不同载体对Pt-Sn催化剂丙烷催化脱氢性能影响

分别以Hβ分子筛和γ-Al₂O₃为载体,采用浸渍法制备不同Sn含量的负载型Pt-Sn双组分丙烷催化脱氢催化剂。在固定床微反装置上对制备的催化剂进行活性评价,并采用NH₃-TPD方法测定催化剂表面酸量和酸强度分布。结果表明,负载型Pt-Sn/Hβ和Pt-Sn/γ-Al₂O₃催化剂对丙烷催化脱氢反应性能与Sn含量密切相关,弱酸中心的存在对丙烷催化脱氢反应有利,对于特定的Pt-Sn体系,γ-Al₂O₃为载体的催化剂性能优于Hβ分子筛为载体的催化剂,当负载Sn质量分数为0.9时,Pt-Sn/γ-Al₂O₃催化剂性能最好。     

Correlating Low-temperature Hydrogenation Activity of Co/Pt(111) Bimetallic Surfaces to Supported Co/Pt/γ-Al2O3 Catalysts

The low-temperature self-hydrogenation (disproportionation) of cyclohexene was used as a probe reaction to correlate the reactivity of Co/Pt(111) bimetallic surfaces with supported Co/Pt/γ-Al₂O₃ catalysts. Temperature-programmed desorption (TPD) experiments show that cyclohexene undergoes self-hydrogenation on the ~1 ML Co/Pt(111) surface at ~219 K, which does not occur on either pure Pt(111) or a thick Co film on Pt(111). Supported catalysts with a 1:1 atomic ratio of Co:Pt were synthesized on a high surface area γ-Al₂O₃ to verify the bimetallic effect on the self-hydrogenation of cyclohexene. EXAFS experiments confirmed the presence of Co–Pt bonds in the catalyst. Using FTIR in a batch reactor configuration, the bimetallic catalyst showed a higher activity toward the self-hydrogenation of cyclohexene at room temperature than either Pt/γ-Al₂O₃ or Co/γ-Al₂O₃ catalysts. The comparison of Co/Pt(111) and Co/Pt/γ-Al₂O₃ provided an excellent example of correlating the self-hydrogenation activity of cyclohexene on bimetallic model surfaces and supported catalysts.     

异丁烷脱氢制异丁烯反应过程Pt-Sn-K/γ-Al2O3催化剂的失活分析

研究了Pt-Sn-K/γ-Al₂O₃催化剂在异丁烷脱氢-器内再生循环过程中脱氢反应性能,采用N₂物理吸附、CO脉冲吸附、NH₃-TPD和TG对催化剂进行表征,提出了催化剂的失活原因。结果表明,新鲜Pt-Sn-K/γ-Al₂O₃催化剂上异丁烯初始收率为39.5%,脱氢反应24 h后异丁烯收率降至20.6%。经2次脱氢-再生循环后,催化剂上异丁烯收率降至11.1%,72 h反应结束时异丁烯收率降至7.9%。积炭覆盖催化剂的活性位是导致催化剂失活的主要原因。Pt烧结及Pt-Sn合金形成使催化剂上Pt分散度降低,导致再生后催化剂活性明显下降。     

载体对Pt催化剂制备邻苯基苯酚催化性能的影响

分别以活性炭(AC)、γ-Al2O3、MgO、TiO2为载体,氯铂酸为活性金属前驱体,采用等体积浸渍法制得不同载体负载的Pt催化剂,考察了它们对环己烯基环己酮(dimer)脱氢制备邻苯基苯酚(OPP)的催化活性和选择性。并用X射线衍射(XRD)、X射线光电子能谱(XPS)、H2程序升温脱附(H2-TPD)、CO2程序升温脱附(CO2-TPD)等对催化剂进行表征。结果表明,载体对所制备的催化剂表面Pt含量、酸碱性和对氢吸附能力等微观性能有影响,以γ-Al2O3为载体制备的Pt-K/γ-Al2O3催化剂,由于催化剂表面Pt质量分数高达0.41%,碱性强和碱中心多,利于氢和中间产物在催化剂表面的吸附,从而提高环己烯基环己酮的转化率和OPP选择性。Pt/γ-Al2O3催化剂在LHSV 0.12 h-1、H2空速33 mL/(g.h)、反应温度380℃的条件下,在200 t/a的工业化装置运转8 000h后,环己酮二聚物转化率仍能达99%以上,OPP选择性达90%以上。     

Pt–Ni/γ-Al2O3 catalyst for the preferential CO oxidation in the hydrogen stream

The preferential CO oxidation (PROX) in the presence of excess hydrogen was studied over Pt–Ni/γ-Al₂O₃. CO chemisorption, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and temperature-programmed reduction were conducted to characterize active catalysts. The co-impregnated Pt–Ni/γ-Al₂O₃ was superior to Pt/Ni/γ-Al₂O₃ and Ni/Pt/γ-Al₂O₃ prepared by a sequential impregnation of each component on alumina support. The PROX activity was affected by the reductive pretreatment condition. The pre-reduction was essential for the low-temperature PROX activity. As the reduction temperature increased above 423 K, the CO₂ selectivity decreased and the atomic percent of Ni in the bimetallic phase of Pt–Ni increased. This catalyst exhibited the high CO conversion even in the presence of 2% H₂O and 20% CO₂ over a wide reaction temperature. The bimetallic phase of Pt–Ni seems to give rise to high catalytic activity for the PROX in H₂-rich stream.     

Selective CO oxidation in the presence of hydrogen over supported Pt catalysts promoted with transition metals

Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize active catalysts. Among them, Pt-Ni/γ-Al₂O₃ showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina was superior to TiO₂ and ZrO₂ as a support. The catalytic activity at low temperatures increased with increasing the molar ratio of Ni/Pt. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Ni and Pt was determined to be 5. This Pt-Ni/γ A1₂O₃ showed no decrease in CO conversion and CO₂ selectivity for the selective CO oxidation in the presence of 2 vol% H₂O and 20 vol% CO₂. The bimetallic phase of Pt-Ni seems to give rise to stable activity with high CO₂ selectivity in selective oxidation of CO in H₂-rich stream.     

Characterization and activity of Pt-Sn/Al2O3 catalysts of different preparation: coimpregnation and new Pt-Sn precursor

A new bimetallic Pt-Sn compound [Pt(NH₃)₄][SnCl₆] has been used as precursor for the preparation of supported Pt-Sn/Al₂O₃ catalysts. A comparison of a dried sample with that prepared by coimpregnation displays different behaviour in TPR, chemisorption. The initial catalytic activity properties were checked in the reactions of cyclohexane dehydrogenation and cyclopentane ring opening, whilen-hexane skeletal reactions were used to probe the quasisteady-state activity. The catalyst prepared via the Pt-Sn complex precursors exhibited some-what lower specific activity. This fact, together with enhanced olefin formation fromn-hexane was taken as an indication of lower amount of contiguous Pt atoms and some electronic interaction between Pt and Sn in that catalyst.On leave from Fachhochschule Ostfriesland, D-26723 Emden, Germany.     

The effects of catalyst modification on the catalytic activity in the dehydrocyclization of paraffins over Pt/γ-Al2O3

In the dehydrocyclization of n-octane over Pt-Sn/γ-Al₂O₃, the bimetallic Pt-Sn catalyst prepared by simultaneous impregnation as a complex showed higher activity than the catalyst prepared by successive impregnation with SnCl₂ and H₂PtCl₆, and the suspended Pt-Sn catalyst showed more enhanced catalytic behaviors in C₈-aromatics formation than the normal one. The geometric factor was an important parameter for the positive effect on the catalytic activity in the n-octane conversion, while the electronic factor, the electron density of the metal, was that in the aromatization of n-hexane.     

Ni-Cu/γ-Al2O3催化剂的制备及其脱氢反应研究

采用共沉淀法、浸渍法和共沉淀-浸渍法制备了3种不同的Ni-Cu/γ-Al2O3双金属催化剂,并利用微型连续管式反应器,考察了3种Ni-Cu/γ-Al2O3催化剂对氢能载体甲基环己烷(MCH)气相脱氢的催化性能。采用XRD、SEM、BET、BJH等手段对所制备的催化剂进行表征。结果表明,使用共沉淀-浸渍法制备的Ni-Cu/γ-Al2O3催化剂优于其他两种〔3种催化剂中Ni和Cu负载量均为26%且n(Ni)∶n(Cu)=8∶1〕。在反应温度673K,反应压力0.6 MPa,MCH与N2体积流量比为19∶27,混合进样体积空速240 h-1条件下,MCH脱氢转化率达到98.5%,产物甲苯的选择性接近100%。与铂等贵金属催化剂以及单金属镍催化剂相比,镍铜双金属催化剂在该反应中具有更好的应用前景。     

Role of cobalt on γ-Al2O3 based NO x storage catalyst

Co/Pt/Ba/γ-Al₂O₃, Co/Ba/γ-Al₂O₃, Pt/Ba/γ-Al₂O₃, Co/Pt/γ-Al₂O₃, Ba/γ-Al₂O₃, Pt/γ-Al₂O₃, and Co/γ-Al₂O₃ type catalysts were prepared by a conventional impregnation method, and their NO _x storage capacities were evaluated by colorimetric assay. Co-containing catalysts had a higher NO _x storage capacity than that of Co-free counterparts. The role of each component, especially Co, for the catalysts prepared was investigated by using in-situ FTIR. The high NO _x storage for Co-containing catalysts including Co/Ba/γ-Al₂O₃ and Co/Pt/Ba/γ-Al₂O₃ is mainly due to the formation of Co₃O₄ on the catalyst surface identified by XAFS.     

Preparation and Characterization of Bifunctional Pt-Sn/H[Al]ZSM5 Catalysts

Bifunctional monometallic Pt/H[Al]ZSM5, Sn/H[Al]ZSM5 and bimetallic Pt-Sn/H[Al]ZSM5 (tin atomic fraction, X _Sn, of 0.46) catalysts were prepared and characterized by means of XPS, EPR, TEM and toluene hydrogenation. The species on their surface as well as the presence of an effect of the electronic and/or geometric type between Pt and Sn in the bimetallic catalyst, which would result in the existence of reduced tin species (Sn⁰ and/or Sn-Pt), were determined. These species were determined through XPS and would explain the decrease in the hydrogenating activity in the toluene hydrogenation reaction.     

Hydrogenation of (–)-Menthone, (+)-Isomenthone, and (+)-Pulegone with Platinum/Tin Catalysts

The hydrogenation of (-)-menthone, (+)-isomenthone, and (+)-pulegone over SiO₂-supported Pt and Pt-Sn catalysts was studied in this work. The modification with tin was performed by means of the techniques of surface organometallic chemistry on metals. This way of modifying the catalysts allowed stereoisomers of menthol to be obtained in a one-step process. The hydrogenation of these terpenones was favored by the presence of tin in the bimetallic phase.     

Activity,selectivity, and methanol tolerance of novel carbon-supported Pt and Pt<Subscript>3</Subscript>Me (Me = Ni,Co) cathode catalysts

The activity, selectivity, and methanol tolerance of novel, carbon supported high-metal loading (40 wt.%) Pt/C and Pt₃Me/C (Me = Ni, Co) catalysts for the O₂ reduction reaction (ORR) were evaluated in model studies under defined mass transport and diffusion conditions, by rotating (ring) disk and by differential electrochemical mass spectrometry. The catalysts were synthesized by the organometallic route, via deposition of pre-formed Pt and Pt₃Me pre-cursors followed by their decomposition into metal nanoparticles. Characteristic properties such as particle sizes, particle composition and phase formation, and active surface area, were determined by transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. For comparison, commercial Pt/C catalysts (20 and 40 wt.%, E-Tek, Somerset, NJ, USA) were investigated as well, allowing to evaluate Pt loading effects and, by comparison with the pre-cursor-based catalyst with their much smaller particle sizes (1.7 nm diameter), also particle size effects. Kinetic parameters for the ORR were evaluated; the ORR activities of the bimetallic catalysts and of the synthesized Pt/C catalyst were comparable and similar to that of the high-loading commercial Pt/C catalyst; at typical cathode operation potentials H₂O₂ formation is negligible for the synthesized catalysts. Due to their lower methanol oxidation activity the bimetallic catalysts show an improved methanol tolerance compared to the commercial Pt/C catalysts. The results indicate that the use of very small particle sizes is a possible way to achieve reasonably good ORR activities at an improved methanol tolerance at DMFC cathode relevant conditions.     

Methane conversion over nanostructured Pt/γAl2O3 catalysts in dielectric-barrier discharge

Spherical nanostructured γ-Al₂O₃ granules were prepared by combining the modified Yoldas process and oil-drop method, followed by the Pt impregnation inside mesopores of the granules by incipient wetness method. Prepared Pt/γ-Al₂O₃ catalysts were reduced by novel method using plasma, which was named plasma assisted reduction (PAR), and then used for methane conversion in dielectric-barrier discharge (DBD). The effect of Pt loading, calcination temperature on methane conversion, and selectivities and yields of products were investigated. Prepared Pt/γ-Al₂O₃ catalysts were successfully reduced by PAR. The main products of methane conversion were the light alkanes such as C₂H₆, C₃H₈ and C₄H₁₀ when the catalytic plasma reaction was carried out with Pt/γ-Al₂O₃ catalyst. Methane conversion was in the range of 38–40% depending on Pt loading and calcination temperature. The highest yield of C₂H₆ was 12.7% with 1 wt% Pt/γ-Al₂O₃ catalysts after calcinations at 500 ‡C.     

The modification of molybdenum nitrides: the effect of the second metal component

A set of Mo2N-based bimetallic catalysts with high surface area around 140 m 2 /g have been successfully prepared from precursors obtained using the coprecipitation method. Both the precursors and the end-catalysts were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The nitriding processes were monitored by differential thermal analysis (TDA). The catalytic properties of Co-Mo bimetallic catalyst under mediumpressure (3.0 MPa) are much better for the hydrodenitrogenation of pyridine than those of pure γ-Mo2N and a commercially used sulfided CoMo/Al2O3 catalyst. The introduction of the second metal component has been shown to disrupt the morphology of the nitride phase with a greater concentration of (111) planes being present compared to (200) planes, a situation that is reversed compared to γ-Mo2N. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of noble metals in the decomposition of nitrous oxide over Fe-ferrierites

The decomposition of nitrous oxide was studied over Fe-ferrierite, Me-ferrierites and Fe/Me-ferrierites (Me: Pt, Rh and Ru). Flow as well as batch experiments were carried out and showed a synergy between Fe and Me ions. Ions of noble metals in Fe-ferrierite increased the catalytic activity in the sequence Pt < Rh ≅ Ru. Addition of NO substantially decreased the decomposition of N₂O over Rh/ferrierite and Ru/ferrierite, but not over bimetallic ferrierites. NO _x species created during the decomposition of nitrous oxide alone as well as with addition of NO, and employment of nitrous oxide labeled with ¹⁸O allowed us to assume a changing decomposition mechanism in the presence of Me ions in Fe-ferrierites.     

均匀沉淀法制备负载型双金属催化剂的正交实验研究

以NiCl2·6H2O和Co(NO3)2·6H2O为原料,CO(NH2)2为沉淀剂,Al2O3为载体,采用均匀沉淀法制备了负载型双金属催化剂(Ni-Co/γ-Al2O3).利用正交实验探讨了不同工艺参数对催化剂合成的影响,并得出了最佳制备工艺.实验得出的最佳工艺参数为:n(NiCl2·6H2O)/n(Co(NO3)2·...     

In situ EXAFS studies of modifications to supported metallic catalysts under reactive atmospheres

Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study the structural evolution of monometallic (Pt/Al₂O₃) and bimetallic (Pt-Re/Al₂O₃) catalysts with metal loadings representative of those used industrially under conditions close to those seen during preparation (calcination and reduction), during catalysis (under a hydrogen-hydrocarbon mixture), and during regeneration (simulated by cycles of reduction and oxidation). During the catalytic reforming ofn-heptane, the formation of bonds to carbon species is observed directly by EXAFS. Despite the fact that only platinum-carbon bonds are observed, bimetallic systems show significant differences compared with monometallic systems with, in the case of Pt-Re, a reduction in the temperature range over which carbon bonding is observed, and structural modifications of the metallic particles. Under the same conditions, no carbon bonding is observed for the Pt-Sn system. In the case of Pt-Sn/Al₂O₃, the EXAFS results, confirmed by transmission electron microscopy, demonstrate the high resistance to sintering of this bimetallic system compared to the monometallic system.     

Decane reforming reaction over Pt,Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite

Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on NaY- and HY-zeolite were examined as a catalyst for producing gasoline from n-decane via simultaneous reforming and cracking. The catalysts were prepared by calcining and reducing metal-ion-exchanged Y-zeolite with O₂ and H₂ at 300°C., respectively. Thus prepared catalysts were characterized by hydrogen chemisorption and temperature programmed desorption of ammonia. Pt-Ni/NaY and Pt-Ir/NaY bimetallic catalysts offered the improved activity maintenance compared to Pt/NaY monometallic catalyst. The catalysts supported on HY-zeolite showed higher selectivity toward C₅–C₇ and skeletal isomers of C₅–C₇- and C₈–C₁₀ than those of the catalysts supported on NaY-zeolite, which is a desired characteristic for increasing octane value of gasoline these days. However, deactivation with reaction time was much more pronounced on HY-zeolite-supported catalyst. When the catalyst was prcsulfided with H,S, the stability with time on stream was enhanced and the selectivity was quite different from that of the catalyst before presulfiding. The acidity of Y-zeolite and presulfiding of catalyst greatly influenced the activny, selectivity and stability of Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite in n-decane reforming reaction.     

Autothermal reforming of n-dodecane, toluene, and their mixture on mono- and bimetallic noble metal zirconia catalysts

Autothermal reforming (ATR) of higher hydrocarbons and their mixture was studied on zirconia-supported mono- (Rh, Pd, or Pt) and bimetallic (RhPt) catalysts. ATR reactions predominated on Rh-containing catalysts at 700–900 °C, whereas thermal cracking predominated on Pt and the support. The thermal stability of Rh was improved when Rh was combined with Pt in the bimetallic catalyst.