Synthesis Of Low-medium Temperature Titanium (cerium) Based SCR Catalyst And The Investigation Of Its Denitration Performance

With the rapid development of social economy,the environmental pollution issue has become serious increasingly.Among them,nitrogen oxides(NO_x)is one of the main culprits of environment pollution.Therefore,the elimination of NO_x is imperative.Among the NO_xelimination methods,the selective catalytic reduction of NO_x with NH₃(NH₃-SCR)is considered as the most promising flue gas control technology.Large-scale thermal power plants have owned relatively mature SCR technology,and main core catalysts were V₂O₅-WO₃(Mo O₃)/Ti O₂.The system catalysts have been applied for stationary source denitration in industry for many years.However,there still exists some disadvantages such as high biological toxicity,high operating temperature,low yield of N₂ and the high conversion rate of SO₂ to SO₃ and so on.In addition,it is difficult to use the high temperature SCR equipment with V₂O₅-WO₃(Mo O₃)/Ti O₂ catalysts as the core directly as a result of the lower exhaust temperature of flue gas(120-300 ?)of industrial boilers,kilns and so on in non-power industry.Hence,exploiting and developing a novel low-temperature de NO_xcatalysts(high efficiency,stability,economical,practical and green environmental protection)to replace the traditional commercial catalysts will effectively solve the major problems for denitration technology at the moment.In view of the above problems,Ti(Ce)-based oxide were taken as the main research object and the catalysts with outstanding denitration performance in the range of medium and low temperature were designed and prepared by doping the different transition metals and rare earth elements or optimizing the morphology/structure of catalysts.The effects of doping various elements or optimizing the structure on the physical and chemical property for the catalysts were investigated by modern characterization methods and in suit DRIFTS.The relationship between the structure and activity was also summarized and arranged.Meanwhile,the reaction mechanism for the catalysts was studied deeply.The main contents are as follows:A serial of novel Ce_mCo_0.1-mTi_0.9O_x(m=0.06,0.07,0.08)mixed-oxide catalysts were synthesized by the sol-gel method.The effects of Ce doping on the NH₃-SCR activity for the Ce_mCo_0.1-mTi_0.9O_x catalysts were investigated.It was found that the Ce_0.07Co_0.03Ti_0.9O_x catalyst had superior de NO_x performance.The characterization results showed that a small amount of Ce doping led to a high dispersion of active species,increased the BET specific surface area and the acidity of catalyst,and reduced the redox ability.This is the main reasons for the improvement of NO conversion,N₂ selectivity,active temperature window and sulfur and water resistance of the catalyst by doping Ce.A series of Ni_mCo_0.3-mTi_0.7O_x(m=0.05,0.10,0.15,0.25)mixed-oxide catalysts were prepared by the sol-gel method.The effects of different Ni/Co ratio,space velocity,H₂O and SO₂ on the de NO_x activity were investigated.The results displayed that the Ni_0.1Co_0.2Ti_0.7O_xcatalyst can maintain 100%NO conversion in the range of 270-450 ? even at high space velocity(120,000 h^-1).The effects of different Ni/Co ratio on the surface structure,redox properties,surface acidity and other physicochemical properties for the Ni_mCo_0.3-mTi_0.7O_xcatalysts were analyzed by various characterization techniques.The Ni_0.1Co_0.2Ti_0.7O_x catalyst showed excellent NH₃-SCR activity which was associated with more surface weak and moderately strong acid amounts,the promotion of the redox cycle(Co³⁺+Ni²⁺(?)Ni³⁺+Co²⁺)and the suitable redox ability derived from the strong interaction between Co and Ni.In situ DRIFTS results revealed that the formed monodentate nitrate and NH₂ species as the main active intermediates were favor of the NH₃-SCR reaction.The existence of H₂O restrained Langmuir-Hinshelwood reaction pathway,which may be the main reason for the catalysts deactivation.The CeTiO_x catalyst(CeTiO_x-T)was synthesized by hydrothermal method using CeTiO_xnanoparticles prepared by the sol-gel method as precursor.The CeTiO_x-T catalyst emerged uniform and hollow nanotube structure with 3.80 nm inner diameter and 7.60 nm outer diameter had superior catalytic activity,SO₂/H₂O resistance and stability.The characterizations results verified that the strong interaction between Ce and Ti over the CeTiO_x-T catalyst induced the formation of short-range ordered Ce-O-Ti species.In such a structure,on one hand,the active species on the surface of the catalyst are highly dispersed,resulting in larger BET specific surface area and more surface Br(?)nsted acidic sites and chemisorption of oxygen,which improved the NH₃-SCR activity of the catalyst.One the other hand,it inhibited the formation of sulfate species,protected Ce active sities and improved the sulfur resistance of the catalyst.In situ DRIFTS and kinetic study results suggested the SCR reaction mainly followed L-H mechanism at low temperature over the CeTiO_x-T catalyst.A series of Nb_mCu_0.1-mCe_0.9O_x(m=0.05?0.06?0.07)mixed-oxide catalysts were synthesized by the citric acid method.The effects of Nb doping on the NH₃-SCR activity for the Nb_mCu_0.1-mCe_0.9O_x catalysts were investigated.Among them,the Nb_0.06Cu_0.04Ce_0.9O_xcatalyst had the best SCR activity,showed higher N₂ selectivity and significant SO₂ and H₂O resistance.The NO conversion reached 100%at 150 ?.The various characterization results revealed that the oxidation ability decreased and the acidity enhanced due to the addition of Nb.The improved acidity by Nb doping was considered as the primary cause for the superior de NO_xperformance of the Nb_0.06Cu_0.04Ce_0.9O_x catalyst at low temperature,which can counteract the negative effects of the reduced oxidation ability on activity.Furthermore,in situ DRIFTS results were applied for the investigation of the reaction process in detail.