Effect of metals on the catalytic activity of sulfated zirconia for light naphtha isomerization

We studied on the function of the metal in the sulfated zirconia(SO₄^2–/ZrO₂) catalyst for the isomerization reaction of light paraffins. The addition of Pt to the SO₄^2–/ZrO₂ carrier could keep the high catalytic activity. The improvement in this isomerization activity is because Pt promotes removal of the coke precursor deposited on the catalyst surface. Though this catalytic function was observed in other transition metals, such as Pd, Ru, Ni, Rh and W, Pt exhibited the highest effect among them. It was further found that the Pd/SO₄^2–/ZrO₂–Al₂O₃ catalyst possessed a catalytic function for desulfurization of sulfur-containing light naphtha in addition to the skeletal isomerization. The sulfur tolerance of catalyst depended on the method of adding Pd, and the catalyst prepared by impregnation of the SO₄^2–/ZrO₂–Al₂O₃ with an aqueous solution of Pd exhibited the highest sulfur tolerance.Further, we investigated the improvement in sulfur tolerance of the Pt/SO₄^2–/ZrO₂–Al₂O₃ catalyst by impregnation of Pd. The results of EPMA analysis indicated that this catalyst was a hybrid-type one (Pt/SO₄^2–/ZrO₂–Pd/Al₂O₃) in which Pt/SO₄^2–/ZrO₂ particles and Pd/Al₂O₃ particles adjoined closely. This hybrid catalyst possessed a very high sulfur tolerance to the raw light naphtha that was obtained from the atmospheric distillation apparatus, although this light naphtha contained much sulfur. We assume that such a high sulfur tolerance in the hybrid catalyst is brought about by the isomerization function of Pt/SO₄^2–/ZrO₂ particles and the hydrodesulfurization function of Pd/Al₂O₃ particles. Besides, since the hybrid catalyst also provides high catalytic activity in the isomerization of HDS light naphtha, we suggest that the Pd/Al₂O₃ particles supply atomic hydrogen to the Pt/SO₄^2–/ZrO₂ particles by homolytic dissociation of gaseous hydrogen and also enhance the sulfur tolerance of Pt/SO₄^2–/ZrO₂ particles. Finally, we also propose the most suitable location of Pd and Pt in the metal-supported SO₄^2–/ZrO₂–Al₂O₃ catalyst.     

Selective catalytic reduction of NO over metal oxide or noble metal-doped In2O3/Al2O3 catalysts by propene in the presence of oxygen

The activities of metal oxide CuO, SnO₂, CoO, Ag₂O, ZnO or noble metal Pt, Pd, Rh-doped In₂O₃/Al₂O₃ catalysts for selective catalytic reduction of NO by propene were investigated. The temperature windows for NO reduction over noble metal-doped In₂O₃/Al₂O₃ catalysts were shifted and broaden slightly compared with single component catalyst alone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of Pt and Pd additives on the state of the surface layer and catalytic activity of niobium oxides in the oxidation of hydrogen

Catalysts prepared by the hydrogen reduction of Nb₂O₅ in the presence of Pt or Pd have specific surface much greater than for the starting oxide and their catalytic activity in the oxidation of hydrogen is much greater than the activity of Pt/Al₂O₃ or Pd/Al₂O₃. X-ray phase analysis and X-ray photoelectron spectroscopy were used to establish the existence of Nb₂O_5–x nonstoichiometric oxides in the catalyst, which enhances the catalytic activity of the surface. The kinetic behavior of the oxidation of hydrogen on these catalysts is explained in the framework of the Eley–Riedel mechanism.     

The role of doped Fe on the activity of alumina-supported Pt and Pd diesel exhaust catalysts

Supported Pt and Pd are most commonly used for oxidation catalysts. They have similar and different characteristics for deactivation factors. The catalytic activity of Pt and Pd catalysts supported on ??-Al₂O₃ was studied in the presence and absence of H₂O and SO₂ during CO oxidation under simulated conditions of diesel exhaust gas. Without the addition of H₂O and SO₂ to the feed gas, Pd/Al₂O₃ had a superior catalytic activity compared to Pt/Al₂O₃. The addition of H₂O to the feed gas strongly and negligibly affected the activity of Pd and Pt, respectively, while the addition of SO₂ to the feed gas had a strong poisoning effect on the catalytic activity of both Pt and Pd catalysts. Although being the most active, Pd catalysts exhibited a strong sensitivity to water and sulfur-containing compounds. Fe was added to the Pt and Pd catalysts to introduce sulfur resistance. The addition of Fe enhanced the activity of the catalysts by suppressing the phase transition of Al₂O₃ to Al₂(SO₄)₃ and by hindering metal sintering.     

Two-stage catalytic system of Sn/Al2O3 and Pt/Al2O3for NO reduction by propene in lean conditions

The Pt/Al₂O₃, Sn/Al₂O₃catalysts were prepared by the single sol-gel method. The two-stage Sn/Al₂O₃and Pt/Al₂O₃catalyst in series for NO reduction with propene were investigated. The coexistance of water vapor enhanced the activity at medium temperature of 300-400^oC, and the NO conversion was above 50% at 225 to 500^oC even in the presence of water vapor and SO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selective Catalytic Reduction of NO with Propene over Au/Fe2O3/Al2O3 Catalysts

A series of Au/Fe₂O₃/Al₂O₃ catalysts were prepared by the homogeneous deposition-precipitation method. The catalytic activity of the catalyst samples for selective catalytic reduction of NO by propene under oxygen-rich atmosphere was evaluated. The results showed that 2%Au/10%Fe₂O₃/Al₂O₃ exhibited good low-temperature activity. The maximum of NO conversion reached 43% at 300 °C, while it was only 21% over the 2%Au/Al₂O₃ catalyst at the same temperature. The addition of 2% steam to the feed gas had little effect on the catalytic activity. X-ray diffraction results indicated that both Au and Fe₂O₃ particles were highly dispersed over Al₂O₃. H₂-temperature-programmed reduction results indicated that there was strong interaction between Au and Fe₂O₃, which made the reduction of Fe₂O₃ easy. The synergistic effect between Au and Fe₂O₃ was probably responsible for the good catalytic performance of the Au/Fe₂O₃/Al₂O₃ catalyst at low temperature.     

Pd Nanoparticles Supported on Triangle-Shaped La2O2CO3 Nanosheets: A New Highly Efficient and Durable Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

A catalyst in which Pd nanoparticles are supported on triangle-shaped La₂O₂CO₃ nanosheets exposing predominantly the (001) planes (Pd/La₂O₂CO₃-TNS; where TNS denotes triangular nanosheets) was prepared by a facile solvothermal method. The Pd/La₂O₂CO₃-TNS catalysts exhibited excellent catalytic activity and recycling stability for hydrogenation of cinnamaldehyde to hydrocinnamaldehyde with turnover frequency of up to 41 238 h⁻¹. This enhanced activity of Pd/La₂O₂CO₃-TNS results from strong metal–support interactions. Structure analysis and characterization demonstrated that surface-oxygen-enriched La₂O₂CO₃-TNS supports exposing (001) planes are beneficial to charge transfer between the Pd nanoparticles and triangle-shaped La₂O₂CO₃ nanosheets and increase the electron density of Pd. Moreover, the modulated electronic states of the Pd/La₂O₂CO₃-TNS catalysts can enhance the adsorption and activation of hydrogen to enhance the hydrogenation activity.     

Effect of platinum and palladium additives on the surface state and catalytic activity of vanadium oxides in the oxidation of carbon monoxide

The Pt/V₂O₅ and Pd/V₂O₅ systems formed upon hydrogen reduction have catalytic activity in the oxidation of carbon monoxide exceeding the activity of Pt/Al₂O₃ and Pd/Al₂O₃. The transition from the low-activity to high-activity state on the Pt/V₂O₅ and Pd/V₂O₅ catalysts is characterized by temperature hysteresis and change in the kinetic equation. X-ray phase analysis (XPA), X-ray photoelectron spectroscopy (XPES), and X-ray spectral microanalysis were used to establish that prior reduction of V₂O₅ by hydrogen gives VO₂, V₆O₁₃, a-H _x V₂O₅, and b-H _x V₂O₅, which facilitates the formation of an active catalyst surface.     

(La0.8A0.2)MnO3 (A = Sr,K) perovskite catalysts for NO and C10H22 oxidation and selective reduction of NO by C10H22

In this work, we studied the catalytic activity of LaMnO₃ and (La_0.8A_0.2)MnO₃ (A = Sr, K) perovskite catalysts for oxidation of NO and C₁₀H₂₂ and selective reduction of NO by C₁₀H₂₂. The catalytic performances of these perovskites were compared with that of a 2 wt% Pt/SiO₂ catalyst. The La site substitution increased the catalytic properties for NO or C₁₀H₂₂ oxidation compared with the non-substituted LaMnO₃ sample. For the most efficient perovskite catalyst, (La_0.8Sr_0.2)MnO₃, the results showed the presence of two temperature domains for NO adsorption: (1) a domain corresponding to weakly adsorbed NO, desorbing at temperatures lower than 270 ℃ and (2) a second domain corresponding to NO adsorbed on the surface as nitrate species, desorbing at temperatures higher than 330 ℃. For the Sr-substituted perovskite, the maximum NO₂ yield of 80% was observed in the intermediate temperature domain (around 285 ℃). In the reactant mixture of NO/C₁₀H₂₂/O₂/H₂O/He, (La_0.8Sr_0.2)MnO₃ perovskite showed better performance than the 2 wt% Pt/SiO₂ catalyst： NO₂ yields reaching 50% and 36% at 290 and 370 ℃, respectively. This activity improvement was found to be because of atomic scale interactions between the A and B active sites, Sr²⁺ cation and Mn⁴⁺/Mn³⁺ redox couple. Thus, (La_0.8Sr_0.2)MnO₃ perovskite could be an alternative free noble metal catalyst for exhaust gas after treatment.     

Catalytic reduction of sulfuric acid to sulfur dioxide

The reduction of H₂SO₄ to SO₂ occurs with a relatively good efficiency only at high temperatures, in the presence of catalysts. Some experimental results, regarding conversion of sulfuric acid (96 wt.%) to sulfur dioxide and oxygen, are reported. The reduction has been performed at 800 ?C 900°C and atmospheric pressure, in a tubular quartz reactor. The following commercial catalysts were tested: Pd/Al₂O₃ (5 wt.% and 0.5 wt.% Pd), Pt/Al₂O₃ (0.1 wt.% Pt) and ??-Fe₂O₃. The fresh and spent catalysts were characterized by X-Ray diffraction and BET method. The highest catalytic activity was determined for 5 wt.% Pd/Al₂O₃, a conversion of 80% being obtained for 5 hours time on stream, at 9 mL h^?1 flow rate of 96 wt.% H₂SO₄. A conversion of 64% was determined for 0.5 wt.% Pd/Al₂O₃ and 0.1 wt.% Pt/Al₂O₃. For ??-Fe₂O₃, a less expensive catalyst, a conversion of 61% for about 60 hours was obtained.      

Catalytic Performance and Characterization of Pt‐Co/Al2O3 Catalysts for CO2 Reforming of CH4 to Synthesis Gas

Pt‐Co/Al₂O₂ catalyst has been studied for CO₂ reforming of CH₄ to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al₂O₃ was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al₂O₃ and Pt/Al₂O₃ catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al₂O₃ > Pt/Al₂O₃ > Co/Al₂O₃. With 9% Co, the Co/Al₂O₃ calcined at 923 K was also active for CO₂ reforming of CH₄, however, its carbon formation was much more fast man that of the Pt‐Co/Al₂O₃ catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl₂O₄, formed during calcining of Co/Al₂O₃ at high temperature before Pt addition. Promoted by Pt, Co/Al₂O₄ in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al₂O₄ reduction are responsible for high activity of the Pt‐Co/Al₂O₃ catalyst, and the remain Co/Al₂O₄ is beneficial to suppression of carbon deposition over the catalyst.     

Effect of sol-gel derived Al2O3-ZrO2 and Al2O3-TiO2 oxides on the selectivity of NO reduction by CO under oxidizing conditions

The role of Al₂O₃-ZrO₂ and Al₂O₃-TiO₂ sol-gel prepared supports in the activity of platinum for the NO reduction by CO under oxidizing conditions has been studied. ²⁷Al MAS-NMR spectra have shown the formation of pentacoordinate Al^V in alumina-zirconia support. ZrO₂ or TiO₂ crystalline phases cannot be identified by XRD diffraction, suggesting the formation of nanosized structures supported on alumina. When the reaction was carried out in presence of oxygen, large amounts of NO₂ were observed on Pt/Al₂O₃-ZrO₂catalyst, while the formation of N₂O is more prononced on Pt/Al₂O₃-TiO₂ catalyst. The effect of water during NO reduction is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

l‐Arginine‐Triggered Self‐Assembly of CeO2 Nanosheaths on Palladium Nanoparticles in Water

Pd@CeO₂ core–shell nanostructures with a tunable Pd core size, shape, and nanostructure as well as a tunable CeO₂ sheath thickness were obtained by a biomolecule‐assisted method. The synthetic process is simple and green, as it involves only the heating of a mixture of Ce(NO₃)₃, l ‐arginine, and preformed Pd seeds in water without additives. Importantly, the synthesis is free of thiol groups and halide ions, thus providing a possible solution to the problem of secondary pollution by Pd nanoparticles in the sheath‐coating process. The Pd/CeO₂ nanostructures can be composited well with γ‐Al₂O₃ to create a heterogeneous catalyst. In subsequent tests of catalytic NO reduction by CO, Pd@CeO₂/Al₂O₃ samples based on Pd cubes (6, 10, and 18 nm), Pd octahedra (6 nm), and Pd cuboctahedra (9 nm) as well as a simply loaded Pd cube (6 nm)–CeO₂/Al₂O₃ sample were used as catalysts to investigate the effects of the Pd core size and shape and the hybrid nanostructure on the catalytic performance.     

钙铝石涂层对整体型钙钛矿氧化物催化剂活性和热稳定性的影响

 采用固相反应法合成了钙铝石材料 12SrO•7Al2O3, 并以此作为涂层制备了堇青石蜂窝陶瓷型 La0.8Sr0.2MnO3 整体催化剂, 在不同温度 (850~1 050 oC) 下对该催化剂进行了热处理, 并采用 N2 吸附-脱附、X 射线衍射和扫描电镜等手段对其进行了表征, 考察了其催化甲基丙烯酸甲酯燃烧反应的活性. 结果表明, 12SrO•7Al2O3 作为涂层明显改善了整体催化剂的热稳定性, 在 850 oC 下焙烧 6 h 后, 含有 12SrO•7Al2O3 涂层的整体催化剂在 260 oC 即可将甲基丙烯酸甲酯完全转化. 12SrO•7Al2O3 涂层可避免 La0.8Sr0.2MnO3 活性组分与堇青石的接触, 减轻了活性组分在催化剂表面的烧结, 有利于保持 La0.8Sr0.2MnO3 活性组分的晶体结构和分散度, 提高整体催化剂的活性和热稳定性.     

Praseodymium Oxide Modified CeO2/Al2O3 Catalyst for Selective Catalytic Reduction of NO by NH3

A series of CeO₂/Al₂O₃ catalysts was modified with praseodymium oxide using an extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction of NO with NH₃ to screen suitable addition of praseodymium oxide. These samples were characterized by XRD, N₂‐BET, NH₃‐TPD, NO‐TPD, Py‐IR, H₂‐TPR, Raman spectra and XPS, respectively. Results showed the optimal catalyst with the Pr/Ce molar ratio of 0.10 exhibited more than 90% NO conversion in a wide temperature range of 290–425°C under GHSV of 5000 h^?1. The number of Lewis acid sites and the chemisorbed oxygen concentration of the catalysts would increase with the Pr incorporation, which was favorable for the excellent catalytic performance. In addition, the Pr incorporation inhibited growth of the Al₂O₃ crystal particles and led to the lattice expansion of CeO₂, which increased catalytic activity. The results implied that the higher chemisorbed oxygen concentrations and the more Lewis acid sites were conductive to obtain the excellent SCR activity.     

Selective Hydrogenation of Acetylene and Physicochemical Properties of Pd–Fe/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Bimetallic Catalysts

The selective hydrogenation of acetylene on Pd–Fe/Al₂O₃ catalysts prepared by decomposition of ferrocene on reduced Pd/Al₂O₃ was studied. The effect of the conditions of treatment of the Pd–ferrocene/ Al₂O₃ precursor on the catalyst activity and selectivity was investigated, and the optimum conditions were determined at which the Pd–Fe/Al₂O₃ catalyst has higher selectivity than Pd/Al₂O₃ without any loss of activity.     

Bimetallic Pd—Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for complete methane oxidation: the effect of the Pt: Pd ratio

Alumina-supported bimetallic Pt—Pd catalysts proved to be more active in the complete oxidation of methane than monometallic systems (Pt/Al₂O₃, Pd/Al₂O₃). The maximum activity of the bimetallic catalysts was achieved at ~40 at.% Pt in Pd on the catalyst surface. After the oxidation reaction, redistribution of platinum and palladium was observed in the active component of the catalysts with the degree of redistribution depending on the initial Pt: Pd ratio.     

Fe-Ag/Al_2O_3催化丙烯还原NO的实验研究

以蜂窝状陶瓷为载体,采用溶胶凝胶法和浸渍法制备了不同Fe/Ag负载量的Fe-Ag/Al_2O_3催化剂。以C_3H_6为还原剂,在模拟烟气条件下和200-700℃范围内,程序控温的陶瓷管流动反应器上进行了催化还原NO的性能评估。结果表明,7.2Fe/1.9Ag/20Al_2O_3/CM在500和550℃时催化C_3H_6还原NO的脱硝效率分别超过90%和达到100%。铁离子能有效地提高Ag/20Al_2O_3/CM催化剂抵抗烟气中的SO_2和H_2O的能力。结果表明,当烟气中含有体积分数为0.02%的SO2和8%的H_2O时,在500℃时7.2Fe/1.9Ag/20Al_2O_3/CM催化C_3H_6还原NO的脱硝效率不受影响,在6 h的连续实验中保持90%的脱硝效率而没有下降。而未经铁离子修饰的2Ag/20Al_2O_3/CM的催化活性则受烟气中的SO2和H_2O影响很大,0.02%的SO2和8%的H_2O分别使2Ag/20Al_2O_3/CM在500℃时催化C_3H_6还原NO的脱硝效率迅速从70%分别下降至46%和25%。XRD和SEM表征结果表明,经铁离子修饰后的7.2Fe/1.9Ag/20Al_2O_3/CM催化剂中,形成了AgFeO_2以及Fe~(3+),催化剂表面变得疏松多孔,形成以Fe_3O_4为主的针状和片状晶体。H_2-TPR结果表明,7.2Fe/1.9Ag/20Al_2O_3/CM比Ag/20Al_2O_3/CM在更宽的温度范围内具有更好的还原特性。吡啶吸附红外光谱(Py-FTIR)实验结果显示,Fe增加了催化剂表面的Lewis酸性位。     

Catalytic Active Site for NO Decomposition Elucidated by Surface Science and Real Catalyst

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al₂O₃ catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al₂O₃. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co₃O₄ serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO₂⁻ species and then NO₂⁻ species react with the adsorbed NO species to form N₂ over the interface between the alkali metal and Co₃O₄.     

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.