Synthesis of neodymium modified CeO_2-ZrO_2-Al_2O_3 support materials and their application in Pd-only three-way catalysts

Ce-Zr-Al-Nd2O3 （CZAN） support materials were prepared by co-precipitation and impregnation methods, respectively. They were characterized by X-ray diffTaction （XRD）, low temperature nitrogen adsorption-desorption, oxygen pulsing technique, H2-temperamre programmed reduction （H2-TPR） and X-ray photoelectron spectroscopy （XPS）. The Pd-only three-way catalysts （Pd-TWC） supported on these materials were prepared by incipient wetness method and studied by activity tests. The results demonstrated that the CZAN supports obtained by the two methods showed better structural, textural and redox properties than the CZA without Nd2O3, and the addition of Nd203 improved the catalytic activity of TWC. Especially, the CZAN-i support prepared by impregnation method had better thermal stability and redox property. Meanwhile, the Pd/CZAN-i catalyst exhibited the best catalytic performance. XPS measurements indicated that the Nd-modified samples possessed more Ce3＋ and oxygen vacancies on the surface of samples, which led to a better redox property. The excellent redox property of support materials helped to improve the catalytic activity of TWC.

Realization approach of Pd-only three-way catalysts with high catalytic performance and thermal stability

Pd-only three-way catalyst （TWC）, Pd supported on washcoating （the mixture of alumina and Ce-Zr solid solution）/cordierite, was prepared and its catalytic performance and the operation window （2-value） at 450 ℃ were evaluated with the simulated automotive exhaust feed gas. Surfactants such as Tween-80 and Span-20 were added in the process of preparing the catalyst in order to improve the thermal stability and catalytic performance of Pd-only TWC. The fresh and aged catalysts at 1000 ℃ for 4 h were characterized by low-temperature N2 adsorption, XRD, XPS, and H2-TPR techniques. The results show that the presence of surfactants in the synthesis slurry could influence the physicochemical properties of the final Pd-only TWC. The FTS catalyst prepared with the mixed surfactant of Tween-80 and Span-20 exhibited excellent three-way catalytic performance. After being aged at 1000℃ for 4 h, the catalytic performances of Pd-only TWCs slightly decreased, but the FTS catalyst still demonstrated higher catalytic performance and better thermal stability compared with the Pd-only catalysts prepared with single surfactant or without any surfactant. And the FTS catalyst has a wider 2 value （operation window） than other catalysts, even after being aged at 1000℃.

Quaternary Oxide of Cerium, Terbium, Praseodymium and Zirconium for Three-Way Catalysts

Oxygen storage-capacity （OSC）, oxygen buffer capacity （OBC）, X-my diffraction and electron diffraction pattern, high resolution electron microscopy were used to study the quaternary oxides, i .e., of Ce, Tb, Pr and Zr. （Ce0.6 Tb0.2Zr0.2O2- δ and Ce0.6Pr0.2Zr0.2O2-δ ）. OSC and OBC data indicate that these oxides have very good oxygen transfer capacity （OTC） and their pseudo-solid solutions exhibit fluorite-type structure. These oxides may act as a good candidate for three-way catalysts （TWC）.

Durability of three-way and close-coupled catalysts for Euro IV regulation

The durability of three-way catalyst （TWC） and corresponding close-coupled catalyst （CCC） for Euro Ⅳ stage regulation was investigated through Vehicle Road Running Mode tests, whereas emissions of regulated pollutants of three car fleet were investigated at every 100,000 km miles. The results showed that HC, NOx, and CO emission values could meet Euro Ⅳ regulation limits at every point. The redox properties of TWC and CCC were measured by CO reduction during each isothermal. It was obvious that both aged TWC and aged CCC behaved a good redox property at 673 and 773 K. Based on XRD and BET measurement results, TWC and CCC washcoat were characterized with good thermal stability.

Influence of Ce_(0.35)Zr_(0.55)Y_(0.10) Solid Solution on Performance of Pt-Rh Three-Way Catalysts

Ce0.35Zr0.55Y0. 10 solid solution was prepared by co-precipitation technique and characterized by specific surface area measurements （BET） and X-ray diffraction （XRD）. Ce0.35Zr0.55Y0.10 was used to prepare low Pt-Rh threeway catalyst （TWC）, and its influence on the performance of TWC was investigated. The results revealed that Ce0.35 Zr0.55Y0.10 had a cubic structure similar to Ce0.50Zr0.50O2 and its specific surface area can maintain higher than Ce0.50 Zr0.50O2 after 1000 ℃ calcination for 5 h. Being hydrothermal aged at 1000 ℃ for 5 h, the catalyst containing Ce0.35 Zr0.55Y0.10 still exhibited higher conversion of C3H8, CO and NO and lower light-off temperature in comparison with Ce0.50Zr0.50O2 TWC.

Effect of Sulfur on the Performance of Three-Way Catalysts

Sulfur content is one of the fuel properties to be monitored. Sulfur dioxide, the major product derived from organic sulfur compounds in the exhaust gas emissions, is a poison to the three-way catalysts (TWC). A gas mixture was applied to simulate the exhaust gases used in the TWC aging procedure tests. Two types of the TWC, REX-IIC and REX-IID, were tested in this study. The performance of both TWC's before and after the 100-hour sulfur aging program was compared. It was concluded that the Pt component in the TWC was apt to be poisoned by sulfur much easily than Rh. The performance of the REX-IID catalyst was generally better than that of the REX-IIC catalyst.

The structure–activity relationships of Rh/CeO_(2)-ZrO_(2) catalysts based on Rh metal size effect in the three-way catalytic reactions

With the continuous tightening of automotive emission regulations and the increasing promotion of energy-efficient hybrid vehicles,new challenges have arisen for the low-temperature performance of three-way catalysts(TWCs).To guide the design of next-generation TWCs,it is essential to further develop our understanding of the relationships between microstructure and catalytic performance.Here,Rh/CeO_(2)–ZrO_(2) catalysts were synthesized with different Rh metal dispersion by using a combination of the wet impregnation method and reduction treatment.These catalysts included Rh single-atom catalysts,cluster catalysts,and nanoparticle catalysts.The results showed that the Rh nanoparticle catalyst,with an average size of 1.9 nm,exhibited superior three-way catalytic performance compared to the other catalysts.Based on the catalytic activity in a series of simple reaction atmospheres such as CO+O_(2),NO+CO,and hydrocarbons(HCs)+O_(2) and operando infrared spectroscopy,we found that metallic Rh sites on Rh nanoparticles are the key factor responsible for the low-temperature catalytic performance.

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method）,CO-chemisorption and X-ray photoelectron spectroscopy （XPS）.The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles.The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor.It was found that the effect of Co significantly depended on the preparation process.PdCo/La-Al2O3 catalyst prepared by co-impregnation exhibited better water-resistant performance.The results of XPS indicated that both CoAl2O4 and Co3O4 were present in the Pd catalysts modified by Co.For the catalyst prepared by sequential impregnation method,the ratio of CoAl2O4/Co3O4 was higher than that of the catalyst prepared by co-impregnation method.It could be concluded that Co3O4 played an important role in improving water-resistant performance.

Influences of (Ce-Zr-La-Pr)O Contents on Three-Way Catalyst Performances

A series of catalysts with (Ce-Zr-La-Pr)O contents range from 0 to 50% in coating and single-palladium loads on substrates were prepared to study effects of (Ce-Zr-La-Pr)O contents on catalytic activities and durability by contrasting the characteristics of light-off, A/F and catalytic conversions of the fresh catalysts with that of the aged catalysts. The results show that (Ce-Zr-La-Pr)O can enhance the catalysts light-off characteristics, widen A/F windows and increase catalytic conversions at a certain extent through optimizing physical structural and chemical property of the mixed coating. However, (Ce-Zr-La-Pr)O contents influence greatly on the catalysts activities and durability, and the catalysts with contents ranging from 10% to 30% exhibited better integrative properties in all samples, and 10% was the optical content to make the catalyst performance highest in this thesis. It is indicated that an suitable content of (Ce-Zr-La-Pr)O plays an important role in assisting catalysis, enhancing durability and increasing oxygen storage capability.

Regulated and Speciated Hydrocarbon Emissions from a Dual Fuel Light Duty Vehicle with and Without a Three-Way Catalyst

The regulated pollutants （CO,HC and NOx） and unregulated pollutants （volatile organic compounds and carbonyl compounds）,emitted from a dual fuel vehicle fueled with gasoline and E10 fuel,are measured under a transient cycle and steady modes.The impacts of a three-way catalyst （TWC） are investigated for the two types of fuels.The measured results show that NOx and acetaldehyde emitted from the E10-fueled car are much more than that from the gasoline-fueled car under the same modes.On the basis of maximum incremental reactivity （MIR） factors and emissions of organic gases,the ozone specific reactivity of the tailpipe gases are evaluated.

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.

Effects of CuO-CeO₂Addition on Structure and Catalytic Properties of Three Way Catalysts

The noble metals (Pt, Pd, Rh) supported on Cu-Ce mixed oxides with γ-Al2O3 washcoat/FeCrAl substrate were investigated as catalytic performance of Three Way Catalysts (TWC) under simulated automotive exhaust feed gas. The structural, morphological features and catalytic activity were observed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS) and GC-TCD (Varian CP-4900). The catalytic performance of noble metals (Pt, Rh, Pd) supported on Cu-Ce mixed oxides with γ-Al2O3 washcoat/FeCrAl substrate was be compared with noble metals (Pt, Rh, Pd) supported on Ce-Zr mixed oxides with γ-Al2O3 washcoat/FeCrAl substrate and only γ-Al2O3 washcoat/FeCrAl substrate at various stoichiometric ratio of oxygen. The results showed that the addition of Cu-Ce mixed oxides improved CO oxidation reaction at lower temperature during stable lambda of 1, the highest CO conversion of 99% is observed for the noble metals (Pt, Pd, Rh) support on Cu-Ce with γ-Al2O3 washcoat/FeCrAl substrate. The results also showed that, the addition of Cu-Ce mixed oxides promoted released oxygen, thus it improved strongly CO and C3H8 conversion at lean oxygen stoichiometric operation.

Low-content and highly effective zoned Rh and Pd three-way catalysts for gasoline particulate filter potentially meeting Euro 7

The next-generation Euro 7 standard proposed much lower pollutant limits from gasoline vehicles,specifically for CO and NO_(x),which would be challenging for the three-way catalysts(TWCs)utilized commercially to eliminate these pollutants.TWCs with reductive(Rh)and oxidative(Pd)active components on gasoline particulate filters(TWC on GPF)play importantly auxiliary roles in the remediation of CO and NO_(x)downstream the close coupled TWCs to meet their emission targets.Here,a low-content Rh-based TWC(0.17 wt%)zoned with a less expensive Pd-based TWC(0.29 wt%)for GPF applications(cGPF)is reported using improved colloidal deposition method.The supporting of Rh on Y-stabilized ZrO_(2)rather than on CeO_(2)-ZrO_(2)inhibits the formation of inactive Ce rhodate species,while Pd on CeO_(2)-ZrO_(2)not only guarantees the high oxygen storage capacity(OSC)but also enhances catalytic activity.The layout of the front one-fifth in volume being 0.29 wt%Pd on Ce_(0.43)Zr_(0.5)7O_(2)and the rear four-fifths being 0.17 wt%Rh on Zr_(0.85)Y_(0.15)O_(2)prevents the possible alloying of Rh with Pd.The highly effective zoned Rh and Pd TWCs show synergistic three-way activity before and after severe hydrothermal aging at 1000℃with 10%water for24 h,which could be potential choices for close coupled GPF application to satisfy the upcoming stringent emission standards,such as Euro 7 and China 6b.

Construction of bimetallic Pt-Pd/CeO_(2)-ZrO_(2)-La_(2)O_(3) catalysts with different Pt/Pd ratios and its structure-activity correlations for three-way catalytic performance

A series of Pt-Pd bimetallic catalysts supported on CeO_(2)-ZrO_(2)-La_(2)O_(3) mixed oxides were synthesized through the conventional impregnation method.Three-way catalytic performance evaluations along with detailed physio-chemical characterizations were carried out to establish possible structure-activity correlations.Results show that on the one hand,different Pt/Pd ratios can strongly affect the TWC behaviors of Pt-Pd/CZL catalysts by modulating the synergistic effect between Pt and Pd.On the other hand,higher Pt/Pd ratio also favors better dispersion of precious metals.Such improved precious metals(PM)dispersion can promote the metal-support interaction and increase the surface oxygen vacancies concentration,thereby raising the dynamic oxygen storage/release capacity,improving the redox ability as well as enha ncing the thermal stability of the Pt-Pd/CZL catalyst.Moreover,the stro ng metal-support interaction can augment surface oxygen vacancy concentration,thereby benefiting low temperature CO and NO reaction via augmented NOxadsorption and nitrate conversion.

Progress on metal-support interactions in Pd-based catalysts for automobile emission control

The interactions between metals and oxide supports,so-called metal-support interactions(MSI),are of great importance in heterogeneous catalysis.Pd-based automotive exhaust control catalysts,especially Pd-based three-way catalysts (TWCs),have received considerable research attention owing to its prominent oxidation activity of HCs/CO,as well as excellent thermal stability.For Pd-based TWCs,the dispersion,chemical state and thermal stability of Pd species,which are crucial to the catalytic performance,are closely associated with interactions between metal nanoparticles and their supporting matrix.Progress on the research about MSI and utilization of MSI in advanced Pd-based three-way catalysts are reviewed here.Along with the development of advanced synthesis approaches and engine control technology,the study on MSI would play a notable role in further development of catalysts for automobile exhaust control.

A new approach of CeO_2 and La_2O_3 effects on the three-way catalysts containing low precious metals

A series of three-way catalysts (TWCs),containing a small amount of precious metals (PMs,including Pt,Pd and Rh) and a large amount of promoters CeO2 and La2O3,were prepared with different precursor compounds and various doped manners.Crystal phases,dispersion of cerium and lanthanum,textural structure and thermal stability of the catalysts were investigated by XRD,XPS and pore parameters determination.The catalytic performance was studied by the measurements of CO,C3H6 and NO conversions on dependence of temperature at stoichimetric number point (S=1.00),and from S=0.75 to 1.30 at 280℃ or 340℃ for fresh or aged samples,respectively.The correlation between the catalytic performance and the characteristics of fresh and aged samples were discussed.The results show that the sample,in which CeO2 and La2O3 are doped with mixed oxide powders,possesses poor dispersion and less thermal stability,and the conversions of NO and C3H6 are apparently lower than those of the samples aged at 850℃ The main reason is due to the lanthanum enrichment on the surface.The precious metals and cerium may be covered and enveloped,and the PMs located on the internal microporous surface where no cerium and lanthanum exist,are easier to sinter and oxidize.For the sample doped with La(NO3)3 and Ce(NO3)3 aqueous solutions,high dispersion and thermal stable CeO2 La2O3 solid solution on all the surface of microporous γ-Al2O3 is identified.The solid solution CeO2-La2O3 also possessed high dispersion in the sample doped with La2O3 powder and Ce(NO3)3 aqueous solution.The last two aged samples keep higher NO conversion at S≥1 region.

Redox behaviors and structural characteristics of Mn_(0.1)Ce_(0.9)O_x and Mn_(0.1)Ce_(0.6)Zr_(0.3)O_x

Mn0.1Ce0.9Ox and Mn0.1Ce0.6Zr0.30x samples synthesized by sol-gel method were tested for redox properties through the dynamic oxygen storage measurement and characterized using X-ray diffraction, BET, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. The results showed that redox performances of ceria-based materials could be enhanced by synergetic effects between Mn-O and Ce-O. Fresh and aged samples were characterized with the fluorite-type cubic structure similar to CeO2, and furthermore, the thermal stability of Mn0.1Ce0.9Ox materials was improved by the introduction of some Zr atoms. From XPS, it could be concluded that Mn^2＋/Mn^3＋ redox couples existed on the surface of Mn0.1Ce0.9Ox and Mn0.1Ce0.6Zr0.3Ox samples. Electron paramagnetic resonance researches revealed that there were three types of Mn^2＋ species： isolated Mn^2＋ substituting for Ce^4＋ ions in the lattice with a cubic symmetry, ones in defect with a noncubic symmetry, and at the surface of samples.

Effect of BaO on Catalytic Activity of Pt-Rh TWC

The effects of BaO doping on the three-way catalytic activity of Pt-Rh catalyst and on water-gas shift were investigated. The results show that the light-off temperatures of hydrocarbon and carbon monoxide and nitrogen oxides of the fresh catalysts slightly differ from those of the aged catalysts, and the catalysts containing CeO2-ZrO2-BaO have lower lightoff temperature and better catalytic activity than these containing BaO and CeO2-ZrO2 after hydrothermal aging for 5 h at 1000 ℃. The catalysts were characterized by means of the temperature-programmed reduction （TPR） in hydrogen and the temperature-programmed desorption （TPD） in oxygen. It is confirmed that the suggested route of CeO2-ZrO2-BaO by coprecipitation can improve the catalytic activity of catalysts.

Steam effects over Pd/Ce_(0.67)Zr_(0.33)O_2 three-way catalyst

In the purification process of automobile exhaust,existing water plays an important role as an oxidant,which converts CO and hydrocarbons（HCs） by the water-gas shift（WGS） and the steam reforming（SR） reactions,respectively,especially at high temperatures.Meanwhile it is major component of the exhaust which can affect significantly the thermal stability of the three-way catalyst.Activity experiments were carried out close to the real operation conditions（GHSV,concentration,etc.） with a Pd/Ce0.67Zr0.33O2 catalyst supplying information on the CO and C3H8 oxidation reactions in feedstream formed by different reactant combinations.The obtained results showed that the activity of the CO and C3H8 oxidation was promoted by the addition of steam due to the WGS and SR reactions.The WGS and SR reaction were competitive under oxygen-lean conditions.The kinetic analysis was considered for WGS and SR reactions.

Surface and Texture Properties of Tb-Doped Ceria-Zirconia Solid Solution Prepared by Sol-Gel Method

The three-way catalysts （TWCs） promoters Ce0.6Zr0.4- x TbxO2-y were prepared by sol-gel method. BET surface areas analysis indicated that an increase of the dopant Tb content from x = 0.05 to x = 0.15 favors an increase of surface area from 66.8 to 80.4 m^2· g^-1 compared with the undoped sample Ce0 .6oZr0.40O2 65.1 m^2·g^- 1 after calcination at 650℃. Transmission electron microscopy （TEM） observation indicated that the doped samples have a higher thermal stability. The XRD and Raman spectra confirmed that the Ce0.6Zr0.4-xTbxO2-y cubic solid solution is formed. XPS analysis revealed that Ce and Tb mainly existed in the form of Ce^4＋ and Tb^3 ＋ , and Zr existed in the form of Zr^4＋ on the surface of the samples. The doped samples were homogenous in composition ; the introduction of Tb into the CeO2-ZrO2 promoters resuited in the formation of a solid solution, and the concentration of surface lattice oxygen was increased.