Solid acid MoO_(3)/ZrO_(2)-TiO_(2)catalysts were prepared by impregnation method,and catalytic hydrolysis of difluorodichloromethane(CFC-12)over the catalyst was studied.The presence of MoO_(3)/ZrO_(2)-TiO_(2)catalyst in polycrystalline state could be clearly observed by transmission electron microscopy(TEM).Mesopores were detected by N2 adsorption-desorption isotherms which further confirmed the MoO_(3)/ZrO_(2)-TiO_(2)structural characteristics of catalyst.The results of NH_(3)-TPD showed that the calcination temperatures had a great influence on the acidity of the catalyst,and the weak acidic site had a strong catalytic activity for the catalytic hydrolysis of CFC-12.Moreover,ZrO_(2)-TiO_(2)was highly dispersed in the MoO_(3)framework,suggested by powder X-ray diffraction(XRD)and N_(2)adsorption-desorption results.The effects of the catalyst calcination temperatures on the conversion rate of CFC-12 were studied.The effects of catalytic hydrolysis temperatures and water vapor concentration on the catalytic hydrolysis rate of CFC-12 were also studied.The solid acid MoO_(3)/ZrO_(2)-TiO_(2)was calcined at 500℃for 3 h at a catalytic hydrolysis temperature of 400℃and water vapor concentration of 83.18%,and catalytic hydrolysis rate of CFC-12 reached 98.65%.The hydrolysis rate of CFC-12 remained above 65.34%after 30 hours continuous reaction.
Groundwater residence time is a fundamental property of groundwater to understand important hydrogeological issues,such as deriving sustainable abstraction volumes,or,the evolution of groundwater quality.The anthropogenic trace gases chlorofluorocarbons (CFC-11,CFC-12 and CFC-113) and sulphur hexafluoride (SF6) are ideal in this regard because they have been released globally at known rates and become dissolved in groundwater following Henry’s Law,integrating over large spatial (global) and temporal (decades) scales.The CFCs and SF6 are able to date groundwater up to w100 years old with the caveat of certain simplifying assumptions.However,the inversion of environmental tracer concentrations (CFCs and SF6) to derive groundwater age rests on the accurate determination of groundwater recharge parameters,namely temperature,elevation,salinity and excess air,in addition to resolving the potential for contamination,degradation and unsaturated zone effects.This review explores the fundamentals of CFC-11,CFC-12,CFC-113 and SF6 as environmental tracers of groundwater age and recommends complementary techniques throughout.Once this relatively simple and inexpensive technique has been used to determine initial concentrations at the recharge zone,setting the groundwater dating ‘clock’ to zero,this review then explores the meaning of groundwater ‘age’ in relation to measured environmental tracer concentrations.It is shown that the CFCs and SF6 may be applied to a wide-range of hydrogeological problems and suggests that environmental tracers are particularly powerful tools when integrated with numerical flow and transport models.
