Evaluation of naphtha reforming catalysts by accelerated deactivation tests

Accelerated deactivation tests of four commercial Pt−Re/Al₂O₃ catalysts have been carried out in a pilot plant at RON values of 98–100. From this 350-hour test, specific performance data for objective comparison of catalysts were obtained.     

The role of urea in Cu–Zn–Al catalysts for methanol steam reforming

Abstract  

Impregnated Cu–Zn over Al₂O₃ exhibits high activity with the use of a lower amount of active metal relative to conventional co-precipitation catalysts. The activity of the catalyst could be enhanced by addition of urea to the metal salt solution during impregnation. The H₂ yield from Cu–Zn catalysts with urea is 42%, while the H₂ yield from catalyst without urea is only 28% in a continuous system at 250 °C and 1.2 atm. The H₂ yield of the catalyst with urea in this study could compete with that of commercial catalysts. The role of urea in the Cu–Zn catalysts was investigated. X-ray diffraction (XRD) analysis of the catalysts shows that the crystal size of CuO could be reduced by the addition of urea. The XRD diffractogram of the catalyst prior to calcination also shows the formation of NH₄NO₃, which could aid in dissociation of metal clusters. Scanning electron microscopy (SEM) images of catalysts show the size of Cu–Zn compound clusters and also their dispersion over the Al₂O₃ surface on the impregnated catalysts. The addition of urea could also yield smaller Cu–Zn compound clusters and better dispersion compared with the impregnated catalyst without urea. Such impregnated Cu–Zn catalysts with urea could be alternative novel catalysts for methanol steam reforming.     

Hydrogen Production by Catalytic Reforming of Liquid Hydrocarbons

In this review, we are reporting the catalytic reforming of liquid hydrocarbon fuels carried out in our research group, covering the catalytic reforming of iso-octane and toluene as surrogate of gasoline, gasoline fuel processor system and steam reforming of n-hexadecane and decahydronaphthalene, main constituents of diesel. The commercial ICI reforming catalyst is prone to be poisoned by sulfur contained in iso-octane. We investigated various supported transition metal formulations and developed Ni/Fe/MgO/Al₂O₃ (KIST-5) catalyst with prolonged catalytic stability (>760 h), higher activity and sulfur tolerance ability over commercial ICI and HT catalysts for ATR reaction of iso-octane. We found that the concentration of CO can be reduced to <1,800 ppm by the gasoline fuel processor system charged with KIST-5 reforming catalyst, commercial HTS catalyst and KIST Pt–Ni/CeO₂ LTS catalyst. The addition of Rh metal to spc-Ni/MgAl catalyst as promoter was found to be very effective in inhibiting the deactivation of spc-Ni/MgAl catalyst by sintering of reduced Ni metal at high temperature during steam reforming of n-hexadecane. A 0.3 wt% Rh loading on spc-Ni/MgAl catalyst was optimized to have the best performance for steam reforming of n-hexadecane among the prepared catalysts. The addition of Rh to spc-Ni/MgAl catalyst also restricted the deactivation of the catalyst due to carbon formation at high reaction temperature. In view point of prolonged stability and higher activity, these developed reforming catalysts have a good scope in the reforming process of gasoline and diesel for hydrogen station and fuel processor system applications.     

Carbon supported electrocatalysts prepared by the sol–gel method and their utilization for the oxidation of methanol in acid media

One of the key objectives in fuel-cell technology is to improve the performance of the anode catalyst for the alcohol oxidation and reduce Pt loading. Here, we show the use of six different electrocatalysts synthesized by the sol–gel method on carbon powder to promote the oxidation of methanol in acid media. The catalysts Pt–PbO _x and Pt–(RuO₂–PbO _x ) with 10% of catalyst load exhibited significantly enhanced catalytic activity toward the methanol oxidation reaction as compared to Pt–(RuO₂)/C and Pt/C electrodes. Cyclic voltammetry studies showed that the electrocatalysts Pt–PbO _x /C and Pt–(RuO₂–PbO _x )/C started the oxidation process at extremely low potentials and that they represent a good novelty to oxidize methanol. Furthermore, quasi-stationary polarization experiments and cronoamperometry studies showed the good performance of the Pt–PbO _x , Pt–(RuO₂–PbO _x )/C and Pt–(RuO₂–IrO₂)/C catalysts during the oxidation process. Thus, the addition of metallic Pt and PbO _x onto high-area carbon powder, by the sol–gel route, constitutes an interesting way to prepare anodes with high catalytic activity for further applications in direct methanol fuel cell systems.     

Metal Oxide Promoted Electrocatalysts for Methanol Oxidation

An important research target in DMFCs is to find better catalyst materials that are cheaper, less-prone to poisoning and more catalytically active. In this context, metal oxides with good catalytic properties and stronger interaction with Pt nanoparticles can generate active interfacial regions for electrocatalysis. Pt catalysts promoted by certain metal oxides show enhanced methanol electro-oxidation activity and CO tolerance behavior. In this paper we summarize the recent progress from our laboratory which explored the possibility of developing Pt–MoO₃/C and Pt–Nb₂O₅/C electrocatalysts in acidic media, and Pt–V₂O₅/C electrocatalyst in alkaline media for direct electro-oxidation of methanol. The oxide electrocatalysts have been prepared by a fast and efficient method of loading the metal oxide on carbon black (Vulcan XC-72) employing an intermittent microwave heating (IMH) method. These materials are found to achieve higher activity and stability towards methanol electro-oxidation.     

Titania-supported mixed HPMoV polyoxometallates as precursors of hydrodesulfurization catalysts

HDS catalysts were prepared by loading H₃PMo₁₂O₄₀ or H₄PMo₁₁V₁O₄₀ polyoxometallates on TiO₂ (0.5 and 1.0 mmol (Mo+V)). Activity of the catalysts was tested in the HDS of thiophene. The activity of catalysts of low concentration was 2–3 times higher than the activity of those of high concentration. Temperature programmed reduction (TPR) and IR spectroscopy were used to determine the properties of the catalyst. TPR measurements proved that vanadium promotes and stabilizes HDS activity due to an increase in the Mo⁵⁺/Mo⁴⁺ ratio.     

Marked Effect of Various Supports and Additives Upon Liquid Phase Methanol Reforming with Water over Supported Group 8–10 Metal Catalysts

The support effects (SiO₂, TiO₂, Al₂O₃, MgO, CeO₂ and ZrO₂) as well as addition effect of group 6b and 7b elements were studied over various supported group 8–10 metal catalysts. Basic oxide support improved the selectivity to CO₂ and acidic support suppressed the catalytic activity and selectivity. Among the investigated catalysts Pt–Mo/TiO₂ was the most active catalysts, whereas Ir–Re/SiO₂ was the most selective catalysts for H₂ and CO₂ formation. The mechanism of the liquid phase methanol reforming reaction over silica supported Pt–Ru catalyst was studied by kinetic investigations. The rate of H₂ formation over Pt–Ru/SiO₂ catalysts was more than 20 times faster than that over Pt/SiO₂ catalysts with high selectivity for CO₂ (72.3%), indicating a marked addition effect of Ru. In the case of HCHO–H₂O reaction over Pt–Ru/SiO₂, the H₂ formation rate was five times larger than that in the CH₃OH–H₂O reaction but selectivity to CO₂ was only 4%. On the contrary, in the HCOOCH₃–H₂O and HCOOH–H₂O reactions, both high activity and selectivity were observed over Pt–Ru/SiO₂. These results clearly indicate that the CO₂ formation does not proceed via HCHO decomposition and following water gas shift reaction.     

Effect of thermal treatment on phase composition and ethanol oxidation activity of a carbon supported Pt50Sn50 alloy catalyst

A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of Sn in the face centered cubic (fcc) Pt and SnO₂. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt₃Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to the presence of a large amount of SnO₂. Dedicated to Teresa Iwasita’s 65th birthday.     

Activities of δ-Al2O3-supported bimetallic Pt?NiO and Co?NiO catalysts for methane autoreforming: Oxidation studies

The methane oxidation activities of Pt−NiO and Co−NiO bimetallic catalysts have been investigated as part of a larger research program on the autothermal reforming of methane (combined methane oxidation and steam reforming) in a fluidized bed reactor. Experiments at atmospheric pressure and 783–1023 K for both catalysts showed that the reaction was more selective towards H₂ production at CH₄∶O₂ ratios greater than unity. Light-off temperature increased with decreasing CH₄∶O₂ ratios, but increase in gas velocity (beyond minimum fluidization) increased the light-off temperature. Co−NiO was as promising as the more expensive Pt−NiO catalyst for the oxidation.     

Effect of rare earth oxides (CeO2, La2O3) on properties of Pd/Al2O3 catalysts for reduction of nitrogen oxides by methane

We have established that the thermal stability of supported Pd/Al₂O₃ catalysts is increased after they are modified by rare earth oxides (La₂O₃, Ce₂O₃). We have observed the effect of thermal activation of an aluminopalladium catalyst modified by lanthanum oxide. This effect is apparent in the increase of the specific catalytic activity in the reaction of high-temperature reduction of nitrogen oxides by methane after heat treatment of the catalyst at 850 °C. We have used X-ray photoelectron spectroscopy (XPS) to show that the reason for the thermal activation effect is stabilization of palladium in the Pd¹⁺ state. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 44–48, January–February, 2006.     

Mo_2C/γ-Al_2O_3催化剂上苯加氢反应的原位红外光谱研究

采用程序升温反应法制备了钝化态、还原钝化态和新鲜态Mo2C/γ-Al2O3催化剂,结合原位红外光谱表征技术和反应性能评价,考察、比较了三种催化剂苯加氢反应活性.原位红外光谱结果表明,新鲜态Mo2C/γ-Al2O3催化剂在室温就显示了较好的苯加氢反应活性,表现了类贵金属的催化活性.CO吸附在反应前后新鲜态Mo2C/γ-Al2O3催化剂上的对比结果表明,低价态的Mo位(Moδ+(0δ2))是苯加氢反应活性中心.三种催化剂的反应活性结果表明,新鲜态Mo2C/γ-Al2O3催化剂反应活性最好,催化剂寿命最长,失活之后在500°C下H2处理即可恢复原有活性.     

Catalytic synthesis of indole from tetrahydroindole on Pd-and Cr-containing catalysts

In the presence of Pd-and Cr-containing catalysts applied to γ-Al₂O₃ or sibunite 4,5,6,7-tetrahydroindole is converted into indole. Indole was obtained in quantitative yield on sulfided 0.15–0.5% Pd/γ-Al₂O₃ catalyst at 360°C and on catalysts containing 5% Cr₂O₃, 5% La₂O₃ (or 5% polirit), 1% K₂O/89% γ-Al₂O₃ at 475–480°C. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1176–1178, August, 2006.     

Pt/CexZr1-xO2 催化剂在含硫合成气中催化水煤气变换反应活性

 采用浸渍法制备了 Pt/Ce_xZr_1-xO₂ 催化剂, 通过 X 射线衍射和程序升温还原等方法对催化剂进行了表征, 并在固定床反应器中评价了催化剂在合成气和含硫合成气中的水煤气变换活性. 结果表明, 铈锆固溶体的氧化还原能力强于 CeO₂, Zr 的掺杂明显改善了 CeO₂ 的孔道结构, 其担载的 Pt 催化剂具有更高的金属分散度, 因而活性更高. 两种催化剂在含硫合成气中的催化活性较无硫合成气中的均有所降低, 且 H₂S 浓度越大, 催化剂活性下降越多, 但这种因吸附硫而引起的失活是可逆的, 即催化剂重新暴露在无 H₂S 重整气的还原性气氛下活性能基本恢复.     

Preparation and electrocatalytic performance of Fe–N–C for electroreduction of H2O2

Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen source, and calcination temperature on the catalytic performance of the Fe–N–C for H₂O₂ electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed good performance and stability for electroreduction of H₂O₂ in alkaline solution. An Al–H₂O₂ semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V and its power density reached 51.4 mW cm⁻² at 65 mA cm⁻².     

Shape selective oxidation by a microporous platinum-polyoxometalate

Shape selective catalytic behaviour of a platinum-promoted polyoxometalate, 0.5 wt% Pt−Cs_2.1H_{0 9}PW₁₂O₄₀, has been studied for complete oxidation of methane and benzene. The pore size of this catalyst determined by adsorptions of n-butane and isobutane was close to the molecular size of n-butane (0.43 nm). Ar and N₂ porosimetries demonstrated that 0.5 wt% Pt−Cs_{2 1}H_{0 9}PW₁₂O₄₀ possesses unimodal distribution of pores in ultramicropore region. External surface area was estimated to be less than 3% that of the total surface area (61 m² g⁻¹) of the catalyst. Owing to the restricted pores, this exhibited efficient shape selectivity; methane (molecular size; 0.38 nm) was readily oxidized, while the oxidations of the larger molecule such as benzene (0.59 nm) were greatly suppressed. These results indicate that 0.5 wt% Pt−Cs_{2 1}H_{0 9}PW₁₂O₄₀ is a promising microporous catalyst.     

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO₂. For example, nickel catalysts co-precipitated with Ce_0.8Zr_0.2O₂ having cubic phase gave synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO₂ having tetragonal phase (Ce_0.8Zr_0.2O₂) or mixed oxide phase (Ce_0.5Zr_0.5O₂) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂ support and the finely dispersed nano size NiO _x crystallites, resulting in the intimate contact between Ni and Ce_0.8Zr_0.2O₂ particles. The Ni/Ce–ZrO₂/θ–Al₂O₃ also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO₂ resulting in the existence of stable NiO _x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO _x formation was more favorable than NiO or NiAl₂O₄ formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO₂/CH₄ ratio and H₂O and/or O₂ addition were also examined.     

Cobalt salts of decamolybdodicobaltic acid as precursors of the highly reactive type II CoMoS phase in hydrorefining catalysts

Catalysts have been synthesized using the Anderson polyoxometalates (POMs) (NH₄)₄[Ni(OH)₆Mo₆O₁₈] (NiMo₆POM), (NH₄)₆[Co₂Mo₁₀O₃₈H₄] · 7H₂O (Co₂Mo₁₀POM), and H₆[Co₂Mo₁₀O₃₈H₄] (Co₂Mo₁₀HPA) as the precursors and hydrogen peroxide as the solvent. The catalysts have been characterized by low-temperature nitrogen adsorption, XPS, and HRTEM. Their catalytic properties have been tested in thiophene hydrodesulfurization and in the hydrodesulfurization and hydrogenation of components of diesel oil. The active phase of the catalysts synthesized using the POMs is the type II CoMoS phase in which the mean plate length is 3.6–3.9 nm and the mean number of MoS₂ plate per plate packet is 1.8–2.0. Use of hydrogen peroxide provides an efficient means to reduce the proportion of Co²⁺ promoter atoms surrounded by oxygen in the case of an impregnating solution containing both an ammonium salt of a heteropoly acid and a Co²⁺ salt. In the catalysts synthesized using cobalt salts of Co₂Mo₁₀HPA, the support surface contains the multilayer type II CoMoS phase and cobalt sulfides. These catalyst show high catalytic properties in thiophene hydrogenolysis and diesel oil hydrorefining. Models are suggested for the catalysts synthesized using Anderson POMs.     

A study on the reduction behavior of silica supported iron and platinum-iron catalysts

The reduction behavior of silica supported iron and platinum-iron catalysts were studied by combinedin situ temperature programmed reduction (TPR)-M?ssbauer Spectroscopy (MBS). The results indicated that the TPR profiles of the supported Fe catalysts were different from that of bulk α-Fe₂O₃. There existed an interaction between the Pt and Fe metals and the SiO₂ support for the Pt−Fe/SiO₂ catalyst. On the supported iron-containing catalysts, the Fe³⁺ species were highly dispersed on the SiO₂ supported before reduction. No Fe⁰ and Fe²⁺ in octahedral vacancy were found in the reduction of SiO₂ supported iron-containing catalysts. Addition of Pt to the Fe/SiO₂ catalyst could promote the reduction of the iron species.     

Catalytic coatings of new generation based on Mo2C and a microstructured reactor for steam conversion of carbon monoxide

Cathodic processes occurring in the course of molybdenum hemicarbide synthesis on molybdenum supports (Mo₂C/Mo) were studied by cyclic voltammetry. The coatings synthesized were tested as catalysts in steam conversion of carbon monoxide. The catalytic activity of the Mo₂C/Mo system in this reaction is higher by 1–3 orders of magnitude than that of the commercial catalyst Cu/ZnO/Al₂O₃. A microstructured heat-exchanging reactor was designed and fabricated on the basis of the kinetic data obtained.     

Cu/Cu_2O nanoparticles co-regulated carbon catalyst for alkaline Al-air batteries

Developing high-efficiency,inexpensive,and steady non-precious metal oxygen reduction reaction(ORR) catalysts to displace Pt-based catalysts is significant for commercial applications of Al-air battery.Here,we have prepared the Cu/Cu_2 O-NC catalyst with excellent ORR performance and high stability,due to the synergistic effect of Cu and Cu_2 O nanoparticles.The half-wave potential(0.8 V) and the limiting-current density(5.20 mA/cm~2) of the Cu/Cu_2 O-NC are very close to those of the 20% Pt/C catalyst(0.82 V,5.10 mA/cm~2).Besides,it exhibits excellent performance with a maximal power density of 250 mW/cm~2 and a stable continuous discharge for more than 90 h in the Al-air battery test The promoting effects of Cu_2 O towards Cu-based ORR catalysts are illustrated as follows:(ⅰ) Cu_2 O is the major ORR active site by the redox of Cu(Ⅱ)/Cu(Ⅰ),which provides excellent ORR activities;(ⅱ) Cu can stabilize the location of Cu_2 O by assisting the electron transfer to Cu(Ⅱ)/Cu(Ⅰ) redox,which is conducive to the high stability of the catalyst.This work provides a useful strategy for enhancing the ORR performance of Cu-based catalysts.