[show abstract][hide abstract] ABSTRACT: The adsorption and desorption of N2O on main-group ion-exchanged ZSM-5 was studied using temperature-programmed desorption (TPD) and density functional theory (DFT) calculations. TPD experiments were carried out to determine the desorbed temperature Tmax corresponding to the maximum mass intensity of N2O desorption peak and adsorption capacity of N2O on metal-ion-exchanged ZSM-5s. The results indicated that Tmax followed a sequence of Ba2+ > Ca2+ > Cs+ > K+ > Na+ > Mg2+ and the amount of adsorbed N2O on main-group metal cation followed a sequence of Ba2+ > Mg2+ > Ca2+ > Na+ > K+ > Cs+. The DFT calculations were performed to obtain the adsorption energy (Eads), which represents the strength of the interaction between metal cations and the N-end or O-end of N2O. The calculation results showed that the N-end of the N2O molecule was favorably adsorbed on ion-exchanged ZSM-5, except for Cs-ZSM-5. For alkali metal cations, the Eads of N2O on cations followed the order which was the same to that of Tmax: Cs+ > K+ > Na+. The calculated and experimental results consistently showed that the adsorption performances of alkaline-earth metal cations were better than those of alkali metal cations.
Journal of Environmental Sciences 01/2011; 23(4):681-6. · 1.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: A series of alkali metal- and alkaline earth metal-doped cobalt-cerium composite oxide catalysts were prepared by the citrate method and tested for the decomposition of N20. Strong promotion effects of alkali and alkaline earth metals on the activity of the catalyst were obtained in the order Li < Na < K < Rb < Cs and Mg < Ca < Sr, Ba. The promotion effects of alkaline earth metals were much weaker than the effects of alkali metals. To investigate the origin of the promotion effect, X-ray diffraction, Brunauer-Emmett-Teller surface area measurement X-ray photoelectron spectroscopy, temperature-programmed desorption, and hydrogen temperature-programmed reduction methods were used to characterize the alkali metal-doped catalyst. The analytical results indicated that alkali metals improved the redox ability of active site Co2+ by acting as electronic promoters. Catalytic decomposition of N2O proceeds through an oxidation-reduction mechanism with participation of electrons from Co2+, thus the increase in the redox ability of Co2+ should lead to an increase in the activity of the catalyst.
Environmental Science and Technology 02/2009; 43(3):890-5. · 5.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity of Co3O4.
[show abstract][hide abstract] ABSTRACT: A series of cobalt–cerium mixed oxide catalysts (Co 3 O 4 –CeO 2) with a Ce/Co molar ratio of 0.05 were prepared by co-precipitation (with K 2 CO 3 and KOH as the respective precipitant), impregnation, citrate, and direct evaporation methods and then tested for the catalytic decomposition of N 2 O. XRD, BET, XPS, O 2 -TPD and H 2 -TPR methods were used to characterize the catalysts. Catalysts with a trace amount of residual K exhibited higher catalytic activities than those without. The presence of appropriate amount of K in Co 3 O 4 –CeO 2 may improve the redox property of Co 3 O 4 , which is important for the decomposition of N 2 O. When the amount of K was constant, the surface area became the most important factor for the reaction. The co-precipitation-prepared catalyst with K 2 CO 3 as precipitant exhibited the best catalytic performance because of the presence of ca. 2 mol% residual K and the high surface area. We also discussed the rate-determining step of the N 2 O decomposition reaction over these Co 3 O 4 –CeO 2 catalysts. # 2007 Elsevier B.V. All rights reserved.
[show abstract][hide abstract] ABSTRACT: Heterogeneous oxidation of carbonyl sulfide (OCS) on mineral oxides including SiO2, Fe2O3, CaO, MgO, ZnO and TiO2, which are the main components of atmospheric particles, were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), ion chromatography (IC), temperature-programmed desorption (TPD), X-ray diffraction (XRD) and Brunauer-Emmett-Teller
(BET) methods. The main products and intermediates of the heterogeneous oxidation of OCS on these oxides were identified with
in situ DRIFTS and IC. The reaction mechanism and kinetics were also discussed. It is found that the reaction mechanism on these
mineral oxides is the same as that on Al2O3 for the same final products and the intermediates at room temperature. Namely, OCS can be catalytically oxidized to produce
species and gaseous CO2 through the surface hydrogen thiocarbonate (HSCO
) and HSO
species. The activity series for heterogeneous oxidation of OCS follows: Al2O3 ≈ CaO > MgO > TiO2 ≈ ZnO > Fe2O3 > SiO2. The specific area, basic hydroxyl and surface basicity of these oxides have effect on the reactivity. This study suggests
that heterogeneous reactions of OCS on mineral dust may be an unneglectable sink of OCS.
Chinese Science Bulletin 07/2007; 52(15):2063-2071. · 1.32 Impact Factor
[show abstract][hide abstract] ABSTRACT: The oxygen poisoning mechanism of the catalytic hydrolysis of carbonyl sulfide (OCS) over alumina at room temperature was investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), XRD, BET, and ion chromatograph (IC). The surface hydroxyl (–OH) species triggered the catalytic hydrolysis of OCS on Al2O3, with the formation of surface hydrogen thiocarbonate (HSCO2−) species as a key intermediate. Surface SO42– was identified with in situ DRIFTS and IC. It was found that the accumulation of sulfate on catalyst led to the poisoning of Al2O3 in the presence of oxygen.