Modified Mn/Al2O3 catalyst for catalytic oxidation of zero-valent mercury study

Title: Modified Mn/Al2O3 catalyst for catalytic oxidation of zero-valent mercury study
　　Author: Li Jianfeng
　　Degree-granting units: Shanghai Jiaotong University
　　Keywords: zero-valent mercury;; catalyst;; modification;; sulfur;; low
　　Summary:
　　Mercury pollution due to its volatile, bio-accumulative and persistent characteristics of strong air pollution is increasingly becoming areas of research focus. China's coal consumption is large and high levels of mercury in coal, so coal has become a major source of anthropogenic mercury emissions. Control of coal-fired flue gas mercury is the main way mercury emissions, Neodymium Magnets mercury in the flue gas is usually particulate mercury, gaseous divalent mercury and mercury in three forms exists zero price. Dust particulate mercury can get most of the capture device, divalent mercury in the desulfurization unit can be absorbed by the desulfurization solution, both relatively easy to control, and flue gas mercury because of its zero-valent gaseous insoluble in water and are difficult to use Some smoke pollution control devices removed. Therefore, the removal of zero-valent mercury flue gas mercury emission control is important and difficult.
　　Flue gas mercury emission control technology is an important principle is to maximize use of existing flue gas pollution control devices to achieve the purpose of simultaneous removal of mercury. Therefore, raising the price of zero to the other two forms of mercury and mercury conversion rate is the main direction of current research. This study is the core of zero-valent catalytic oxidation of mercury, the flue gas dust removal devices that try after using modified metal oxide catalyst has been artificially increased by adding zero-valent mercury oxidation rate of HCl, oxidation to form the bivalent mercury, and then later remove the desulfurization unit.
　　Catalyst based on pre-screening group, selected for this study manganese oxide as the main catalyst. First of temperature and gas composition on the catalytic performance, the results show that: Mn/Al_2O_3 zero-valent mercury catalyst catalytic activity of the best reaction temperature is 300 ℃, under the same conditions, low temperature catalytic oxidation efficiency is much lower than 300 ℃; SO_2 gas fractions greater inhibition of Mn/Al_2O_3 catalyst.
　　In order to improve Mn/Al_2O_3 catalyst at low temperature catalytic performance and resistance to sulfur, this paper focuses on the modification of the catalyst, which has selected four elements and four rare earth transition metal elements doped catalyst for Mn/Al_2O_3 complex modification. Through at different temperatures, HCl concentration, SO_2 concentration, the amount of doping elements modified under the conditions of the study found that different elements of the modified Mn/Al_2O_3 metal catalyst performance, especially under conditions of low temperature catalytic performance and resistance to sulfur are There are varying degrees of improvement. Transition metal-modified catalysts show the following trends: Mo> W> Cu> Sr; rare earth elements modified catalysts show the following trends: Ce> La> Sm> Y.
　　Elements of the modified Mn/Al_2O_3 Mo catalyst at low temperature 150 ℃, the adsorption of mercury on the zero-valent half-time from 34min http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets penetration increased to 2000min, oxidation efficiency of 35%, which leads to SO_2, its catalytic oxidation efficiency decreased only 11%; under the same conditions, Ce Mn/Al_2O_3 elements of the modified catalyst, the adsorption of mercury on the zero-valent half-penetration time increased to 1000min, oxidation efficiency of 26%, which leads to SO_2, the The catalytic oxidation efficiency dropped only 2%. Mo, Ce modified the Mn/Al_2O_3 catalyst, the low-temperature properties are close to the precious metal catalyst Pd / Al_2O_3.
　　With part of the experiment, the impact of this mechanism of SO_2 initial guess: SO_2 with Hg ~ 0 and HCl competitive adsorption of the catalyst surface active sites, the impact of mercury adsorption and oxidation processes; the same time, SO_2 persistence may lead to its long-term catalyst surface adsorption or sulfate, which led to a decline in catalyst activity. This article also by XRD, TEM, XPS, TPR and other characterization methods to explore the mechanism of modification of doping elements.
　　The results show that: the elements doped by Mo, you can reduce the activity of the catalyst component in the preparation process of sintering and crystallization of MnOx to improve Mn/Al_2O_3 catalyst surface dispersion of the active component, the catalyst surface of the crystal particles smaller and more evenly distributed, is conducive to the catalytic activity; the same time, Mo likely to elements after doping with Mn catalyst active component in the formation of a more stable Mo-Mn bimetallic compound, and this SO_2 compounds have a stronger tolerance.
　　Through this paper some of the macro-and micro-characterization experiments we can see, after Mn/Al_2O_3 doped catalysts can be used in flue gas treatment plant in the dust removal equipment, that sort of fly ash in flue gas can be avoided and the negative impact of the catalyst, but also can maintain high performance and low-temperature catalytic anti-sulfur performance, with good prospects for industrial use. At the same time, this research on coal-fired flue gas mercury emission control technology research and development has a certain significance.
　　Degree Year: 2010