Understanding the Electrochemical Induction of Urea to Ammonia on Nickel Based Catalyst in Alkaline Medium

Abstract

Background Ammonia is an important chemical used in many fields such as the fertilizer industry and food industry. One popular application of ammonia is to control nitrogen oxide (NOx) emissions and ammonia has been proved to be an effective reductant to remove NOx, this technology is known as selective catalytic reduction (SCR) and is commercially available. Conventionally, urea can be thermally hydrolyzed or converted into to ammonia on demand as shown in eqn. (1). The electrochemical dissociation of urea has been investigated at the Center for Electrochemical Engineering Research (CEER) for the purpose of producing hydrogen using Ni catalyst, two parallel reactions are found as shown in eqn. (2) and (3).It is proposed that urea to ammonia conversion will be induced with the electrochemically generated NiOOH in alkaline medium. Therefore higher yield of ammonia in eU2A is expected comparing to thermal hydrolysis or urea (THU) under the same conditions. This work will demonstrate that eU2A enables higher reaction rate of ammonia production and experiments will be conducted to understand how the urea to ammonia reaction could be induced through an electrochemical approach. Methodology An electrochemical induced urea to ammonia (eU2A) reactor was developed at CEER for the production of ammonia from urea. In the reactor, both the cathode and anode are Ni-based materials and during the experiment, different voltages will be applied to the electrodes at various temperatures. If no potential is applied to these electrodes, the reactor will work at thermal hydrolysis of urea (THU) mode. The alkaline supporting medium used in this investigation is hydroxide (KOH). The produced ammonia in the experiments will be determined using an ion selective electrode (ISE) and the residual urea concentration in the reactors will be monitored by spectrophotometric methods such as UV-vis spectroscopy [6]. Preliminary data has already shown that eU2A mode enables higher generation rate of ammonia compare to THU mode at 70 °C with the feed of diesel exhaust fluid (DEF) in the presence of 7 M KOH. Raman Spectroscopy will be used to monitor the surface change of Ni electrodes and how urea to ammonia reaction occurs heterogeneously. In addition, liquid FTIR will be utilized to identify and quantify the intermediates and products to further understand eU2A process in the reactor. Figure 1