Catalytic Oxidation Of Nitric Oxide Under High Humidity At Ambient Temperature

The nitrogen oxide?NO_x?emission from marine engine has following features:high-concentrated NO,low-concentrated O₂ and SO₂,high moisture.Compared with the existing technologies,Gas-phase Oxidation-Alkali Absorption is favorite way to treat marine amond-NO_x pollution.Thus,the catalyst for NO oxidation is necessary to adapt to its severe condition.High silica HZSM-5 holds catalytic performance for NO oxidation at low temperature,and excellent water resistance.In order to improve its NO conversion,we modified ZSM-5 with metal ion,and studied its sulfur tolerance.The results indicates the modification with alkali metallic ion would introduce alkaline sites to the surface,and is against the desorption of NO₂.The metallic ion Co²⁺presents obvious catalytic action for NO oxidation,due to its valence d-ions.However,its sulfur tolerance is poor,even modified with sulfuric acid.We also modified ZSM-5 with sulfuric acid,its sulfur tolerance couldn't be improved,and made its active declined.The pure silica molecular sieve Silicalite-1 holds also good water resistance,and has been applied to catalyze NO oxidation in this paper.The study reveals that O₂have not been adsorbed on the surface of Silicalite-1,and reacted directly with NO that has been adsorbed.Competitive adsorptions exist on the surface between H₂O and NO,and lead to long equilibration time and low conversion for NO oxidation.SO₂ has not accumulated by chemical deposition,and no influence on NO oxidation.The stability test for Silicalite-1 has been done with time-on-stream.The NO conversion keeps 52%for 60h.This meets the requirements of Alkali Absorption after Gas-phase Oxidation.Furthermore,after the test,the composition,structure and surface groups of the spent catalyst have no obvious changes.These results indicate that Silicalite-1 has not only excellent catalytic performance for NO oxidation,but also good water resistance and sulfur tolerance.For getting better catalytic performance,we have designed the pores of Silicalite-1.The results indicate that the micro-spaces are provided by the opening hollow pores show obvious catalytic action for NO oxidation.However,it is not benefits for the diffusion of NO,and leads to the longer equilibration time.For the macro hollow pores,the catalyst present short equilibration time,and high NO conversion due to its high surface and amounts of active sites.