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La0.67Fe0.83Cu0.17O3 with perovskite structure was prepared by sol–gel method, and 1.5 wt% Pd/Al2O3 was prepared by initial wet impregnation method. Pd/Al2O3 and perovskite prepared above were mixed by mechanical ball-milling with mass ratios of 10:1, 5:1 and 3:1, respectively, and represented by 10Pd/Al-La, 5Pd/Al-La and 3Pd/Al-La. Pd/Al refers to Pd/Al2O3 catalyst. In theoretical air–fuel ratio conditions (λ =1), the simulation of chemical metering of natural gas vehicle exhaust gas mixture on the catalysts were tested. The results showed that the perovskite could significantly reduce the ammonia formation in the exhaust gas. Moreover, the three-way catalytic performance of Pd/Al and 3Pd/Al-La were also tested in the feeds without water, CH4 or CO. The results demonstrated that the perovskite greatly reduced the ammonia content in the three exhaust gases. However, the ammonia content over bare Pd/Al was much higher in the presence of CO, and almost no ammonia was generated in the absence of CH4. The catalysts were also investigated by N2-physisorption, CO-chemisorption, XRD, EDX mapping and XPS techniques. The results showed that the perovskite may promote the reaction of NO and CO towards high N2 selection in the presence of CH4 and H2O, resulting in lower ammonia formation. Our work provided a new method for reducing ammonia formation over TWC catalysts for stoichiometric natural gas vehicles. [ABSTRACT FROM AUTHOR]

• High efficient phosphorus resistant Pd-based three-way catalyst was prepared by using aluminum-phosphate as support. • Phosphorus poisoning can cause strong changes in physical and chemical properties of Pd/Al 2 O 3 catalysts. • P will lead to the increase of palladium particle size, the decrease of dispersion and the reduction of Pd relative content. • The catalyst modified with phosphate can effectively inhibit the accumulation of phosphorus. • Phosphate modified catalysts show high activity in the periodic test. Natural gas vehicles (NGVs) have less CO 2 emission and have been attracting more attention. However, catalyst is needed to remove pollutants such as CO, NO x and unburned methane in NGVs' exhausts. The development of catalysts with high resistance to chemical poisoning, especially to phosphorus poisoning induced by lubricating oil of NGVs' engine, is a challenge. Herein, we developed a new strategy to improve the phosphorus resistance of model palladium catalyst using phosphate-modified alumina as support for NGVs. The catalysts were analyzed by N 2 -physisorption, X-ray fluorescence spectrum (XRF), X-ray diffraction (XRD), CO-chemisorption, in-situ DRIFTS and X-ray photoelectron spectrum (XPS). The results show that phosphate-alumina support helps the model catalyst maintain its textual properties, otherwise phosphorus species from lubricating oil would deposit on the surface of catalyst and block the catalytically active sites. Moreover, the relative content of active Pd0 on phosphate-modified alumina support will not decrease. Therefore, compared with conventional Pd catalyst on alumina, the model Pd catalyst on phosphate-modified alumina can show significantly enhanced phosphorus resistance under operating conditions for NGVs, and can nearly maintain its catalytic performance of removing pollutants upon phosphorus poisoning. Our work would provide a general method for development of catalyst with high performance for NGVs. [ABSTRACT FROM AUTHOR]

In this work, a series of CeO 2 -ZrO 2 -Al 2 O 3 (CZA) materials were prepared by deposition-precipitation method, among that, the Al(NO 3) 3.9H 2 O, pseudo-boehmite and Al 2 O 3 were worked as aluminum precursor, respectively. The results of N 2 adsorption-desorption, H 2 -TPR, TEM-mapping, XRD, and XPS show that the aluminum precursor has an impact on interaction between Al 2 O 3 and CeO 2 -ZrO 2 (CZ), resulting in differences in textural, structural and reduction properties of CZA materials. The CZA material from Al(NO 3) 3.9H 2 O displays superior textural properties and thermal stability due to the uniform distribution of Ce, Zr and Al. However, its reducing performance is limited own to stronger interactions among the components. On the contrary, the interaction between ZrO 2 and Al 2 O 3 is weaker when aluminum precursor is pseudo-boehmite or Al 2 O 3 , it facilitates the improvement of the reducing properties, but the obtained CZA material with a poor thermal stability due to the "mechanical-like" mixing mode between Ce-Zr and Al. Especially, the CZA deriving from pseudo-boehmite, possesses more oxygen vacancies and O β after aging, so it displays better redox performance. [Display omitted] • The effects with different aluminum precursors on CZA materials were studied. • The CZA deriving from Al(NO 3) 3.9H 2 O shows superior texture properties and thermal stability. • When aluminum precursor is pseudo-boehmite, the derived CZA exhibits the best reducibility. [ABSTRACT FROM AUTHOR]

[Display omitted] • The two-step structure transformation of the Mg promoter enhanced the stability of the Pd/CeO 2 -ZrO 2 -Al 2 O 3 catalyst. • Hydrothermal aging at 800 °C for 10 h slightly improved the activity of the Mg-modified catalyst. • The MgO resulting from the decomposition of Mg(NO 3) 2 transformed into MgAl 2 O 4 during hydrothermal aging. • The strong electronic interaction between PdO and MgO resulted in more PdO-MgAl 2 O 4 structures in the aged catalyst. • More PdO-MgAl 2 O 4 structures compensated for the sintering-induced catalytic deactivation during aging. The Pd/Al 2 O 3 -based catalysts are highly effective for removing low-concentration methane (CH 4), a strong greenhouse gas. The sintering of palladium (Pd) particles on the catalysts during long-term utilization causes catalytic deactivation. Magnesium (Mg) promoter would improve the hydrothermal stability of Pd/Al 2 O 3 -based catalysts by constructing PdO-MgAl 2 O 4 structures on the catalyst surface. In this study, we report an innovative strategy wherein a two-step structure transformation of Mg promoter in a Mg-modified Pd/CeO 2 -ZrO 2 -Al 2 O 3 (Pd/CZA) catalyst achieved exceptional hydrothermal stability of the catalyst. The Mg promoter in the form of MgAl 2 O 4 spinel improved PdO reducibility, as indicated by TPR test results, resulting in a 15–17 °C decrease in the temperature of 90% CH 4 conversion (T 90) over the fresh catalyst. Conversely, the MgO impeded CH 4 conversion and caused an increased T 90 of 21 °C due to forming an electron-rich PdO, as evidenced by XPS and CO-FTIR test results. Accelerated hydrothermal aging (A) at 800 °C for 10 h induced a second structure transformation of MgO to MgAl 2 O 4 in Pd/MgO-CZA catalyst to produce substantial PdO-MgAl 2 O 4 structures, which compensated for the catalytic deactivation caused by the sintering of palladium particles, as demonstrated by XRD, HAADF-STEM, and CH 4 -TPR test results. As a result, the Pd/MgO-CZA-A exhibited a 13 °C decrease in T 90 compared to Pd/MgO-CZA, achieving a T 90 of 425 °C with reaction gases containing 10 vol% water vapor. This work provides valuable insights for enhancing the hydrothermal stability of Mg-modified Pd/Al 2 O 3 -based catalysts. [ABSTRACT FROM AUTHOR]

• Introducing CeO 2 overlayers on Pt/Al 2 O 3 and Pt/Ce 0.5 Zr 0.5 O 2 to generate or increase Pt − CeO 2 interfacial sites. • Generated or increased Pt − CeO 2 interfacial sites significantly promoted CO oxidation activity and stability. • The promotion effect of CeO 2 overlayers on Pt/Al 2 O 3 is more significant. • The high performance of CeO 2 /Pt/Al 2 O 3 effectively reduce the use of rare earth CeO 2 − based materials in TWCs. Having both low temperature activity and high temperature hydrothermal stability of three − way catalysts (TWCs) remain a challenge. Tailoring the metal − oxide interface is an important strategy in the design and development of novel TWCs with superior catalytic performance. In this work, CeO 2 were introduced as overlayers onto typically Pt − based TWCs (Pt/Al 2 O 3 and Pt/Ce 0.5 Zr 0.5 O 2) to construct metal − oxide interface, in order to ease the contradiction between the activity and stability. The high resolution transmission electron microscope, reducibility, chemical states, and the vibrational spectra characterizations support the generated or increased Pt − CeO 2 interfacial sites in CeO 2 overlayers modified Pt/Al 2 O 3 and Pt/Ce 0.5 Zr 0.5 O 2. Obviously, the high chemical activity and reducibility of Pt − CeO 2 interfacial sites in the modified catalysts significantly promoted CO oxidation rates, and the enhanced metal-support interaction at interface stabilize Pt nanoparticles to slow down sintering under harsh reaction conditions. Meanwhile, the promotion effect of CeO 2 overlayers on Pt/Al 2 O 3 is more significant. CO oxidation rates on CeO 2 /Pt/Al 2 O 3 exhibits higher values than that of on CeO 2 /Pt/Ce 0.5 Zr 0.5 O 2 catalyst even after severe aging. The method of constructing interfacial sites by using the three-way catalyst key component CeO 2 to form overlayers provided a new idea for Pt − based TWCs design. [ABSTRACT FROM AUTHOR]

Stable support with abundant surface oxygen vacancies (O v) is indispensable for robust sintering-resistant heterogeneous catalysts. Herein, a strategy of lanthanum (La) atom selectively doping has been put forward to construct the desirable CeO 2 -ZrO 2 /Al 2 O 3 (CZA) support for high-temperature applications with the precise control of its distribution and location through two distinct addition processes. In the first addition process, La3+ was introduced to Al 2 O 3 component by precipitation process to stabilize its structure by occupying the surface –OH sites and forming thermodynamically stabled LaAlO 3. In the second addition process, the low-valence La3+ is surface grafted and preferentially captured by CZ component during preparation due to electrostatic attraction, thus generating abundant asymmetric O v as anchor sites for metal nanoparticles. The resulting CZA supported Pd-based three-way catalyst exhibits superior intrinsic activity even being hydrothermally aged at 900 °C/10 h since the as-prepared CZA could anchor Pd species in smaller size and oxidized state due to the enhanced metal-support interactions. This work provides new insights into doping effects and offers an avenue to design stable and active support material for industrial applications. [ABSTRACT FROM AUTHOR]

Abstract To design and construct CeO 2 -ZrO 2 -Al 2 O 3 (CZA) materials with controlled structure via co-precipitation method, the NH 3 ·H 2 O and (NH 4) 2 CO 3 were worked as precipitants, respectively. And the influence of the precipitants on nucleation, growth and thermal behavior of the CZA materials were investigated. Results of H 2 -TPR, XRD, XPS, UV–Vis, TEM and HAADF-TEM elemental mapping show that using NH 3 ·H 2 O as precipitant facilities to form homogeneous CeO 2 -ZrO 2 (CZ) solid solution with better solid solubility but the resulting CZA materials sinters severely due to the "mechanical-like" mixing mode between Ce, Zr and Al. On the contrary, the CZA materials precipitated by (NH 4) 2 CO 3 shows a better textural and structural stability due to the uniform distribution of Ce, Zr and Al. However, the H 2 consumption of CZA precipitated by (NH 4) 2 CO 3 is limited by the inferior Ce and Zr solid solubility due to stronger interactions among the components. It is also found that the surface and subsurface reduction of CZA materials are controlled by specific surface area and crystal size, while the bulk reduction of CZA materials correlates with solid solubility of Ce and Zr, crystal size and surface Ce/Zr ratio simultaneously. [ABSTRACT FROM AUTHOR]

As is well known, impregnation of precursors of Ce and Zr onto as-prepared Al 2 O 3 powders is a commonly used approach to prepare CeO 2 -ZrO 2 /Al 2 O 3 composite. In this work, a highly thermal stable CeO 2 -ZrO 2 /Al 2 O 3 composite was synthesized by modifying the conventional preparation procedure, i.e., the precursor of Al 2 O 3 thermal treated at comparatively lower temperature (200 °C) was applied to conduct the impregnation process. The characterization results of the supported Pd-only three-way catalysts reveal that in the modified sample, stronger interaction between CeO 2 -ZrO 2 and Al 2 O 3 is achieved, which consequently gives rise to higher thermal stability of the catalyst. Upon hydrothermal aging treatment, only slight aggregation of the CeO 2 -ZrO 2 and Al 2 O 3 particles takes place, meanwhile phase transformation of γ-Al 2 O 3 and phase separation of CeO 2 -ZrO 2 component are successfully suppressed. As a consequence, Pd species supported on the modified CeO 2 -ZrO 2 /Al 2 O 3 composite remain finely dispersed, and more oxidative PdO species are maintained owing to the intimate interaction between Pd and CeO 2 -ZrO 2 . Therefore, improved reduction capability and superior three-way catalytic performance are achieved for the modified Pd/CeO 2 -ZrO 2 /Al 2 O 3 catalyst after aging treatment. [ABSTRACT FROM AUTHOR]

Hydrothermal stability of catalysts for selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) has always been recognized as a challenge in development of candidate catalysts for applications in diesel engine emissions. In this study, Al 2 O 3 was introduced into CeO 2 -ZrO 2 to improve the NH 3 -SCR activity of WO 3 /CeO 2 -ZrO 2 after hydrothermal aging (HA) treatment at 800 °C for 12 h. The activity results indicated that the NH 3 -SCR activity of WO 3 /CeO 2 -ZrO 2 -HA was obviously improved in the whole reaction temperature range after doping Al 2 O 3 into CeO 2 -ZrO 2 , for example, the average and maximum NO x conversion were separately increased by ca. 20% and 25% after HA treatment. XRD, Raman, TEM and EDX results revealed that the introduction of Al 2 O 3 inhibited the sintering and agglomeration of CeO 2 -ZrO 2 and WO 3 and the formation of Ce 2 (WO 4 ) 3 after HA treatment. Accordingly, WO 3 /CeO 2 -ZrO 2 -Al 2 O 3 -HA showed remarkably improved structural stability and reducibility, increased surface acidity, and facilitated the reactivity between adsorbed NH 3 and nitrate species, which together contributed to its better catalytic performance after hydrothermal aging treatment. [ABSTRACT FROM AUTHOR]

Hydrogen production from n -decane steam reforming was researched over mono- and bi-metallic Co-Ni catalysts supported on Ce-Al 2 O 3 (CA), with the purpose of obtaining high H 2 yield and lowest inactivation by carbon deposition. Physicochemical characteristics studies, involving N 2 adsorptione-desorption, X-ray diffraction, Infrared spectrometer, Raman spectroscopy, and Scanning electron microscope-energy dispersive spectrometer, were carried out to reveal the textural, structural and morphological properties of the catalysts. The results showed that catalytic activity over mono- Co or Ni catalyst was increased compared with CA contrast catalyst at the range of 650–800 °C, meanwhile the catalytic activity was further improved over bimetallic Co-Ni catalyst. Moreover, carbon deposition was effectively suppressed with the synchronous addition of Ni and Co. The metal-support interaction was enhanced, and there was obvious synergistic effect between Ni and Co. In addition, the reforming activities over regenerated catalysts were almost close to the fresh ones. The effective information presented in this work is that, firstly, modified Al 2 O 3 with Ce before active species loading in order to maintain larger surface area and improve thermal stability, secondly, introduced Ni and Co into Ce-Al 2 O 3 synchronously to maintain both catalytic activities and anti-carbon ability, should be an effective approach to develop the excellent catalyst. [ABSTRACT FROM AUTHOR]

By a facile doping strategy, a new Pd catalyst supported on ZrO 2 -Al 2 O 3 composite doped by Mg was developed. The catalyst was carefully characterized by X-ray diffraction (XRD), CO chemical adsorption, transmission electron microscope (TEM), NH 3 temperature programmed desorption (NH 3 -TPD) and X-ray photoelectron spectroscopy (XPS). The results revealed that the physical and chemical properties of the catalyst can be modulated by Mg dopant. An MgAl 2 O 4 spinel was formed by Mg doping, which can stabilize Pd 2+ species and inhibit the formation of hydroxyl groups on the surface of support. Compared with its analogous catalyst without Mg dopant, the Mg-doped catalyst had higher Pd dispersion and smaller Pd nanoparticles. Moreover, a more suitable acidity for methane oxidation can be generated on the surface of the catalyst upon Mg doping. Therefore, the introduction of Mg doping strongly enhanced the low-temperature activity and hydrothermal resistance of the catalyst for the total oxidation of methane under lean conditions. Notably, the complete conversion temperature of methane can decreased significantly by 40–50 °C with the doped catalyst before and after harsh hydrothermal aging treatment. [ABSTRACT FROM AUTHOR]

Steam reforming reactions of hydrocarbon fuels were investigated in a fixed bed tubular reactor over nickel supported on Ce–Al 2 O 3 (NCA) bifunctional catalysts promoted with different content of SrO (NCA/ x %SrO), in order to obtain high H 2 yield with minimum deactivation by carbon deposition. Physicochemical characteristics of the catalysts were detected by using automatic adsorption instrument, X-ray diffraction, Temperature programmed reduction/desorption, Raman spectroscopy, and Scanning/transmission electron microscope-energy dispersive spectrometer. It was found that the catalytic activities over series NCA/ x %SrO catalysts were obviously improved compared with CA catalyst at the range of 550 °C–800 °C, meanwhile the amount of carbon deposition was significantly decreased with the addition of SrO promoter. In addition, the promotion effect became more stable when the introduction of SrO, which indicated that SrO played an essential role in the catalytic action. The regeneration experiments over the same NCA/5%SrO catalyst were performed three times, and the reforming activities were quite close to the results of fresh ones. The valuable information indicated in this work is that based on the specific properties of NCA/ x %SrO, three kinds of metal particles can be introduced into Al 2 O 3 by different way, which should be an effective approach to maintain both catalytic activities, thermal stability and anti-carbon ability. [ABSTRACT FROM AUTHOR]

Supports with different redox properties (Al 2 O 3 , Ce 0.5 Zr 0.5 O 2 -Al 2 O 3 , Ce 0.5 Zr 0.5 O 2) and their corresponding Pt-based catalysts were prepared to investigate the effect of the suitability between Pt and different supports and the promotion of the NO NO 2 cycle on the catalytic activity of soot combustion. It is interesting that Pt-loaded nonredox support Al 2 O 3 exhibited a poor catalytic activity for soot combustion in the absence of NO but an excellent catalytic activity in the presence of NO. However, unlike the Al 2 O 3 support, Pt loaded Ce 0.5 Zr 0.5 O 2 -Al 2 O 3 and Ce 0.5 Zr 0.5 O 2 as redox supports showed an opposite result. N 2 adsorption-desorption and XRD results indicated that Pt loading had no obvious effect on the texture properties of the supports. More zero-valent Pt (Pt0) on Pt/Al 2 O 3 revealed by XRD, CO chemisorption and XPS was suggested as a major factor for promoting NO oxidizing cycles. Therefore, an amount of NO 2 molecules produced on Pt0 is key to accelerate soot combustion under loose contact. The weak interaction between Pt and Al 2 O 3 kept more Pt in the lower valence state. The Pt from Pt/Ce 0.5 Zr 0.5 O 2 -Al 2 O 3 and Pt/Ce 0.5 Zr 0.5 O 2 reduced the number of NO NO 2 cycles and further limited the assistance of NO 2 in soot combustion due to a high-valence state of most of Pt. However, the preferable reducibility of the redox supports benefit soot combustion in O 2 /N 2 because of the presence of active oxygen. This work would provide a new understanding for the further improvement of soot oxidation with the catalysts. [ABSTRACT FROM AUTHOR]

This study involves a new series granulate Ni modified La-Al 2 O 3 (NLA) catalysts with high temperature resistant and large specific surface area for n -decane steam reforming. NLA catalysts were prepared by using a specially designed co-precipitation technique in combination with incipient wetness impregnation. Physicochemical characteristics of as-prepared catalysts were detected by using automatic adsorption instrument, X-ray diffraction (XRD), infrared spectroscopy (IR), temperature programmed reduction (H 2 -TPR), temperature programmed desorption (NH 3 -TPD), and scanning electron microscope-energy dispersive spectrometer (SEM-EDS). Significantly, the results of characterizations showed that the series NLA catalysts presented a typical mesoporous structure with a large surface area of ∼150.0 m 2 /g, and metal Ni was strongly interacted with Al 2 O 3 to generate nickel aluminate spinel structures, and the addition of La improved the thermal stability of catalysts. Based on these data, the catalytic activities over NLA catalysts were evidently heightened compared with the corresponding La-Al 2 O 3 catalyst, moreover, the 9.0 wt% NLA catalyst exhibited higher H 2 yield and showed 100% n -decane conversion at 800 °C. The valuable information indicated in this work is that based on the special characters of NLA, bimetal particles can be supported on Al 2 O 3 with different way, which should be an effective approach to maintain both catalytic activities and thermal stability. [ABSTRACT FROM AUTHOR]

The migration metallic species between Al 2 O 3 and CeO 2 -ZrO 2 (CZ) is one of the main causes for the deactiviation of the three-way catalysts (TWCs). In order to address this issue, κappa-phase κ -Ce 2 Zr 2 O 8 was constructed to strengthen Pd-CZ interaction and thus stabilize palladium species. For comparison, tetragonal-phase Ce 0.5 Zr 0.5 O 2 with κ -Ce 2 Zr 2 O 8 phase (κ CZ) and without (t CZ) were prepared. The (κ CZ+Al 2 O 3) supported catalyst (Pd/ κ CZA) exhibited a higher activity than Pd/ t CZA even after aging at 900 °C or 1000 °C for 4 h. The larger reaction rate and TOF values of Pd/ κ CZA-900 evidenced its higher intrinsic activity, especially for C 3 H 8 conversion. The analyses proved that κ -Ce 2 Zr 2 O 8 could strengthen Pd-CZ interaction, subsequently induced Pd to selectively interact with CZ rather than Al 2 O 3 and inhibited palladium from migrating from CZ to Al 2 O 3. Additionally, in situ DRIFTS analysis proved that the strengthened Pd-CZ interaction facilitated to regenerate active palladium and NO transforming to reactive monodentate nitrate/nitrite. [Display omitted] • Constructing κ -Ce 2 Zr 2 O 8 enhances the catalytic performance of Pd-only catalyst. • κ -Ce 2 Zr 2 O 8 could induce Pd to selectively interact with CZ rather than Al 2 O 3. • Strengthened Pd-CZ interaction can promote the regeneration of active palladium. • Monodentate nitrate/nitrite has a higher reactivity with C 3 H 8 than other ones. [ABSTRACT FROM AUTHOR]

A series of Pt/ZrO 2 –TiO 2 –Al 2 O 3 (PZTA) composite oxides with different Al 2 O 3 mass ratio (ZrO 2 :TiO 2 :Al 2 O 3 = 1:1: x , where x = 1, 2, 3, 4, 5) were coated on the wall of stainless-steel microchannels by using a co-precipitation method. Catalytic cracking of RP-3 over such PZTA-coated catalysts were investigated under high temperature and pressure conditions. It was found that the gas yield and heat sink of catalytic cracking of RP-3 were evidently heightened compared with the thermal cracking. Furthermore, catalytic cracking activities and high-temperature stabilities of the catalysts were greatly depending on the mass ratio of Al 2 O 3 . PZTA (ZrO 2 :TiO 2 :Al 2 O 3 with a mass ratio of 1:1:3) performed a better catalytic cracking activity and high-temperature stability, which is in accordance with its higher amount of strong acid, larger surface area and pore volume. Deactivation of the increasing rate of gas yield and heat sink over PZTA at 700 °C was possibly caused by decrement of their amount of surface acid, the collapse of the catalysts pores partly and the crystallizations of ZTA above 650 °C, and the quickly generation of carbon deposition at 700 °C. Even so, PZTA (ZrO 2 :TiO 2 :Al 2 O 3 in the mass ratio of 1:1:3) kept a better catalytic cracking activity and high-temperature stability. [ABSTRACT FROM AUTHOR]

Three Ce 0.5 Zr 0.5 O 2 -Al 2 O 3 compounds were prepared using conventional coprecipitation method, mechanical mixing technique and a novel modified coprecipitation route, afterwards the corresponding Pd-only three-way catalysts were obtained by wet-impregnation method. Differences in textural, structural, morphological, reduction properties and catalytic performance, together with the thermal aging behaviors of the catalysts were investigated systematically. The results revealed that different mixing strategies of Ce 0.5 Zr 0.5 O 2 (CZ) and Al 2 O 3 led to different interaction between CZ and Al 2 O 3 , thus modified the textural, structural and reduction properties of the supported catalysts to different extents, and brought about various atom rearrangements during the aging process. The catalyst supported on Ce 0.5 Zr 0.5 O 2 -Al 2 O 3 obtained by the modified coprecipitation method displayed the least distinction before and after aging treatment, and it presented superior textural, structural and reduction properties after aging, which consequently resulted in enhanced three-way catalytic performance, the light-off temperatures of C 3 H 8 , CO and NO were 327 °C, 164 °C and 208 °C, respectively, obviously lower than those of the catalysts originated from the conventional coprecipitation method and mechanical mixing route. [ABSTRACT FROM AUTHOR]

[Display omitted] • Better dispersion and smaller Pt particle can be obtained when loaded on MgAl 2 O 4. • Strong interaction between Pt and MgAl 2 O 4 can stabilize Pt particles. • The doping of MgAl 2 O 4 can promote the catalytic reaction. • Pt/MgAl 2 O 4 -Ce 0.5 Zr 0.5 O 2 catalyst exhibited the excellent catalytic activity. Improving the high temperature stability of three-way catalyst (TWC) is of great importance for the purification of automobile exhaust. In this work, Pt/MgAl 2 O 4 -Ce 0.5 Zr 0.5 O 2 TWC with high activity and stability was prepared by liquid phase reduction impregnation combined with high-energy ball milling technology, aiming to study the effect of MgAl 2 O 4 on the activity and high temperature stability. The results showed that the catalytic activity of Pt/MgAl 2 O 4 -Ce 0.5 Zr 0.5 O 2 catalyst was superior to Pt/Al 2 O 3 -Ce 0.5 Zr 0.5 O 2 and Pt/Ce 0.5 Zr 0.5 O 2 before and after aging. Combined with the characterization results, the considerable stability of Pt/MgAl 2 O 4 -Ce 0.5 Zr 0.5 O 2 catalyst was due to the increased specific surface area and redox performance, smaller Pt particle size and improved dispersion. In addition, the strong interaction between MgAl 2 O 4 and Pt effectively realized that Pt anchored on the support more stable and distributed more uniformly under high temperature conditions. Hence, the method of MgAl 2 O 4 doping modification provided a new idea and solution for improving high temperature stability of TWC. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen-storage materials CeO2–ZrO2–Al2O3 (CZA), with alumina contents 10, 25, 50, 75 and 90wt%, respectively, were prepared by the co-precipitation method. To compare our results with those of CeO2–ZrO2 (CZ), the prepared materials were characterized by Brunauer-Emmet Teller method (BET), X-ray diffraction (XRD), Raman spectrum, temperature-programmed reduction (H2-TPR) and oxygen pulsing technique (OSC). The XRD and Raman results show that all samples (except sample with 90wt% alumina) can keep the single CeO2 cubic fluorite structure after calcination at 873 and 1273K for 5h, respectively. Compared with the fresh samples, the particle sizes of aged samples increase, but no phase separation occurs. According to the results of BET and OSC, after calcination at 1273K, alumina doped can make this system materials maintain higher specific surface area (114.5m2 g−1) and larger pore volume (0.36mlg−1) without losing characteristics of CeO2. As Al2O3 contents increase, the ratio of utilizable cerium also increases, indicating that the OSC of CZA is more stable than that of CZ. In this work, the prepared CZA materials are highly dispersed composite solid solutions. After calcination at 1273K, those compounds can still keep the structural and textural stability, and simultaneously hold excellent OSC and stable redox property. [Copyright &y& Elsevier]

[Display omitted] • A Pd-Pt bimetallic nano-catalyst stabilized by magnesia-alumina spinel was developed via a facile doping strategy. • This catalyst presents significantly enhanced hydrothermal stability for lean methane combustion. • Pt stabilized by magnesia-alumina spinel helps Pd species stabilize in active PdO phase. • The sintering resistance of Pt and PdO and the electron interaction between them result in the enhanced durability. It is an urgent desire to decrease release of methane, a potential greenhouse gas, over methane-oxidation catalysts. However, the commonly used Pd-based catalysts normally suffer from poor hydrothermal stability. Here, we report a Pd-Pt bimetallic nano-catalyst stabilized by magnesia-alumina spinel via a facile doping strategy for lean methane combustion. The promoted effects of platinum on the hydrothermal stability of the catalyst are confirmed by XRD, HRTEM, STEM, XPS, CO-DRIFTS characterizations. Pd-Pt bimetallic catalyst can almost maintain its intrinsic catalytic activity (2.7 × 10−5 mol CH4 g noble metal -1s-1 at 260 °C) after harshly hydrothermal aging, while the aged analogous sample without Pt promotion presents remarkably reduced catalytic performance with an increment in CH 4 light-off temperature of ca. 50 °C. Kinetic analysis further reveals a much higher turnover frequency (0.011 s-1 at 260 °C) and lower apparent activation energy (119 kJ/mol) of CH 4 oxidation on the aged Pd-Pt bimetallic samples. Pt stabilized by magnesia-alumina spinel has a strong interaction with PdO. This interaction could stabilize Pd species in active PdO and also suppress the decomposition of active PdO to less reactive Pd°. Consequently, the sintering resistance of Pt and PdO crystallite and the electron interaction between them could be responsible for the enhanced hydrothermal stability. [ABSTRACT FROM AUTHOR]

The different loading sequence CeO 2 and Pd over Al 2 O 3 support influences palladium dispersion by the interaction, which is main factor in influencing the catalytic activity. Ce/Pd/Al catalyst owns smaller palladium particle size and higher palladium dispersion than Pd/Ce/Al catalyst, which is considered as active site. A simple process is described as is shown above, and specific process is illustrated in my article. [Display omitted] • The different loading sequence of CeO 2 and Pd over Al 2 O 3 influences different palladium dispersion, resulting in different catalytic activity. • Pd dispersion and catalytic activity are investigated by many characterization methods, such as TEM, CO-Pd adsorption and in situ DRIFTS spectra. • The catalysts obtained by novel loading sequence show the better catalytic activity, especially at the lower temperature. The Pd-only close-coupled catalysts of the different loading sequence of CeO 2 and Pd over Al 2 O 3 were prepared using consecutive wetness impregnation method. Differences in structural, surface properties and catalytic performance, together with the thermal aging behaviors of catalyst at 1000 °C were investigated systematically by XRD, TPR, XPS, ICP, CO adsorption and TEM. Consequently, the Ce/Pd/Al catalysts loaded Ce after Pd over the alumina show superior structural properties before and after aging treatment, suggesting the Ce/Pd/Al catalysts possess better thermal resistance than Pd/Ce/Al catalysts loaded Pd after Ce. Moreover, the aged Ce/Pd/Al catalysts possess stronger reducible probed by TPR, and HRTEM and CO adsorption show smaller particles size of Pd and higher palladium dispersion. As a result, for Ce/Pd/Al catalysts, more palladium sites play a role as active site, which promotes low temperature conversion of pollutants effectively. The catalytic performance of the catalysts is forcefully subject to palladium dispersion and reduction property, especially for NO conversion, and the light-off temperature of NO over aged Ce/Pd/Al is 27 °C lower than aged Pd/Ce/Al. The results have demonstrated that novel loading sequence is beneficial to catalytic activity which is maintained even after aging treatment. [ABSTRACT FROM AUTHOR]