Ce联合Nb/Co改性稀土尾矿催化剂NH3-SCR性能及脱硝机理研究

Study on Denitration Performance and Mechanism of NH3-SCR Catalyst for Modification of Rare Earth Tailings by Ce Combined with Nb/Co

摘要:

白云鄂博稀土尾矿含有Fe、Ce等利于催化脱硝的活性元素，作为天然矿物对环境友好且成本低，是做脱硝催化剂的天然原料，但稀土尾矿催化剂温度窗口较窄(350~450℃)。为拓宽稀土尾矿催化剂的温度窗口，用Ce、Nb、Co改性稀土尾矿，采用水热法制备了一系列Ce-M(Nb、Co)改性稀土尾矿催化剂，探究元素比例及元素种类对脱硝性能的影响。通过BET、XRD、XPS、H2-TPR和NH3-TPD对改性稀土尾矿进行表征分析，并利用In situ DRIFTS 技术对Ce-Co改性稀土尾矿的NH3-SCR机理进行了探究。结果显示，Ce-Nb(2:1)改性稀土尾矿在300~400℃脱硝效率最高为85%，Ce-Co(2:1)改性稀土尾矿在250~400℃脱硝效率能够达到90%。Nb和Co的加入提高了催化剂表面CeCO3F的分散度，暴露更多活性吸附位点。同时，元素之间的相互作用促进了电子的转移，Nb5+的形成阻碍了Ce4+的还原，调节了氧化还原性能，使得Ce-Nb改性稀土尾矿具有优异的N2选择性。而Co的加入提高了催化剂氧化还原能力，使得Co3+增加，进而提高Br?nsted酸性位的吸附强度，NH4+及Co3+-NH2能够首先与NO反应，形成NH3HNO及NH2NO等中间产物，催化剂表面同时遵循E-R机理和L-H机理，E-R机理占主导。

Abstract:

Bayan Obo rare earth tailings contain Fe, Ce and other active elements conducive to catalytic denitration. As a natural mineral, it is environment-friendly and low-cost. It is a natural raw material for denitration catalyst, but the temperature window of rare earth tailings catalyst is narrow (350-450℃). In order to broaden the temperature window of rare earth tailings catalysts, a series of Ce-M (Nb, Co) modified rare earth tailings catalysts were prepared by hydrothermal method. Exploring the effect of element ratio and element type on denitrification performance. In particular, the experimental materials are Bayan Obo rare earth tailings, cerium nitrate, niobium oxalate and cobalt nitrate. The mixed solution of Bayan Obo rare earth tailings and cerium nitrate is made, poured into the reactor, and then placed in the muffle furnace, hydrothermal at 120℃ for 12h. After washing with water and drying at 80 ℃, the Ce modified rare earth tailings catalyst was prepared. The preparation methods of other modified rare earth tailings catalysts are the same. The modified rare earth tailings were characterized and analyzed by BET, XRD, XPS, H2-TPR and NH3-TPD. Finally, the NH3-SCR mechanism of Ce-Co modified rare earth tailings was explored by in situ DRIFTS technology. The steady-state reaction is carried out at 350℃ and the transient reaction is carried out at 50-400℃, which can analyze the existing forms of adsorbed NH3 and NOx species in the catalytic process and their changes with temperature. Therefore, the NH3-SCR reaction mechanism of Ce co modified rare earth tailings catalyst is analyzed. The results show that the maximum denitration efficiency of Ce-Nb (2:1) modified rare earth tailings is 85% at 300-400℃, and the denitration efficiency of Ce-Co (2:1) modified rare earth tailings can reach 90% at 250-400℃. The addition of Nb and Co improved the dispersion of CeCO3F on the catalyst surface and exposed more active adsorption sites. At the same time, the interaction between elements promotes the transfer of electrons. The existence of Nb5+ hinders the reduction of Ce4+, regulates the redox performance, and makes the Ce-Nb modified rare earth tailings have excellent N2 selectivity. The addition of Co improves the redox capacity of the catalyst and increases Co3+. Further, the adsorption strength of Br?nsted acid site is improved. NH4+ and Co3+-NH2 can react with NO first, form intermediate products such as NH3HNO and NH2NO. The surface of the catalyst follows both E-R mechanism and L-H mechanism, and E-R mechanism is dominant.