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The crystal structure of perovskite-type catalysts, Ca_xLa_(1-x)MnO_(3+λ), remains unchangedwhen x varies from 0 to 1 as identified by X-ray analysis. Both non-stoichiometric amountof oxygen (denoted by λ) and Mn~(4+) content are functions of x. ESR analysis showed thatvarying the substitution value x in A, the oxidation state of B could simultaneously be adjust-ed, this permits one to change the oxygen chemisorpting ability of these catalysts and toraise their catalytic activity. Based upon the experimental results and from the point ofview of solid defect chemistry, a theoretical analysis for the possible formation of defecttypes is made, and the assumption that the formation of the active species O_2~- or O~- isthrough the reaction of oxygen anion defect with molecular oxygen in gas phase is proposed.This idea is supported by the data obtained by XPS investigation. The reaction mechanism ofpcrovskite-type catalyst for ammonia oxidation is discussed accordingly.
The crystal structure of perovskite-type catalysts, Ca_xLa_ (1-x) MnO_ (3 + λ), remains unchanged when x varies from 0 to 1 as identified by X-ray analysis. Both non-stoichiometric amount of oxygen (denoted by λ) and Mn 4+ content are functions of x. ESR analysis showed that varying the substitution value x in A, the oxidation state of B could simultaneously be adjust-ed, this permits one to change the oxygen chemisorption ability of these catalysts and toraise their catalytic activity. Based upon the experimental results and from the point of view of solid defect chemistry, a theoretical analysis for the possible formation of defecttypes is made, and the assumption that the formation of the active species O_2 ~ - or O ~ - isthrough the reaction of oxygen anion defect with molecular oxygen in gas phase is proposed. This idea is supported by the data obtained by XPS investigation. The reaction mechanism of pcrovskite-type catalyst for ammonia oxidation is discussed accordingly.