| Nitrous oxides in automobile exhaust emissions is the main source of air pollutant. The technology of selective catalytic reduction (SCR) is an effective method to removal NOX at the condition of oxygen-rich atmosphere. At present, the researches of diesel emission catalysts have been reported widely, but there are many disadvantages needed to be solved.The cordierite honeycomb with low pressure drop, good mechanical strength and durability is widely used as support in diesel exhaust purification catalyst. So how to apply powder catalyst to the cordierite catalyst and make strong-durable monolithic catalysts becomes a important issue to scientists. In this paper, Fe-Mo/ZSM-5power catalyst was selected as active component for its excellent catalytic reduction of NOX performance and deposited it to monolithic. The impacts of different surfactants and different preparation methods to the monolithic catalyst have been researched, the coating process was optimized, and the SCR catalytic properties of the monolithic catalysts were tested. Meanwhile, the coating homogeneity, micropore structure and surface morphology of the honeycomb monolithic catalyst were analyzed by XRD, N2-adsorption, SEM and other techniques in order to ensure the connection between the structure composition and catalytic activities, which offers experimental foundation and theoretical basis for the monolithic catalyst. The main results are summarized as follows:(1) When adding15%PEG4000, the coating efficiency and the coating stability of slurry reached the best, and the monolithic catalyst also exhibited the best catalytic activity, with NOx conversion of more than95%in the reaction temperature range of160-430℃.(2) Different coating methods have greatly effect on the monolithic catalysts. Under the action of ultrasonic wave, a large number of tiny bubbles which produce instant high temperature and pressure in the process of growth and burst generated in the coating slurry, those special environment may contribute the coating quality of power catalysts on the surface of cordierite and make the monolithic form more microstructures which make for the improvement of the activities of monolithic catalysts. Through the contrast experiment, the monolithic catalysts prepared by the ultrasonic assisted dip-coating method of coating temperature of55℃,5min for each coating time and three times can meet the require of the coating and loss rate.(3) The result of XRD-analyse showed that owing to a small amount of active constituents such as Fe and Mn, they can be highly decentralized on the surface of HZSM-5. Obvious HZSM-5and cordierite carrier characteristic peak appeared on honeycomb catalyst, which proves good adhesion has been formed between catalyst and the carrier. And the stronger diffraction of HZSM-5, the weaker diffraction peak of cordierite, the better activity of the samples. The uniformity and coverage of coating layer on the PEG-15samples are significantly better than other samples, which help to improve the activity of the monolithic catalyst.(4) N2adsorption-desorption testing showed that Samples with larger surface area and more microporous structure have higher SCR catalytic activities, while more macroporous structure of the catalysts have the opposite effect.(5) The SEM results figure that Fe-Mn/ZSM-5catalyst coats uniformly on the surface of the cordierite and form rich, uniform microporous when15%PEG is added under the condition of ultrasonic wave. |
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