Superior resistance to alkali metal potassium of vanadium-based NH_(3)-SCR catalyst promoted by the solid superacid SO_(4)^(2-)-TiO_(2)

The significant decrease of acid sites caused by alkali metal poisoning is the major factor in the deactivation of commercial V_(2)O_(5)-WO_(3)/TiO_(2)NH_(3)-SCR catalysts.In this work,the solid superacid SO_(4)^(2-)-TiO_(2) modified by sulfate radicals,was selected as the catalyst support,which showed superior potassium resistance.The physicochemical properties and K-poisoning resistance of the V_(2)O_(5)-WO_(3)/SO_(4)^(2-)-TiO_(2)(VWSTi) catalyst were carried out by XRD,BET,H2-TPR,NH3-TPD,XPS,in situ DRIFTS and TG.The results pointed out that the introduction of SO_(4)^(2-)significantly increased the NH3-SCR catalytic activity at high temperatures,with an exceptionally high NO_(x) conversion over 90% between 275℃ and 500℃.When 0.5%(mass) K_(2)O was doped on the catalysts,the catalytic performance of the traditional V_(2)O_(5)-WO_(3)/TiO_(2)(VWTi) catalyst decreased significantly,while the VWSTi catalyst could still maintain a NOxconversion over 90%in the range of 300–500℃.The characterizations suggested that the support of SO_(4)^(2-)-TiO_(2) greatly increased the number of acidic sites,thereby enhancing the adsorption capacity of the reactant NH_(3).The results above demonstrated a potential approach to achieve superior potassium resistance for NH3-SCR catalysts using solid superacid.

Spatiotemporal patterns of snow cover retrieved from NOAA-AVHRR LTDR: a case study in the Tibetan Plateau, China

Snow cover plays an important role in hydrological processes and seasonal water balance.Especially in the Tibetan Plateau(TP),snow cover is an important source of the Yangtze River,Yellow River and Lancang River(SRYYL),which greatly influences regional water balance.In this study,we quantified the temporal trend and spatial variation of snow cover across the TP by calibrating and developing the Advance Very High Resolution Radiometer(AVHRR)Long Term Data Record(LTDR)-derived snow cover products during 1982-2011.We also examined the relationship of snow cover with temperature and precipitation over the TP during 1982–2011.The results indicate that seasonal snow cover generally starts to accumulate from central plateau in October,while significant melting starts to occur from the southeastern plateau in May of following year.The long-term variability of snow cover is characterized by the tendency for a slight decrease in the mean snow coverage during the period of hydrological year(HY)1982–1993 and a slight increase from HY2001 to 2011,but the total snow cover area remains relatively stable over the past 30 years.The results also show that temperature plays a critical role in controlling the snow cover days.