助剂Ba对Pd/Al_2O_3和Pt/Al_2O_3催化剂的C1-C3烷烃催化燃烧性能的影响

通过浸渍法制备了Al_2O_3负载的Pd和Pt催化剂,考察催化剂的甲烷、乙烷和丙烷催化燃烧活性,以及助剂Ba对催化性能的影响。对于Pd/Al_2O_3催化剂,加入Ba使活性物种PdO颗粒变大和还原温度升高,形成更稳定的PdO活性物种,是Pd-Ba/Al_2O_3催化剂活性提升的主要原因。对于Pt/Al_2O_3催化剂,加入Ba助剂使活性物种Pt0含量降低,PtO_x与Al_2O_3载体相互作用增强,使PtO_x物种更难被还原为Pt~0,导致Pt-Ba/Al_2O_3催化剂活性降低。Pd和Pt催化剂催化烷烃氧化反应活性规律一致:丙烷乙烷甲烷。Pd/Al_2O_3催化剂有利于C—H键活化,Pt/Al_2O_3催化剂有利于C—C键活化。Pt/Al_2O_3催化剂对C1-C3烷烃氧化活性的差别明显大于Pd/Al_2O_3催化剂。Pt/Al_2O_3催化剂对碳比例高的烷烃活性更高。     

Pd-Pt-Ce/Al_2O_3催化剂在VOC净化处理中的催化性能

采用浸渍法制备Pd-Pt-Ce/Al_2O_3催化剂,考察贵金属Pd和Pt负载量、助剂种类及负载量、空速对催化甲苯燃烧活性的影响。结果表明,适宜的贵金属负载量和助剂可极大提高Pd-Pt/Al_2O_3催化剂活性,当Pd和Pt质量分数分别为0.05%和0.005%、助剂Ce质量分数为1%时,Pd-Pt-Ce/Al_2O_3催化剂在低温条件下表现出较好的催化性能。空速对催化剂的催化活性影响较为明显,适宜的空速低于20 000 h-1。     

The size effect and high activity of nanosized platinum supported catalysts for low temperature oxidation of volatile organic compounds

Pt/Al₂O₃ catalysts with smaller size of Pt nanoparticles were prepared by ethylene glycol reduction method in two different way and their oxidation activities for three typical VOCs (volatile organic compounds) were evaluated. The catalyst prepared by first adsorption and then reduction procedure is denoted as L-Pt/Al₂O₃ while the catalyst prepared by first reduction and then loading procedure is defined as R-Pt/Al₂O₃. The results show that L-Pt/Al₂O₃ with the stronger interaction between Pt species and Al₂O₃ exhibit smaller size of Pt nanoparticles and favorable thermal stability compared with R-Pt/Al₂O₃. L-Pt/Al₂O₃ is favor of the formation of more adsorbed oxygen species and more Pt²⁺ species, resulting in high catalytic activity for benzene and ethyl acetate oxidation. However, R-Pt/Al₂O₃ catalysts with higher proportion of Pt⁰/Pt²⁺ and bigger size of Pt particles exhibits higher catalytic activity for n-hexane oxidation. Pt particles in R-Pt/Al₂O₃ were aggregated much more serious than that in L-Pt/Al₂O₃ at the same calcination temperature. The Pt particles supported on Al₂O₃ with~10 nm show the best catalytic activity for n-hexane oxidation.     

顺丁橡胶尾气净化催化剂的研究与应用

顺丁橡胶尾气排放中主要污染物是正己烷,选择性催化氧化法是处理正己烷的主要技术。以聚乙二醇为助剂,制备Pt/Al_2O_3催化剂,利用侧线测试其催化性能,采用CO化学吸附与透射电子显微镜对催化剂进行表征。侧线测试结果表明,催化剂活性优于进口同类催化剂,250℃时,正己烷被完全氧化;CO化学吸附结果表明,Pt/Al_2O_3催化剂中贵金属分散度为75.9%,进口催化剂只有58.7%;TEM表明,Pt/Al_2O_3催化剂上金属分布更均匀。Pt/Al_2O_3催化剂应用于顺丁橡胶尾气处理,催化活性稳定。     

Catalytic performance of Ni/CeO2/Al2O3 modified with noble metals in steam gasification of biomass

In the steam gasification of biomass, the additive effect of noble metals such as Pt, Pd, Rh and Ru to the Ni/CeO₂/Al₂O₃ catalyst was investigated. Among these noble metals, the addition of Pt was most effective even when the loading amount of added Pt was as small as 0.01 wt.%. In addition, the catalyst characterization suggests the formation of the Pt–Ni alloy over the Pt/Ni/CeO₂/Al₂O₃.     

负载型Pt-Fe/Al2O3催化剂用于室温催化氧化甲醛

采用胶体沉积法制备不同载体（Ni₂O₃、Co₃O₄、TiO₂、Al₂O₃）的Pt-Fe/MeO_x催化剂用于甲醛室温催化氧化。活性测试表明,以γ-Al₂O₃为载体的Pt-Fe/Al₂O₃催化剂具有较高的催化活性,在25℃时甲醛的转化率可达到100%,而且Pt-Fe/ Al₂O₃催化剂还表现出良好的稳定性。采用各种表征技术对Pt-Fe/Al₂O₃的形貌、价态及氧化还原性等物理化学性质进行了研究,结果表明：Pt-Fe/Al₂O₃催化剂中Pt物种和Fe物种在Al₂O₃载体的表面上均匀分散;二者之间存在着较强的相互作用,在Al₂O₃载体的表面上形成一些类似Pt-O-Fe活性物种,有效促进了Pt-Fe/Al₂O₃催化性能,从而显示出较高的氧化活性。     

Catalytic combustion of methane over bimetallic Pd–Pt catalysts: The influence of support materials

The effect of support material on the catalytic performance for methane combustion has been studied for bimetallic palladium–platinum catalysts and compared with a monometallic palladium catalyst on alumina. The catalytic activities of the various catalysts were measured in a tubular reactor, in which both the activity and stability of methane conversion were monitored. In addition, all catalysts were analysed by temperature-programmed oxidation and in situ XRD operating at high temperatures in order to study the oxidation/reduction properties.

The activity of the monometallic palladium catalyst decreases under steady-state conditions, even at a temperature as low as 470 °C. In situ XRD results showed that no decomposition of bulk PdO into metallic palladium occurred at temperatures below 800 °C. Hence, the reason for the drop in activity is probably not connected to the bulk PdO decomposition.

All Pd–Pt catalysts, independently of the support, have considerably more stable methane conversion than the monometallic palladium catalyst. However, dissimilarities in activity and ability to reoxidise PdO were observed for the various support materials. Pd–Pt supported on Al₂O₃ was the most active catalyst in the low-temperature region, Pd–Pt supported on ceria-stabilised ZrO₂ was the most active between 620 and 800 °C, whereas Pd–Pt supported on LaMnAl₁₁O₁₉ was superior for temperatures above 800 °C. The ability to reoxidise metallic Pd into PdO was observed to vary between the supports. The alumina sample showed a very slow reoxidation, whereas ceria-stabilised ZrO₂ was clearly faster.     

Performance and characterization of supported metal catalysts for complete oxidation of formaldehyde at low temperatures

Activities of a series of metals (Pt, Pd, Rh, Cu, Mn) supported on TiO₂ were investigated for the catalytic oxidation of formaldehyde. Among them, Pt/TiO₂ was found to be the most promising catalyst. Nitrogen adsorption, hydrogen chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed reduction (TPR) by H₂ were used to characterize the platinum catalysts. Using Ce_0.8Zr_0.2O₂, Ce_0.2Zr_0.8O₂, SiO₂ as supports instead of TiO₂, the activity sequence of 0.6 wt.% platinum with respect to the supports is TiO₂ > SiO₂ > Ce_0.8Zr_0.2O₂ > Ce_0.2Zr_0.8O₂, and this appears to be correlated with the dispersion of platinum on supports rather than the specific surface areas of the catalysts. Platinum loading on TiO₂ has a great effect on the catalytic activity, and 0.6 wt.% Pt/TiO₂ catalyst was observed to be the most active, which could be attributed to the well-dispersed platinum surface phase. The reduction temperature greatly affects the particle size and, consequently, the catalytic activity. The smaller particle size of platinum, due to its high dispersion on support, has a positive effect on catalytic performance. Increasing formaldehyde concentration and space velocity exhibits an inhibiting effect on the catalytic activity.     

A comparative study of Ag/Al2O3 and Cu/Al2O3 catalysts for the selective catalytic reduction of NO by C3H6

The selective catalytic reduction (SCR) of NO by C₃H₆ in excess oxygen was evaluated and compared over Ag/Al₂O₃ and Cu/Al₂O₃ catalysts. Ag/Al₂O₃ showed a high activity for NO reduction. However, Cu/Al₂O₃ showed a high activity for C₃H₆ oxidation. The partial oxidation of C₃H₆ gave surface enolic species and acetate species on the Ag/Al₂O₃, but only an acetate species was clearly observed on the Cu/Al₂O₃. The enolic species is a more active intermediate towards NO + O₂ to yield—NCO species than the acetate species on the Ag/Al₂O₃ catalyst. The Ag and Cu metal loadings and phase changes on Al₂O₃ support can affect the activity and selectivity of Ag/Al₂O₃ and Cu/Al₂O₃ catalysts, but the formation of enolic species is the main reason why the activity of the Ag/Al₂O₃ catalyst for NO reduction is higher than that of the Cu/Al₂O₃ catalyst.     

Pt/TiO_2催化二甲醚部分氧化重整制氢

二甲醚是一种理想的氢载体,可用于解决氢的储存和运输。以Pt/TiO_2为部分氧化催化剂,结合Ni/Al_2O_3重整催化剂,考察钛前驱体和焙烧温度对二甲醚部分氧化重整制氢反应的影响。结果表明,以Ti(C4H9O)4为原料制备的TiO_2为金红石相,Ti(SO4)2或Ti O(OH)2为原料制备的TiO_2为锐钛矿相;以Ti(C4H9O)4为原料制备的Pt/TiO_2-E催化剂催化性能略好,转化率接近100%,H2收率约90%,表明金红石相TiO_2负载的Pt催化剂略佳;以Ti(SO4)2为原料制备的Pt/TiO_2-S催化剂500℃焙烧可获得金红石相TiO_2。与Pt/Al_2O_3催化剂相比,Pt/TiO_2催化剂具有更好的催化性能,H2收率超过90%,而Pt/Al_2O_3催化剂H2收率约80%。     

Complete oxidation of methane at low temperature over Pt and Pd catalysts for the abatement of lean-burn natural gas fuelled vehicles emissions: influence of water and sulphur containing compounds

The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH₄ traces under lean-burn conditions was studied in the presence or the absence of water or H₂S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H₂S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H₂S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H₂S-poisoned Pd/Al₂O₃ catalyst was studied by TPD in O₂/He. Poisoning species decompose above 873 K as SO₂ and O₂ in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O₂/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H₂S-poisoned Pd/Al₂O₃. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested.     

Effect of rare-earth element oxides (La2O3, Ce2O3) on the structural and physico-chemical characteristics of Pd/Al2O3 monolithic catalysts of nitrogen oxide reduction by methane

It is shown that introduction of additives of rare-earth element oxides (La₂O₃, CeO₂) enables regulating the structural and functional characteristics of Pd/Al₂O₃-catalysts (applied on ceramic monoliths of honeycomb structure) of nitrogen oxide reduction by methane. Modifying additives provide increase of thermal stability of porous structure of both highly dispersed Al₂O₃, as the second support, and the catalyst as a whole.

Contribution of La₂O₃ and CeO₂ in increasing the thermal stability is of an additive nature, and lanthanum oxide shows the higher efficiency than cerium one. According to X-ray phase analysis data, stabilizing action is conditioned by occurrence of rare-earth element oxides into lattice of Al₂O₃, which retards diffusional processes leading to phase transitions of low-temperature crystalline modifications of alumina into high-temperature ones with a low specific surface. For the catalyst samples modified with La₂O₃ an effect of thermal activation is observed, which is revealed by increase in catalytic activity as a result of annealing at 850 °C. Such a phenomenon, as shown by means of X-ray photoelectron spectroscopy technique, can be explained via stabilization of palladium in singly charged state in the form of groups of Pd⁺O₂⁻ and corresponding increase in concentration of active centers.     

Reactivation of sulphated Pt/Al2O3 catalysts by reductive treatment in the simultaneous oxidation of CO and C3H6

A Pt/Al₂O₃ catalyst prepared by incipient wetness impregnation was used as a diesel oxidation model catalyst and tested in the simultaneous total oxidation of CO and C₃H₆. Sulphur incorporation by wet impregnation results in deactivation of the Pt/Al₂O₃ catalyst in both oxidation reactions. Characterization of the catalysts by evolved gas analysis by mass spectrometry (EGA-MS), X-ray diffraction (XRD), isotherm of adsorbed nitrogen, X-ray photoelectron spectroscopy (XPS), infrared spectroscopy of probe molecules (pyridine and carbon monoxide) and finally temperature-programmed surface reaction (O₂-TPSR of chemisorbed CO) demonstrated that the formation of aluminium sulphate modifies the acidic properties of the support and the electronic properties of the platinum particles. Thus, new Brønsted acid sites are formed and, moreover, the capacity of the Pt particles to chemisorb CO and O₂, the latter as strongly chemisorbed O species, is seriously deteriorated. The alteration of the electronic properties of the particles (they become electronically deficient) is related to the modification of the acidic properties of the support. Treatment of the deactivated catalysts by a reductive treatment at 873 K resulted in the removal of the sulphur due to decomposition of the aluminium sulphate. Thus, the original acidic properties of the support and the electronic properties of the Pt particles were largely recovered and a high degree of catalytic reactivation was achieved.     

Reactivation of sintered Pt/Al2O3 oxidation catalysts

The reactivation of thermally sintered Pt/Al₂O₃ catalysts used in the simultaneous oxidation of CO and propene has been achieved by an oxychlorination treatment. The catalyst can be considered to model the active component of the catalytic converter fitted to diesel driven cars. Platinum crystallites redispersion was verified by XRD, H₂ chemisorption, TEM and FTIR. The extent of regeneration reflects the platinum particle redispersion achieved by such a treatment. Oxychlorination also introduced electronic effects in the Pt particle caused by the presence of chlorine at the Pt-Al₂O₃ interface but no detrimental result of this was observed in the oxidation reactions. The results indicate that the deactivation of the diesel oxidation catalysts (DOCs) can be reverted by this simple treatment resulting in a remarkable recovery of the catalytic activity.     

CO oxidation over promoted Pt catalysts

A study of CO oxidation by O₂ over Pt catalysts, promoted by MnO_x and CoO_x, is described. The activities of Pt/SiO₂, Pt/MnO_x/SiO₂ and Pt/CoO_x/SiO₂ are compared with commercial Pt/Al₂O₃, Pt/Rh/Al₂O₃ and Pt/CeO_x/Al₂O₃ catalysts. Since these catalysts differ in dispersion and weight loading of platinum, the turnover frequencies are also compared. The following order in activity in CO oxidation after a reductive pretreatment is found: Pt/CoO_x/SiO₂ > Pt/MnO_x/SiO₂, Pt/CeO_x/Al₂O₃ > Pt/Al₂O₃, Pt/Rh/Al₂O₃, Pt/SiO₂. Over Pt/CoO_x/SiO₂ CO is already oxidised at room temperature. Possible models to account for the high activity of Pt/CoO_x/SiO₂ in the CO/O₂ reaction are presented and discussed. Partially reduced metal oxides are necessary to increase the activity of the Pt/CoO_x/SiO₂, Pt/MnO_x/SiO₂ or Pt/CeO_x/Al₂O₃ catalysts. It was shown that mild ageing treatments did not affect the activity of the Pt/CoO_x/SiO₂ catalyst in CO oxidation.     

Hydrodesulfurization over noble metals supported on ZSM-5 zeolites

Pt/HZSM-5 showed high and stable catalytic activity for the hydrodesulfurization of thiophene at 400°C and its catalytic activity was higher than that of commercial CoMo/Al₂O₃ catalyst. Pt/HZSM-5 zeolite was not poisoned by hydrogen sulfide in the hydrodesulfurization of thiophene and hydrocracking of hydrocarbons. The catalytic activity of Pt/HZSM-5 decreased with increase of SiO₂/Al₂O₃ ratio in HZSM-5. The Brønsted acid site of HZSM-5 and spillover hydrogen formed on Pt particle in Pt/HZSM-5 catalyst play an important role for the hydrodesulfurization of thiophene.     

Oxidation of carbon black over various Pt/MOx/SiC catalysts

Catalytic activities of various Pt/MO_x/SiC systems for carbon oxidation under simulated diesel exhaust gas were investigated in temperature-programmed reactions. When Pt/MO_x (MO_x=TiO₂, ZrO₂, Al₂O₃) was loaded onto silicon carbide (SiC), the oxidation activities became higher than those of Pt/MO_x alone or other Pt/MO_x/SiC systems (MO_x=Ta₂O₅, WO₃, Nb₂O₅, SnO₂, SiO₂, CeO₂, MoO₃, V₂O₅). Among them, Pt/TiO₂/SiC exhibited the highest activity. We discuss the activity of MO_x=TiO₂, ZrO₂, and Al₂O₃ in connection with NO oxidation activity, adsorption of sulfate onto the support, Pt dispersion, and specific surface area of the catalyst. Furthermore, we investigated the catalytic performance of Pt/TiO₂/SiC in more detail under isothermal conditions and in a staged arrangement.     

Pt–Ba–Al2O3 for NOx storage and reduction: Characterization of the dispersed species

Pt–Ba–Al₂O₃ active and selective for NO_x storage and selective reduction to N₂ has been prepared and tested. Characterization of the parent Al₂O₃, Pt–Al₂O₃ and Ba–Al₂O₃ materials, as well as of Pt–Ba–Al₂O₃ catalyst in the oxidized, reduced and sulphated state has been performed by FT-IR spectroscopy of low-temperature adsorbed carbon monoxide and of adsorbed acetonitrile. XRD, TEM and XPS analyses have also been performed. Evidence for the predominance of Ba species, which are highly dispersed on the alumina support surface, and may be carbonated or sulphated, has been provided. Competitive interaction of Pt and Ba species with the surface sites of alumina has also been found.     

Structural and chemical promoter effects of alkali (earth) and cerium oxides in CO oxidation on supported gold

Nanostructured Au/Al₂O₃ catalysts prepared by deposition–precipitation with urea were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) and tested for low temperature CO oxidation. The paper is focused on the effect of two different kinds of additives on the structure and reactivity of Au/Al₂O₃ for CO oxidation: (1) alkali (earth) metal oxides and (2) ceria. The structural properties of nanosized Au particles are drastically affected by the presence of additives. The main role of the alkali (earth) metal oxides is to stabilize the small Au particles against sintering, such that when BaO is added to Au/Al₂O₃, full CO conversion is already achieved at room temperature. For this reaction ceria addition does not result in a higher activity. However, when both BaO and CeO_x are added to Au/Al₂O₃, the catalytic performance of the multicomponent catalyst resembles that of Au/BaO/Al₂O₃.     

C5/C6烷烃异构化Pt/Al2O3-Cl催化剂的性能

采用浸渍法制备了Pt/Al₂O₃,在300℃、CCl₄氯化1h,制备出Pt/Al₂O₃-Cl催化剂。采用FT-IR、XRD、TEM、CO-IR、Py-IR和TPD等方法表征了催化剂,并与中温型RISO催化剂的催化性能进行比较。结果表明,在氯化处理过程中氯取代了氧化铝的表面羟基,导致3000～3800cm^-1红外吸收峰强度大幅度减小,但催化剂的晶相不发生改变;氯化使Pt粒子的平均粒径增大,粒径分布变宽,金属分散度降低;氯化后金属Pt主要以+2价的PtCl₂的形式出现,其中一部分生成了易升华的PtCl₂·2AlCl₃,从而导致Pt含量降低;氯化后的催化剂上只有L酸,评价后既有L酸,又有B酸;氯化后的催化剂热稳定不高,随着温度升高,3种类型的氯化物相继脱出;Pt/Al₂O₃-Cl相对于中温型RISO催化剂表现出较好的异构化性能,正己烷转化率达88.17%,2,2-二甲基丁烷选择性达29.68%,裂化和氢解几乎没有发生。