【作者】 王卉；

【导师】 郑小明；

【作者基本信息】 浙江大学 ， 物理化学， 2014， 博士

【摘要】 氮氧化物(NOx)作为主要的大气污染物之一,对环境的破坏作用极大。近年来,随着低温等离子体化学的开拓与发展,利用低温等离子体和催化剂协同脱除氮氧化物的方法已引起学术界的广泛关注。本论文通过对低温等离子体协同吸附催化剂脱除NOx反应的研究,实现了模拟烟气条件下的NOx高效脱除,为等离子体协同催化剂在脱硝反应中的实际应用提供了有益的探索和发展。主要成果如下：(1)创造性地提出了低温等离子体协同吸附催化剂脱除NOx的反应,在室温下实现了模拟烟气中NOx的高效脱除同时又显著节省了能耗,具有巨大的潜在应用价值。(2)研究了天然丝光沸石(NMOR)吸附催化剂上NO的吸附性能和吸附机理。天然丝光沸石在改性之后对NO的吸附性能明显提高。其中,酸处理过程能够除去堵塞在天然丝光沸石孔道中的杂质,使沸石的孔道变得畅通；而金属离子交换过程则提高了NMOR对于NO的氧化性。与此同时,考察了实际烟气成分对于NMOR上NO的吸附影响。由于共吸附和化学作用,O2能够提高NMOR上NO的吸附；由于竞争吸附或毒化吸附,H2O, CO2, SO2对于NO的吸附则会造成消极的影响。其中Ni-NMOR对于NO的饱和吸附量高达1.20mmol/g,优于众多文献报道的人工合成吸附剂。原位红外结果表明,Ni-NMOR一方面可以促进NO氧化为NO2,另一方面又易于和NO形成二齿配体,因此对于NO的吸附性能很优异。在Ni-NMOR上,初步探索了低温等离子体协同吸附催化剂分解脱除NOx的反应,验证了该脱硝方案的可行性。(3)研究了以甲烷为还原剂作用下低温等离子体协同吸附催化剂H-ZSM-5脱除NOx的NSR反应。H-ZSM-5在吸附阶段起到吸附NOx的作用,在放电阶段则起到催化NOx脱除的作用。重点考察了还原剂CH4浓度、Oz浓度、气体空速和等离子体放电功率等对NOx脱除反应的影响,并对反应机理进行了相应的分析和探讨。等离子体中能量密度是影响NOx脱除的首要因素,较高的能量密度有益于NOx脱附和转化。高浓度的O2与N2发生的化合反应则是干扰NOx脱除的主要因素。CH4的引入,能显著提高NOx的转化。一方面,一定量的CH4在NOx脱除反应中起到还原剂的作用；另一方面,CH4的氧化能够消耗体系中的02,抑制逆反应的发生。同时,对富氧条件下低温等离子体协同H-ZSM-5脱除NOx的循环反应也做了评价,NOx的转化率始终能够维持在90%以上。XRD和SEM结果表明,H-ZSM-5的晶型结构维持稳定。(4)为进一步适应甲烷为还原剂的低温等离子体协同吸附催化剂ZSM-5脱除NOx反应的实际应用需要,详细地研究了水蒸气对于该反应的影响及其作用机理,并最终提出解决方案。在反应的吸附阶段,H20和NOx在ZSM-5表面发生竞争吸附从而降低了ZSM-5对于NOx的吸附量。Ni2+改性后则可显著加强ZSM-5的抗水性。在反应的放电阶段,H2O的作用机理较为复杂。首先,大量的吸附水消耗高能电子,降低体系的能量密度,不利于NOx脱附和转化；其次,在等离子体作用下H20与N2反应生成NOx；再次,在等离子体作用下H20与还原剂CH4反应,CH4被过度消耗因而无法实现理想的脱硝效果。提高体系的能量密度以及增加原料气中的CH4浓度能够恢复NOx的脱除效率至97%。(5)为适应大型电厂排放烟气的净化,研究了以氨为还原剂作用下低温等离子体协同吸附催化剂脱除NOx的反应。考察了还原剂NH3浓度、O2浓度、NOx吸附量和等离子体放电功率等对NOx脱除反应的影响,并对反应机理进行了相应的分析和探讨。相比于以CH4为还原剂或者无还原剂的条件下,以NH3为还原剂可以在相对较低的放电功率下实现吸附态的NOx高效脱附与转化。此外,高浓度H20引入反应体系后,NOx转化为N2的转化率基本不变,这是十分有意义的结果。有水蒸气参与的循环实验,其NOx转化率始终维持在90%以上,并且H-ZSM-5的晶型结构依旧保持稳定。更多还原

【Abstract】 As a major source of air pollution, nitrogen oxides NOx mainly emitted from mobile and stationary sources. They are main contributors to a series of environmental issues. Nowadays, the nonthermal plasma (NTP) technology has been researched widely for NOx removal because NTP can activate molecules even at room temperature. The present work is focused on the study of a combined adsorption-discharge plasma process for NOx removal. The efficiency of this new process for NOx removal could achieve95%at ambient temperature. The main contents and results are as follows:(1) A combined adsorption-discharge plasma process was proposed for DeNOx in simulated flue gas at room temperature. The efficiency of this new process for NOx removal could achieve95%under the condition of simulated flue gas. The energy efficiency of the new process proposed was improved. Thus we believe that this new deNOx technology has broad application prospects.(2) Natural mordenite (NMOR), modified by acid treatment and ion-exchange, was employed for NO adsorption in the present study. The NO storage capacity of modified NMOR was greatly improved compared with its original correspondents, mainly due to the preservation of crystalline structure and the improvement of surface area of NMOR. Among all the modified NMOR, Ni-NMOR exhibited the highest adsorption capacity for NOx (1.20mmol/g). The influence of the main ingredients in flue gas on the storage capacity of NMOR for NO had also been investigated. H2O, CO2and SO2all displayed negative impact on NO adsorption due to their competitive adsorption on the surface of NMOR with NO, while the presence of02greatly improved the adsorption of NO because of the formation of NO2. Moreover, Ni-NMOR exhibited high efficiency for NOx removal through the NOx adsorption-plasma discharge process.(3) NOx storage and reduction with CH4by a plasma process was proposed for (4) NOx removal at ambient temperature. H-ZSM-5acted as an adsorbent for NOx at the adsorption stage and a catalyst at the discharge stage. The influence factors including the discharge power, flow rate, O2concentration and CH4concentration were investigated. High energy density is beneficial to NOX conversion. Obviously, CH4enhanced the total NOx conversion. On one hand, a suitable amount of CH4could play a role as a reducing agent in NSR; on the other hand, CH4oxidation consumed O2to restrain the reverse reaction of NOX decomposition. NOx removal via cyclic operation has also been investigated, maintaining efficieniency above90%.(5) The effect of water vapor on NOx storage and reduction in combination with non-thermal plasma was investigated. H2O could lower NOX adsorption capacity of H-ZSM-5at the adsorption stage, due to the competitive adsorption between H2O and NOx on HZSM-5. Ni-ZSM-5exhibited better resistance to H2O than H-ZSM-5. At the discharge stage, the introduction of H2O decreased the total NOx conversion. When increasing the CH4concentration and the discharge power, the conversion of adsorbed NOx to N2moved up to97.4%.(6) NOx storage and reduction with NH3by a plasma process was proposed for NOx removal in simulated flue gas. The influence factors including the discharge power, flow rate, O2concentration and NH3concentration were investigated. The introduction of NH3is able to reduce the energy consumption for the discharge process, while raising the total NOx conversion. Moreover, H2O did not affect the NOx conversion in this process. NOx removal via cyclic operation has also been investigated, maintaining efficieniency above90%.更多还原