Mn-Zr复合氧化物负载贵金属催化剂的氯乙烯催化燃烧性能

Reaseching on Supported Noble Metals over Mn-Zr Composite Oxides for the Catalytic Combustion of Vinyl Chloride

以共沉淀法制备了Mn-Zr复合氧化物,通过浸渍法引入贵金属(Ru、Pd、Pt),考察了贵金属对于氯乙烯催化燃烧反应性能的影响;并对催化剂的结构和化学状态,氧化还原性能和酸性能,表面酸类型的分布特征进行表征。研究发现,贵金属主要以氧化态的形式存在于催化剂表面,贵金属的引入促进了复合氧化物的还原,从而提高了催化剂的氧化还原性能,同时也提高了催化剂表面酸的总量、改变了表面Brönsted酸和Lewis酸中心的分布。贵金属引入后,促进了反应性能的提高,使得氯乙烯全转化温度向低温偏移;不同贵金属对于反应促进的效果不同,其中Ru的引入,对于反应的促进效果高于Pd和Pt的引入。Ru/MZ(Ru/Mn_(0.7)Zr_(0.3)O_(x))催化剂上氯乙烯转化50%和90%的温度(t50、t90)分别为206、243℃,比纯复合氧化物催化剂的相应温度向低温偏移69、71℃。贵金属引入后也改变了有机含氯副产物的分布并降低了其浓度,Ru/MZ催化剂在t90时的含氯副产物总体积分数为5.7μL/L,比Mn0.7Zr0.3Ox在相同转化率下的有机氯代副产物体积分数低70%。

The Mn-Zr composite oxides were prepared by co-precipitation,loading with noble metals(Ru,Pd,Pt)on the surfaces by a following impregnation method.The effects of noble metals on catalytic combustion of vinyl chloride(VC)were further investigated.The structure and chemical state,the oxidation-reduction ability and acidity,the distribution of acid over the noble metal loading catalysts were studied.Noble metals exist in the form of oxidation state on catalyst surface to promote the reduction of Mn-Zr composite oxides and improve the redox ability of the catalysts.In addition,noble metals not only increased total acid amount but also changed the distribution of Brönsted and Lewis acid centers on catalyst surface.Therefore,the noble metal made the completely VC conversion temperature shift to lower temperature.However,the activities of noble metals for catalytic combustion of VC varied with the kind of noble metal.Among them,Ru had the more positively activity enhancement than that of Pd and Pt.The catalytic temperatures were 206 and 243℃,when the VC conversion over Ru/MZ(Ru/Mn_(0.7)Zr_(0.3)O_(x))reached to 50%(t50)and 90%(t90),respectively,which were 69 and 71℃ lower than that using Mn-Zr composite oxide.Meanwhile,the loading of noble metals also changed the composition of chlorinated by-products and reduced their concentration.The total concentration of chlorinated by-products over Ru/MZ catalyst was only 5.7μL/L with 90%VC conversion rate,which was 70%lower than MZ composite oxide at the same conversion rate.