Abstract
This review paper provides an overview of the use of hydrogen (H2) gas towards the selective catalytic reduction of nitrogen oxides (NOx) under strongly oxidizing conditions found in many industrial flue gas streams and in the exhaust emissions of diesel-powered vehicles. Patenting activities in the last 15 years are discussed. The advantages in using the H2-SCR of NOx control technology especially at low-temperatures as to the current NH3-SCR technology are also discussed. Regarding the stationary NOx control applications, Pd-based catalysts exhibit NOx conversion and N2-selectivity values in the 80-95% range, depending on the chemical promoter and support composition used have been reported. On the other hand, Pt-based catalysts present lower NOx conversion and N2-selectivity values (<90%) especially when 10-20 vol% water is present in the flue gas stream. For mobile applications, different formulations of Pd-based catalysts (support and promoter chemical composition) have been reported with NOx conversions higher than 85%. The issue of hydrogen supply has been tackled through the development of on-board hydrogen generation technologies, such as plasma reforming and partial oxidation of diesel fuel.
Keywords: H2-SCR, hydrogen selective catalytic reduction, NH3-SCR, NOx control, supported-Pd catalyst, supported-Pt catalyst
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