The design and synthesis of robust sintering-resistant nanocatalysts for high-temperature oxidation reactions is ubiquitous in many industrial catalytic processes and still a big challenge in ...implementing nanostructured metal catalyst systems. Herein, we demonstrate a strategy for designing robust nanocatalysts through a sintering-resistant support via compartmentalization. Ultrafine palladium active phases can be highly dispersed and thermally stabilized by nanosheet-assembled γ-Al
O
(NA-Al
O
) architectures. The NA-Al
O
architectures with unique flowerlike morphologies not only efficiently suppress the lamellar aggregation and irreversible phase transformation of γ-Al
O
nanosheets at elevated temperatures to avoid the sintering and encapsulation of metal phases, but also exhibit significant structural advantages for heterogeneous reactions, such as fast mass transport and easy access to active sites. This is a facile stabilization strategy that can be further extended to improve the thermal stability of other Al
O
-supported nanocatalysts for industrial catalytic applications, in particular for those involving high-temperature reactions.
Ceria nanocrystallites with different morphologies and crystal planes were hydrothermally prepared, and the effects of ceria supports on the physicochemical and catalytic properties of Pd/CeO2 for ...the CO and propane oxidation were examined. The results showed that the structure and chemical state of Pd on ceria were affected by ceria crystal planes. The Pd species on CeO2-R (rods) and CeO2-C (cubes) mainly formed Pd x Ce1–x O2−σ solid solution with −Pd2+–O2––Ce4+– linkage. In addition, the PdO x nanoparticles were dominated on the surface of Pd/CeO2-O (octahedrons). For the CO oxidation, the Pd/CeO2-R catalyst showed the highest catalytic activity among three catalysts, its reaction rate reached 2.07 × 10–4 mol gPd –1 s–1 at 50 °C, in which CeO2-R mainly exposed the (110) and (100) facets with low oxygen vacancy formation energy, strong reducibility, and high surface oxygen mobility. TOF of Pd/CeO2-R (3.78 × 10–2 s–1) was much higher than that of Pd/CeO2-C (6.40 × 10–3 s–1) and Pd/CeO2-O (1.24 × 10–3 s–1) at 50 °C, and its activation energy (E a) was 40.4 kJ/mol. For propane oxidation, the highest reaction rate (8.08 × 10–5 mol gPd –1 s–1 at 300 °C) was obtained over the Pd/CeO2-O catalyst, in which CeO2-O mainly exposed the (111) facet. There are strong surface Ce–O bonds on the ceria (111) facet, which favors the existence of PdO particles and propane activation. The turnover frequency (TOF) of the Pd/CeO2-O catalyst was highest (3.52 × 10–2 s–1) at 300 °C and its E a value was 49.1 kJ/mol. These results demonstrate the inverse facet sensitivity of ceria for the CO and propane oxidation over Pd/ceria.
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Ruthenium (Ru) nanoparticles (∼3 nm) with mass loading ranging from 1.5 to 3.2 wt % are supported on a reducible substrate, cerium dioxide (CeO2, the resultant sample is called Ru/CeO2), for ...application in the catalytic combustion of propane. Because of the unique electronic configuration of CeO2, a strong metal–support interaction is generated between the Ru nanoparticles and CeO2 to stabilize Ru nanoparticles for oxidation reactions well. In addition, the CeO2 host with high oxygen storage capacity can provide an abundance of active oxygen for redox reactions and thus greatly increases the rates of oxidation reactions or even modifies the redox steps. As a result of such advantages, a remarkably high performance in the total oxidation of propane at low temperature is achieved on Ru/CeO2. This work exemplifies a promising strategy for developing robust supported catalysts for short-chain volatile organic compound removal.
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Supported gold (Au) nanocatalysts hold great promise for heterogeneous catalysis; however, their practical application is greatly hampered by poor thermodynamic stability. Herein, a general synthetic ...strategy is reported where discrete metal nanoparticles are made resistant to sintering, preserving their catalytic activities in high-temperature oxidation processes. Taking advantage of the unique coating chemistry of dopamine, sacrificial carbon layers are constructed on the material surface, stabilizing the supported catalyst. Upon annealing at high temperature under an inert atmosphere, the interactions between support and metal nanoparticle are dramatically enhanced, while the sacrificial carbon layers can be subsequently removed through oxidative calcination in air. Owing to the improved metal–support contact and strengthened electronic interactions, the resulting Au nanocatalysts are resistant to sintering and exhibit excellent durability for catalytic combustion of propylene at elevated temperatures. Moreover, the facile synthetic strategy can be extended to the stabilization of other supported catalysts on a broad range of supports, providing a general approach to enhancing the thermal stability and sintering resistance of supported nanocatalysts.
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It is very challenging to improve the catalytic activity of Pt-based catalysts since the strong CO chemisorption on Pt inhibits oxygen activation leading to poor activity at low temperature. Here, we ...report that introducing MO x (M = Fe, Co, Ni) to modify Pt catalysts (0.5 wt % Pt/CeO2) is a facile way to improve catalytic activity for CO oxidation at ambient temperature. The chemical state of Pt and the reducibility of doped MO x dominate the activity for CO oxidation. The electron-deficient Pt due to the strong interaction between Pt and MO x leads to the weaker CO adsorption strength. Meanwhile, the higher reducibility of FeO x and CoO x extends the reaction routine due to the improved activity of oxygen with the help of the redox cycle between FeO x /CoO x and CeO2. However, the stability of catalyst depends on the ability to recover consumed oxygen, and the reversible compensation of consumed oxygen species makes CoO x /Pt/CeO2 and NiO x /Pt/CeO2 remain stable with time on stream. Our study shows that CoO x is a potential candidate to increase Pt atom efficiency for CO oxidation on Pt/CeO2 catalysts.
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Controlling the physical and chemical properties of alloy nanoparticles (NPs) is an important approach to optimize NP catalysis. Unlike other tuning knobs, such as size, shape, and composition, ...crystal structure has received limited attention and not been well understood for its role in catalysis. This deficiency is mainly due to the difficulty in synthesis and fine-tuning of the NPs’ crystal structure. Here, Exemplifying by AuCu alloy NPs with face centered cubic (fcc) and face centered tetragonal (fct) structure, we demonstrate a remarkable difference in phase segregation and catalytic performance depending on the crystal structure. During the thermal treatment in air, the Cu component in fcc-AuCu alloy NPs segregates more easily onto the alloy surface as compared to that in fct-AuCu alloy NPs. As a result, after annealing at 250 °C in air for 1 h, the fcc- and fct-AuCu alloy NPs are phase transferred into Au/CuO and AuCu/CuO core/shell structures, respectively. More importantly, this variation in heterostructures introduces a significant difference in CO adsorption on two catalysts, leading to a largely enhanced catalytic activity of AuCu/CuO NP catalyst for CO oxidation. The same concept can be extended to other alloy NPs, making it possible to fine-tune NP catalysis for many different chemical reactions.
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The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxidation. The activities of In2O3–Co3O4 increased with an increase in In2O3 content, in the form of a volcano ...curve. Twenty-five wt % In2O3–Co3O4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co3O4. The doping of In2O3 induced the expansion of the unit cell and structural distortion of Co3O4, which was confirmed by the slight elongation of the Co–O bond obtained from EXAFS data. The red shift of the UV–vis absorption illustrated that the electron transfer from O2– to Co3+/Co2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H2-TPR and O2-TPD results also revealed that In2O3–Co3O4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In2O3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co3O4, which tuned the adsorption strength of CO and oxygen activation simultaneously.
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•Sr substitution and acid treatment promoted vinyl chloride combustion and decreased the chloric by-product concentration.•The oxidation capability great affected the chloric ...by-product distribution and their formation followed different pathways.•The strong oxidation capacity made VC complete oxidation at low temperature inhibiting the Deacon reaction and chlorination.
Active Sr substituted LaMnO3 perovskite type catalysts were prepared by sol-gel method and further modified by acid, and the catalytic activity for vinyl chloride (VC) combustion were investigated. The techniques of XRD, N2 adsorption-desorption, H2-TPR, XPS were employed for the catalyst characterization. The HCl modified La0.5Sr0.5MnO3 (L0.5S0.5MO -H) showed the highest activity under stable test condition, VC could be completely converted to CO2 at 300 °C, and the main chloric organic by-products were trichlormethane (TCM), tetrachloromethane (CTC) and 1,1,2-Trichloroethane (TCE), and their concentration were all below 5ppm. The characterization results showed that the pretreatment obviously promoted the amount of the active Mn4+ species and oxygen activation ability. The oxidation capability greatly affected the chloric by-product distribution, for the difference in oxidation capacity made the formation of chloric by-products followed different pathways. The lower temperature for VC complete oxidation would inhibited the Deacon reaction and chlorination occurred. However, the strong basicity of Sr and the preference to form SrCl bond were inclined to keep Cl species on Sr and made active Mn species free of Cl.
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•Pd state transfers from Pd4+ to PdO with increasing CeO2 calcination temperature.•C3H8 and CO oxidation show reversed activity trend with Pd state transformation.•NO conversion in ...low temperature correlates to CO oxidation and NO adsorption.•PdO promotes C3H8 activation and reaction with NO3–/ NO2– in high temperature.
To investigate the correlation of activity and chemical state of Pd species in the three-way catalytic reaction, the supported Pd catalysts were prepared by using CeO2 calcined at different temperatures as supports. It turned out that the chemical state of Pd could severely affect the catalytic activity of Pd/CeO2, which depended on the CeO2 properties and the interaction between Pd and CeO2. With increasing CeO2 calcination temperature from 500 to 1200 °C, the state of Pd gradually transferred from Pd4+ as PdxCe1-xO2-σ to Pd2+ as PdO due to the decreased interaction between Pd and CeO2. Meanwhile, the TOFs of C3H8 oxidation linearly increased and the TOFs of CO oxidation showed a reversed trend, demonstrating the active states of Pd in C3H8 and CO oxidation were different. NO conversion was correlated to the activity of CO oxidation in low-temperature zone and C3H8 oxidation in high-temperature zone during the three-way catalytic reaction. Among them, Pd/CeO2(500) showed the highest CO oxidation activity and low-temperature NO conversion due to the enhanced adsorption ability of CO and NO. The existence of PdO on the surface of high-temperature calcined CeO2 facilitated C3H8 activation and reaction with surface nitrate/nitrite, which promoted NO conversion in high temperature.
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•Fe addition into Cu/zeolites significantly decreases N2O formation.•Fe addition into Cu/zeolites suppresses coking formation.•Fe addition modifies (lowers) dispersion of Cu in ...zeolites.•The adding of Fe can be applied as a method to fine-tune performance of commercial SCR catalysts.
Cu, Fe and Cu+Fe ion exchanged Beta and SSZ-13 catalysts were prepared by solution ion exchange using commercial NH4/Beta, and NH4/SSZ-13 that was prepared in-house. To study hydrothermal aging effects, Beta supported catalysts were aged hydrothermally at 700°C and SSZ-13 supported catalysts were aged at 750°C. In order to reveal the effects of Fe addition in the co-exchanged catalysts, these catalysts were characterized by means of powder X-ray diffraction (XRD), N2 adsorption-desorption, electron paramagnetic resonance (EPR), 27Al-nuclear magnetic resonance (27Al-NMR) and propylene coking followed with temperature programmed reaction (TPR), and further tested with standard NH3-SCR with and without the presence of propylene. Collectively, the catalyst characterizations and reaction testing indicated minor beneficial effects of Fe addition in Cu,Fe/Beta, where NH3-SCR activity, N2 selectivity and hydrothermal stability were all slightly improved. In contrast, Fe addition did not show apparent beneficial effects in low-temperature SCR for the Cu,Fe/SSZ-13 case. At elevated reaction temperatures, however, the presence of Fe indeed considerably improved NO conversion and N2 selectivity for the hydrothermally aged Cu,Fe/SSZ-13 catalyst in the presence of propylene.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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