生物质基活性炭负载金属催化还原NO_x

Catalytic Reduction of NO_x by Biomass-Derived Activated Carbon Supported Metals

为研究生物质材料的脱硝性能,利用木质素与纤维素2种生物质基活性炭作为还原剂,用碱金属与过渡金属作为催化活性相,制备了一系列生物质基活性炭负载金属催化剂用于富氧环境中催化还原NO_x,考察了生物质原料种类、炭化温度以及催化剂组分对脱硝效率的影响.结果表明:(1)当反应温度低于250℃时,炭表面主要是NO_x的吸附过程;而当反应温度高于250℃时,炭还原NO_x行为占主导,并伴随N2、CO_2与CO的生成.炭化温度对炭反应活性的影响主要依赖于炭化温度对炭材料表面含氧官能团、比表面积以及炭表面金属还原性的影响.(2)研究中考察的金属(K、Cu、Fe、Ni)均对还原NO_x与O_2有催化作用,其中,K对C-NO_x反应具有明显促进作用,但对C-O_2反应并无明显促进作用,所有样品中SAC-K的选择性因子为0.56,对还原NO_x的选择性最高,且恒温反应过程NO_x还原量(以C计)达到了1 293μmol/g.(3)与传统煤基活性炭催化剂相比,木屑基活性炭负载钾催化剂表现出了优良的NO_x还原选择性;X-射线光电子表征结果显示,木屑基活性炭负载钾催化剂优良的性能与其表面钾活性相的高度分散有关.研究显示,相比于煤基炭材料,生物质基炭材料具有更加优异的选择性还原NO_x性能.

In order to study the deNOx performance of biomass materials,activated carbons derived from lignocellulosic and herbaceous biomasses were selected as the reducing agents,and alkali and transition metals were used as the catalytic active phases to prepare a series of activated carbon-supported metals for the catalytic reduction of NOx to N2 in excess O2.The effects of the type of biomass,carbonization temperature and catalyst composition on NOx reduction efficiency were analyzed.The results showed that:(1)Two temperature regimes are present for the NO x-carbon reaction:at temperatures below 250℃,the NOx adsorption process on the carbon surface was predominant,whereas true NOx reduction by carbon occurred at temperatures above 250℃,producing N2,CO2 and CO.The influence of the carbonization temperature on carbon reactivity depended on the effect of the carbonization temperature on the oxygen-containing functional groups,the carbon surface area and the reduction of the metal species on carbon.(2)All studied metals catalyzed both NOx and O2 reduction by carbon,and potassium could strongly enhance the C-NO x reaction without substantial carbon consumption by O 2.The sample SAC-K showed the highest selectivity factor of 0.56 among the samples,and the NO x reduction by SAC-K was 1293μmol g C.(3)Moreover,the potassium supported by sawdust-derived activated carbon exhibited higher selectivity and capacity towards NO x reduction than its previously reported coal-derived counterparts.These properties were ascribed to the high dispersion of the active potassium species on the carbon surface,as observed through comparison of powder X-ray diffraction results for the carbons made from biomass and coal-based precursors.The above results suggested that in comparison with coal-derived carbon materials the biomass-derived carbon materials showed better selective reduction of NO x.