Effect Of Ce Modifcation On In-situ Synthesized Cu-SSZ-13 For NO_x Removal From Diesel Vehicle Exhausts

Growing concerns over climate change, our ecological footprint, and human health have resulted in more and more strict regulations to control the release of pollutants into the atmosphere, especially for the exhaust of motor vehicle. Owing to their efficiency and durability, diesel engines have seen their fair share of use in road transport. Although more efficient compared to their gasoline counterpart, diesel engines still form air pollutants as a consequence of the use of a fossil fuel, in which NOx is one of primary concern. Studies within European member countries have confirmed that about 40% of the total NOx released into the atmosphere comes from road transport alone, of which 75% is from the use of diesel engines. In order to meet the increasingly strict emission standards, the researchers have made unremitting efforts for cleaning automobile exhaust streams. Selective catalytic reduction (SCR) is an effective and promising technology for the reduction of NOX. With catalyst for SCR, the need to have high catalytic activity, wide active temperature window and good thermal stability etc. is of significant importance to utility.In this study, we prepared Cu-SSZ-13 catalyst by in-situ hydrothermal synthesis using Cu-TEPA as template, and optimized the catalyst preparation time, the effect of hydrothermal aging on the catalyst activity, selectivity of N2 and its physical structure were also investigated. In addition, the catalyst samples modified by Ce were researched for perform better catalytic activity, hydrothermal stability. The mechanism of modifying catalyst with Ce was also studied. The main conclusions of this work are as follows:(1) The Cu-SZZ-13 samples were prepared by in situ hydrothermal synthesis under different crystallization time. The Cu-SSZ-13 crystallized 72 h performed best deNOx activity and hydrothermal stability. The conversion of NOx of fresh samples could up to 80% in temperature range of 320℃to 570℃ under very high space velocity (640,000 h-1). The samples after further aging treatment (800℃aged 20 h) performed excellent NOx reduction efficiencies (above 90%) in the active temperature window range of 220℃to 560℃.(2) The further aging treatment made the Cu species in the catalyst changed, framework dealumination occurred and the morphology of samples destroyed, which resulted in decrease of catalytic activity.(3) The catalytic activity of samples modified by Ce increased to a certain extent (to maximum 20%), the sample with ion exchanged 2 h showed the best catalytic activity and anti-aging properties. Moreover, no more N2O was found.(4) The introduction of Ce (about 1%) not only changed the active center Cu migration or transformation route and degree of catalyst in the process of hydrothermal aging treatment, but also had an effect of stabilization on zeolite framework which could abate the framework dealumination action.