臭氧催化氧化脱除低浓度甲醛的新方法（英文）

甲醛作为一种典型的室内挥发性有机污染物,对人体健康危害很大.目前,在可用于室内甲醛脱除的诸多方法之中,臭氧催化氧化法因可于室温下使用廉价的金属氧化物催化剂实现对甲醛的高效脱除,从而受到了科研工作者的广泛关注.然而,考虑到室内甲醛的浓度极低,且存在着长期缓慢释放的特点,传统的臭氧催化氧化法应用于实际的室内甲醛脱除不仅会造成能量的浪费,而且还易因未完全分解臭氧的连续释放带来二次污染问题.为了提高臭氧催化氧化脱除甲醛过程的臭氧利用率,降低能耗,并有效缓解未分解臭氧引起的二次污染,本文将一种循环的甲醛存储-臭氧催化氧化新方法应用于室内低浓度甲醛的脱除.该新方法包含甲醛存储与臭氧催化氧化两个过程,在存储阶段低浓度甲醛吸附存储于催化剂表面,而在臭氧催化氧化阶段臭氧将存储的甲醛氧化为CO_2与H_2O,并重新释放催化剂表面的吸附位.因负载型氧化锰具有优良的臭氧分解能力,本研究以Al_2O_3负载的MnO_x为催化剂,通过研究前驱体及担载量对甲醛脱除反应的影响,筛选出了最优的MnO_x/Al_2O_3催化剂,并对相对湿度的影响规律进行了考察,最后通过低浓度甲醛存储-臭氧催化氧化循环实验验证了该甲醛臭氧催化氧化新过程的可靠性.我们采用传统的等体积浸渍法,基于不同的前驱体制备MnO_x/Al_2O_3催化剂.XRD表征结果表明,乙酸锰为前驱体制得的MA/Al_2O_3催化剂中MnO_x相主要为Mn3O4(粒径约为6.0 nm);而硝酸锰前驱体所得MN/Al_2O_3催化剂中则含有MnO2与Mn_2O_3相,且其MnO_x颗粒粒径较大,约为9.5 nm.XPS测试结果表明,MA/Al_2O_3催化剂含有Mn^(2+),Mn^(3+)及Mn^(4+),其中Mn^(3+)与Mn^(4+)的含量分别为75%与12%;而MN/Al_2O_3催化剂则仅含有Mn^(3+)与Mn^(4+),含量分别为35%与65%.上述XRD与XPS结果相一致,说明以乙酸锰为前驱体所得催化剂的分散度较高且易形成低氧化态的Mn.甲醛存储-臭氧催化氧化实验结果表明,与Al_2O_3及MN/Al_2O_3相比,MA/Al_2O_3催化剂具有更高的甲醛存储与催化氧化脱除性能.基于MA/Al_2O_3催化剂,不同Mn负载量下的甲醛存储与臭氧催化氧化实验结果表明,Mn负载量为10 wt%时MA/Al_2O_3的性能最佳.因而,进一步的实验中我们均选用最优的10 wt%MA/Al_2O_3为催化剂,其在50%相对湿度下的甲醛存储量为26.9μmol/mL,臭氧催化氧化阶段碳平衡为92%,CO_2选择性为100%.相对湿度的影响结果(23°C)则表明,由于水分子与甲醛分子间存在着竞争吸附作用,甲醛存储容量随相对湿度的增加而降低;但因相对湿度增加可建立利于甲醛氧化的新途径,故臭氧催化氧化性能随相对湿度增加而增强.综合考虑,10 wt%MA/Al_2O_3上甲醛存储-臭氧催化氧化的最优相对湿度为50%.为验证所提出新方法的实用性,我们基于10 wt%MA/Al_2O_3开展了甲醛存储-臭氧催化氧化的4次循环实验.4次循环实验中的甲醛存储以及臭氧催化氧化处理的规律可基本保持一致.50%相对湿度下,低浓度甲醛(15×10-6)在空速为27000 h-1时的穿透时间为110 min,而在臭氧催化氧化阶段(150×10-6臭氧,空速15000 h-1)仅需约50 min即可实现对存储甲醛的氧化脱除(碳平衡大于92%,CO_2选择性100%),表明该新方法较传统的臭氧催化氧化方法臭氧用量可节省60%.

Enhanced effect of plasma on catalytic reduction of CO2 to CO with hydrogen over Au/CeO2 at low temperature

In terms of the reaction of COreduction to CO with hydrogen, COconversion is very low at low temperature due to the limitation of thermodynamic equilibrium（TE）. To overcome this limitation, plasma catalytic reduction of COto CO in a catalyst-filled dielectric barrier discharge（DBD） reactor is studied. An enhanced effect of plasma on the reaction over Au/CeOcatalysts is observed. For both the conventionally catalytic（CC） and plasma catalytic（PC, Pin= 15 W） reactions under conditions of 400 °C, H/CO= 1,200 SCCM, GHSV = 12,000 mL·gcat·h, COconversions over Au/CeOreach 15.4% and 25.5% due to the presence of Au, respectively, however, those over CeOare extremely low and negligible. Moreover,COconversion over Au/CeOin the PC reaction exceeds 22.4% of the TE conversion. Surface intermediate species formed on the catalyst samples during the reactions are determined by in-situ temperatureprogrammed decomposition（TPD） technique. Interestingly, it disclosed that in the PC reaction, the formation of formate intermediate is enhanced by plasma, and the acceleration by plasma in the decomposition of formate species is much greater than that in the formation of formate species on Au/CeO. Enhancement factor is introduced to quantify the enhanced effect of plasma. Lower reactor temperature, higher gas hourly space velocity（GHSV）, and lower molar ratio of H/COwould be associated with larger enhancement factor.

Effect of O_2/CH_4ratio on the optimal specific-energy-input (SEI) for oxidative reforming of biogas in a plasma-shade reactor

In a novel plasma-shade reactor for oxidative reforming of biogas(CH4/CO2=3/2),the effects of specific-energy-input (SEI) on CH4 and CO2 conversions and energy cost of syngas were investigated at O2/CH4ratios ranged from 0.42 to 0.67.At each of O2/CH4 ratios,V-shape profiles of energy cost of syngas increasing with SEI were observed,reaching the lowest value at the optimal SEI(Opt-SEI).With the increase of O2/CH4 ratio,the Opt-SEI decreased significantly.Moreover,at the Opt-SEI,O2 and CH4 conversions and dry-basis concentration of syngas increased and energy cost of syngas decreased greatly with the increase of O2/CH4 ratio.