Decomposition of Nitrous Oxide over Cu/TiO2 Catalysts: The Effect of Cu Loading, TiO2 Structure, and Reaction Conditions (original) (raw)
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Catalysis Letters, 2009
A series of Cs promoted copper oxide catalysts were prepared by co-precipitation method and tested for the direct decomposition of nitrous oxide (N2O). The Cs promoted catalysts were more active particularly with a molar ratio of Cs/Cu at 0.1 compared to bulk CuO. Methods of XRD, BET, XPS, H2-TPR, and N2O-TPD were used to characterize these catalysts to evaluate structure activity relationship. The characterization results indicated that the addition of Cs could improve the reduction of Cu2+–Cu0 by facilitating the desorption of adsorbed oxygen species, during the N2O decomposition. The influences of oxygen and steam on N2O decomposition over these catalysts were also studied.
Catalytic decomposition of nitrous oxide on CuxCo3—xO4 spinels
Applied Catalysis, 1991
The catalyst series CuxCo~_ x04 (0 ~< x ~< 1) was synthesised by the decomposition of nitrate precursors. Higher copper containing spinels (x ~> 0.5) were in partially inverted forms. The decomposition of nitrous oxide was carried out at the initial pressures of 50 and 200 Torr (1 Torr = 133.3 Pa). Two regions of activity were observed based on the mechanism x<0.5 and x>~0.5. The activity pattern has been explained on the basis of the number of active sites and solid state interactions. In both regions, the catalyst with the highest copper content was found to be less active.
Catalyzed decomposition of N2O on metal oxide supports
Applied Catalysis B: Environmental, 1997
The catalytic decomposition of N20 using metal oxides supported on silica, magnesium oxide, calcium oxide and hydrotalcite-like supports was studied. Co0 is much more active than CuO and Fe20s when supported on silica. A conversion of 95% was achieved using Co0 on Si02 at 1500 hh' GHSV, 500°C and 50,000 ppm feed N20. However,the use of higher flow rates resulted in lower conversions. We found that when supporting Co0 on MgO, a much more active catalyst is attained. A conversion of 95% was achieved using this catalyst at 40,000 h-l, 5OO"C, 100,000 ppm N20 feed. This is a significant improvement over any catalyst currently in the literature. The activity of this catalyst was decreased by calcination at 1000°C. XPS and XRD studies revealed that higher temperature calcination led to an inactive crystalline phase. The active catalyst displayed a less crystalline phase involving the support and the metal oxide. Other oxide combination catalysts were found to be less active than the CoO/MgO catalyst. Based on our findings, a modification of the reactions proposed for NaO decomposition is suggested.
Journal of Catalysis, 2005
The formation of nitrous oxide in the selective catalytic reduction of NO x with ammonia was studied in nitric acid plant exhaust gas under low-temperature conditions. The important role played by the support in this process was evidenced by a comparison of CuO/γ -Al 2 O 3 and CuO/TiO 2 monolithic catalysts. Textural properties and CuO crystal phases were analysed. Temperature-programmed desorption of NH 3 , NO, and NO 2 and X-ray photoelectron spectroscopy (XPS) after in situ adsorption of NO and NO 2 experiments were carried out. Even at low temperature, N 2 O generation takes place at a greater rate for the catalysts supported on titania than for those on alumina. In the case of alumina, the N 2 O concentration detected was independent of the CuO content. For the CuO/TiO 2 system it was associated with the active phase configuration. After in situ adsorption of NO and NO 2 , a band associated with nitrate species was identified in the XPS spectra. Adsorbed NO 3 − species seem to be responsible for the NO 2 , NO, and O 2 desorbed products detected in the NO x -TPD. The results suggests that NO − 3(ads) along with NH x(ads) species, were involved in N 2 O formation at low temperature. (S. Suárez).
Study of Na/Cu/TiO2 catalysts for the storage and reduction of NO
Applied Catalysis B: Environmental, 2012
A Pt-free system based on Na/Cu/TiO 2 catalysts was used to study the adsorption of NO under lean conditions. The results show that the NO adsorption activity dramatically increased when both sodium and copper are in intimate contact. Although copper is the active phase in the oxidation of NO to NO 2 , it was found that the addition of sodium species is of vital importance on the subsequent adsorption of NO 2 , which mainly occurs on the surface of the alkali in the form of nitrates and nitrites. It was found that a loading increase of the alkali led to an increase in the reduction temperature of the copper phase, which is ascribed to a close interaction between the copper and the sodium phases. Among the Na loadings that were studied, the addition of 5% Na gave the optimum adsorption of NO. After successive cycles of adsorption, the catalysts were fully regenerated at temperatures higher than 250 • C using either CO or H 2 as a reducing agent.
Journal of Environmental Chemical Engineering, 2015
The de-N 2 O performance of low content (0.25, 0.5 and 1.0 wt. %), Al 2 O 3 supported noble metals (Pt, Pd, Ir) is comparatively explored in the present study. Several parameters related to the effect of temperature, metal content and feed composition are investigated. An extensive characterization study involving BET, TPR, XRD and TEM was also carried out to reveal the impact of metal entity and content on the structural, morphological and redox characteristics of the catalysts. The results imply that the de-N 2 O performance is in general increased upon increasing metal loading, a fact being more intense over Ir-based catalyst. Under oxygen deficient conditions N 2 O conversions as high as ~100% and ~80% are reached at 600 o C over Ir-and Pd-based catalysts, respectively, instead of ~30% achieved over Pt-based catalysts. A moderate deactivation in oxygen excess conditions is observed with Ir and Pd catalysts, while Pt-based catalysts are totally deactivated. The enhanced de-N 2 O performance of Ir-, Pd-based catalyst can be mainly interpreted taking into account the formation of active metal oxide phases, not easily susceptible to oxygen poisoning.
Characterization of Ni/TiO2 catalysts by TEM, X-ray diffraction, and chemisorption techniques
Journal of Catalysis, 1981
Nickel crystallite sizes calculated from H,, CO, and OZ chemisorption are compared to those determined from X-ray diffraction (XRD) and transmission electron microscopy (TEM). Good agreement is obtained among all techniques for typical Ni/SiO% and Ni/Al,OI catalysts, whereas sizes calculated from H, and CO chemisorption are far too large for Ni/TiO, catalysts. In contrast, oxygen chemisorption provides values in excellent agreement with those from XRD and TEM, and indicates that monolayer coverages of CO and HP are much lower on TiO,-supported nickel. This agreement also implies that oxygen monolayer coverage on TiO,-supported nickel does not exceed unity regardless of crystallite size, whereas coverages of two or higher are observed on SiO,-and A&O,-supported nickel, in agreement with previous studies. Isobars for CO and H, adsorption on Ni/TiO, clearly show that activated adsorption is not responsible for the low CO and H2 uptakes at 300 K. Low-contrast nickel crystallites on titania are observed in the TEM micrographs, indicating that nickel may exist with a raft-like morphology on this support. These results provide evidence that strong metal-support interaction behavior exists in the Ni/TiO* system.
Aluminum Doped Titania as a Support of Copper Catalysts for SCR of Nitrogen Oxides
Materials, 2021
Aluminum doped titania samples were synthesized as supports of copper oxide catalysts for NO reduction with ammonia. Samples were prepared by the sol-gel method with various ratios of aluminum to titanium. Their thermal stability was examined by TG/DSC methods which revealed that precursors were decomposed at 450 °C. The XRD measurements showed that aluminum caused the diminishing of titania crystallites and was built into the anatase structure or formed an amorphous phase. The admixture of aluminum in titania resulted in a significant increase in specific surface area of mesoporous supports as determined by low temperature sorption of nitrogen. Results of the catalytic tests over copper/aluminum-titania samples obtained by impregnation pointed out that the addition of aluminum broadened the temperature window of high catalytic activity. The increase in Al concentration shifted the temperature of maximum activity to higher values, and at the same time lowered nitrous oxide formation...