Deactivation characteristics inn-heptane reforming reaction catalyzed over small Pt,Ir and Pt-Ir bimetallic clusters in NaY

The deactivation characteristics of highly dispersed (about 1 nm) Pt, Ir and Pt-Ir bimetallic clusters in NaY were studied by hydrogen chemisorption, coke analysis and temperature programmed oxidation of used catalyst inn-heptane reforming reaction. As the Ir content was increased, the amount of coke decreased. Most of coke was located around the metal cluster and this coke decreased the selectivity of dehydrocyclization inn-heptane reaction. The higher activity and more improved activity maintenance of Pt-Ir/NaY bimetallic catalysts than those of Pt/NaY are related to the less amount of coke formation.     

Aqueous-phase reforming of ethylene glycol over supported Pt and Pd bimetallic catalysts

More than 130 Pt and Pd bimetallic catalysts were screened for hydrogen production by aqueous-phase reforming (APR) of ethylene glycol solutions using a high-throughput reactor. Promising catalysts were characterized by CO chemisorption and tested further in a fixed bed reactor. Bimetallic PtNi, PtCo, PtFe and PdFe catalysts were significantly more active per gram of catalyst and had higher turnover frequencies for hydrogen production (TOF_H2) than monometallic Pt and Pd catalysts. The PtNi/Al₂O₃ and PtCo/Al₂O₃ catalysts, with Pt to Co or Ni atomic ratios ranging from 1:1 to 1:9, had TOF_H2 values (based on CO chemisorption uptake) equal to 2.8–5.2 min⁻¹ at 483 K for APR of ethylene glycol solutions, compared to 1.9 min⁻¹ for Pt/Al₂O₃ under similar reaction conditions. A Pt₁Fe₉/Al₂O₃ catalyst showed TOF_H2 values of 0.3–4.3 min⁻¹ at 453–483 K, about three times higher than Pt/Al₂O₃ under identical reaction conditions. A Pd₁Fe₉/Al₂O₃ catalyst had values of TOF_H2 equal to 1.4 and 4.3 min⁻¹ at temperatures of 453 and 483 K, respectively, and these values are 39–46 times higher than Pd/Al₂O₃ at the same reaction conditions. Catalysts consisting of Pd supported on high surface area Fe₂O₃ (Nanocat) showed the highest turnover frequencies for H₂ production among those catalysts tested, with values of TOF_H2 equal to 14.6, 39.1 and 60.1 min⁻¹ at temperatures of 453, 483 and 498 K, respectively. These results suggest that the activity of Pt-based catalysts for APR can be increased by alloying Pt with a metal (Ni or Co) that decreases the strengths with which CO and hydrogen interact with the surface (because these species inhibit the reaction), thereby increasing the fraction of catalytic sites available for reaction with ethylene glycol. The activity of Pd-based catalysts for APR can be increased by adding a water-gas shift promoter (e.g. Fe₂O₃).     

Effect of support on hydrogen production by auto-thermal reforming of ethanol over supported nickel catalysts

Nickel catalysts supported on various supports such as ZnO, MgO, ZrO₂, TiO₂, and Al₂O₃ were prepared by an impregnation method to investigate the effect of support on catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Among the supported catalysts, the Ni/ZrO₂ and Ni/TiO₂ catalysts showed better catalytic performance than the other catalysts. The electronic structure of nickel species supported on ZrO₂ and TiO₂ was favorably modified for the reaction, and thus, the reducibility of nickel species supported on ZrO₂ and TiO₂ was increased due to the weak interaction between nickel and support. On the other hand, the Ni/MgO and Ni/ZnO catalysts exhibited poor catalytic performance in the auto-thermal reforming of ethanol due to the formation of a solid solution phase.     

Methane reforming reaction with carbon dioxide over SBA-15 supported Ni-Mo bimetallic catalysts

A series of mesoporous molecular sieves SBA-15 supported Ni-Mo bimetallic catalysts (xMo1Ni, Ni = 12 wt.%, Mo/Ni atomic ratio = x, x = 0, 0.3, 0.5, 0.7) were prepared using co-impregnation method for carbon dioxide reforming of methane. The catalytic performance of these catalysts was investigated at 800 °C, atmospheric pressure, GHSV of 4000 ml·g_cat^− 1·h^− 1 and a V(CH₄)/(CO₂) ratio of 1 without dilute gas. The result indicated that the Ni-Mo bimetallic catalysts had a little lower initial activity compared with Ni monometallic catalyst, but it kept very stable performance under the reaction conditions. In addition, the Ni-Mo bimetallic catalyst with Mo/Ni atomic ratio of 0.5 showed high activity, superior stability and the lowest carbon deposition rate (0.00073g_c·g_cat^− 1·h^− 1) in 600-h time on stream. The catalysts were characterized by power X-ray diffraction, N₂-physisorption, H₂-TPR, CO₂-TPD, TG and TEM. The results indicate that the Ni-Mo bimetallic catalysts have smaller metal particle, higher metal dispersion, stronger basicity, metal-support interaction and Mo₂C species. It is concluded that Mo species in the Ni-Mo bimetallic catalysts play important roles in reducing effectively the amount of carbon deposition, especially the amount of shell-like carbon deposition.     

The hydrogenation of acetylene on supported bimetallic Pt-Ir and Pt-Re catalysts

Hydrogenation of acetylene has been studied with a series of Pt-Re and Pt-Ir catalysts. The results supplied some information concerning the importance of the potential electronic structure (ligand) effect of alloying and on the effect of selfpoisoning.     

Nano-structured CeO2 supported Cu-Pd bimetallic catalysts for the oxygen-assisted water–gas-shift reaction

The present work focuses on the development of novel Cu-Pd bimetallic catalysts supported on nano-sized high-surface-area CeO₂ for the oxygen-assisted water–gas-shift (OWGS) reaction. High-surface-area CeO₂ was synthesized by urea gelation (UG) and template-assisted (TA) methods. The UG method offered CeO₂ with a BET surface area of about 215 m²/g, significantly higher than that of commercially available CeO₂. Cu and Pd were supported on CeO₂ synthesized by the UG and TA methods and their catalytic performance in the OWGS reaction was investigated systematically. Catalysts with about 30 wt% Cu and 1 wt% Pd were found to exhibit a maximum CO conversion close to 100%. The effect of metal loading method and the influence of CeO₂ support on the catalytic performance were also investigated. The results indicated that Cu and Pd loaded by incipient wetness impregnation (IWI) exhibited better performance than that prepared by deposition–precipitation (DP) method. The difference in the catalytic activity was related to the lower Cu surface concentration, better Cu–Ce and Pd–Ce interactions and improved reducibility of Cu and Pd in the IWI catalyst as determined by the X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) studies. A direct relation between BET surface area of the CeO₂ support and CO conversion was also observed. The Cu-Pd bimetallic catalysts supported on high-surface-area CeO₂ synthesized by UG method exhibited at least two-fold higher CO conversion than the commercial CeO₂ or that obtained by TA method. The catalyst retains about 100% CO conversion even under extremely high H₂ concentration.     

Catalytic hydrogenolysis of CFC-12 (CC1<Subscript>2</Subscript>F<Subscript>2</Subscript>) over bimetallic palladium catalysts supported on activated carbon

Experiments were conducted for the hydrogenolysis of CFC-12 (CCl₂F₂) to CH₂F₂ over bimetallic palladium catalysts (Pd-Bi, Pd-Ru) supported on activated carbon. The characteristics of the bimetallic palladium catalysts were examined with ICP, XRD, TPD, TEM, and N₂ physisorption/H₂ chemisorption and the Pd-F formation was identified by XPS analysis. The catalytic activity of the bimetallic palladium catalyst (Pd-Bi/C, or Pd-Ru/C) was superior to that of the monometallic palladium catalyst. The bimetallic palladium catalysts showed much higher conversion rates (more than 99% of it was converted) than did the monometallic palladium catalyst (< 92%) and were deactivated to a lesser extent, even at high temperatures (>320 ‡C). The bimetallic components maintained the good dispersion of the Pd on the activated carbon support.     

Low-temperature 1,3-butadiene hydrogenation over supported Pt/3d/γ-Al2O3 bimetallic catalysts

Low-temperature 1,3-butadiene hydrogenation is used as a probe reaction to investigate the hydrogenation activity over several γ-Al₂O₃ supported Pt/3d (3d = Co, Ni, Cu) bimetallic catalysts. Batch and flow reactor studies are employed to quantify the kinetic activity and steady-state conversion, respectively, of each catalyst. Transmission electron microscopy (TEM) is utilized to characterize particle sizes and extended X-ray absorption fine structure (EXAFS) measurements are performed to verify the Pt–3d bimetallic bond formation. Pulse carbon monoxide chemisorption measurements are also performed to characterize the number of active sites. Additionally, density functional theory (DFT) calculations are included to determine the binding energies of 1,3-butadiene and atomic hydrogen on the corresponding model surfaces. The binding energies of the adsorbates are found to correlate with the hydrogenation activity, allowing for use of such correlation to potentially predict hydrogenation catalysts with enhanced activity based on the binding energies of the adsorbates of interest.     

CO2 reforming of methane to syngas over highly active and stable Pt/MgO catalysts

Pt/MgO catalysts were prepared by wet impregnation. At 800 °C and atmospheric pressure, Pt/MgO catalysts exhibited a high stability at high gas hourly space velocity of 36,000 ml/g h with a CH₄/CO₂ ratio of 1.0. During 72 h time on stream, the conversion of CH₄ and CO₂ remained almost constant, at about 88% and 90%, respectively. There was no loss of Pt. After reaction, the XRD peaks of MgO became broader, indicating amorphization of MgO, which was supported by TEM results. XPS indicated that the reforming reaction had little influence on Pt. CO₂-TPSR results showed that some carbon deposition occurred under stoichiometric feed of CH₄ and CO₂, but it did not result in the deactivation of the catalyst. The deposited carbon came mainly from the decomposition of methane.     

Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures

The partial oxidation of methane/oxygen mixtures with large exhaust gas dilution (46.3 vol% H₂O and 23.1 vol% CO₂) has been investigated experimentally and numerically over Rh/CeO₂-ZrO₂, Rh/ZrO₂ and Rh/α-Al₂O₃ catalysts. Experiments were carried out in a short-contact-time reactor at 5 bar and included exhaust gas analysis, temperature measurements along the reactor, and catalyst characterization. Additional experiments were performed in an optically accessible channel-flow reactor and involved in situ Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and laser-induced fluorescence (LIF) of formaldehyde. A full elliptic two-dimensional numerical code that included elementary hetero-/homogeneous chemical reaction schemes and relevant heat transfer mechanisms in the solid was used in the simulations. The employed heterogeneous reaction mechanism, including only active Rh sites, reproduced the experiments with good accuracy. The ratio of active to geometrical surface area, deduced from hydrogen chemisorption measurements, was the single model parameter needed to account for the effect of different supports. This indicated that water activation occurring on support sites, resulting in inverse OH spillover from the support to the noble metal sites, could be neglected under the present conditions with high water dilution. An evident relationship between noble metal dispersion and catalytic behavior, in terms of methane conversion and synthesis gas yields, could be established. Both measurements and predictions indicated that an increasing Rh dispersion (in the order Rh/α-Al₂O₃, Rh/ZrO₂, and Rh/CeO₂-ZrO₂) resulted in higher methane conversions, lower surface temperatures, and higher synthesis gas yields.     

XPS and reactivity study of bimetallic nanoparticles containing Ru and Pt supported on a gold disk

We report a new method of immobilization of catalytic metal/alloy nanoparticles on a gold disk for transfer from an electrochemical cell to UHV (without sample exposure to air) for XPS analyses. Using this immobilization approach, several samples were examined: a core-shell Pt-on-Ru catalyst prepared from Ru black onto which Pt was spontaneously deposited, commercial Pt/Ru 50:50 nanoparticle alloy, as well as single metal Ru and Pt nanoparticle samples. The catalysts were characterized for the Ru oxidation state and for the methanol electrooxidation activity (as Pt was always metallic). For all bimetallic samples, we found that the reduced nanoparticles were more active towards methanol oxidation than the fully or partially oxidized samples. Regardless the Ru oxidation state however, the activity was lower than that previously reported for Ru decorated Pt nanoparticle catalysts (Ru-on-Pt). Possible reasons for the reactivity differences are discussed.     

Hydrodesulfurization over supported monometallic, bimetallic and promoted carbide and nitride catalysts

The preparation of alumina-supported β-Mo₂C, MoC_1−x (x≈0.5), γ-Mo₂N, Co–Mo₂C, Ni₂Mo₃N, Co₃Mo₃N and Co₃Mo₃C catalysts is described and their hydrodesulfurization (HDS) catalytic properties are compared to conventional sulfide catalysts having similar metal loadings. Alumina-supported β-Mo₂C and γ-Mo₂N catalysts (Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃, respectively) are significantly more active than sulfided MoO₃/Al₂O₃ catalysts, and X-ray diffraction, pulsed chemisorption and flow reactor studies of the Mo₂C/Al₂O₃ catalysts indicate that they exhibit strong resistance to deep sulfidation. A model is presented for the active surface of Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃ catalysts in which a thin layer of sulfided Mo exposing a high density of sites forms at the surface of the alumina-supported β-Mo₂C and γ-Mo₂N particles under HDS conditions. Cobalt promoted catalysts, Co–Mo₂C/Al₂O₃, have been found to be substantially more active than conventional sulfided Co–MoO₃/Al₂O₃ catalysts, while requiring less Co to achieve optimal HDS activity than is observed for the sulfide catalysts. Alumina-supported bimetallic nitride and carbide catalysts (Ni₂Mo₃N/Al₂O₃, Co₃Mo₃N/Al₂O₃, Co₃Mo₃C/Al₂O₃), while significantly more active for thiophene HDS than unpromoted Mo nitride and carbide catalysts, are less active than conventional sulfided Ni–Mo and Co–Mo catalysts prepared from the same oxidic precursors.     

Support effect on the low-temperature hydrogenation of benzene over PtCo bimetallic and the corresponding monometallic catalysts

PtCo bimetallic and Co, Pt monometallic catalysts supported on γ-Al₂O₃, SiO₂, TiO₂ and activated carbon (AC) were prepared and evaluated for the hydrogenation of benzene at relatively low temperatures (343 K) and atmospheric pressure. Results from flow reactor studies showed that supports strongly affected the catalytic properties of different bimetallic catalysts. AC supported PtCo bimetallic catalysts exhibited significantly better performance than the other bimetallic catalysts, and all the bimetallic catalysts possessed higher activity than the corresponding monometallic catalysts. Results from CO chemisorption and H₂-temperature-programmed reduction (H₂-TPR) studies suggested that different catalysts possessed different properties in chemisorption capacity and reduction behavior, and AC supported PtCo catalysts possessed significantly higher CO chemisorption capacity compared to the other catalysts. Extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) analysis provided additional information regarding the formation of Pt–Co bimetallic bonds and metallic particle size distribution in the PtCo bimetallic catalysts on different supports.     

Ammoxidation of methylaromatics over vanadium phosphate catalysts II. Catalyst formation, active sites and reaction mechanism

The interactions of VOHPO₄· 0.5H₂O and (VO)₂P₂O₇ with the ammoxidation feed and the single components such as ammonia, oxygen, water and component mixtures were studied in detail using XRD and temperature-programmed reaction spectroscopy. The aim of this work was to improve the knowledge of the formation of the active phases or active sites of the catalysts from their precursors under the condition of the ammoxidation reaction. Similar catalytic properties of various applied VPO materials were discussed in terms of the presence of similar structure elements (domains of adjacent edge-sharing VO₆ octahedra-units and P-O-NH₄ groups).     

以类水滑石为前体的Ni催化剂及其催化甲烷水蒸气重整制氢:催化活性和动力学(英文)

Ni/Mg–Al catalysts derived from hydrotalcite-type precursors were prepared by a co-precipitation technique and applied to steam reforming of methane. By comparison with Ni/γ-Al2O3 and Ni/α-Al2O3 catalysts prepared by in-cipient wetness impregnation, the Ni/Mg–Al catalyst presented much higher activity as a result of higher specific surface area and better Ni dispersion. The Ni/Mg–Al catalyst with a Ni/Mg/Al molar ratio of 0.5:2.5:1 exhibited the highest activity for steam methane reforming and was selected for kinetic investigation. With external and inter-nal diffusion limitations eliminated, kinetic experiments were carried out at atmospheric pressure and over a temperature range of 823–973 K. The results demonstrated that the overal conversion of CH4 and the conversion of CH4 to CO2 were strongly influenced by reaction temperature, residence time of reactants as wel as molar ratio of steam to methane. A classical Langmuir–Hinshelwood kinetic model proposed by Xu and Froment (1989) fitted the experimental data with excellent agreement. The estimated adsorption parameters were consistent thermodynamical y.     

Steam reforming of methane over Ni catalysts prepared from hydrotalcite-type precursors:Catalytic activity and reaction kinetics

Ni/Mg–Al catalysts derived from hydrotalcite-type precursors were prepared by a co-precipitation technique and applied to steam reforming of methane. By comparison with Ni/γ-Al2O3 and Ni/α-Al2O3 cataly...     

Probability of chain growth in coke formation on metals and on supports during catalytic reforming over Pt, Pt-Sn and Pt-Sn-K catalysts mixed physically with Al2O3

The main goal of this contribution was to study the probability of chain growth of coke on metal sites and on support sites for hexane dehydrogenation. The coke structure of the catalysts examined by IR was found to have the aromatic structure. Soxhlet extraction coupled with GC-14B (DB1 column) analysis was mainly employed for coke composition analysis and determination of the probability of chain growth (alpha value). It was found that the soluble coke was mainly composed of C₈–C₁₂ on both sites. Interestingly, the probabilities of chain growth on both sites were identical. However, the extracted coke on the metal site was more easily removable and had lower carbon numbers than that on the support site. Moreover, the addition of promoter, especially of K promoter, was sensitive to inhibit the probability of chain growth, resulting in the reduction of the amount of coke.     

Reducibility and CO hydrogenation over Pt and Pt-Co bimetallic catalysts encaged in NaY-zeolite

Temperature programmed techniques (TPR, TPD) and X-ray diffraction (XRD) have been used to study ion migration and location as well as reducibility of platinum and cobalt ions encapsulated in Pt/NaY, Co/NaY and Pt-Co/NaY zeolites prepared by ion exchange. The temperature required to reduce Co²⁺ in NaY was significantly lowered by the presence of Pt and dependent upon the relative locations of Pt and Co ions in zeolite cages. The exact location was controlled by the calcination condition and the metal contents. For bimetallic catalyst with low Pt content (0.5 wt% Pt and 0.9 wt% Co), the TPR results indicated that reduction of Co²⁺ ions in the vicinity of Pt shifted toward lower temperature, while that of Co²⁺ staying alone was not affected. With high Pt loading (4.5 wt% Pt, 0.7 and 2.6 wt% Co), however, most of the Co²⁺ ions were reduced by means of Pt at temperature below 723 K after calcination at 573 K. The temperature for Pt reduction in bimetallic catalysts was somewhat higher than Pt/NaY and increased with Co atomic fraction, indicating that mixed oxide, PtCo _x O _y , might be formed during calcination. After reduction in hydrogen at 723 K, highly dispersed metal particles were formed. These fine particles were most probably confined inside zeolite cages as indicated by the absence of XRD peak for all samples after calcination and reduction. Surface composition of the bimetallic particles may be different for catalysts with similar Pt content but different Co loading. Accordingly, H/Pt ratios of 1.0 and 0.72 for catalysts with low and high Co content, respectively, were shown by hydrogen chemisorption. It was further supported by the increase in TPD peak intensity with Co loading in the high temperature range, which was related to the reoxidation of Co in bimetallic particles by surface hydroxyl groups. Preliminary results on CO hydrogenation demonstrated that activity and methanol selectivity were higher on Pt-Co bimetallic catalysts than either over monometallic Pt or Co catalyst, which was consistent with the Pt enhanced Co reduction and formation of Pt-Co bimetallic particles.     

Pd and Pt catalysts supported on carbon-coated monoliths for low-temperature combustion of xylenes

Carbon-coated monoliths were prepared from polyfurfuryl alcohol coated cordierite structures obtained by dip-coating. In this way, thin, homogeneous, consistent and good adhered carbon layers were obtained. The different steps followed in the preparation of these catalyst supports were studied by scanning electron microscopy. Pd and Pt catalysts were prepared by equilibrium impregnation of the monolithic supports with an aqueous solution of the corresponding tetraammine metal (II) nitrates. The catalysts were pretreated in H₂ at 300 °C before their characterization by chemisorption or before testing their catalytic activity. This pretreatment was monitored by temperature programme reduction. Catalytic activities in xylene combustion were evaluated as a function of the reaction temperature as well as against time on stream. The monolithic catalysts were thermally stable during the reaction. The Pt catalysts were more active than the Pd ones. The Pd catalysts with smaller Pd-particle sizes were more active. In the case of Pt catalysts however, the opposite was observed, which might be due to a structure sensitivity effect. Complete xylene combustion was reached in the range between 150 and 180 °C with a total selectivity to CO₂ and H₂O. Combustion of m-xylene was easier than p-xylene over Pt.     

Non-oxidative methane transformations into higher hydrocarbons over bimetallic Pt–Co catalysts supported on Al2O3 and NaY

The methane conversion under non-oxidative conditions over Al₂O₃ and NaY supported cobalt, platinum and Pt–Co bimetallic catalysts in a flow system has been investigated. The two-step process was applied in the temperature range between 523 and 673 K and 1 bar pressure and the one-step process was carried out under the conditions of 1073 K and 10 bar pressure. Addition of platinum to NaY and alumina supported cobalt samples results in the formation of metallic Co particles and Pt–Co bimetallic particles. On bimetallic catalysts in the two-step process, the amount of C₂₊ products formed were higher than that on mono-metallic samples. The synergism shown by the bimetallic system can be explained by: (i) enhanced reducibility of cobalt, and (ii) the co-operation of two types of active components (Co facilitates the chain-growth of partially dehydrogenated species produced on Pt in Pt–Co bimetallic particles). The use of higher pressures and high temperature makes it possible to run the process to form primarily ethane (and ethylene) which is predicted from thermodynamic calculations. For NaY as support, significantly enhanced activity and C₂₊ selectivity are obtained compared with Al₂O₃ as support, which can be attributed to the structural differences of metal particles (location, dispersion and reducibility).