Promotional effect of Ag-doped Ag-V/TiO2 catalyst with low vanadium loadings for selective catalytic reduction of NOX by NH3

A series of Ag-doped Ag-V/TiO2 catalysts with low vanadium loadings were prepared by one-step sol-gel methods and the effects of the Ag doping on the selective catalytic reduction (SCR) of NOx with NH3 were investigated. The catalytic activity of the catalysts increased about 20% by the addition of 1-3 wt% of Ag. The catalysts were characterized by XRD and H-2-TPR. The results indicated that the V and Ag were well dispersed on the TiO2 support and the Ag doping inhibited the growth of TiO2 anatase crystallite and improved the oxidation ability of adsorption sites. The reduction temperature of vanadium oxide decreased and the activity for NH3-SCR enhanced. The doped Ag also had NH3-SCR activity, but it was very low. The durability of the catalysts was acceptable and the resistance to H2O was not very good. The effects of the calcination temperature and GHSV were also investigated; it was found that the optimal calcination temperature was 450 A degrees C and the GHSV should not be higher than 48,000 h(-1)

Seasonal and diurnal variations in DIC, NO3- and TOC concentrations in Check for spring-pond ecosystems under different land-uses at the Shawan Karst Test Site, SW China: Carbon limitation of aquatic photosynthesis

Human activities have altered terrestrial carbon (C) and nitrogen (N) dynamics via changes to land cover and use such as deforestation, agriculture, application of fertilizers, etc. and have influenced the patterns of organic C input and eutrophication in downstream freshwater ecosystems. Biogeochemical cycling of C and N and the related organic carbon (OC) production may display correlated diurnal and seasonal variations due to photosynthesis and respiration in these ecosystems, whose underlying mechanisms still need to be resolved. In this study, we document the diurnal and seasonal variations measured in DIC (dissolved inorganic carbon), NO3-, TOC (total organic carbon) and other related hydrochemical parameters (pH and DO-dissolved oxygen) in five artificial spring-pond ecosystems with differing land-uses in tanks draining into springs and corresponding ponds, constructed at the Shawan Karst Test Site, SW China. It was found that diurnal changes in DIC, NO3- and TOC in all ponds were dominated by aquatic ecosystem metabolism (i.e., photosynthesis and respiration), as evidenced by the pertinent variations in DO and pH. Daily DIC and NO3- uptake and OC production were higher in October (growing period) and lower in January (dormant period), indicating seasonal differences in assimilation that were determined by both changes in weather (temperature and light) and nutrient inputs. Under conditions of bare rock or bare soil, there was very low DIC and NO3- additions to the spring-pond ecosystems, resulting in lower OC productivity in the ponds. Cropped land yielded higher DIC and NO3- to the pond, due to growth of corn and use of fertilizers that enhanced OC production. Highest productivity and densest vegetation cover on tanks with grassland or shrubs (with higher N retention in soils) resulted in higher DIC but limited NO3- addition to the ecosystems downstream. The highest DIC concentration (in the grassland) resulted in maximum OC production in the pond. These results indicate that OC production in the ponds with elevated pH was limited by DIC fertilization. In general, the supply of DIC is not considered to limit aquatic primary productivity because its concentration exceeds that of other plant macronutrients such as NO3 and PO43- by two or three orders of magnitude. Therefore, the carbon limitation detected here may indicate that photoautotrophs in karst dominated aquatic terrains (dominated by Charophyta and Spirogyra) cannot use the total DIC for photosynthesis but only the dissolved CO2, which comprises 8.2 that is characteristic in these environments. This may have implications for control of eutrophication in such alkaline aquatic ecosystems, i.e., rates of eutrophication in freshwater ecosystems may be regulated not only by N and/or P but also by C. It is also projected that there will be an increase in OC sequestration with the current land-use and global climate change-driven increases in DIC, due to carbon limitation of aquatic primary production

Synergetic Promotional Effects Between Cerium Oxides and Manganese Oxides for NH3-Selective Catalyst Reduction Over Ce-Mn/TiO2

Ce and Mn codoped Ce-Mn/TiO2 catalysts were synthesized by sol-gel method and were used as model catalysts to investigate the synergetic promotional effects between cerium oxides and manganese oxides for selective catalytic reduction of NO by NH3. The catalysts were characterized by SEM, XRD, XPS, and temperature-programmed hydrogen reduction (H-2-TPR) and ammonia desorption (NH3-TPD) techniques. The experimental results showed that cerium oxides and manganese oxides affected each other, and their catalystic activities improved both at low and high temperatures. The catalysts yielded more than 90% NOx conversion in the temperature range 250-450 degrees C and W/F of 0.00125 g min mL(-1) (W/F represents the ratio of the catalyst weight to the gas flow rate). It was suggested that the mobility of oxygen species enhanced through the sandwiched structure sic-Mn-O-Ce (sic represents the oxygen vacancy), leading to the enhancement of the NOx conversion over Ce-Mn/TiO2 significantly. Moreover, the Ce and Mn codoping improved the acid concentration with both medium acid sites and strong acid sites. Ce doping inhibited the growth of crystal size of TiO2, while Mn doping had little influence on it

Effects of land cover on variations in stable hydrogen and oxygen isotopes in karst groundwater: A comparative study of three karst catchments in Guizhou Province, Southwest China

Studying the spatial and temporal variations of stable hydrogen and oxygen isotopic values (delta D and delta O-18, respectively) in precipitation and groundwater in catchments with different land cover is of great significance to understanding the hydrologic cycles within the catchments. This study is focused on three karst catchments, Banzhai, Chenqi and Dengzhanhe, in Guizhou Province, Southwest China, a region with a subtropical humid monsoon climate. We analyzed the spatial and temporal variations in the SD and delta O-18 of precipitation and groundwater in these areas from September 2007 to September 2009. Local meteoric water lines (LMWLs) for the study areas and their relationships with groundwater were established. The seasonal variations of 8121 and delta O-18 for both precipitation and groundwater were similar, being depleted in the heavier isotopomer in the rainy season and enriched in the heavier isotopomer in the dry season. The similarity of patterns between groundwater and precipitation indicates short groundwater residence times in the three catchments, typical of karst terrains. The isotopic values of the Banzhai catchment, which is covered by a thin soil layer beneath virgin forest floor, had the largest variation among the three catchments. The isotopic compositions of the Banzhai catchment groundwater were close to those of precipitation in the rainy season and responded rapidly to it, indicating that precipitation quickly recharges groundwater in this area. In comparison, in the Chenqi and Dengzhanhe catchments, the thicker soil layers and large numbers of paddy fields and dry lands in the catchments resulted in more intense evaporation, and therefore relatively higher isotopic values in the infiltration water. Consequently, the isotopic values of spring water in these two areas were higher and varied to a lesser extent in the rainy season than those of precipitation. The Rayleigh fractionation model based on the correlation between the deuterium excess (d) and evaporation was employed in this study. The model calculation results showed that the catchment evaporation was more intense in Dengzhanhe than in Chenqi, with 14 +/- 1% and 6 +/- 4% of the water evaporated in Dengzhanhe and Chenqi, respectively. The higher percentage of evaporation in Dengzhanhe was mainly due to the larger percentage of paddy fields in the catchment. In contrast, the effects of evaporation from free water surfaces or soil surfaces on groundwater in the virgin forest-covered Banzhai catchment were extremely weak. Based on the isotopic and high-resolution continuous meteorological and discharge data, the transpiration rates were estimated to be 78% for Banzhai, 10 +/- 4% for Chenqi, and 24 +/- 1% for Dengzhanhe, and the differences among these values are mainly attributed to differences in vegetation types in those areas. These results show that the variation in stable isotopes in groundwater can be used as a key index in evaluating the effects of different land cover changes and environmental changes on the water cycle in a catchment

Reflections on the dynamic zero-COVID policy in China

The coronavirus disease 2019 (COVID-19) pandemic has posed a serious threat to global healthcare and economy. In order to curb its spread, China adopted the dynamic zero-COVID policy, aiming to diagnose and isolate cases and close contacts as soon as possible. However, there is a controversy about the impact of isolation measures on social order, including the economy, personal employment and public mental health. Therefore, this review discusses and analyzes in detail the advantages and challenges of implementing dynamic zero-COVID policy. Although this public health policy might cause a shock to the economy in the short term, China still achieved a continued healthy economic performance with stable unemployment and strong export growth. Moreover, the rates of infection and mortality in China were lower than those in the United States and the European Union. However, due to the high transmissibility and low pathogenicity of the Omicron variant and prolonged lockdown-induced psychological damage, people questioned the effectiveness and necessity of this policy. Now that China has adjusted its policy in a timely manner, but many problems still remain unsolved. Some practical suggestions in terms of mental health, vaccine development, drugs supply, and economic recovery are put forward at the end of our paper to minimize negative impacts and provide a reference for future efforts

Using deuterium excess, precipitation and runoff data to determine evaporation and transpiration: A case study from the Shawan Test Site, Puding, Guizhou, China

Separating watershed evapotranspiration into its evaporation and transpiration components is important for calculating the carbon that is assimilated by terrestrial vegetation in carbon cycle studies. The key step in this separation is to quantify the evaporation component. The deuterium excess (d-excess) in meteoric water has been shown to be an important indicator of both the original source of the water vapor and the humidity at the vapor source area. It has also shown promise for use in investigating the evaporation losses. While many studies have used the delta D/delta O-18 method to study watershed evaporation, few have discussed the differences between the delta D/delta O-18 (single isotope system) and d-excess (dual isotope system) methods in quantifying watershed evaporation. Given the complexity of natural watersheds, the Shawan Test Site was established at Puding, China, to study the water cycle in five concrete tanks (simulated watersheds) with different land uses over one hydrologic year. There were no plants in two of the tanks (bare rock and bare soil), which allowed verification of evaporation calculations derived from the d-excess and delta D/delta O-18 methods. delta D or delta O-18 values of precipitation in the rainy season, when most of the groundwater recharge occurs, showed great variability. In contrast, the d-excess of the meteoric waters collected during the same rainy season was much more stable than the delta D or delta O-18 values. We quantified the annual evaporative loss of the five watersheds using both methods. Comparison of the results indicated that the d-excess method is more acceptable than the delta D/delta O-18 method due to the stability of d-excess. Calculated ratios of transpiration to evapotranspiration in three tanks planted with vegetation were 56.8% in cultivated land, 70.9% in shrub land, and 85.9% in grassland, demonstrating that in well vegetated watersheds, this component of the cycle is controlled chiefly by plant transpiration. Land use has an important impact on the hydrologic cycle in a watershed, and the d-excess calculations conducted in this study provide new insights for quantifying components of the cycle, especially in the East Asian monsoon region which has rainfall with a large range in delta D or delta O-18 values. (C) 2018 Elsevier Ltd. All rights reserved