【摘要】：氮氧化物一直被視為一種主要的環(huán)境污染源。近幾年,針對氮氧化物(NOx)的減排問題,相關(guān)學(xué)者的研究層出不窮,已成為當(dāng)今科研領(lǐng)域的熱點(diǎn)之一。其中,利用碳?xì)浠衔镒鳛檫�原劑來選擇性催化還原NOx(HC-SCR)在眾多方案中脫穎而出,具有決定性的優(yōu)勢。因?yàn)槠渌捎玫倪�原劑與煙道廢氣的成分組成非常相似,從而引起了人們廣泛的關(guān)注。然而反應(yīng)過程大多采用貴金屬催化劑,其高昂的成本限制了其廣泛使用。本文從經(jīng)濟(jì)性考慮,結(jié)合貴金屬催化劑和非貴金屬催化劑的優(yōu)勢,在貴金屬催化劑的基礎(chǔ)上通過添加適量的非貴金屬以降低貴金屬用量,從而制備出貴金屬-非貴金屬復(fù)合型催化劑,提高催化劑的活性和穩(wěn)定性,降低催化劑的成本,為其推廣應(yīng)用打下基礎(chǔ)。本文通過篩選一系列非貴金屬最后選擇Mo和Nb作為摻雜金屬,主要的研究內(nèi)容和結(jié)果如下:1、Nb摻雜的低貴金屬含量催化劑體系考察了將Nb摻雜到Pd/Al_2O_3和Pt/Al_2O_3中對催化劑的催化性能的影響,發(fā)現(xiàn)Nb的添加顯著地提高Pd和Pt催化劑的催化活性,使Pd/Al_2O_3和Pt/Al_2O_3催化劑的T90分別下降39℃、52℃。隨著Nb含量的增加,催化活性先升高后降低,對Pd/Al_2O_3而言Nb的負(fù)載量為5%時(shí),催化活性提高最明顯;對Pt/Al_2O_3而言Nb的負(fù)載量為10%時(shí),催化活性提高最明顯。研究發(fā)現(xiàn),Nb的添加,一方面促進(jìn)了Pd/Al_2O_3和Pt/Al_2O_3催化劑中貴金屬顆粒尺寸變小、分散度提高,表面濃度增多,表明存在明顯的結(jié)構(gòu)效應(yīng);另一方面Nb通過調(diào)整載體表面的酸性,同時(shí)還提高了表面氧物種的氧化能力和催化劑表面氧濃度,表明存在電子效應(yīng)。以上兩種效應(yīng),使得Pd/Al_2O_3和Pt/Al_2O_3催化劑催化還原反應(yīng)的活性提高。2、Mo摻雜的低貴金屬含量催化劑體系考察了將Mo摻雜到Pd/Al_2O_3和Pt/Al_2O_3中對催化劑的催化性能的影響,發(fā)現(xiàn)Mo的添加顯著地提高Pd和Pt催化劑的催化活性,使Pd/Al_2O_3和Pt/Al_2O_3催化劑的T90分別下降37℃、44℃。隨著Mo含量的增加,催化活性先升高后降低,對Pd/Al_2O_3而言Mo的負(fù)載量為5%時(shí),催化活性提高最明顯;對Pt/Al_2O_3而言Mo的負(fù)載量為10%時(shí),催化活性提高最明顯研究發(fā)現(xiàn),Mo的添加可以有效使Pd/Al_2O_3和Pt/Al_2O_3催化劑中貴金屬顆粒尺寸變小、提高其分散度、增加表面濃度,同時(shí)Mo可以通過調(diào)整載體表面的酸性來提高了表面氧物種的氧化能力和催化劑表面氧濃度,從而提高Pd/Al_2O_3和Pt/Al_2O_3催化劑催化還原反應(yīng)的活性。特別指出的是,適當(dāng)Nb和Mo的添加不僅使Pd和Pt催化劑的活性分別高于2%Pd/Al_2O_3和2%Pt/Al_2O_3催化劑,而且具有較好的穩(wěn)定性,意味著Nb、Mo的添加可使貴金屬的用量至少降低50%,從而大幅降低催化劑成本,為SCR技術(shù)在氮氧化物脫除處理中的大規(guī)模推廣應(yīng)用創(chuàng)造了有利條件。
[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，

本文編號：2437975