Development of Metal Oxide Materials for Rapid and Reversible DeNOx by Absorption into Solid Phase

本研究的范围是开发一种新型固体吸附剂，能够在高浓度O_2、CO_2和H_2O共存的情况下，对含有稀氮氧化物的废气进行快速、可逆的脱氧处理。我们发现了MnO_y-ZrO_2和Pt-ZrO_2-Al_2O_3混合金属氧化物在大量氧气存在下作为deNOx固体吸附剂的优良性能。MnO_y-ZrO_2对NOx的吸收能力最高，可以完全去除75 ppm的NOx。脱氧是快速可逆的，通过加热或改变气氛从氧化到还原很容易重复，重现性高。氮氧化物吸附的可能机理是NO在Mn位点被氧化，然后通过形成硝酸锆（Zr）将NO_2吸附到固相中。由于混合氧化物不含碱金属和碱土金属，CO_2和H_2O的共存对材料的脱氧能力没有影响。在还原剂C_3H_8和C_2H_5OH的作用下，MnO_y-ZrO_2的主要解吸物为NO和NO_2，同时还含有大量的N_2和n2o。此外，还发现Pt-ZrO_2-Al_2O_3具有可逆吸收NOx的能力。在还原气氛下，Pt- zro_2 - al_2o_3的脱附组分中N_2的含量高达70%，表明吸附剂负载的Pt催化剂对脱附NOx的选择性还原作用显著。此外，Pt-ZrO_2-Al_2O_3对SO_2的耐受性较好，而MnO_y-ZrO_2在SO_2存在下反复操作，其脱硝能力逐渐下降。综上所述，本文研究的金属氧化物基吸附剂在O_2、CO_2和H_2O存在下，能够在相对较低的温度（如300℃）下将稀NOx快速、完全可逆地吸附到固相中。氮氧化物的吸附-解吸可以通过提高温度或改变气氛由氧化向还原循环进行，从而释放出集中在固体吸收剂中的氮氧化物。少

The scope of this research is to develop a new solid absorbent capable for rapid and reversible deNOx of exhaust gases containing dilute nitrogen oxides in the presence of coexisting gases such as O_2, CO_2, and H_2O at high concentrations.We have discovered excellent ability of MnO_y-ZrO_2 and Pt-ZrO_2-Al_2O_3 mixed metal oxides as solid absorbents for deNOx in the presence of a large amount of oxygen. The highest capability for NOx absorption was found on MnO_y-ZrO_2, which demonstrated complete elimination of NOx as dilute as 75 ppm.DeNOx was rapid and reversible, being easily repeated with high reproducibility by heating or changing the atmosphere from oxidizing to reducing. The plausible mechanism of NOx absorption is oxidation of NO at the Mn site followed by absorption of NO_2 into solid phase via formation of metal (Zr) nitrate. Because the mixed oxide contains no alkali or alkaline earth metals, coexisting CO_2 and H_2O had no influence on the deNOx ability of the material. Th … More e major species desorbed from MnO_y-ZrO_2 were NO and NO_2, while they also contained a substantial amount of N_2 and N_2O when exposed to the reducing atmosphere by use of reducing agents such as C_3H_8 and C_2H_5OH.Moreover, Pt-ZrO_2-Al_2O_3 was also found to be capable for reversible NOx absorption. Desorbed species from Pt-ZrO_2-Al_2O_3 under the reducing atmosphere was revealed to consist of as much as 70% of N_2, indicating that selective reduction of desorbing NOx is significant on the Pt catalyst supported on the absorbent. Furthermore, Pt-ZrO_2-Al_2O_3 was revealed to be highly tolerant to SOx in contrast to MnO_y-ZrO_2, whose deNOx capacity gradually decreased by repeated operation in the presence of SO_2.In conclusion, the metal oxide-based absorbents investigated in the present research were confirmed to be capable for rapid and completely reversible absorption of dilute NOx into solid phase at relatively low temperature such as 300ﾟC in the presence of O_2, CO_2, and H_2O.The sorption-desorption of NOx can be cycled by elevating temperature or changing the atmosphere from oxidizing to reducing, resulting in releasing NOx having concentrated in the solid absorbents. Less