低贵金属含量催化剂的制备、表征及在HC-SCR反应中的应用
发布时间：2019-03-10 20:10
【摘要】：氮氧化物一直被视为一种主要的环境污染源。近几年,针对氮氧化物(NOx)的减排问题,相关学者的研究层出不穷,已成为当今科研领域的热点之一。其中,利用碳氢化合物作为还原剂来选择性催化还原NOx(HC-SCR)在众多方案中脱颖而出,具有决定性的优势。因为其所采用的还原剂与烟道废气的成分组成非常相似,从而引起了人们广泛的关注。然而反应过程大多采用贵金属催化剂,其高昂的成本限制了其广泛使用。本文从经济性考虑,结合贵金属催化剂和非贵金属催化剂的优势,在贵金属催化剂的基础上通过添加适量的非贵金属以降低贵金属用量,从而制备出贵金属-非贵金属复合型催化剂,提高催化剂的活性和稳定性,降低催化剂的成本,为其推广应用打下基础。本文通过筛选一系列非贵金属最后选择Mo和Nb作为掺杂金属,主要的研究内容和结果如下:1、Nb掺杂的低贵金属含量催化剂体系考察了将Nb掺杂到Pd/Al_2O_3和Pt/Al_2O_3中对催化剂的催化性能的影响,发现Nb的添加显著地提高Pd和Pt催化剂的催化活性,使Pd/Al_2O_3和Pt/Al_2O_3催化剂的T90分别下降39℃、52℃。随着Nb含量的增加,催化活性先升高后降低,对Pd/Al_2O_3而言Nb的负载量为5%时,催化活性提高最明显;对Pt/Al_2O_3而言Nb的负载量为10%时,催化活性提高最明显。研究发现,Nb的添加,一方面促进了Pd/Al_2O_3和Pt/Al_2O_3催化剂中贵金属颗粒尺寸变小、分散度提高,表面浓度增多,表明存在明显的结构效应;另一方面Nb通过调整载体表面的酸性,同时还提高了表面氧物种的氧化能力和催化剂表面氧浓度,表明存在电子效应。以上两种效应,使得Pd/Al_2O_3和Pt/Al_2O_3催化剂催化还原反应的活性提高。2、Mo掺杂的低贵金属含量催化剂体系考察了将Mo掺杂到Pd/Al_2O_3和Pt/Al_2O_3中对催化剂的催化性能的影响,发现Mo的添加显著地提高Pd和Pt催化剂的催化活性,使Pd/Al_2O_3和Pt/Al_2O_3催化剂的T90分别下降37℃、44℃。随着Mo含量的增加,催化活性先升高后降低,对Pd/Al_2O_3而言Mo的负载量为5%时,催化活性提高最明显;对Pt/Al_2O_3而言Mo的负载量为10%时,催化活性提高最明显研究发现,Mo的添加可以有效使Pd/Al_2O_3和Pt/Al_2O_3催化剂中贵金属颗粒尺寸变小、提高其分散度、增加表面浓度,同时Mo可以通过调整载体表面的酸性来提高了表面氧物种的氧化能力和催化剂表面氧浓度,从而提高Pd/Al_2O_3和Pt/Al_2O_3催化剂催化还原反应的活性。特别指出的是,适当Nb和Mo的添加不仅使Pd和Pt催化剂的活性分别高于2%Pd/Al_2O_3和2%Pt/Al_2O_3催化剂,而且具有较好的稳定性,意味着Nb、Mo的添加可使贵金属的用量至少降低50%,从而大幅降低催化剂成本,为SCR技术在氮氧化物脱除处理中的大规模推广应用创造了有利条件。
[Abstract]:Nitrogen oxides have been regarded as a major environmental pollution source. In recent years, the research on NOx (NOx) emission reduction has become one of the hot spots in the field of scientific research. Among them, the selective catalytic reduction of NOx (HC-SCR) with hydrocarbons as reducing agent has the decisive advantage in many schemes. Because the reducing agent used is very similar to the composition of flue gas, people pay more attention to it. However, precious metal catalysts are mostly used in the reaction process, and their high cost limits their wide use. Considering the economy, combining the advantages of precious metal catalyst and non-precious metal catalyst, this paper reduces the amount of precious metal by adding appropriate amount of non-precious metal on the basis of precious metal catalyst. Thus the precious metal-non-precious metal composite catalyst was prepared, which improved the activity and stability of the catalyst, reduced the cost of the catalyst, and laid a foundation for its popularization and application. In this paper, Mo and Nb are selected as doping metals by screening a series of non-precious metals. The main research contents and results are as follows: 1, The effect of doping Nb into Pd/Al_2O_3 and Pt/Al_2O_3 on the catalytic performance of Nb-doped catalysts with low precious metal content was investigated. It was found that the addition of Nb significantly improved the catalytic activity of Pd and Pt catalysts. The T90 of Pd/Al_2O_3 and Pt/Al_2O_3 catalysts decreased by 39 鈩，
本文编号：2437975
[Abstract]:Nitrogen oxides have been regarded as a major environmental pollution source. In recent years, the research on NOx (NOx) emission reduction has become one of the hot spots in the field of scientific research. Among them, the selective catalytic reduction of NOx (HC-SCR) with hydrocarbons as reducing agent has the decisive advantage in many schemes. Because the reducing agent used is very similar to the composition of flue gas, people pay more attention to it. However, precious metal catalysts are mostly used in the reaction process, and their high cost limits their wide use. Considering the economy, combining the advantages of precious metal catalyst and non-precious metal catalyst, this paper reduces the amount of precious metal by adding appropriate amount of non-precious metal on the basis of precious metal catalyst. Thus the precious metal-non-precious metal composite catalyst was prepared, which improved the activity and stability of the catalyst, reduced the cost of the catalyst, and laid a foundation for its popularization and application. In this paper, Mo and Nb are selected as doping metals by screening a series of non-precious metals. The main research contents and results are as follows: 1, The effect of doping Nb into Pd/Al_2O_3 and Pt/Al_2O_3 on the catalytic performance of Nb-doped catalysts with low precious metal content was investigated. It was found that the addition of Nb significantly improved the catalytic activity of Pd and Pt catalysts. The T90 of Pd/Al_2O_3 and Pt/Al_2O_3 catalysts decreased by 39 鈩，
本文编号：2437975
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