Simultaneous Reduction Of NO And SO_x From FCC Regenerator Flue Gas

Chinese economy has made great progress since the reform and opening-up policy.However,the rapid development of it has brought a series of environment problems,such as acid rain,photochemical smog,etc.,which are caused by the excess emission of NO_x and SO_x pollutents.NO_x and SO_x emitted from fluidized catalytic cracking?FCC?make a contribution of over 40%of which emitted in the whole refining process.Therefore,it is very important to reduce the emission of the pollutents to protect the environment.So far,the published literatures about simultaneous reduction of NO_x and SO_x are very few?no more than 20related literatures published since 1999?.Based on the background,this study focused on the simultaneous reduction of NO and SO₂ with CO,H₂ and CH₄.And the mechanism was deeply investigated.Firstly,we conducted a preliminary screening of the active metal elements involved in the desulfurization and/or denitrification with CO reported in the relevant literatures,and found Fe-Zr O_x mixed oxide was the target.Then,after conducting the optimization of the conditionds,it found that Fe?0.4?-ZrO_x designed with critic method and calcinated at 400?exhibited an excellent performance with nearly complete NO and SO₂ removal,and 100%selectivity of N₂ and S above 350?at a very high space velocity of 72,000 ml/g·h(91,000h^-1).In addition,this catalyst exhibited a fairly good water resistance with no activity decrease above 450?in the presence of 6.5%water.Moreover,the catalyst showed an excellent stability with almost no activity decline even after 88 h evaluation test because of the retained good redox property at the certain temperature?450??.Compared with pure FeO_x,the enhanced catalytic activity was attributed to the highly increased surface area,amorphous iron phase,more redox centers and acidic sites,higher surface iron concentration and molar ratio of Fe³⁺to Fe²⁺.The in-situ DRIFTS results and XPS analysis of used catalyst suggested that the applicable mechanism of this study was quite different from the conventional mechanisms such as the redox and COS intermediate mechanisms.It could be explained that in the first step SO₂ predominantly adsorbed on surface and got it reduced and sulfated,followed by NO interacting with the sulfated surface and resulted in the oxidation of some sulfites into sulfates.Then CO attacks the surface further and some vacancies produced,which were in favor of the redox process.NO or/and SO₂ reacted with the vacancies further for another cycle.The sulfur products may embed into the vacancies or/and the lattice and resulted in the transform of metal oxides into metal sulfides?FeS and/or FeS₂?,then COS intermediate process may happen.The second part was H₂ used as reductant.After the similar screening process,it found Cr?0.4?-NiO_x/HZSM-5 achieved complete NO removal and over 90%SO₂ conversion with96%N₂ and 100%S selectivity above 400?at a space velocity of 30,000 ml/g·h.And the catalyst showed no activity decrease even the space velocity increased to 60,000 ml/g·h.The enhanced activity was owed to the addition of Cr resulting in highly disepersing of active ingredient Ni on the support,better redox properties,more and stronger acidic sites and more Ni³⁺ions with higher binding energy dispersed on the surface.Finally,we investigated the system of CH₄.It is a pity that no expected result achieved in the temperature range of 300⁵00??NO and SO₂ conversion are less than 68%and 26%respectively?.Overall,it is still quite difficult to activate methane for the reduction of NO and SO₂,especially at relatively low tempeture?<500??,which needs further exploration.