Influence of CeO_2 loading on structure and catalytic activity for NH_3-SCR over TiO_2-supported CeO_2

A series of supported CeO_2/TiO_2 catalysts were prepared to explore the influence of CeO_2 loading on these catalysts for the selective catalytic reduction of NO_3 by NH_3(NH_3-SCR).The catalysts were investigated in detail by means of XRD,Raman,H_2-TPR,NH_3-TPD,XPS,in situ DRIFTS,and NH3-SCR reaction.The activity of the catalyst is closely related to the content of CeO_2.When the loading of CeO_2 is near the dispersion capacity(1.16 mmol Ce~(4+)/100 m~2 TiO_2),the catalytic activity is better.This may be because that the dispersed CeO_2 is the active species and the catalyst has appropriate redox property,along with the larger amounts of surface Ce content and surface adsorbed oxygen species.Finally,a possible reaction mechanism via the Langmuir-Hinshelwood(L-H) mechanism is tentatively proposed to further understand the NH_3-SCR reaction.     

碱中毒对烧结烟气SCR催化剂脱硝脱二噁英的影响

采用湿式浸渍法对商用V₂O₅-WO₃/TiO₂催化剂进行了碱金属硫酸盐(Na/K/Rb)中毒实验。在模拟铁矿烧结烟气条件下,对比了新鲜和中毒催化剂同时脱除NO_x和二噁英的活性(以氯苯作为二噁英的模拟物),并通过N₂吸脱附、XRD、NH₃-TPD、H₂-TPR和XPS等检测手段对催化剂进行了表征。结果表明:中毒催化剂的脱除NO_x和催化降解氯苯活性明显降低,失活率顺序为K₂SO₄>Rb₂SO₄>Na₂SO₄。催化剂中毒后,碱金属离子可以占据催化剂表面化学吸附氧空位,导致表面化学吸附氧数量减少,物质的量之比n(V⁵⁺)/n(V⁴⁺)降低,V物种可还原性减弱。     

Roles of Lewis and Brnsted acid sites in NO reduction with ammonia on CeO_2-ZrO_2-NiO-SO_4~(2-) catalyst

Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an in...     

Synergetic catalysis of ceria and titania for selective reduction of NO

The promotional effect of the interaction between titania and ceria on the catalytic performance for selective reduction of NO was studied.The catalysts,CeO 2,TiO 2,CeO 2 /TiO 2 and Ti x Ce 1-x O 2,were synthesized and tested in NH 3-Selective catalytic reduction(SCR) of NO,and the samples were characterized by the Brunaller,Emmett and Teller(BET absorbed gas N 2),X-ray diffraction(XRD),high resolution transmission electron microscopy(HR-TEM),and temperature programmed desorption(TPD NH 3) techniques.The improvement mechanism of the interaction between the titania and ceria had been explored and discussed from two aspects of micro-structure and surface acidity.The interaction between the titania and ceria greatly improved the catalytic activity but had little effect on the active temperature.It was first reported that the acid amount determined the catalytic activity and the acid strength determined the active temperature for NH 3-SCR of NO.     

New insights into the role of vanadia species as active sites for selective catalytic reduction of NO with ammonia over VO_x/CeO_2 catalysts

A series of VO_x/CeO_2 catalysts we re synthesized via vanadia supported on ceria with different BET surface areas.The catalysts were employed to investigate the active sites for the selective catalytic reduction of NO with NH_3(NH3-SCR).The kinetic results show that VO_x/CeO_2 catalysts exhibit nearly constant apparent activation energies(E_a),indicating the same SCR reaction mechanism.The V-O-Ce bridging modes and oligomeric VO_x were identified and quantified by Raman,FT-IR and H_2-TPR.The amounts of the V-O-Ce bridging modes calculated by H_2-TPR are correlated to the NH_3-SCR intrinsic reaction rates.The turnover frequencies(TOFs) show a constant value at the same temperature,which were calculated based on the number of V-O-Ce bridging modes of VO_x/CeO_2 catalysts.Therefore,it can be concluded that the V-O-Ce bridging modes are the active sites of VO_x/CeO_2 catalysts for the NH3-SCR reaction.     

Simultaneous Desulfurization and Denitrification by Microwave Catalytic over FeCoCu/Zeolite 5A Catalyst

FeCoCu/zeolite 5A was used as a catalyst for microwave catalytic desulfurization and denitrification and for microwave catalytic reduction of SO2 and NOx with ammonium bicarbonate (NH4HCO3) as a reducing agent. Microwave catalytic desulfurization and denitrification efficiency attained 99.5 and 86.1%, respectively. The reaction efficiencies of microwave catalytic reduction of SO2 and NOx could be up to 95.8 and 95.1% separately; the optimal microwave power and empty bed residence time on microwave catalytic reduction of SO2 and NOx simultaneously are 280 W and 0.358 s, respectively. Microwave accentuates catalytic reduction treatment, and microwave addition can increase the SO2 and NOx removal efficiency. The microwave catalytic SO2 and NOx removal follows the Langmuir-Hinshelwood model.     

Field Study, Design, and Catalyst Cost of Selective Catalytic Reduction Process

A pilot TiO2∕V2O5 based selective catalytic reduction (SCR) system was installed in a glass manufacturing factory. The effects of important operation parameters such as the reaction temperature, space velocity, and inlet NH3∕NOx molar ratio on the NO removal were evaluated. It was observed that >1 mol of NOx is reacted for every 1 mol of NH3 injected. This observation is different from that reported in the literature for laboratory experiments. The key design parameter values of the reaction rate and the NH3 adsorption rate were determined based on results of the pilot tests using a theoretical SCR model developed by the same research group. The SCR model is a simple analytical solution that accounts for the simultaneous mass transfer and chemical reaction of an SCR reactor. The model results were compared to field data of NOx conversion efficiency and NH3 slip, and they were in reasonable agreement. The required catalyst volume and the cost of catalysts were then determined with the assistance of the design model.     

A novel catalyst of silicon cerium complex oxides for selective catalytic reduction of NO by NH3

A series of CeO2/SiO2 and SixCe1-xO2 complex oxides supported on an activated Al2TiO5-TiO2-SiO2 complex phase (ATS) ceramics were prepared by step impregnation and co-impregnation methods, and characterized by N2-BET, XRD, SEM and NH3-TPD techniques. The effects of reaction temperature, CeO2/SiO2 loadings and Si/Ce molar ratio on the granular catalysts for NO selective catalytic reduction with ammonia (NH3-SCR) were studied. Results indicated that both CeO2/SiO2/ATS and CeO2/ATS catalysts showed the same ac...     

Rare earths (Ce,Y, Pr) modified Pd/La_2O_3-ZrO_2-Al_2O_3 catalysts used in lean-burn natural gas fueled vehicles

14%REO_x-2.5%La_2 O_3-33.5%ZrO_2-50%Al_2 O_3(RE = Ce, Y, Pr) composites were prepared by a coprecipitation method. The Pd catalysts were obtained by an aqueous solution of Pd(NO_3)_2 loaded on the rare earths modified composites with an initial wet impregnated method. The experiment results show that catalytic activity of the rare earths modified Pd/La_2 O_3-ZrO_2-Al_2 O_3 catalysts is better than bare sample for methane oxidation. The structural characterization results reveal that the rare earths modified Pd catalysts increase amounts of surface active oxygen species by X-ray photoelectron spectroscopy(XPS) analysis and improve the dispersion of active component from H2-temperature programmed reduction(H2-TPR) measurement compared with bare sample. Especially,Pd/14%Y_2 O_3-2.5%La_2 O_3-33.5%ZrO_2-50%Al_2 O_3 sample exhibits highly active stability, it is related to the Pd particles highly dispersion,which was observed by transmission electron microscope(TEM) images.     

A novel fused iron catalyst for ammonia synthesis promoted with rare earth gangue

Rare earth gangue, which mainly consists of mixtures of light rare earths such as lanthana, ceria, neodymium oxide and praseodymium oxide, was used as the promoter of fused iron catalysts for ammonia synthesis. The result showed that the activity of the catalyst promoted with rare earth gangue was comparable with those of commercial iron catalysts with high amount of cobalt. The role of rare earths was owed to their advantages for favoring the deep reduction of the main composite in catalyst, i.e., iron oxide. This fmding indicated that the use of rare earth gangue could decrease the content of cobalt or even completely replace cobalt, which was used to be regarded as unsub- stitutable promoters for high performance ammonia catalyst; therefore, the cost of fused iron catalysts would decrease significantly.     

SO2 poisoning and regeneration of Mn-Ce/TiO2 catalyst for low temperature NOx reduction with NH_3

SO2 poisoning and regeneration of Mn-Ce/TiO2 catalyst prepared by a novel co-precipitation method for low temperature selective catalytic reduction (SCR) of NOx with ammonia were investigated in this study. When 700 ppm SO2 was fed in, the Mn-Ce/TiO2 catalyst had good resistance to SO2, but the deactivation of Mn-Ce/TiO2 poisoned by SO2 still occurred. The NO conversion of Mn-Ce/TiO2 (the molar ra-tio of Ce to Ti is 0.075) catalyst decreased from 92.5% to 34.6% in 13 h. Characterizations of fresh and SO2-poisoned Mn-Ce/TiO2 catalysts were carried out by Brunauer-Emmett-Teller method (BET), ion chromatography (IC), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The characterized results indicated that the deposition of sulfates and nitrates on the surface made the catalyst deactivated. Water washing, thermal regeneration and reductive regeneration were used to regenerate the deactivated Mn-Ce/TiO2. And water washing showed best performance on the regeneration of poisoned catalysts, especially with ultrasonic vibration. The Mn-Ce/TiO2 catalyst showed high stability under a series of deactivation-regeneration experiments for ten cycles.     

掺杂稀土BaTiO3的制备及镍基催化剂的活性

采用柠檬酸盐法和溶胶-凝胶法合成出稀土掺杂的BaTiO3,并考察了稀土离子掺杂对BaTiO3颗粒粒径的影响。测定了掺杂BaTiO3的比表面积、晶相、粒度等粉体性能,指出稀土离子有抑制BaTiO3晶粒长大的作用。稀土掺杂的BaTiO3作镍基催化剂载体,以CO2/CH4重整制合成气为探针反应,评价了这些催化剂的催化活性,实验表明掺杂稀土有助于提高催化活性。     

Reduction of SO2 to elemental sulfur over rare earth-iron catalysts

With coal gas as a reducing agent, the catalytic reduction of SO2 to sulfur in the flue gas produced in metallurgical processes was studied over catalysts of rare earth-Fe/Al2O3 (REFe/Al2O3). The catalytic activity of the REFe/Al2O3 catalyst on the reduction of SO2 to sul-fur was investigated based on kinds and the contents of rare earths and different preparation method of the catalyst. Additionally, the mecha-nism of this catalytic reduction reaction was also explored. Results showed that different rare earth imposed different effect on the activity of the Fe/Al2O3 catalyst. Especially, the addition of Sm and Dy greatly improved the catalytic activity of Fe/Al2O3. The yield of sulfur over SmFe/Al2O3was increased to 86.62% at 360 ℃, which was 40.5% higher than that over Fe/Al2O3at the same temperature; and the sulfur yield over DyFe/Al2O3was increased to 91.62% at 400 ℃, 26.4% higher than that over Fe/Al2O3. The catalytic activity of REFe/Al2O3 was somehow dependent on the content of rare earth. For SmFe/Al2O3, the content of Sm was optimized to be about 1.0 wt.%. The rare earth catalyst prepared with different methods also showed varied activity. The sulfur yield over rare-earth transition metal catalysts follows the order: Sm and iron solution mixing impregnationSm first, then iron solution impregnationiron first, then Sm solution impregnation. The reaction mechanism of SO2 reduction to sulfur with coal gas was proposed to be an intermediate mechanism.     

Enhancing low-temperature NH3-SCR performance of Fe–Mn/CeO2 catalyst by Al2O3 modification

In the work, supported catalysts of FeO_x and MnO_x co-supported on aluminum-modified CeO₂ was synthesized for low-temperature NH₃-selective catalytic reduction (NH₃-SCR) of NO. Impressively, the SCR activity of the obtained catalyst is markedly influenced by the adding amount of Al and the appropriate Ce/Al molar ratio is 1/2. The activity tests demonstrate that Fe–Mn/Ce1Al2 catalyst shows over 90% NO conversion at 75–250 °C and exhibits better SO₂ resistance compared to Fe–Mn/CeO₂. Fe–Mn/Ce1Al2 shows the expected physicochemical characters of the ideal catalyst including the larger surface and increased active reaction active sites by controlling the amount of Al doping. Also, the better catalytic activity is well correlated with the present advantaged surface adsorption oxygen species, Mn⁴⁺ species, Ce³⁺ species and the enhanced reducibility of Fe–Mn/Ce1Al2, which is superior to the Fe–Mn/CeO₂ catalyst. More importantly, we further demonstrate that the amount and strength of surface acid sites are improved by Al-doping and more active intermediates (monodentate nitrate) is generated during NH₃-SCR reaction. This work provides certain insight into the rational creation of simple and practical denitration catalyst environmental purification.     

Application of rare earths in fluid catalytic cracking: A review

The need for more active and hydrothermally stable fluid catalytic cracking(FCC)catalysts to combat the effect of metal contaminants has led to an increase in demand for rare earth oxides.Rare earth oxides enhance catalyst activity and prevent the loss of acid sites during the FCC unit operation,especially when heavy residue with high metal content is used as feed.In this paper,a review was carried out to show the effects of rare earth elements on the structure,activity,and stability of FCC catalysts.Also,the use of rare earth elements as vanadium traps was analyzed in conjunction with the mechanism of catalyst deactivation by vanadium.The objective was to elucidate the interaction of vanadium species with the zeolite component of the FCC catalysts and the role of rare earth elements in countering the deleterious effects of vanadium on the FCC catalysts.     

Influences of Platinum Precursors and Solution Acidities on REO-Based Catalysts Performances

Important effects exist between precious metals and rare earths oxides in three-way catalyst, especially the coordinated effects. These effects were studied by using H2PtCl6, Pt(NH3)2(NO2)2 and Pt(OH)2(C2H5ONH2)2 as Pt precursors, and the mixed oxide of (Ce-Zr-La-Pr)O as base material to prepare a series of catalysts, and their performances of the catalysts were studied by TPR and CO pulse titration technologies. The results shown that Pt precursors and their solutions pH values influenced the oxygen storage capabilities, the active metal distribution degrees of the catalysts obviously, and every catalyst prepared by different precursors had an optimal pH values. It indicates that the active metals precursors and their solutions acidities have outstanding influences on the catalysts performances for the mutual effects existing between the active metals and the Rare Earth metal oxides, which results from the mate groups of the precursors and the solution acidity.     

Getting insights into gas-phase sulfation effect on catalytic performance of praseodymium oxides in NH3-SCR of NO

Sulfation treatment has been widely used to promote the catalytic performance of ceria(CeO₂) based catalysts for the selective catalytic reduction of NO by NH₃(NH₃-SCR of NO).Praseodymium oxide(PrO_x),another commonly used rare earth material with similar structural properties as CeO₂,also shows satistactory redox properties due to the facile redox cycle of Pr³⁺■Pr⁴⁺.In this work,gas phase sulfation treatment with varied...     

Physicochemical and isomerization property of Pt/SAPO-11 catalysts promoted by rare earths

Monometallic catalyst Pt/SAPO-11 was prepared by impregnation method.Bimetallic catalysts LaPt/SAPO-11 or CePt/SAPO-11 was prepared by sequential impregnation method.The catalysts were characterized by X-ray diffraction(XRD),nitrogen adsorption,temperature-programmed desorption of ammonia(NH3-TPD),and Fourier transform infrared spectroscopy(FT-IR) techniques.The results showed that with the addition of rare earths the BET surface areas,pore volume,the amount of Bronsted acid and the total acidity of catalys...     

Study on Coke Formation and Stability of Nickel-Based Catalysts in CO2 Reforming of CH4

CO2 reforming of CH4 over nickel-based catalysts was investigated by using a fixed-bed reactor. Catalytic activity and amount of carbon deposition effects by nickel loading content, rare earth promoter and promoter contents were evaluated. It is found that nickel loading as well as reaction temperature can influence the activity and carbon deposition amounts, and with the addition of rare earth promoter, it can greatly improve the catalytic activity and exert a strong effect on the anticoking performance of the catalysts. The 5.0% (mass fraction)Ni-0.75% La BaTiO3 catalyst shows great resistance to coke formation and higher thermal stability as well as the catalytic activity.     

Enhancement of potassium resistance of Ce-Ti oxide catalyst for NH3-SCR reaction by modification with holmium

Alkali metal K in exhaust gas has a deactivation effect on NH₃-SCR catalysts.In this work,it is discovered that the addition of Ho on CeTi catalyst can remarkably strengthen its K tolerance.The conclusions of Brunauer-Emmett-Teller(BET),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),NH₃ temperature programmed desorption(NH₃-TPD)and H₂temperature programmed reduction(H₂-TPR)analyses demonstrate that the enhancement of K resistance mainly originates from its stronger surface acidity and redox capability,the higher concentration of Ce³⁺species and surface chemisorbed oxygen.In situ DRIFT analysis reveals that the introduction of Ho on CeTi can remarkably improve the adsorption of NH₃ and NO_x species on catalyst surface,accompanied by the intensified reactivity of ad-NH₃ species,which should also administer to improve the K resistance.