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甲醛是一种常见的室内空气污染物,人们针对其消除已经做了大量的研究工作.催化氧化法是脱除挥发性有机物的一种重要方法,能在较低温度下通过催化剂作用将甲醛完全氧化为无毒的CO_2和H_2O.所用催化剂主要为负载型贵金属催化剂和非贵金属催化剂,但只有担载贵金属Pt或Pd的催化剂可在室温下将甲醛完全氧化,而非贵金属一般则需要较高的温度.Au催化剂是近年来催化领域的一个研究热点,但是关于纳米Au催化剂室温消除甲醛的研究较少.本课题组前期研究发现,以可还原性氧化物(CeO_2,Fe O_x)为载体负载的Au催化剂具有优异的室温氧化甲醛活性;并且突破以可还原性载体负载金的传统思路,首次发现“惰性载体”γ-Al_2O_3,负载的金催化剂在室温、有水条件下具有优异的甲醛氧化活性.本文对比了还原性氧化物(CeO_2,Fe O_x)和非还原性氧化物(Al_2O_3,SiO_2和HSZM-5)载体负载金催化剂,研究了载体氧化还原性质对负载金催化剂在高空速(600000 ml/(g·s))条件下室温催化氧化甲醛的活性和稳定性影响.结果表明,在室温、高空速且相对湿度为50%的条件下,Au/Al_2O_3催化剂的初活性最高,且较为稳定.Au/SiO_2和Au/HZSM-5催化剂的初活性虽然较高,但很快失活.而还原性氧化物载体(CeO_2,FeO_x)负载的金催化剂初活性较低,但是稳定性较好.通过电镜对负载金催化剂表面Au粒子大小的表征,并将粒子尺寸与负载金催化剂室温氧化甲醛初活性相关联,它与催化氧化甲醛反应速率成线性关系.Au粒子尺寸较小的催化剂(Au/Al_2O_3和Au/SiO_2),在高空速条件下具有更高的氧化甲醛活性,而Au粒子尺寸较大的Au/Fe O_x催化剂活性较差.载体的氧化还原性质虽然不直接影响Au催化剂初活性,但直接影响催化剂稳定性.由于Au与SiO_2或HZSM-5载体的相互作用较弱,导致反应过程中Au粒子聚集长大,使其失活较快;而Au/Al_2O_3催化剂表面则富含羟基物种,能够与Au形成配体或产生锚定作用,因此反应过程中金粒子没有明显长大.而表面中间物种的沉积并覆盖活性位是负载金催化剂缓慢失活的主要原因.
Formaldehyde is a common indoor air pollutant, and people have done a lot of research on its elimination.Catalytic oxidation is an important method to remove volatile organic compounds and can completely formaldehyde at a lower temperature by a catalyst Oxidized to non-toxic CO 2 and H 2 O. The catalysts used are mainly supported noble metal catalysts and non-noble metal catalysts, but only the catalyst carrying precious metal Pt or Pd can completely oxidize formaldehyde at room temperature, whereas non-noble metals generally require higher Temperature.Au catalyst is a hot topic in the field of catalysis in recent years, but there are few researches about nanometer Au catalyst to eliminate formaldehyde at room temperature.Our previous study found that supported by reducible oxides (CeO 2, Fe O x) Au catalyst has excellent room-temperature oxidative formaldehyde activity; and breaking through the traditional idea of supporting gold with a reducible carrier, the first discovery of “inert carrier” γ-Al 2 O 3, the supported gold catalyst has excellent formaldehyde (CeO 2, Fe O x) and non-reducing oxides (Al 2 O 3, SiO 2 and HSZM-5) The effect of redox properties of supported catalysts on the activity and stability of supported gold catalysts catalyzed by formaldehyde at room temperature under high space velocity (600000 ml / (g · s)) was studied. The results showed that at room temperature, airspeed and relative humidity The initial activity of Au / Al_2O_3 catalyst was the highest and stable at 50%, while the initial activity of Au / SiO_2 and Au / HZSM-5 catalysts was higher than that of Au / Al_2O_3 catalyst, , FeO_x) supported gold catalysts showed low initial activity but good stability.The characterization of Au particle size on gold supported catalysts was carried out by electron microscopy, and the particle size was correlated with the initial activity of oxidized formaldehyde loaded with gold catalyst at room temperature. Oxidation of formaldehyde reaction rate has a linear relationship.Au particle size smaller catalyst (Au / Al_2O_3 and Au / SiO_2), at higher space velocities have higher oxidative formaldehyde activity, and Au particle size larger Au / Fe O_x catalyst The activity of the support is poor.The redox properties of the support do not directly affect the initial activity of the Au catalyst but have a direct impact on the stability of the catalyst.Because of the weak interaction between Au and SiO_2 or HZSM-5 support, Large, making it deactivate faster; and the surface of the Au / Al 2 O 3 catalyst is rich in hydroxyl species, can form a ligand with Au or anchored, so gold particles did not grow significantly during the reaction. The deposition of surface intermediate species And covering the active site is the main reason for the slow inactivation of the gold catalyst.