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应用O_2-TPD,脉冲实验,原位Weiss磁测量以及TAP(temporal analysis of products)技术对NiO上的乙烷氧化脱氢制乙烯催化作用机理进行了研究.结果表明,NiO中的非化学计量氧表现出与气相氧交换的可逆性,其中在较低温度下脱附的α氧(很可能是O_2~-,O_2~(2-))仅存在于催化剂表面,与气相氧交换迅速,而较高温下脱附的β氧(很可能是O~-)不仅存在于催化剂表面,还存在于催化剂体相.β氧较α氧表现出更高的乙烯选择性.在反应条件下,Ni均应处于高氧化态(Ni~((2+δ)+),0≤δ≤1),一旦催化剂中有微量Ni~0生成,乙烷便发生裂解反应,乙烯选择性立即降为零.乙烷在NiO上的氧化脱氢(ODHE)的可能反应机理为:首先乙烷与NiO中的非化学计量氧O_(n(s))作用脱除一个α-H生成乙基自由基,然后进一步脱除一个β-H生成乙烯,乙烯生成的整个过程是在催化剂表面上进行的;副产物CO_2是由表面乙烯进一步氧化(很可能是与O_2~-,O_2~(2-)作用)生成的.失去O_(n(s))的NiO在反应体系(一定的氧分压)中,重新生成含非化学计量氧的NiO.
The mechanism of ethylene catalyzed by the oxidative dehydrogenation of ethane over NiO to ethylene was investigated by means of O 2 -TPD, pulse experiments, in-situ Weiss magnetic measurements and TAP (temporal analysis of products). The results show that the non-stoichiometric oxygen Showed reversibility of oxygen exchange with gas phase, in which α - desorption at low temperature (probably O_2 ~ -, O_2 ~ (2-)) existed only on the catalyst surface, Beta-oxygen (probably O ~ -) desorbed at high temperature exists not only on the catalyst surface but also in the bulk of the catalyst, and β-oxygen exhibits higher ethylene selectivity than α-oxygen. Under the reaction conditions, In the high oxidation state (Ni2 + δ), 0≤δ≤1), once the catalyst has a small amount of Ni0, the ethane will be cleaved and the ethylene selectivity will be immediately reduced to zero. The possible reaction mechanism of oxidative dehydrogenation (ODHE) on NiO is as follows: firstly, ethane and non-stoichiometric oxygen O_ (n (s)) in NiO act to remove an α-H to generate ethyl radical, With the exception of a β-H to ethylene, the entire ethylene production takes place on the surface of the catalyst; CO 2, a by-product, is further oxidized by surface ethylene It is O_2 ~ -, O_2 ~ (2-) action) produced lose O_ (n (s)) of NiO in the reaction system (the oxygen partial pressure constant), the regenerated oxygen-containing non-stoichiometric NiO..