A Comparison of Hydrothermal Aging, SO2 and Propene Poisoning Effects on NH3-SCR over Cu-ZSM-5 and Cu-SAPO-34 Catalysts

This study was aimed to investigate the effects of hydrothermal aging, propene and SO2 poisoning on the ammonia-selective catalytic reduction (NH3-SCR) performance of both Cu-SAPO-34 and Cu-ZSM-5. The catalytic activities of fresh, aged and poisoned samples were tested in ammonia-selective catalytic reduction (NH3-SCR) of NOx conditions. The XRD, TG and N2-desorption results showed that the structures of the Cu-SAPO-34 and Cu-ZSM-5 remained intact after 750˚C hydrothermally aged, SO2 and propene poisoned. After hydrothermal aging at 750˚C for 12 h, the NO reduction performance of Cu-ZSM-5 was significantly reduced at lower temperatures, while that of Cu-SAPO-34 was less affected. Moreover, Cu-SAPO-34 catalyst showed high NO conversion with SO2 or propene compared to Cu-ZSM-5. However, Cu-ZSM-5 showed a larger drop in catalytic activity with SO2 or propene compared to Cu-SAPO-34 catalyst. The H2-TPR results showed that Cu2 ions could be reduced to Cu and Cu0 for Cu-ZSM-5, while no significant transformation of copper species was observed for Cu-SAPO-34. Meanwhile, the UV-vis DRS results showed that CuO species were formed in Cu-ZSM-5, while little changes were observed for the Cu-SAPO-34. Cu-SAPO-34 showed high sulfur and hydrocarbon poison resistance compared to Cu-ZSM-5. In summary, Cu-SAPO-34 with small-pore zeolite showed higher hydrothermal stability and better hydrocarbon and sulfur poison resistant than Cu-ZSM-5 with medium-pore.

A comparative study of the thermal and hydrothermal aging effect on Cu-SSZ-13 for the selective catalytic reduction of NOx with NH_(3)

In this work,the characterizations of Cu-SSZ-13 after hydrothermal aging(HTA)and thermal aging(TA)at different temperatures(750,800,and 850°C)are compared,and the differences between those two serious aged samples are analyzed.With this data,the effect of steam on catalysts deactivation during hydrothermal aging is analyzed.The TA at 750 and 800°C causes the dealumination and the agglomeration of Cu^(2+)ions to Cu O,resulting in the activity loss of Cu-SSZ-13.The presence of steam upon HTA at750 and 800°C aggravates the catalyst deactivation by increasing the Al detachment and the Cu^(2+)agglomeration.The structure and cupric state are almost the same in the Cu-SSZ-13 after TA and HTA at 850°C,respectively,indicating that the steam has little influence on the deactivation.The formation of CuAl_(2)O_(4) spinel is the primary reason for the deactivation after both HTA and TA at 850°C,probably attributed to the strong interaction between Cu^(2+)ions and framework Al sites at high temperatures.

Investigation of Ce/BEA as a passive NO_(x)adsorber:2.Hydrothermal aging deactivation mechanism

Ce/BEA has the potential to be applied as a novel passive NO_(x)absorber(PNA)in the after-treatment of vehicles due to its considerable NO_(x)storage capacity.However,as a vehicle exhaust after-treatment material,it must withstand the test of long-term hydrothermal aging.This work examined the deactivation mechanism of Ce/BEA during hydrothermal aging.3.0 wt%Ce/BEA was prepared using the ionexchange method,and then subjected to hydrothermal treatment at 650℃with 10%H_(2)O for 1-12 h to obtain samples with different aging extent.For comparison,the H-BEA support was aged under the same conditions.Brunauer-Emmett-Teller(BET)method,X-ray diffraction(XRD),NH_(3)temperature programmed reduction(NH_(3)-TPD),^(27)Al MAS nuclear magnetic resonance(^(27)Al MAS NMR),H_(2)temperature programmed reduction(H_(2)-TPR),and high resolution-transmission electron microscopy(HR-TEM)were performed to characterize the changes in PNA performance,structure,Ce species,and acidity.The HR-TEM and H_(2)-TPR results show that CeO_(x)particles appear after hydrothermal aging,which results from the detachment and aggregation of active Ce species.Based on the^(27)Al MAS NMR results,we conclude that BEA zeolite dealumination leads to the loss of acidic sites and the transformation of active Ce species on the acidic sites into the less active CeO_(x).This is the primary reason for the hydrothermal aging deactivation of Ce/BEA.

Effect of Sizing on the Interfacial Shear Strength of Carbon Fiber/Epoxy Resin Monofilament Composite

The single fiber fragmentation test （SFFT） was used to measure the interracial shear strength （IFSS） of sized and unsized CF800/epoxy resin monofilament composite in order to evaluate the effect of sizing respectively. Besides, the interfacial reinforcing mechanism was explored by analyzing the surface morphology of the carbon fibers, the wettability between the carbon fibers and the epoxy resin, and the chemical characteristics of the fiber surface. Moreover, the effect of sizing on heat and humidity resistance of interface was investigated by aging test. The results show that sizing improves IFSS of CF800/epoxy resin monofilament composite by 59% through increasing the functional groups containing oxygen and through enhancing wettability, while after sizing the heat and humidity resistance of interface is decreased.

Application of silica-alumina as hydrothermally stable supports for Pt catalysts for acid-assisted soot oxidation

In this work,silica-alumina mixed oxides with different SiO_(2)contents(5%and 30%)were adopted as acidic supports for platinum catalysts for soot oxidation.The obtained catalysts were hydrothermally aged in 10%H_(2)0/air at 750℃for 20 h.The catalysts were characterized by X-ray diffraction(XRD),N_(2)adsorption,inductively coupled plasma(ICP),CO chemisorption,NH3temperature-programmed desorption(TPD),infrared(IR)spectroscopy of CO adsorption,temperature-programmed oxidation(TPO)of NO,and TPD of NO_(x).The surface acidity of catalyst was positive correlated with the content of SiO_(2),which kept platinum in metallic and partially oxidized states in an oxidizing atmosphere.Compared with sulfation treatment on the alumina support,the application of SiO_(2)-Al_(2)O_(3)mixed oxides does not result in the coverage of Pt active sites and the prepared catalysts exhibit excellent activity for NO oxidation.They promote NOxpreferential adsorption on soot and decomposition of surface oxygenated compounds(SOCs)as the sulfated Pt/Al_(2)O_(3)catalyst does.

Synthesis,Crystal Structure and Fluorescent Properties of Silver and Cadmium Complexes

Two new complexes [Ag（bix）]n·n NAA·n H2O（1） and [Cd（NAA）（phen）2（H2O）]2· 2CH3COO-·H2O（2）（bix = 1,4-bis（imidazol-1-ylmethyl）benzene,HNAA = α-naphthylacetic acid,phen = 1,10-phenanthroline） have been successfully synthesized under hydrothermal conditions.Their structures have been determined by elemental analyses,IR spectroscopy,TG and single-crystal X-ray diffraction analysis.The intermolecular hydrogen bonding or π-π stacking interactions extend the complexes into a 3D supramolecular structure.Moreover,the luminescent properties of complex 2 have been investigated in the solid state.

Unraveling the nature of cerium on stabilizing Cu/SAPO-34 NH_(3)-SCR catalysts under hydrothermal aging at low temperatures

To reveal how cerium stabilizes Cu/SAPO-34 at low-temperature hydrothermal aging,various amounts of cerium were introduced into Cu/SAPO-34 via impregnation method and treated at 70℃with RH 80%for 96 h.Cerium as Ce^(3+)and CeO_(2)nanoparticle is located on the surface of Cu/SAPO-34,and Ce^(3+)plays a vital role on gradually decreasing surface acidity and blocking defect sites with an increase of Ce loading.After hydrothermal aging,Cu/SAPO-34 with high Ce loading shows the superior SCR activity comparable to fresh samples.It is proven that the surface acidity determines the stability of the structure during hydrothermal aging process,and lower surface acidity prevents the number of Cu(Ⅱ)ions from decreasing significantly.Furthermore,the structure's stability helps the recovery of Cu(Ⅱ)ions and renders an outstanding regene ration ability.Our finding paves the way for the design of new Cu/SAPO-34catalysts with good SCR activity and long-term stability in real application.

CO and C_3H_8 total oxidation over Pd/La-Al_2O_3 catalysts: Effect of calcination temperature and hydrothermal treatment

A series of Pd/La-Al2O3（PLA） catalysts with La-Al2O3（LA） support calcined at different temperatures（500, 700, 900 and 1050 oC） were prepared using an incipient wetness impregnation method. The activity of the fresh and hydrothermally aged PLA catalysts were tested for total oxidation of CO and C3H8. The activity of the fresh PLA catalysts for CO and C3H8 oxidation increased with increasing calcination temperature of the support, while the activities of the aged catalysts declined and became essentially the same. CO chemisorption results revealed that the suppressed activities of the aged catalysts were mainly due to the decline of palladium dispersion. The turnover frequency（TOF） of CO oxidation increased with increasing reduction ability of the catalysts, with a fresh catalyst calcined at 1050 oC having the highest value（0.048 s–1）. However, the TOF of C3H8 total oxidation was affected by not only the redox properties of catalysts but also the size of Pd particle, and large Pd particles possessed higher TOF value of C3H8 oxidation, with the highest value（0.125 s–1） being obtained on an aged catalyst calcined at 500 oC.

CO and C3Hs Total Oxidation over Pd Catalysts Supported on Commercial Ce-Zr Solid Solution： Effects of the Calcination Temperature and Hydrothermal Treatment

A series of Pd catalysts supported on commercial Ce-Zr solid solution（Pd/CZ） calcined at different tem- peratures（750, 900 and 1050 %℃） was prepared via an incipient wetness impregnation method. The activities of the fresh and hydrothermally aged PdTCZ catalysts were tested for total oxidation of CO and C3H8. For CO oxidation, the activity of either fresh or aged Pd/CZ catalysts decreased with the elevating of calcination temperature of CZ support, with a fresh catalyst calcined at 750 ℃ possessing the highest activity and hydrothermal stability. For C3H8 total oxidation, the activity of Pd/CZ catalysts could be improved by increasing the calcination temperature of support. However, the aged Pd/CZ catalysts showed higher activity than corresponding fresh Pd/CZ catalysts. The turnover frequency（TOF） over Pd/CZ catalyst for CO oxidation increased with increasing reduction ability of the catalysts, with a fresh catalyst calcined at 750 ℃ having the highest value（0.27 s^-1）. However, the TOF of Pd/CZ catalyst for C3Hs total oxidation was mainly affected by the size of Pd particles, and large Pd particles possessed a higher activity, with the highest TOF value（0.96s^-1） obtained over an aged catalyst calcined at 1050 ℃.