Activity of Au,Ni, and Au-Ni catalysts in the water-gas shift reaction and carbon monoxide oxidation

Au/Al₂O₃, NiO _x /Al₂O₃, and (Au + NiO _x )/Al₂O₃ composites have been prepared by ion exchange and impregnation. Their structural and electronic properties, including the size and shape of supported metal particles and the oxidation state and ligand environment of the Au and Ni atoms, have been investigated. The catalytic action of Au/Al₂O₃, NiO _x /Al₂O₃, and (Au + NiO _x )/Al₂O₃ in the water-gas shift reaction and carbon monoxide oxidation is reported. At 300–450°C, the CO conversion over (Au + NiO _x )/Al₂O₃ exceeds the sum of the CO conversions over the monometallic catalysts Au/Al₂O₃ and NiO _x /Al₂O₃ by a factor of 2–3. An explanation is suggested for the nonadditive increase in the CO conversion over the Au-Ni catalysts.     

Thermal analysis and calorimetry in the study of materials and processes for fundamental sciences and various applications in Central and Eastern Europe

We investigated the influence of B substitution for Al₂W₃O₁₂ on thermal changes of UV–Vis and Raman spectra, and colors. First, B-substituted Al₂W₃O₁₂ powder was synthesized by a solid-state reaction method. Single-phase Al_2?xB_xW₃O₁₂ powders with x = 0, 0.10 and 0.20 were successively prepared. B substitution promoted thermal changes of the UV–Vis spectra, resulting in a more pronounced color change of Al₂W₃O₁₂ in the range of 30–150 °C. Raman spectra of the Al_2?xB_xW₃O₁₂ powders with x = 0 and 0.20 indicated that the lattice vibrations of Al_2?xB_xW₃O₁₂ with x = 0.20 were larger than those of Al₂W₃O₁₂. The thermal change of the color phase (ΔE) in the range 30–150 °C of Al₂W₃O₁₂ was increased by B substitution. The color of the B-substituted Al₂W₃O₁₂ powders changed reversibly from pale white at 30 °C to light yellowish green at 150 °C.     

Review of Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Reductant System in the Selective Catalytic Reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Ag/Al₂O₃ is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO _x in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO _x over a Ag/Al₂O₃ catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al₂O₃-reductant systems for the SCR of NO _x ; the low-temperature activity improvement of H₂-assisted HC-SCR of NO _x over Ag/Al₂O₃; and the application of a Ag/Al₂O₃-ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/Al₂O₃-reductant systems and H₂-assisted HC-SCR of NO _x over Ag/Al₂O₃. A SO₂-resistant surface structure in situ synthesized on Ag/Al₂O₃ by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight into the design of a high-efficiency NO _x reduction system. The diesel engine bench test results showed that a Ag/Al₂O₃-ethanol system is promising for catalytic cleaning of NO _x in diesel exhaust.     

Nox Reduction Characteristics for Different Composition Ratios of Pt/Al2O3, Rh/Al2O3 Catalyst Mixtures Using Model Gas as Reformates

This study investigated the selective catalytic reduction (SCR) of nitrogen oxides (NO_x) with hydrocarbon in the presence of excess oxygen using various composition ratios of Pt/Al₂O₃, Rh/Al₂O₃ catalyst mixtures. The composition ratios were 1:1, 1:2, 2:1, 1:3 and 3:1 of 1 wt% Pt/Al₂O₃ and Rh/Al₂O₃, which are known to exhibit efficient NO_x reduction at low and high temperatures among the noble metal catalysts. Experiments conducted on a single reductant revealed that more efficient NO_x conversion could be obtained when Pt/Al₂O₃ and Rh/Al₂O₃ were mixed at a ratio of 3:1, rather than 1:1 or 1:3. In a single reductant condition, C₃H₆ 800 ppm (2400 ppmC₁) and 400 ppm (1200 ppmC₁) exhibited 50% and 38% NO_x conversion efficiency at 200°C, respectively. However, NO_x conversion efficiency gradually decreased when temperatures were increased above 250°C. With regard to Pt/Al₂O₃ and Rh/Al₂O₃ ratio, higher ratios of Rh/Al₂O₃ activated this Pt+Rh/Al₂O₃ catalyst in the high temperature range.     

An iets study of alumina and magnesia supported —sihx and their use as substrates for inorganic vibrational spectroscopy

Tunneling spectra of Al₂O₃/—SiH_x, MgO/—SiH_x, Al₂O₃/—SiD_x, and Al₂O₃/—SiH_x + NCS^? are reported. Analysis of the vibrational spectra observed from isotopic substitution of the barriers obtained by deposition of a thin film of SiO onto alumina and magnesia indicate that the supported species is —SiH. The Al₂O₃/—SiH barrier can be used as a support for studying inorganic ions by IETS.     

Shielded Sliding Discharge-Assisted Hydrocarbon Selective Catalytic Reduction of NOx over Ag/Al2O3 Catalysts Using Diesel as a Reductant

The nonthermal plasma generated in a shielded sliding discharge reactor was used to reform diesel for the hydrocarbon-selective catalytic reduction (HC-SCR) of NO_x on Ag/Al₂O₃ catalysts. Compared with raw diesel, the reformed diesel enhanced the NO_x reduction efficiency, mitigated hydrocarbon poisoning of the catalyst and reduced the fuel penalty for the HC-SCR reaction. The NO_x conversion values obtained with a commercial Ag/Al₂O₃ catalyst exceeded that of a 2.0 wt% Ag/Al₂O₃ catalyst prepared by wet impregnation. A significant amount of NH₃ was produced as a by-product during the HC-SCR reaction, which suggests that further NO_x conversion enhancement can be achieved by placing a second NH₃-SCR catalyst in series with the Ag/Al₂O₃ catalyst.     

碳纳米管-氧化铝:高抗硫及再生性能的Pt基催化剂载体及在NO_x还原反应中的应用(英文)

通过乙炔在Al2O3上的分解制备碳纳米管-氧化铝(Al2O3-CNTs)载体.采用浸渍法,分别制备了Pt/Ba/Al2O3-CNTs和Pt/Ba/Al2O3催化剂.利用XRD,SEM,TEM,低温N2物理吸附,XPS和in-situ DRIFTS等手段对催化剂的物化性质进行了表征.结果表明,在SO2存在下的NOx还原反应中,Pt/Ba/Al2O3-CNTs比Pt/Ba/Al2O3具有更高的抗SO2性能和再生性能.In-situ DRIFTS表明SO2的存在对NOx储存还原的途径没有影响.     

铁和锰的化学状态对 LaFexMnyAl12-x-yO19 催化剂上 N2O 分解的影响

 以共沉淀法制备了 LaFexMnyAl12-x-yO19 六铝酸盐催化剂, 并用 X 射线衍射、扫描电镜、N2 吸附-脱附、紫外-可见漫反射光谱和穆斯堡尔谱对催化剂进行了表征, 考察了催化剂上高浓度 N2O 分解反应的性能. 结果表明, 在所考察的条件下, Mn 比 Fe 更有利于促进六铝酸盐晶相的形成. LaFexAl12-xO19 (x = 0.5, 1) 中 Fe 以 Fe3+位于六铝酸盐尖晶石结构中的四面体位和镜面层结构中的三角双锥位, 其中后者为 N2O 分解的主要活性中心. LaMnyAl12-yO19 (y = 0.5, 1) 中 Mn 优先以 Mn2+进入四面体位, 然后以 Mn3+进入尖晶石结构中的八面体位, 并成为 N2O 分解的主要活性中心.     

A facile synthetic route for the preparation of the Au/Mox/Al2O3 catalysts towards CO oxidation

Summary A new facile single-step synthetic route is reported for the preparation of Au/MO_x/Al₂O₃ catalysts. The preparation method has the merit of facility but leads to not only the simultaneous load of both gold source and MO_x precursor on Al₂O₃ support, but also the formation of Au/MO_x/Al₂O₃ with high gold loading ratio, high dispersion and high activity for CO oxidation.     

Preparation of the Solid Electrolytes Li4＋xAlxSi1—xO4—yAl2O3 by the Sol—Gel Method and Study of Their Ionic Conductivity

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Nox reduction with CO over supported Pd catalysts under simulated post Euro-IV diesel exhaust conditions

The catalytic reduction of NO_x with CO over Pd/Al₂O₃ and Pd/TiO₂/Al₂O₃ under simulated post Euro-IV diesel exhaust conditions was studied. The catalytic activities obtained by using various Pd and TiO₂ loadings and total amounts of reductant and the influence of H₂ and H₂O was investigated.     

Mechanochemical-thermal preparation and structural studies of mullite-type Bi2(GaxAl1−x)4O9 solid solutions

A series of Bi₂(Ga_xAl_1−x)₄O₉ solid solutions (0≤x≤1), prepared by mechanochemical processing of Bi₂O₃/Ga₂O₃/Al₂O₃ mixtures and subsequent annealing, was investigated by XRD, EDX, and ²⁷Al MAS NMR. The structure of the Bi₂(Ga_xAl_1−x)₄O₉ solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi₂(Ga_xAl_1−x)₄O₉ series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the ²⁷Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi₂(Ga_xAl_1−x)₄O₉. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.     

Structural Variations in the Solid‐Solution Series LnxCa2−xAl[Al1+xSi1−xO7] with 0 ≤ x ≤ 1 and Ln = La,Eu, Er

Gehlenite, Ca₂Al[AlSiO₇], has melilite‐type structure with space group . It contains two topologically distinct positions coordinated tetrahedrally by oxygen. One is completely occupied by Al³⁺, whereas the other one contains Al³⁺ and Si⁴⁺. Normally, the Al³⁺ molar fraction in the second tetrahedrally coordinated position does not exceed x_Al = 0.5, i.e. the so‐called Loewenstein‐rule is obeyed. In this contribution the structural variations in the melilite‐type compounds of the compositions La_xCa_2?xAl[Al_1+xSi_1?xO₇], Eu_xCa_2?xAl[Al_1+xSi_1?xO₇] and Er_xCa_2?xAl[Al_1+xSi_1?xO₇] are discussed. All members of the solid solution except the end‐members violate Loewenstein's rule. Rietveld refinements against X‐ray powder diffraction patterns confirm that the compounds have space group , without changes in the Wyckoff‐positions of the ions compared to gehlenite.     

Optimized Pt-MnOx interface in Pt-MnOx/3DOM-Al2O3 catalysts for enhancing catalytic soot combustion

The catalysts of three-dimensionally ordered macroporous (3DOM) Al₂O₃-supported core-shell structured Pt@MnO_x nanoparticles (3DOM-Pt@MnO_x/Al₂O₃) were successfully prepared by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. Pt@MnO_x core-shell nanoparticles (NPs) are highly dispersed on the inner surface of 3DOM-Al₂O₃ support. Pt@MnO_x/3DOM-Al₂O₃ catalysts, which combine both advantages of high-efficiency soot-catalyst contact by 3DOM-Al₂O₃ structure and the abundant active sites by the optimized Pt-MnO_x interface, exhibit high catalytic activities for soot combustion, and the catalytic activities are strongly dependent on the thickness of MnO_x shell. Among the catalysts, 3DOM-Pt@MnO_x/Al₂O₃-1 catalyst with optimized Pt-MnO_x interface shows the highest catalytic activity for soot combustion, i.e., its values of T₅₀ and S_CO2^m are 351 °C and 98.6%, respectively. The highest density of Pt-MnO_x active sites for adsorption-activation of gaseous O₂ is responsible for enhancing catalytic activity for soot combustion. Pt@MnO_x/3DOM-Al₂O₃ catalysts are promising to practical applications for the emission reduction of soot particles.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Synthesis and electrochemical characterization of LiMn2−xAlxO4 powders prepared by mechanical alloying and rotary heating

LiMn_2−xAl_xO₄ (0.0⩽x⩽0.10) intercalation powders have been synthesized by mechanical alloying followed by rotary heating. The precursor of LiMn_2−xAl_xO₄ has been prepared using LiOH · H₂O, MnO₂, and Al₂O₃ by mechanical alloying, which ensured a high level of homogeneity in the chemical composition of the precursor and resulted in a reduction in the synthesis temperature and heating time. Highly crystallized LiMn_2−xAl_xO₄ powders were obtained by subsequent rotary heating of the precursor at 600 °C for 3 h. Rotary heating enhanced the experimental control in particle size distribution of the final products. The synthesized LiMn_2−xAl_xO₄ powder has a narrow particle size distribution, high discharge capacities and good cycleability. Compared with the conventional solid-state reaction process, the present method of mechanical alloying combined with rotary heating should be a suitable technique of decreasing synthesis temperature and shortening heating time, and enhancing the uniformity of particle size of the product.     

Sol-Gel Processing of Functional and Structural Ceramic Oxide Fibers

Structural ceramic oxide fibers like α-Al₂O₃, MgAl₂O₄ (spinel), Y₃Al₅O₁₂ (YAG) and eutectic Al₂O₃−Y₃Al₅O₁₂ as well as the functional Pb(Zr_1−xTi_x)O₃ (PZT) fibers were successfully prepared by sol-gel processing. All precursors are based on metal oxohydroxopropionates. A comparative study of sol-gel routes leading to spinnable sols demonstrates the key role of propionic acid as an excellent agent for controlling hydrolysis and condensation reactions.     

Time‐Resolved,In Situ DRIFTS/EDE/MS Studies on Alumina‐Supported Rhodium Catalysts: Effects of Ceriation and Zirconiation on Rhodium–CO Interactions

The effects of ceria and zirconia on the structure–function properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ‐Al₂O₃) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on γ‐Al₂O₃ from [Ce(acac)₃] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)_x] (M=Ce, x=3; M=Zr, x=4) on Rh/γ‐Al₂O₃. The structure–function correlations of ceria and/or zirconia‐doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier‐transform spectroscopy/energy‐dispersive extended X‐ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time‐resolved, in situ conditions. CeO_x and ZrO₂ facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/γ‐Al₂O₃ samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.     

Pentacoordinated Al3+‐Stabilized Active Pd Structures on Al2O3‐Coated Palladium Catalysts for Methane Combustion

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO₂ catalysts with porous Al₂O₃ overlayers coated by atomic layer deposition (ALD). ²⁷Al magic angle spinning NMR analysis showed that Al₂O₃ overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al³⁺ sites capable of strongly interacting with adjacent surface PdO_x phases on supported Pd particles. Consequently, Al₂O₃‐decorated Pd/SiO₂ catalysts exhibit active and stable PdO_x and Pd–PdO_x structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al₂O₃ overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.     

Transparent glass-ceramics doped with Cr(III): Low-temperature time-resolved spectra and characterization of gahnite and virgilite crystalline phases

Trivalent chromium in transparent glass-ceramics (73.6 SiO₂ :11.8 Al₂O₃:4.2 Li₂O: 7.0 ZnO: 1.6 TiO₂: 1.5 ZrO₂: 0.3 As₂O₃: 0.024 Cr₂O₃ mole%) enters mainly the gahnite phase after an equilibrium has been reached. The intermediate phase during heat treatment is of virgilite-type Li_xAl_xSi_3−xO₆. This glass-ceramic has been studied by X-ray diffraction and time-resolved spectroscopy at low temperatures under laser excitation