Effect of Al2O3 doping on the structure and performance of an Al2O3/Fe2O3 catalyst for mercury oxidation

In this study,the thermal stability of a Fe_2 O_3 catalyst for mercury oxidation was significantly improved by doping with Al_2 O_3.After 1 hr,the catalyst doped with 10 wt.% Al_2 O_3 still exhibited a mercury conversion efficiency of 70.9%,while the undoped sample even lost its catalytic activity.Doping with Al_2 O_3 retarded the collapse of the catalyst mesoporous structure during high-temperature calcination,and the doped samples maintained a higher specific surface area,smaller pore size,and narrower pore size distribution.Transmission electron microscope images revealed that after calcination at 350℃,the average size of the catalyst grains in Fe_2 O_3 was 23.4 nm;however,the corresponding values for 1%Al_2 O_3/Fe_2 O_3,3%Al_2 O_3/Fe_2 O_3,and 10%Al_2 O_3/Fe_2 O_3 were only 13.3,7.1,and 4.7 nm,respectively.Results obtained from X-ray diffraction and thermogravimetry coupled with differential scanning calorimetry confirmed that doping with Al_2 O_3 also retards the crystallization of the catalysts at high temperature,constraining catalyst grains to a smaller size.     

Sulfur(IV) oxidation by hydrogen peroxide in aqueous suspensions of SiO2, Al2O3, TiO2 and zeolite

Normal and stopped-flow spectrophotometry were used to study the rate of oxidation of sulfur(IV) (SO₃²⁻/HSO₃⁻) by H₂O₂ in aqueous suspensions of finely divided SiO₂, Al₂O₃, TiO₂ and Na-A-zeolite buffered at pH 8.2 and 4.0. Within the limits of error, the rate constants obtained agree with those measured in the absence of suspended material, i.e. under the given conditions there is no surface catalytic effect to be observed.     

ZnO包覆Al_2O_3的制备表征及光催化性能研究

采用化学沉积法制备了ZnO包覆Al2O3光催化剂,并通过X射线衍射(XRD)、扫描电镜(SEM)进行了表征。在自制的光化学反应器中,以中压汞灯作光源,一定浓度的甲基橙为光催化反应模型化合物,研究了光催化剂的活性。考察了甲基橙初始浓度、催化剂加投量、pH值、温度、光照强度、反应液体积等因素对脱色率的影响。实验结果表明,ZnO包覆Al2O3复合光催化剂具有较高的光催化活性。在250W中压汞灯下光照3h,0.10g复合光催化剂能使200mL,10mg/L甲基橙溶液的脱色率达到92.21%。     

掺杂La或Si对Ag/Al2O3催化剂热稳定性和脱NO活性的影响

利用BET比表面测定和X-射线衍射技术考察了掺杂La或Si的Ag/Al2O3催化剂的热稳定性,并研究了富氧条件下,丙烯在这些催化剂上选择性还原NO的活性.结果表明,掺杂La或Si能抑制Al2O3相变,使γ-Al2O3完全转化为a-Al2O3的温度升至1100℃以上.相应地,延缓催化剂比表面下降,从活性角度来看,当焙烧温度为1100℃时,与掺杂La或Si相比,不掺杂La或Si的Ag/Al 2O3催化剂活性要低得多;当焙烧温度低于1000℃时,掺杂少量La(2%La2O3)对Ag/Al2O3催化剂活性影响不大,但是,掺杂Si(2%或8%SiO2)或较高含量La(8%La2O3)会导致催化剂活性降低.综合考虑热稳定性和富氧条件下的NO还原活性,认为掺杂较低含量La(2%La2O3)的Ag/Al2O3催化剂性能最佳.     

Impact of elevated O3 and CO2 exposure on potato (Solanum tuberosum L. cv. Bintje) tuber macronutrients (N,P, K,Mg, Ca)

It was investigated whether exposure of elevated ozone (O₃) and carbon dioxide (CO₂) concentrations affected the macronutrient (N, P, K, Mg, Ca) concentrations in potato (Solanum tuberosum L.) tubers in three open-top chamber experiments from Sweden and Finland. The tuber concentrations of N, P, K and Mg correlated positively with O₃ exposure (although not significantly in the case of N and P) but the O₃ exposure had no effect on the tuber concentration of Ca. A likely mechanism behind the observed O₃ effects was suggested to be that the more progressed senescence of O₃ exposed plants was associated with a larger extent of reallocation of mobile nutrients from the haulm to the tubers. In addition, the uptake of macronutrients may have been less negatively affected by O₃ exposure than the assimilation of carbon. O₃ tended to reduce the total tuber contents of all investigated nutrients, which imply a reduced fertilizer need per unit field area. This was not associated with a decreased fertilizer need per tonnage of yield, as the tuber nutrient concentrations were increased by O₃ exposure. The increased CO₂ concentration did not significantly affect any of the investigated macronutrients in the present dataset but did generally prevent the O₃ induced increases in nutrient concentrations to be expressed (only significant in the case of N and Mg). The O₃ induced increase in tuber K concentration, may mediate earlier observed O₃ effects on potato tuber concentrations of citric and malic acids. To conclude, anticipated future (and even presently occurring) O₃ exposure has a negative impact on the total tuber contents of K and Ca and probably also on the total tuber contents of N, P and Mg. O₃ exposure causes increased tuber concentrations of N, P, K and Mg at an early harvest. The O₃ induced increase in tuber concentration tended to diminish by a CO₂ elevation.     

Catalytic performance of Fe3O4-CoO/Al2O3 catalyst in ozonation of 2-(2,4-dichlorophenoxy)propionic acid, nitrobenzene and oxalic acid in water

Fe3O4-CoO/Al2O3 catalyst was prepared by incipient wetness impregnation using Fe(NO3) 3·9H2O and Co(NO3) 2·6H2O as the precursors,and its catalytic performance was investigated in ozonation of 2-(2,4-dichlorophenoxy) propionic acid(2,4-DP) ,nitrobenzene and oxalic acid.The experimental results indicated that Fe3O4-CoO/Al2O3 catalyst enabled an interesting improvement of ozonation eciency during the degradation of each organic pollutant,and the Fe3O4-CoO/Al2O3 catalytic ozonation system followed a radical-type mechanism.The kinetics of ozonation alone and Fe3O4-CoO/Al2O3 catalytic ozonation of three organic pollutants in aqueous solution were discussed under the mere consideration of direct ozone reaction and OH radical reaction to well investigate its performance.In the catalytic ozonation of 2,4-DP,the apparent reaction rate constants(k) were determined to be 1.456×10-2 min-1 for ozonation alone and 4.740×10-2 min-1 for O3/Fe3O4-CoO/Al2O3.And O3/Fe3O4-CoO/Al2O3 had a larger Rct(6.614×10-9) calculated by the relative method than O3 did(1.800×10-9) ,showing O3/Fe3O4-CoO/Al2O3 generated more hydroxyl radical.Similar results were also obtained in the catalytic ozonation of nitrobenzene and oxalic acid.The above results demonstrated that the catalytic performance of Fe3O4-CoO/Al2O3 in ozonation of studied organic substance was universal to a certain degree.