Study On Poisoning Of V₂O₅/TiO₂ Catalyst And Development Of A Novel Poisoning-resistant Catalyst

The selective catalytic reduction of NOx with NH3 as reductant is most efficient and widely technology for abating NOx emitted from stationary power stations at present. As the core of SCR technology, catalysts are the main factor affecting the NOx removal efficiency and economical efficiency of the whole SCR system. Poisoning is inevitable for SCR catalysts in the actual application process and relates with the fuel characteristics intimately. The burning coal in power plant of our country is complex and diverse, containing a variety of components which may lead to poisoning and deactivation of catalysts. Therefore, the study on the poisoning order of components containing in coal for SCR catalysts is important and meaningful.The key research point of the present work is taking V2O5/TiO2 SCR catalyst as research object, studying the single poisoning order as were as the compound poisoning order of some representative components detected in the burning coal of power plant in our country. The SCR catalyst was improved to be a novel catalyst with good resistance to poisoning. The main results are shown as following:1. The effect of K, Na, Ca, Pb oxides and salts on the NO conversion of V2O5/TiO2 catalyst was studied. The results show that potassium has the strongest poisoning effect on the catalysts among all four metals whatever in form of oxides or salts. K2O and Na2O may inhibit the reducing capability of V2O5 on the surface of V2O5/TiO2 catalyst, while CaO and PbO have little effect on the reducing capability of V2O5. The deactivation of V2O5/TiO2 catalyst by KCl and NaCl are much stronger than K2SO4and Na2SO4. The decreases of NO conversion for catalysts doped with K2SO4and Na2SO4 are approximate, which is according to the leading role of the effect of SO42- on catalysts.2. The compound poisoning order of K, Na, Ca, Pb oxides and chlorides on V2O5/TiO2 catalystwas investigated. When two kinds of oxides were doped on the catalysts simultaneously, the interaction between the two components will weaken the role of one component on catalyst deactivation, especially when CaO was doped. PbO has the same. The catalyst doped with CaO and PbO has the same activity as fresh V2O5/TiO2 catalyst above 400℃. Unlike the compound poisoning order of metal oxides, the deactivation level of catalysts by salts depends on the contents of KCl, higher KCl content leads stronger catalyst deactivation.3. The effect of the Sb and Nb additives on the V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3 was investigated. The experimental results show that Nb can improve the activity of V2O5/TiO2 catalyst. Higher Nb loading led to higher N2 selectivity at high temperature above 350℃. The optimal Nb loading is 6 (atomic ratio to V). Sb can improve the activity of V2O5/TiO2 catalyst at low below 350℃. Higher Sb loading cannot improve the activity but lead to more N2O generated from the reaction at high temperature above 350℃. As both of the catalyst activity and the value of N2 selectivity were considered, the optimal Sb loading is 0.5 (atomic ratio to V).4. The effect of simul-doping of Sb and Nb on the V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3 was investigated. The experimental results show that simul-doping of Sb and Nb can improve the activity of V2O5/TiO2 catalyst highly, while ensuring the N2 selectivity of the catalyst at high temperature above 350℃. The simul-doping of a bit of Sb and Nb can gain the same effectiveness as a lot of Nb was doped, which is conductive to the economical efficiency of catalyst. According to the means of XPS, the doping of Sb and Nb may increase the chemisorbed oxgen and weakly boned oxygen species on the surface of catalyst, which might be one of the reasons to improve the catalytic activity.5. The effect of some representative poisoning components on catalytic activity of V-Sb-Nb/TiO2 catalyst improved form V2O5/TiO2 catalyst was investigated. According to the comparison of V2O5/TiO2 catalyst and V-Sb-Nb/TiO2 catalyst, it can be seen that the decrease of catalytic activity for V-Sb-Nb/TiO2 catalyst doped with poisoning components is much lower than the decrease of catalytic activity for V2O5/TiO2 catalyst doped with poisoning components. The catalytic activity of V-Sb-Nb/TiO2 catalyst doped with poisoning components is still higher than the fresh V2O5/TiO2 catalyst. This means that the V-Sb-Nb/TiO2 catalyst has good anti-poisoning ability from metal oxides and salts.