# Development of a Novel De-NOX Technology for the Aftertreatment of Ship Exhaust Gases
## 1 Introduction  
According to [PERSON] et al. [1], the total emissions from transport-related annual emissions and fuel consumption in Tg/year are presented in Table 1. The contribution of each sector is presented in brackets next to the number of emissions and fuel consumption. As can be clearly seen from Table 1, the shipping industry is a major contributor in the main gas pollutant emissions globally. In January 2011, a total of 103,392 commercial ships were in service with a combined tonnage of 1396 million Dead Weight Tornage (DWT). Looking at individual sectors, oil tankers accounted for 475 million DWT and dry bulk carriers for 532 million DWT, representing an annual increase of 5.5% and 16.5%, respectively; the containership fleet reached 184 million DWT in January 2011 (8.7% over 2010). The fleet of general cargo ships stabilized at 109 million DWT. The tonnage of liquefied gas carriers continued to grow, reaching 43 million DWT (an increase of 6.6%) [2]. During the past few years, the International Maritime Organization (IMO) has issued strict regulations in order to minimize these emissions, deriving mainly from newly constructed vessels [1; 2; 3]. The IMO has adopted these new regulations in Marine Pollution Legislation (MARPOL) Annex VI for progressive reduction of Nitrogen Oxides (NO\({}_{\rm x}\)),Sulphur Oxides (SO\({}_{\rm x}\)) and Particulate Matter (PM). The new regulations require ships to achieve a SO\({}_{\rm x}\) reduction equivalent to 0.1% sulfur fuel since 2015. This requirement can be met by using more expensive, low sulfur fuel or by using marine diesel scrubbers. Considering that the average age of the world fleet of propelled sea-going merchant ships of no less than 100 gross tons is 22 years and the average age of the world cargo-carrying ships is 19 years [4], it is important to implement end of pipe technologies that prevent air pollution from NO\({}_{\rm x}\), SO\({}_{\rm x}\) and PM gases since significant modifications on these ships cannot be easily accomplished. The abatement of SO\({}_{\rm x}\) and particulates emitted from ships could be considered an easier task, since quite mature and technologically ready solutions are already available in the market and could be utilized for this purpose. Open- or closed-circuit scrubbers were found to achieve very high SO\({}_{\rm x}\) removal efficiencies, reaching up to 99%, even when using Heavy Fuel Oil with 3.5% sulfur content [5]. Moreover, under certain conditions, scrubbers were found to be also efficient towards a significant reduction in PM emissions [6]. In addition, as long as SO\({}_{\rm x}\) are removed from the exhaust stream, particulates can be eliminated by using oxidative catalysts or catalytic filters, similar to those already used on diesel-powered automobiles [7]. On the contrary, the abatement of NO\({}_{\rm x}\) from ship exhaust gases is not a straightforward task. Available commercial technologies, which have been developed for the reduction of NO\({}_{\rm x}\) emitted from mobile (TWC) or stationary (urea-SCR) sources, are either not suitable or cannot be easily adapted to perform equally well on ships. Selective Catalytic Reduction using urea as a reducing agent (Urea-SCR) is the only technology which is attracting some interest in terms of commercial application [8]. However, recent reviews report that deficiencies in the overall system design with a combination of technical issues (related with the use of urea), maintenance access problems and untrained operators with inadequate understanding of the SCR process have led to inefficient, costly and unsafe operations [9]. Since most of the above problems derive from the use of urea (ammonia) as a reducing compound in the SCR process, it can be claimed that an alternative reducing agent that will be less corrosive and toxic and more \"friendly\" to the environment (as compared to ammonia/urea) is needed.