Optimizing activity of tungsten oxides for 1-butene metathesis by depositing silica on γ-alumina support

A series of catalysts made of tungsten oxide loaded on SiO₂, γ-Al₂O₃, SiO₂–Al₂O₃ and silica deposited γ-alumina are tested for 1-butene metathesis. Among these catalysts, the catalyst 6W/20SiO₂/Al₂O₃ gives the highest activity for 1-butene metathesis reaction with 1-butene conversion up to 71 mol% and the yield of propene up to 21 mol%. The excellent catalytic activity is related to the moderate dispersion of tungsten oxide and the suitable acidity of the support. The dispersion of WO_x species and the acidity of supports were studied by characterization of XRD, Raman spectra, UV–vis, H₂-TPR and NH₃-TPD in detail. The surface properties of silica modified γ-alumina leads to the moderate aggregation of supported tungsten oxide, which appears to be more effective for 1-butene metathesis at the low temperature of 453 K. Optimized activity was realized by tuning the dispersion of tungsten species on silica deposited alumina.     

EXAFS characterization of bimetallic Pt–Pd/SiO2–Al2O3 catalysts for hydrogenation of aromatics in diesel fuel

Bimetallic Pt–Pd/SiO₂–Al₂O₃ catalysts exhibited much higher activities in aromatic hydrogenation of distillates than monometallic Pt/SiO₂–Al₂O₃ and Pd/SiO₂–Al₂O₃ catalysts. The studies of extended X‐ray absorption fine structure (EXAFS) indicated that there was an interaction between Pt and Pd in the Pt–Pd/ SiO₂–Al₂O₃ catalyst. Furthermore, from the EXAFS, it was assumed that the active metal particle on the Pt–Pd/SiO₂–Al₂O₃ catalysts is composed of the “Pd dispersed on Pt particle” structure. Regarding both the activities of aromatic hydrogenation and the EXAFS results, it was concluded that the Pd species dispersed on Pt particles were responsible for the high activity of the bimetallic Pt–Pd/SiO₂–Al₂O₃ catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modification of the alumina‐supported Mo‐based hydrodesulfurization catalysts by tungsten

The incorporation effect of tungsten as an activity‐promotional modifier into the Ni‐promoted Mo/γ‐Al₂O₃ catalyst was studied. Series of W‐incorporated catalysts with different content of tungsten were prepared by changing the impregnation order of nickel and tungsten onto a base Mo/γ‐Al₂O₃. Catalytic activities were measured from the atmospheric reactions of thiophene hydrodesulfurization (HDS) and ethylene hydrogenation (HYD). The HDS and HYD activities of the WMo/γ‐Al₂O₃ catalysts (WM series) initially increased and subsequently decreased with increasing content of tungsten as compared with those of their base Mo/γ‐Al₂O₃. The maximal activity promotion occurred at the W/(W + Mo) atomic ratio 0.025. For the Ni‐promoted Mo/γ‐Al₂O₃ catalysts, the effect of W incorporation was greatly dependent on the impregnation order of tungsten. The catalysts prepared by impregnating Ni onto the WMo/γ‐Al₂O₃ catalysts showed the same trend of activity promotion as for the WM series, while those by impregnating W onto a NiMo/γ‐Al₂O₃ catalyst resulted in lower activities than their base NiMo/γ‐Al₂O₃ catalyst. To characterize the catalysts, temperature‐programmed reduction and low‐temperature oxygen chemisorption were conducted. The effects of W incorporation on the NiMo‐based catalysts were discussed in reference to those on the CoMo‐based catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dehydration of Ethanol into Ethylene over Solid Acid Catalysts

The dehydration of ethanol into ethylene was investigated over various solid acid catalysts, such as zeolites and silica–alumina, at temperatures ranging 453–573 K under atmospheric pressure. Ethylene was produced via diethyl ether during the dehydration process. H-mordenites were the most active for the dehydration. It was suggested that the catalyst activity could be correlated with the number of strong Br?nsted acid sites in the catalyst. Further, the H-mordenite was more stable with a SiO₂/Al₂O₃ ratio of 90 than with a SiO₂/Al₂O₃ ratio of 20.     

Promoting effect of propane traces on the activity of Pt/γ-Al2O3 and Pt–Sn/γ–Al2O3 catalysts in CH4–SO2–O2 reactions

A strong promoting effect of the presence of C₃H₈ or C₃H₆ was determined for the CH₄–SO₂–O₂ reaction, over pre-sulfated 1%Pt/γ–Al₂O₃ and pre-sulfated 1%Pt–2%Sn/γ–Al₂O₃ catalysts. These results suggest that over 1%Pt–2%Sn/γ–Al₂O₃ catalysts, small amounts of propane or propylene in the gas feed may eliminate methane emissions at low temperatures from lean-burn NGV exhausts.     

Benzene Alkylation with Propane over Mo Modified HZSM-5

Benzene alkylation with propane has been studied over HZSM-5 loading 3.1–15.4 wt% Mo in continuous-flow microreactor under 350 °C and atmospheric pressure with the highest activity obtained at 6.7 wt% Mo loading. C_7–9 aromatics were obtained as main products while the total amount of benzene rings kept unchanged. i-Propylbenzene and n-propylbenzene are formed primarily, while toluene, ethylbenzene, and ethyl-toluene are formed secondly from the propylbenzenes. Catalytic performance of 6.7 wt% Mo/HZSM-5(38) partially poisoned by NH₃ shows that the strong acid sites play a crucial role in the alkylation. Low SiO₂/Al₂O₃ ratio of HZSM-5 in the Mo modified catalysts gives high propane conversion. Two hydrothermal treatment methods were applied to the 6.7 wt% Mo/HZSM-5(38) catalyst, caused decrease of propane conversion but result in different product distribution. A possible reaction mechanism concerning bifunctional active centers resulted from combination of loaded Mo species and strong acid centers on HZSM-5 is proposed.     

New water‐tolerant supported molten indium catalyst for the selective catalytic reduction of nitric oxide by ethanol

The catalytic activity and selectivity of indium supported on controlled pore glass (In‐CPG‐SMMC) were investigated and compared with those of H‐ZSM‐5 and In/γ‐Al₂O₃ for the selective catalytic reduction of nitric oxide by ethanol under net oxidizing conditions, in the absence and presence of water vapors. Even though the support of In‐CPG‐SMMC is almost pure silica (94–99% SiO₂, 1–6% B₂O₃, 0.05–0.3% Na₂O), the activity of this catalyst was found to be comparable with that of the conventional catalysts. The presence of steam in the feed enhanced catalyst activity over the entire temperature range studied. At temperatures above 500°C the ability of H‐ZSM‐5 and In/γ‐Al₂O₃ to reduce NO to N₂ was surpassed by the supported indium catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of TiO2 surface treatment on the mechanical properties of cured epoxy resin

Mechanical properties of epoxy resin toughened with two different submicron particles of TiO₂ at different weight fractions (1, 3, and 5%, respectively) were investigated. The first TiO₂ particles are surface treated with Al₂O₃–SiO₂, and the second are surface treated with Al₂O₃–ZrO₂. The composites were characterized by tensile, flexural, pull off and abrasion tests, followed by X-ray photoelectron spectroscopy and scanning electron spectroscopy of the fracture surfaces. A small amount of TiO₂ (~1%) submicron particles improves the flexural, abrasion and pull-off strengths, while amounts up to 5% significantly enhance tensile properties only. TiO₂ particles surface treated with Al₂O₃–ZrO₂ produce an epoxy composite with higher strength and weight loss but lower pull off strength and more brittle than that prepared with Al₂O₃–SiO₂ particles. The TiO₂ particles surface treated with Al₂O₃–SiO₂ have a higher adherence to the epoxy composite matrix than the particles treated with Al₂O₃–ZrO₂ as shown by scanning electron spectroscopy.     

Highly Active and Selective Nickel–Platinum Catalyst for the Low Temperature Hydrogenation of Maleic Anhydride to Succinic Anhydride and Synthesis of Succinic Acid at 40 °C

Abstract  

PtNi bimetallic and Ni monometallic catalysts supported on HY–Al₂O₃, HX–Al₂O₃, ZSM-5–Al₂O₃, USY–Al₂O₃, Beta–Al₂O₃ and Al₂O₃ were prepared and evaluated for the hydrogenation of maleic anhydride in the temperature range of 40–150 °C. Results from flow reactor studies showed that supports strongly affected the catalytic properties of different bimetallic and monometallic catalysts. The results showed that the HY–Al₂O₃ support exhibited the highest activity and selectivity. Using NiPt/Al₂O₃–HY catalyst and performing the reaction, it was possible to carry out the lowest reaction temperature ever carried at 100% conversion. Adding a small amount of Pt (0.5) to the Ni (5%)/Al₂O₃–HY catalyst that is effective for increasing the selectivity and activity. We also found that PtNi is an efficient catalyst for the one-pot conversion of maleic acid into succinic acid with 100% conversion at 40 °C.     

Thiophene hydrodesulfurization over bimetallic and promoted nitride catalysts

Alumina-supported bimetallic (Co₃Mo₃N/Al₂O₃” and promoted (Co–Mo₂N/Al₂O₃) nitride catalysts have been prepared and characterized. Thiophene hydrodesulfurization (HDS) measurements show that the Co₃Mo₃N/Al₂O₃ and Co–Mo₂N/Al₂O₃ catalysts are significantly more active than a Mo₂N/Al₂O₃) catalyst with the same Mo loading. Furthermore, the Co–Mo₂N/Al₂O₃ catalyst has a substantially higher HDS activity than a sulfided Co–MoO₃/Al₂O₃ catalyst with an identical metal loading. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oscillatory Behaviour during C<Subscript>2</Subscript>–C<Subscript>4</Subscript> Hydrocarbon Oxidation over Palladium Catalysts

Abstract  

Oscillatory behaviour during ethane, propane and butane oxidation over a palladium foil had been studied using on-line mass-spectrometry and a catalyst temperature monitoring. The striking similarity of oscillations properties in all these reactions had been observed. In reactant mixtures with the constant carbon atoms content no significant differences in the parameter space, oscillation shape, or period of temperature oscillations in all three reactions studied had been detected. It was shown that the temperature range of the oscillation phenomena on Pd coincides not only for C₂–C₄ hydrocarbon oxidation, but also for methane oxidation. However, by contrast to the oscillations during methane oxidation, the sustained oscillations with the large amplitude during C₂–C₄ hydrocarbon oxidation could be obtained only for the diluted reactant mixtures. It was demonstrated that the oscillatory phenomena during all light hydrocarbons oxidation reactions have the common origin and are related to oxidation–reduction processes of a Pd catalyst.     

Effect of SiC and Al2O3 particles on the electrodeposition of Zn, Co and ZnCo: II. Electrodeposition in the presence of SiC and Al2O3 and production of ZnCo–SiC and ZnCo–Al2O3 coatings

SiC or Al₂O₃ microsized particles were added to acid sulfate-based solutions for the electrodeposition of Zn, Co, and ZnCo. Initially, their effects on the electrochemical processes were evaluated. The Zn electrodeposition rate was increased in both SiC and Al₂O₃-loaded solutions. The Co electrodeposition rate was also increased by SiC. However, Al₂O₃ decreased it, especially at the beginning. Both SiC and Al₂O₃ influenced the electrodeposition of ZnCo positively at moderate loadings. The factors involved in producing ZnCo–SiC and ZnCo–Al₂O₃ composites were evaluated. ZnCo–SiC composites could be deposited with a higher [Co/Zn] ratio in the metal matrix than for pure ZnCo. In ZnCo–Al₂O₃, the [Co/Zn] ratio was smaller than in ZnCo and ZnCo–SiC. It was necessary to reduce the CoSO₄ concentration to improve the Al₂O₃ co-deposition. The variation in [Co/Zn] ratio could, in principle, be related to the effects of SiC and Al₂O₃ on the individual Zn and Co electrodeposition.     

Fusion-cast chromium-bearing refractories — the most durable materials in aggressive melts

Information is presented on fusion-cast materials that have been developed in recent years on the basis of the systems Cr₂O₂–Al₂O₃–ZrO₂–SiO₂, Cr₂O₃–MgO–SiO₂, and Cr₂O₃–MgO–Al₂O₃. Such materials have good service properties in mineral melts at high temperatures. It is shown that fusion-cast chromium-bearing refractories KhPL-85 and KhMG are as corrosion-resistant as chromium-oxide-based ceramic refractories in melts of alkali-free borosilicate glass E and basalt fibers.     

Confirmation of sulfur tolerance of bimetallic Pd–Pt supported on highly acidic USY zeolite by EXAFS

The sulfur tolerance (i.e., degree of sulfidation) of Pd and Pt in sulfided bimetallic Pd–Pt catalysts (Pd : Pt mole ratio of 4 : 1) supported on USY (ultrastable Y) zeolites (SiO₂/Al₂O₃ = 10.7, 48, and 310) was investigated using an extended X‐ray absorption fine structure (EXAFS) method. The sulfidation of the catalysts was done in a 1000 ppm H₂S–2% H₂/N₂ stream at 573 K for 0.5 h. In the Fourier transforms of Pd K‐edge and Pt L_III‐edge EXAFS spectra, both of the peaks due to metallic Pd and to metallic Pt for the Pd–Pt/USY (SiO₂/Al₂O₃ = 10.7) catalyst remained most after sulfidation. Further, the results of the Fourier transforms confirmed that the sulfur tolerance of both Pd and Pt decreased with increasing SiO₂/Al₂O₃ ratio, suggesting that Pd and Pt become sulfur‐tolerant when Pd–Pt bimetallic particles are supported on highly acidic USY zeolite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rheotechnological properties of mixed suspensions in the SiO2 - Al2O3 system and some properties of materials based on them. 1. Molten quartz – Alumina system

The rheotechnological properties of mixed suspensions in the SiO₂ - Al₂O₃ system obtained by the method of mixing of individual suspensions of molten quartz and alumina are described. Some properties of the materials after their heat treatment at 1000 – 1300°C are investigated. The ranges of compositions (30 – 40% Al₂O₃, 60 – 70% SiO₂) in which the parameters of thermal expansion of the materials are 2 – 3 times lower than those calculated under the condition of additivity are determined. The obtained materials possess an elevated mechanical strength. Translated from Ogneupory i Tekhnicheskaya Keramika, No.7, pp. 18 – 23, July, 2000.     

CO hydrogenation over a RhVO4/SiO2 catalyst after H2 reduction

The hydrogenation of CO over a RhVO₄/SiO₂ catalyst has been investigated after H₂ reduction at 773 K. A strong metal–oxide interaction (SMOI) induced by the decomposition of RhVO₄ in H₂ enhanced not only the selectivity to C₂ oxygenates but also the CO conversion drastically, compared with an unpromoted Rh/SiO₂ catalyst. The selectivity of the RhVO₄/SiO₂ catalyst was similar to those of conventional V₂O₅‐promoted Rh/SiO₂ catalysts (V₂O₅–Rh/SiO₂), but the CO dissociation activity (and TOF) was much higher than for V₂O₅–Rh/SiO₂, and hence the yield of C₂ oxygenates was increased. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrotreating of Heavy Gas Oil Derived from Athabasca Bitumen Over Co–Mo/γ-Al2O3 Catalyst Prepared by Sonochemical Method

Co–Mo/γ-Al₂O₃ oxide containing 9.8 wt% Mo and 2.9 wt% Co was prepared by high-intensity ultrasonic irradiation of Mo(CO)₆, Co₂(CO)₈, and γ-Al₂O₃ in decahydronapthalene under air flow. The oxidic Co–Mo catalyst thus formed was characterized by elemental analysis, BET N₂ adsorption and XRD. The surface sites on the sulfided Co–Mo/γ-Al₂O₃ catalyst were characterized by infrared spectroscopy of CO adsorption. Hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities were evaluated for heavy gas oil derived from Athabasca bitumen in a trickle bed reaction system using the following conditions: temperatures ranging from 370 to 400 °C, a pressure of 8.8 MPa, a liquid hourly space velocity of 1 h⁻¹, and a H₂/feed ratio of 600 ml/ml. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared with the conventionally prepared Co–Mo/γ-Al₂O₃ catalyst containing similar wt% of Mo and Co. The Co–Mo catalyst prepared by sonochemical method has higher HDN and HDS rate constants than the conventional catalyst due to an improved dispersion of MoS₂.     

Catalytic dehydrogenation of propane on chromia,palladium and platinum supported catalysts

The dehydrogenation of propane to propylene over Cr₂O₃/Al₂O₃, Pd/Al₂O₃ and Pt/SiO₂ has been investigated in the temperature range 580–618°C. Runs were performed on propane, alone or in the presence of nitrogen (as a diluent), with complete analysis of the reaction products. The reaction was carried out in a fixed bed reactor at space velocities from 450–800 h^?1 which are close to industrial values and at pressures from 0.3 to 1 atm. A set of runs was made over a commercial chromia-alumina catalyst (10% Cr₂O₃) and over a promoted catalyst prepared in the laboratory by impregnation (16.8% Cr₂O₃ + 2% K₂O). The latter catalyst showed high selectivity and stability even when subjected to continuous cycles of dehydrogenation, regeneration and purging. Of the two noble metal supported catalysts used, reduced Pd/Al₂O₃ showed higher activity than Pt/SiO₂ at 618°C. The former catalyst gave a propylene yield of around 98% at 20% conversion level.     

Kinetic modeling of oxidative dehydrogenation of propane with CO2 over MoOx/La2O3–Al2O3 in a fluidized bed

A 4-step kinetic model of CO₂-assisted oxidative dehydrogenation (ODH) of propane to C₂/C₃ olefins over a novel MoO_x/La₂O₃–γAl₂O₃ catalyst was developed. Kinetic experiments were conducted in a CREC Riser Simulator at various reaction temperatures (525–600 °C) and times (15–30 s). The catalyst was highly selective towards propylene at all combinations of the reaction conditions. Langmuir-Hinshelwood type kinetics were formulated considering propane ODH, uni- and bimolecular cracking of propane to produce a C₁-C₂ species. It was found that the one site type model adequately fitted the experimental data. The activation energy for the formation of propylene (67.8 kJ/mol) is much lower than that of bimolecular conversion of propane to ethane and ethylene (303 kJ/mol) as well as the direct cracking of propane to methane and ethylene (106.7 kJ/mol). The kinetic modeling revealed the positive effects of CO₂ towards enhancing the propylene selectivity over the catalyst.     

Promoting effect of carbon dioxide on the dehydrogenation and aromatization of ethane over gallium‐loaded catalysts

Ga₂O₃ and Ga₂O₃/TiO₂ catalysts were found to be effective agents for the dehydrogenation of ethane to ethene in the presence of carbon dioxide at 650 °C. The activity of the Ga₂O₃ and Ga₂O₃/TiO₂ catalysts in the presence of CO₂ was 2–4 times higher than that without CO₂. Ethene yields reached ca. 20–25% and selectivity was ca. 70–90% at 650°C in the 17% ethane and 83% CO₂ feed at an SV of 9,000 ml/(g‐cat h). The presence of CO₂ markedly promoted dehydrogenation of ethane over Ga₂O₃ and Ga₂O₃/TiO₂ catalysts. Furthermore, the promoting effect of CO₂ on the aromatization of ethane and ethene over a Ga₂O₃+H/ZSM‐5 catalyst was also observed above 650 °C. Aromatics yields were higher than those without CO₂. This revised version was published online in July 2006 with corrections to the Cover Date.