炭载体对Pt-C复合物非碱性条件下催化甘油氧化性能的影响

采用等量浸渍法制备了具有相似平均粒径的活性炭（AC）和碳纳米管（CNTs）负载的Pt催化剂,并比较研究了非碱性条件下两种催化剂催化甘油氧化反应的性能。结果表明,炭载体对Pt-C复合物催化甘油氧化反应的活性、选择性和稳定性有重要影响。相对于Pt/CNTs催化剂,Pt/AC催化剂中Pt 4f结合能较低,导致其表面氧的覆盖度相对较高,因而抑制了甘油的吸附,降低了甘油氧化反应的初始活性;Pt/AC催化剂会促进甘油醛进一步氧化成甘油酸以及C₃产物的氧化断键;Pt/AC催化剂失活的主要原因是氧中毒和中间产物的吸附,而Pt/CNTs催化剂的失活主要是由于甘油酸的吸附堵塞Pt表面的活性位造成的。     

Partial oxidation and combined reforming of methane on Ce-promoted catalysts

Pt/ZrO₂ and Pt/Ce_0.14Zr_0.86O₂ catalysts containing 0.5 and 1.5 wt.% Pt were studied in order to evaluate the effect of the support reducibility and metal dispersion on the catalyst stability for the partial oxidation and the combined partial oxidation and CO₂ reforming of methane. The Pt/Ce_0.14Zr_0.86O₂ catalysts proved to be more active, stable and selective than Pt/ZrO₂ catalysts during the partial oxidation reaction. No increase in deactivation was observed when the CH₄:O₂ feed ratio was increased from 2:1 to 4:1. In addition, no water formation was observed at the high CH₄:O₂ ratios. The activity of the catalyst is dependent upon both the dispersion and the ability of the catalyst to resist carbon deposition.

The addition of CO₂ resulted in a decrease in the methane conversion and a decrease in the H₂/CO ratio for the Ce_0.14Zr_0.86O₂ and ZrO₂ supported catalysts. Small increases in the temperature of the bed have been recorded during the partial oxidation reaction. However, within a few minutes the temperature stabilizes below the furnace temperature providing indirect evidence for the combined combustion and reforming mechanisms previously proposed. The 1.5 wt.% Pt/CeZrO₂ catalyst shows promise for the autothermal reforming reaction based on the stability during transient operation.     

Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol.     

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.     

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。     

On the mechanism of model diesel soot-O2 reaction catalysed by Pt-containing La-doped CeO2: A TAP study with isotopic O2

Pt supported on CeO₂ and 10 wt.% La³⁺-doped CeO₂ catalysts have been prepared, characterised and tested for soot oxidation by O₂ in TGA. The reaction mechanism has been studied in a TAP reactor with labelled O₂. Isotopic oxygen exchange between molecular O₂ and ‘O’ on the support/catalyst was observed and soot oxidation is being carried out by lattice oxygen. TAP studies further show that Pt improves O₂ adsorption and, therefore, 5 wt.% Pt-containing catalysts are more active for soot oxidation than the counterpart supports. In addition, CeO₂ doping by La³⁺ leads to an improved support, since La³⁺ stabilises the structure of CeO₂ when calcined at high temperature (1000 °C) and minimises sintering. In addition, La³⁺ improves the Ce⁴⁺/Ce³⁺ reduction as deduced from H₂-TPR experiments and favours oxygen mobility into the lattice. A synergetic effect of Pt and La³⁺ is observed, Pt-containing La³⁺-doped CeO₂ being the most active catalyst for soot oxidation by O₂ among the samples studied.     

Fe2O3对V2O5-WO3/TiO2催化剂表面性质及其性能的影响

催化剂是选择性催化还原(SCR)脱硝技术的核心,研究Fe对钒钛系SCR催化剂脱硝活性及SO₂/SO₃转化率的影响具有重要意义。采用等体积浸渍法制备了不同Fe/V质量比的Fe₂O₃-V₂O₅-WO₃/TiO₂催化剂,并进行表征,研究Fe对钒钛系SCR催化剂脱硝活性及SO₂/SO₃转化率的影响,并讨论Fe对于钒钛系SCR催化剂表面性质的影响。结果表明,随着催化剂表面Fe₂O₃含量增加,催化剂的脱硝效率及二氧化硫氧化率均是先上升后下降,当Fe/V质量比为3.0时,催化剂的脱硝效率和二氧化硫氧化率均达到最大值91.78%、1.01%。XPS及H₂-TPR结果表明,随着Fe₂O₃含量增加,催化剂表面钒活性组分的相对含量及V⁴⁺/V⁵⁺比减小,催化剂表面吸附氧(O_α)浓度增加,催化剂的氧化能力增强。NO-TPD结果表明,随着Fe₂O₃含量增加,催化剂表面吸附NO的能力增强。     

Pt/Pt-Ce/γ-Al2O3催化氧化甲苯研究

通过等体积浸渍法制备单贵金属Pt/γ-Al₂O₃和双金属Pt-Ce/γ-Al₂O₃催化剂,考察Ce对催化剂活性的影响,确定催化剂最优配比。结果表明,当Pt的负载量为质量分数0.5%时,Pt/γ-Al₂O₃催化活性最高;当Pt的负载量为质量分数0.2%,Ce的负载量为质量分数1.0%时,Pt-Ce/γ-Al₂O₃催化剂的催化活性最高。Pt-Ce/γ-Al₂O₃催化剂的甲苯转化率高于Pt/γ-Al₂O₃催化剂。随着Pt负载量增大,催化剂孔容、孔径减小。粉体式催化剂性能优于整体式催化剂,但差别不大;Ce的添加有助于催化剂活性的提升。     

Potential rare-earth modified CeO2 catalysts for soot oxidation part II: Characterisation and catalytic activity with NO + O2

Ceria (CeO₂) and rare-earth modified ceria (CeReO_x with Re = La³⁺, Pr^3+/4+, Sm³⁺, Y³⁺) supports and Pt impregnated supports are studied for the soot oxidation under a loose contact with the catalyst with the feed gas, containing NO + O₂. The catalysts are characterised by XRD, H₂-TPR, DRIFT and Raman spectroscopy. Among the single component oxides, CeO₂ is significantly more active compared with the other lanthanide oxides used in this study. Doping CeO₂ with Pr^3+/4+ and La³⁺ improved, however, the soot oxidation activity of the resulting solid solutions. This improvement is correlated with the surface area in the case of CeLaO_x and to the surface area and redox properties of CePrO_x catalyst. The NO conversion to NO₂ over these catalysts is responsible for the soot oxidation activity. If the activity per unit surface area is compared CePrO_x is the most active one. This indicates that though La³⁺ can stabilise the surface area of the catalyst in fact it decreases the soot oxidation activity of Ce⁴⁺. The lattice oxygen participates in NO conversion to NO₂ and the rate of this lattice oxygen transfer is much faster on CePrO_x. In general, the improvement of the soot oxidation is observed over the Pt impregnated CeO₂ and CeReO_x catalysts, and can be correlated to the presence of Pt°. The surface reduction of the supports in the presence of Pt occurred below 100 °C. The surface redox properties of the support in the Pt catalysts do not have a significant role in the NO to NO₂ conversion. In spite of the lower surface area, the Pt/CeYO_x and Pt/CeO₂ catalysts are found to be more active due to larger Pt crystal sizes. The presence of Pt also improved the CO conversion to CO₂ over these catalysts. The activation energy for the soot oxidation with NO + O₂ is found to be around 50 kJ/mol.     

Isomerization of n-hexane over mono- and bimetallic Pd–Pt catalysts supported on ZrO2–Al2O3–WOx prepared by sol–gel

The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO₂ (70, 85 wt.%)–Al₂O₃ (15, 0 wt.%)–WO_x (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N₂ physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO_x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO₃ bulk phase. The catalysts increased their S_BET for about 15% promoted by Al₂O₃ addition. Various oxidation states of WO_x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO_x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W⁶⁺ and reduced-state WO_x species (either W⁴⁺ or W⁰). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers.     

Catalytic wet air oxidation of carboxylic acids at atmospheric pressure

Catalytic wet air oxidation of carboxylic acids (maleic acid, oxalic acid and formic acid) was carried out in a batch reactor operated at 160 psi or atmospheric pressure. Pt/Al₂O₃ and the sulfonated poly(styrene-co-divinylbenzene) resin were used as catalysts. Maleic acid was proved to be a refractory substance which could not be oxidized on the Pt/Al₂O₃ catalyst at all atmoshperic pressure, and needed high pressure and high temperature operation for its oxidation. On the contrary, oxalic acid and formic acid were readily oxidized into carbon dioxide and water at 353 K and atmospheric pressure. The pathways of maleic acid oxidation were proposed, and the conversion of maleic acid into oxalic acid was the rate-determining step. When the sulfonated resin catalyst was present together with the Pt/Al₂O₃ catalyst, maleic acid could be oxidized at 353 K and atmospheric pressure. The sulfonated resin catalyst was suggested to hydrolyze maleic acid into readily oxidizable compounds.     

氯的脱除对丙烷脱氢PtSnNa/Al2O3催化剂结构的影响

考察了氯的脱除对丙烷脱氢铂锡催化剂结构和反应性能的影响,并采用XRD、N₂吸脱附、TPR、NH₃-TPD、TEM和Raman等方法进行表征。结果表明,氯的脱除温度显著影响催化剂的酸性、孔体积、比表面积、孔径和Pt颗粒尺寸。随着处理温度的提高,催化剂酸性、比表面积、孔体积都呈现下降的趋势,平均孔径增加,Pt颗粒的烧结程度加剧。随着处理温度的增加,催化剂初活性逐渐降低,丙烯选择性增加,稳定性出现先增加后降低趋势。研究表明,氯的较佳的脱除温度为540℃,催化剂具有很好的脱氢性能和稳定性,收率最高。     

WO3对Pt/α-Al2O3催化萘深度加氢的促进作用

采用无酸性的α-Al₂O₃为载体,预先沉积WO₃然后浸渍法负载Pt物种,合成了系列Pt-WO₃/α-Al₂O₃催化剂用于萘深度加氢反应,系统地研究了氧化钨物种在萘加氢反应中的作用。通过XRD、Raman、HRTEM、XPS和H₂-TPR技术表征了Pt和WO₃物种在载体表面的分散情况和状态,并利用Py-IR研究了载体负载氧化钨和Pt前后的酸性质变化。在温和的反应条件下（70℃、3 MPa、1 h）Pt-WO₃/α-Al₂O₃催化剂表现出优异的萘深度加氢活性,萘的转化率和十氢萘的选择性均达到100%。结果表明,预先在载体表面引入的WO₃和Pt产生了强相互作用,WO₃提高了Pt物种的分散程度,催化剂的酸性来源于氧化钨物种的引入且和负载量成正比关系。催化剂较强的酸性和较高的Pt分散程度是Pt-WO₃/α-Al₂O₃在低温条件下能够使萘深度加氢的关键因素,对于十氢萘作为储氢介质工艺具有重要的意义。     

Complete benzene oxidation over Pt-Pd bimetal catalyst supported on γ-alumina: influence of Pt-Pd ratio on the catalytic activity

Pt-Pd bimetal catalysts were prepared in order to develop and investigate catalysts with excellent activity and stability for benzene destruction. In the reaction results, the addition of Pt to Pd/γ-Al₂O₃ catalyst brought about the increase of catalytic activity. Moreover, it was effective in preventing the deactivation of the catalysts in benzene combustion. The addition of some amount of Pt made Pd particles available for better benzene combustion. On the contrary, the addition of Pt beyond a certain amount decreases activity because of the Pd active sites overlapped with the Pt active sites. The activity of the catalysts is related to oxidation state of metal, Pd/Al ratio and particle size on γ-Al₂O₃. These effects of Pt addition to Pd catalysts were studied by XPS, XRD, and TEM analyses.     

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.     

INVESTIGATION OF INSTABILITY OF OXIDATION OF H2 AND NH3 + H2 PLATINUM

Kinetics of oxidation reactions of H₂; and mixture H₂ + NH₃ on Pt has been studied at atmospheric pressure using a compensative electrothermography method. Existence of multiple steady states of catalyst activity and of isothermal critical phenomena is demonstrated for the system H₂ + O₂. Regions of reaction occurence are singled out and studied. Relaxation autooscillations of activity are detected. The phenomena observed are interpreted in terms of the hypothesis of branching-chain surface process. The study of critical phenomena in the mixture H₂ + NH₃; points to a common nature of active centres at oxidation of H₂ and NH₃ on Pt. A possible explanation of physical nature of active centres (a.c.) in the branching-chain surface process is proposed; the hypothesis suggests that a.c. are represented by catalyst adatoms.     

硫氮化合物在磷改性NiW/Al2O3加氢催化剂上的吸附行为研究

采用等体积浸渍法制备了一系列以γ-Al₂O₃及磷改性γ-Al₂O₃为载体,Ni、W为活性金属组分的加氢催化剂,以N₂物理吸附-脱附、XRD、NH₃-TPD、Py-IR等技术对Al₂O₃及P/Al₂O₃系列催化剂进行了表征,考察了磷改性对加氢催化剂理化性质的影响,探究了喹啉、吲哚和二苯并噻吩（DBT）吸附行为与催化剂理化性质以及吸附质本身性质的关系。研究发现,喹啉最易于吸附在Al₂O₃及P/Al₂O₃系列催化剂上,吲哚和DBT的吸附能力较为接近;磷的引入会降低催化剂的比表面积和孔体积,但是能够提高喹啉、吲哚及DBT的吸附能力;硫氮化合物在催化剂上的吸附能力随着催化剂表面酸性的增强或酸中心数量的增多、活性金属分散度的增大以及硫氮化合物杂原子电子云密度或分子极性的增大而增大。     

甲烷直接催化氧化制甲醇催化剂及反应机理

研究甲烷合成甲醇的催化剂及催化机理是甲烷直接催化氧化制甲醇的关键。本文综述了甲烷合成甲醇的Pt系催化剂、Pd系催化剂、Rh系催化剂、Fe改性沸石催化剂、Cu改性沸石催化剂、改性金属有机框架材料催化剂以及相应的催化机理。结果表明,Pt系催化剂中K₂PtCl₄、Pt(bpym)Cl₂、Pt(bipy)Cl₂催化甲烷制甲醇机理为亲电取代反应。Pd系催化剂中Pd(OAc)₂在CF₃COOH水溶液中通过多步电子传递链将甲烷转化为甲醇;Pd/C在乙酸水溶液中催化甲烷合成甲醇是亲电取代和活性氧物种氧化两种机理共同作用的结果。Rh系催化剂中的Rh/ZSM-5、Rh/TiO₂通过锚定在载体孔道内的一价Rh与CO、H₂O和O₂作用将甲烷转化为甲醇。Fe、Cu改性沸石催化剂及改性金属有机框架材料催化剂通过均裂、异裂等自由基反应转化甲烷得到甲醇。指出研究高效活化甲烷分子和抑制甲醇深度氧化催化剂的设计、制备及深入探究其催化机理仍然是今后的研究重点。     

Comparative study of Pt-based catalysts on different supports in the low-temperature de-NOx-SCR with propene

Pt-based catalysts have been prepared using supports of different nature (γ-Al₂O₃, ZSM-5, USY, and activated carbon (ROXN)) for the C₃H₆-SCR of NO_x in the presence of excess oxygen. Nitrogen adsorption at 77 K, pH measurements, temperature-programmed desorption of propene, and H₂ chemisorption were used for the characterization of the different supports and catalysts. The performance of these catalysts has been compared in terms of de-NO_x activity, hydrocarbon adsorption and combustion at low temperature, and selectivity to N₂. Maximum NO_x conversions for all the catalysts were achieved in the temperature range of 200–250°C. The order of activity was, Pt-USY>Pt/ROXNPt-ZSM-5Pt/Al₂O₃. At temperatures above 300°C only Pt/ROXN maintains a high activity caused by the consumption of the support, while the other catalysts present a strong deactivation. Propene combustion starts at the same temperature for all the catalytic systems (160°C). Complete hydrocarbon combustion is directly related to the acidity of the support, thus determining the temperature of the maximum NO_x reduction. The support play an important role in the reaction mechanism through the hydrocarbon activation. N₂O formation was observed for all the catalysts. N₂ selectivity ranges from 15 to 30% with the order, Pt/ROXN>Pt-USYPt/Al₂O₃>Pt-ZSM-5. The catalytic systems exhibit a stable operation under isothermal conditions during time-on-stream experiments.     

Bimetallic Pt–Sn catalysts supported on activated carbon. II. CO oxidation

A commercial activated carbon (AC) was used as a catalyst support either in its original form or after two different oxidation treatments, namely air oxidation and HNO₃ oxidation, aiming at the enhancement of its textural and surface chemical characteristics. These properties were determined by N₂ adsorption and temperature programmed desorption (TPD), respectively. Monometallic Pt and bimetallic Pt–Sn catalysts were prepared on the AC supports. Impregnation was used in the preparation of the monometallic samples. For the bimetallic samples, coimpregnation and a sequential impregnation procedure, in which the Sn precursor is introduced prior to Pt, were used. The Pt load was kept fixed as 1 wt.% for all monometallic and bimetallic samples. Two different Sn loads, 0.25 and 0.50 wt.%, were used for the bimetallic samples in order to investigate the effects of Sn load on the catalytic properties. The catalyst samples were characterized by H₂ adsorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and structure insensitive benzene hydrogenation. The activities of all samples were measured in CO oxidation. The results indicate the strong effects of the surface chemistry of the AC supports, the Pt:Sn ratio, the preparation procedure and the reduction procedure, on the CO oxidation activities of the catalysts.