Production of ammonia from plasma-catalytic decomposition of urea: Effects of carrier gas composition.

Effects of carrier gas composition (N/air) on NH production, energy efficiency regarding NH production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an AlO-packed dielectric barrier discharge (DBD) reactor at room temperature. Results show that the presence of O in the carrier gas accelerates the conversion of urea but leads to less generation of NH. The final yield of NH in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23kV, respectively when air was used as the carrier gas instead of N. From the viewpoint of energy savings, however, air carrier gas is better than N due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and AlO catalyst to give NH and CO as the main products. Compared to a small amount of NO formed with N as the carrier gas, however, more byproducts including NO and NO in the gas phase and NHNO in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma.