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The effects of SO2 on the selective catalytic reduction of NO by NH3 over a Ce/TiO2 catalyst were studied. Conversion of NO remained above 90% in the presence of 100 ppm SO2 at 350 °C for 48 h. However, when 180 ppm SO2 was added at 300 °C, NO conversion only remained above 90% during the first 12 h and then gradually decreased with time. Characterizations of fresh and SO2-poisoned Ce/TiO2 catalysts were carried out using Brunauer−Emmett−Teller method, ion chromatography, X-ray photoelectron spectroscopy, and X-ray diffraction. The analytical results indicate that there was no obvious change in the crystal structure of the different samples; however, the specific area decreased with SO2 poisoning time. Sulfates were formed and preferentially diffused from the surface to a bulk phase during the poisoning process. Temperature-programmed desorption and diffuse reflectance infrared Fourier-transform spectroscopy results show that in the presence of O2, SO2 could react with NH3 to form NH4HSO4, which is deposited on the surface of the catalyst and blocked the active sites. Moreover, the main reason for the deactivation is that SO2 could react with the catalyst to form high thermally stable Ce(SO4)2 and Ce2(SO4)3, resulting in the disruption of the redox properties between Ce(IV) and Ce(III) and the inhibition of the formation and adsorption of nitrate species.

The coupling effect of polymeric vanadyl species greatly promotes the NH3-SCR de-NOx process over vanadia-based catalysts.

Selective catalytic reduction of NO x using NH 3 or hydrocarbons (NH 3 -SCR or HC-SCR) in oxygen-rich exhaust from diesel engines remains a major challenge in environmental catalysis. The development of highly efficient, stable and environmentally-benign catalysts for SCR processes is very important for practical use. In this feature article, the structure-activity relationship of vanadium-free catalysts in the NH 3 -SCR reaction is discussed in detail, including Fe-, Ce-based oxide catalysts and Fe-, Cu-based zeolite catalysts, which is beneficial for catalyst redesign and activity improvement. Based on our research, a comprehensive mechanism contributing to the performance of Ag/Al 2 O 3 in HC-SCR is provided, giving a clue to the design of a catalytic system with high efficiency.

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[1] The exchange of carbonyl sulfide (COS) between lawn and the atmosphere was investigated by using a static enclosure under natural field conditions. The results indicated that the lawn acted as a sink for atmospheric COS and a source of dimethyl sulfide (DMS). The exchange fluxes of COS and DMS ranged between À3.24 pmol m À2 s À1 and À94.52 pmol m À2 s À1 , and between 0 and 3.14 pmol m À2 s À1 , respectively. The lawn was capable of continuously absorbing COS in nighttime as well as in daytime. The COS fluxes depended strongly on the ambient COS mixing ratios. The dependency of DMS emission fluxes on temperature was observed in November 2002. Soil also acted as a sink for COS during our study. However, the COS exchange fluxes of the lawn were much higher than that of the soil. The average COS and DMS fluxes were much higher in spring than in autumn and in summer. The daytime vertical profiles of COS also indicated that the lawn acted as a net sink for COS.

Samples of cerium supported on titania with different Ce loadings have been prepared by an impregnation method and tested for the selective catalytic reduction of NO by NH 3 in the presence of excess oxygen. The catalysts with 5% Ce and above had high activity in the temperature range 275-400°C at a space velocity of 50,000 h À1 . All the catalysts showed an excellent selectivity to N 2 and high tolerance to SO 2 and H 2 O under our test conditions.

In situ DRIFTS was used to investigate the formation and reactivity of surface species on Ag/Al2O3 during partial oxidation of CH3CHO, C2H5OH, and C3H6. The exposure of Ag/Al2O3 to CH3CHO/C2H5OH/C3H6 + O2 in a steady state leads to the formation of two kinds of partial oxidation products:  acetate and a novel enolic surface species. Peaks at 1633, 1416, and 1336 cm-1 are assigned to an adsorbed enolic species. The adsorbed enolic species is more prone to react with NO + O2 on Ag/Al2O3 than acetate is, and plays a crucial role in the formation of NCO, which is a key intermediate during selective catalytic reduction of NO.