar concentration ratio of urea to NO 2 − at 1/2 in electrolyte, urea can completely react with NO 2 − to form N 2 , while CNO − can be converted into NH 4 + to form compound fertilizer in the second step of H 3 PO 4 treatment, achieving complete conversion of urea without by‐products formation. This method remarkably reduces H 2 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.