Fundamental Study On The Catalytic Elimination Of NO Or CO By Ceria Based Catalysts

Ceria(CeO2),with high oxygen storage capacity(OSC)and excellent redox behavior,has been widely adopted in the three-way catalyst(TWC),and also applied as a support of metal oxides or noble metal catalysts for CO oxidation,NO reduction and catalytic abatement of hydrocarbon.Numerous studies have been conducted to promote the catalytic performance of CeO2 by doping another element to form a solid solution and/or controlling the morphology of ceria.In the current work,we focused on the following issues with the help of characterizations including in-situ FTIR and ssNMR.(1)Study the effect of CuO dispersion state on the activity of CuO modified Ce0.7Zr0.3O2 for NO removal.(2)Clarify the exposed crystal plane of CeO2 with different morphologies,and discuss their surface oxygen species.Results suggested that:1.The dispersion state of CuO on ceria-zirconia solid solution have a great influence on the catalytic activity of NO reduction.The decomposition of surface adsorbed nitrates take place at lower temperature,the product was mainly N2O.At higher temperature,the-NCO species was the principal intermediate to generate N2.The dispersion states of CuO species have an important role in both reactions.Surface modified copper oxide species in Cu/CZ could form an unstable,asymmetrical five-coordination structure.H2-TPR and CO-IR result revealed that the synergetic effect between surface modified copper species and CZ support could easily promote the reducibility of Cu2+ which enhanced the catalytic performance of Cu/CZ.CuO species in Cu-CZ introduced into the CZ fluorite structure,Cu2+ ions substitute a small portion of Ce4+ or Zr4+,form a relatively simplified and stabilized structure,thus these Cu2+were relatively difficult to be reduced.These factors can explain the superior activity of Cu/CZ towards Cu-CZ.2.Ceria,with various shapes and no impurities,were manufactured by a hydrothermal method.We have discovered that ceria-octahedral and ceria-cube were mainly enclosed with well-grown {111} facets and {100} facets,respectively.The exposed crystal facets are complicated in ceria-rod,which contains a number of intrinsic defects.The surface vacancy concentration is not the only factor in the catalytic activity of ceria.The adsorption behavior of CO molecule are differs a lot on different ceria facets.We have found that ceria {111 facet can be more reductive in CO atmosphere,which can be responsible for the better catalytic activity of ceria-octahedral and ceria-rod than ceria-cube.3.Ceria with natural abundance 17O have been characterized by DNP enhanced 170 ssNMR.Cluster like oxygen vacancy(VO2)can be observed with 17O DNP-N-MR spectra.The relative concentration of VO2 shows positive correlation with the activity in CO oxidation.Importantly,H217O selective enrichment experiment demonstrated that oxygen ions diffusion ability shows a significant crystal facet dependence.These methods can be applied to monitor the relationship between structure and the nature of surface oxygen species in the future catalysts study.It is beneficial for corresponding catalytic performance of ceria materials with their structure...