Preparing and studying Pt/WO<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> catalysts for the isomerization of <Emphasis Type="Italic">n</Emphasis>-heptane

The effect of the temperature of WO₃/ZrO₂ support calcination in the range of 700–1000°C on the phase composition, acid, and catalytic properties of Pt/WO₃/ZrO₂ catalysts is studied. Using ammonia TPD, it is found that calcination in the temperature range of 850–950°C results in the formation of strong acid sites that increase the yield of the target products of the reaction of n-heptane isomerization: high octane di- and trimethylsubstituted isomers. DRIFT is used to determine the role of catalyst calcination in an air flow plays in the formation of charged platinum atoms, which results in higher catalyst activity.     

Comparative study of aromatization selectivity during N‐heptane reforming on sintered Pt/Al2O3 and Pt‐Re/Al2O3 catalysts

BACKGROUND: The metal dispersed over a support can be present as small crystallites with sizes less than 5 nm. The smaller crystallites favour aromatization while larger crystallites favour cracking/hydrogenolysis. Sintering results in the agglomerization of smaller metal crystallites. Correlation of size with aromatization selectivity was investigated. RESULTS: The primary products of n‐heptane reforming on fresh Pt were methane, toluene, and benzene, while on fresh Pt‐Re, the only product was methane. Both catalysts exhibited enhanced aromatization selectivity at different oxygen sintering temperatures. The reaction products ranged from only toluene at 500 °C sintering temperature to methane at a sintering temperature of 650 °C with no reaction at 800 °C for the Pt/Al₂O₃ catalyst. On Pt‐Re/Al₂O₃ catalyst, methane was the sole product at a sintering temperature of 500 °C while only toluene was produced at a sintering temperature of 800 °C. CONCLUSION: This is the first time that sintering has been used to facilitate aromatization of supported Pt and Pt‐Re catalysts. A superior selectivity behaviour associated with bi‐metallic Pt catalysts is established. It was found that no reaction occurred on Pt catalyst after sintering at 800 °C whereas sintering Pt‐Re at 800 °C promoted aromatization solely to toluene. Copyright © 2008 Society of Chemical Industry     

Selective hydrogenation of acetylene over Pd/CeO2

Five hundred ppm Pd/CeO₂ catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction. Pd/CeO₂ catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction. Excellent ethylene selectivity of ~100% was obtained in the whole reaction temperature range of 50°C–200°C for samples calcined at temperatures of 600°C and 800°C. This could be ascribed to the formation of Pd_xCe_1−xO_2−y or Pd-O-Ce surface species based on the X-ray diffraction and X-ray photoelectron spectroscopy results, indicating the strong interaction between palladium and ceria.     

Influence of support on surface basicity and catalytic activity in oxidative coupling of methane of Li–MgO deposited on different commercial catalyst carriers

Deposition of Li–MgO catalyst on commonly used supports (containing SiO₂, Al₂O₃, SiC, ZrO₂, HfO₂, etc.) causes a drastic reduction in the catalytic activity/selectivity for the oxidative methane coupling reaction and also in both the total and strong surface basicity. The decrease in the catalytic activity/selectivity and basicity is attributed to strong chemical interactions between the catalyst and support which occur during the high temperature (750°C) calcination/pretreatment of the catalyst. The chemical interactions result in catalytically less active binary and ternary metal oxides containing Li and/or Mg, thus deactivating the Li–MgO catalyst by consuming its active components. © 1998 SCI     

The effect of the calcination temperature of LaFeO3 precursors on the properties and catalytic activity of perovskite in methane oxidation

In the synthesis of perovskite-type LaFeO₃ oxides iron and lanthanum nitrates were used as a precursors. The nitrates were dissolved in water, evaporated, crushed and calcined in temperature range of 650–850?°C. The obtained perovskites were applied as an active layer on monolithic catalysts for the oxidation of methane. The increase in the calcination temperature of the perovskite precursors from 650° to 850°C results in a reduction in the surface area of the powders from 10.1 to 4.2?m²/g. XRD studies revealed that calcination at 800–850?°C caused the formation of an almost homogeneous LaFeO₃ perovskite phase. A decrease in the La/Fe surface ratio from 12 to 5.2 with the rise in calcination temperature from 650° to 800°C was detected by XPS. EDX results confirmed that at 750–850?°C, the La/Fe ratio in the perovskite layer is close to the stoichiometric and amount to 1.01–1.03. The highest activity in methane oxidation was achieved when the LaFeO₃ perovskite was calcined at 700?°C. A further slight increase in the activity was noticed after H₂ treatment. As the calcination temperature of the perovskites is increased, the catalyst activity decreases due to a reduction in the specific surface area, despite the more complete LaFeO₃ perovskite phase formation.     

Preparation and high temperature activation of ruthenium on carbon hydrogenation catalysts

Treatment of ruthenium on carbon support in air (calcination) or in hydrogen (reduction) at temperatures of 400–500°C is not a suitable step in the catalyst preparation procedure because of the catalytic activity of ruthenium in the oxidation and hydrogenation of carbon. No substantial methanation of the carbon support occurs, however, when the reduction with hydrogen is performed at high temperatures (700–800°C) for short contact times. Calcination in nitrogen in combination with this high temperature reduction procedure results in catalysts with high activity in the liquid phase hydrogenation of benzene.     

Effect of calcination temperature on catalyst reducibility and hydrogenation reactivity in rice husk ash–alumina supported nickel systems

Nickel catalysts supported on rice husk ash–alumina (Ni/RHA–Al₂O₃) were prepared by an incipient wetness impregnation method. Characterization included TGA, DSC, TPR, XRD, and BET. Results show that the decomposition of the nickel compound to nickel oxide was complete above 500 °C. The TPR analysis revealed a strong interaction between nickel and support, and a decrease in reducibility of NiO with increasing calcination temperature. The XRD analysis of Ni/RHA–Al₂O₃ catalyst precursors demonstrated the presence of spinel. It also showed that the size of crystallites in the supported NiO first decreased with increase in calcination temperature up to 700 °C, and then increased due to phase transformation of nickel oxide to spinel. The pores are mesopores and their meshy surface structure was not affected by calcination temperature in the range investigated. The catalytic activity was tested by CO₂ hydrogenation with an H₂/CO₂ ratio of 4/1 at 500 °C. The CO₂ conversion and CH₄ yield for CO₂ hydrogenation over 15 wt% Ni/RHA–Al₂O₃ catalyst were almost independent of calcination and reduction temperatures. Copyright © 2004 Society of Chemical Industry     

Some catalytic properties of silica‐supported base and metal porphyrins for hydrocarbon cracking and hydrogenation

A base porphyrin, etioporphyrin (EPI), has been synthesised and a number of metal–etioporphyrin compounds have been derived from EPI by metal insertion, these being nickel, vanadyl, palladium and platinum. The metal–etioporphyrins were supported on silica gel with loadings of 0.5–5.0% (w/w) to be employed as catalysts for hydrocarbon cracking and to a minor extent for hydrogenation. The porphyrins themselves were characterised using temperature programmed decomposition (TPD), temperature programmed reduction (TPR), mass spectroscopy (MS) and infra‐red (IR) spectroscopy. TPD studies up to 550 °C indicated complete stability and TPR studies (20–500 °C) showed interaction with hydrogen, nickel–EPI and Pd–EPI especially showing strong interaction. MS studies showed that metal insertion had occurred for VO–EPI and Ni–EPI and Pd insertion was demonstrated to have occurred using an analytical method. IR spectroscopy carried out on VO–EPI and Ni–EPI showed an absence of ? NH linkages, again confirming metal insertion. The behaviour of the catalysts for hydrocarbon cracking was studied using 2,2‐dimethylbutane (2,2‐DMB) as the model reactant in the temperature range 440–550 °C and thermally in the temperature range 440–600 °C and at 1 at, m (101.3 kPa) pressure. All porphyrins, even the base porphyrin, exhibited cracking activity and the catalysed reaction had an energy of activation, depending on the porphyrin, in the range 78–113 kJ/mol^?1, compared with a value of 210 kJ mol^?1 for the thermal reaction. The product distribution was dominated by C₁ and C₂ hydrocarbons and is typical of a free radical reaction, the thermal reaction giving a similar product distribution, so that the porphyrin catalyst acts as a free radical initiator. Hydrogenation studies using hex‐1‐ene at 150 °C and at 1 atm. pressure showed that Pd–EPI/SiO₂ was an active and possibly stable hydrogenation catalyst, whereas Ni–EPI/SiO₂ while of only slightly lower activity initially, lost that activity so that the Pd–EPI catalyst was over 16 times more active at the end of a 2 h period. © 2001 Society of Chemical Industry     

Phase structure of V2O5/TiO2 catalyst and catalytic behavior with removal of NO by ammonia

V₂O₅/TiO₂ catalyst with 3% (w/w) V loading has been prepared by sol–gel method. The characterization results of the catalyst structure and catalytic activity show that VO _X state is strongly dependent on the calcination temperature. Little effect is found for phase structure of TiO₂ support on catalytic activity. High catalytic activity in wide temperature range (240–420 °C) is observed for the catalysts calcinated at different temperatures at a space velocity of 50,000 h^?1. Space velocity and alkali metal oxides strongly influence the catalytic activity of the catalyst which was calcinated at 450 °C, furthermore, the one has high tolerance to SO₂ in our test conditions.     

Activity behavior of samaria-doped ceria-supported copper oxide catalyst and effect of heat treatments of support on carbon monoxide oxidation

Activity behavior of CO oxidation was studied over samaria-doped ceria (SDC)-supported CuO catalysts. The material properties of the SDC support were changed by heat treatments, which were carried out by the variations of the calcination temperatures of SDC (500–1100°C) and the cooling methods (with quenching after calcination or without it). The X-ray diffraction, N₂ physisorption, N₂O chemisorption, energy dispersive X-ray spectrum, carbon monoxide temperature-programmed reduction, and the activity test were carried out. The results showed that, when the calcination temperature of SDC was lower, its surface area was higher, and thus more interfacial active sites were formed over the CuO/SDC catalyst; this led to higher activity. Quenching after calcination was beneficial to increase the surface area of SDC and thus increase the activity of the CuO/SDC catalyst. It was also found that the specific activity of the interfacial active site was not affected by the heat treatment. The light-off of the CO oxidation activity of the CuO/SDC catalyst was observed at a temperature as low as 75°C. It was concluded that the concentration of the interfacial active sites was key for the occurrence of light-off.     

Effects of calcination temperature on performance of Cu–Zn–Al catalyst for synthesizing γ-butyrolactone and 2-methylfuran through the coupling of dehydrogenation and hydrogenation

The results of the coupling process over Cu–Zn–Al catalysts show that the different calcination temperature has significant effect on catalytic performance. Lower temperature cannot facilitate the precursor to complete decomposition and higher calcination temperature will decline the surface area of the catalyst, which finally decline the yield for desired products. It is worth mentioning that the specific activities for BDO and furfural conversions are improved at high calcination temperature, but the simultaneous loss of surface area offsets the gain in specific activity and finally causes the decline in the overall activity of catalyst. In contrast to this, the specific activities for 2-methylfuran and tetrahydrofuran formation dramatically decrease when the calcination temperature reaches 750 °C. This strongly indicates that the active sites of the catalyst for 2-methylfuran and tetrahydrofuran formation were significantly destroyed at calcination temperature higher than 750 °C, and these sites are different from those for γ-butyrolactone and furfuryl alcohol formation.     

Thermal stability of NO 2 ⋅ and NO⋅ radicals formed in an Al23 catalyst during its preparation from a nitrate precursor

During the preparation of alumina as a catalyst support from aluminium nitrates by precipitation with a NH₄OH base, NO ₂ ^⋅ radicals have been formed in the catalyst after calcination under air in the solid at different temperatures. These radicals remained stable until a calcination temperature of 800°C. When the calcined catalyst was degassed under vacuum above 300 °C, the NO ₂ ^⋅ was reduced to give NO^⋅ and O^- species which were both tightly trapped in the solid. These latter species remained stable until vacuum treatment at 800 °C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Insights into the calcination temperature and loading amount of the catalyst support (TiO2) in the fibrous ceramic-based catalytic filter element prepared by microwave drying

The fibrous ceramic-based catalytic filter element (CFE) is a promising multifunctional material capable of simultaneously removing dust and NO_x from hot gases. In this study, various calcination temperatures and titanium sols with different solid contents were used to prepare CFEs based on microwave drying, and their influences on the catalytic performance were experimentally investigated. The results showed that both the calcination temperature and the solid content of the titanium sol had important impacts on the catalytic activity. As the calcination temperature increased, the particle size, crystallite size, and average pore diameter of the loaded catalyst support (TiO₂) increased, while the specific surface area decreased, ultimately resulting in a decline in the catalytic activity. However, a suitable calcination temperature ranging from 300 to 400 °C was required to achieve a good combination between the catalyst and the fibrous ceramic and a relatively uniform mesoporous structure. Furthermore, the increase in the solid content gave rise to a corresponding increase in the TiO₂ loading amount, which increased the pressure drop and reaction surface area of the CFE. Excessive vanadium content caused by insufficient catalyst support induced side reactions of NH₃ oxidation under high-temperature conditions, thereby reducing catalytic activity. Therefore, the preferred calcination temperature and solid content were set at approximately 300–400 °C and 8 wt%, respectively. The final prepared CFE demonstrated superior catalytic performance and adaptable gas velocity properties.     

Biomorphic SiC pellets as catalyst support for partial oxidation of methane to syngas

Biomorphic silicon carbide (bioSiC) pellets prepared from carbonized millet were employed as nickel catalyst support for the partial oxidation of methane to syngas in a fixed-bed quartz reactor at 800 °C. To reduce the loss of nickel active component during the reaction, alumina was used to modify the bioSiC surface. The temperature programmed reduction reveals that the alumina modification can evidently increase the reduction temperature of nickel oxide and therefore enhance the interaction between nickel and support. Due to the enhanced interaction, the nickel component becomes stable and difficult to migrate on the support surface. As a result, the modified bioSiC catalyst shows higher catalytic activity and stability than the unmodified. Compared with the catalyst supported on powdered SiC, the pelletized catalyst shows higher activity, especially at high gas hourly space velocity.     

Oxidative coupling of methane over Sm-promoted MgO: Influence of composition and preparation conditions

Influences of promoter concentration (or Sm/Mg ratio), precursor for MgO (viz. Mg-acetate, Mg-carbonate and Mg-hydroxide), calcination temperature of Sm-promoted MgO catalyst on the catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different temperatures (650–850°C) and CH₄/O₂ ratios in feed (2·0–8·0) at a high space velocity (51600 cm³ g⁻¹ h⁻¹) have been investigated. The catalytic activity/selectivity of Sm–MgO catalysts in the OCM are found to be strongly influenced by the Sm/Mg ratio, precursor used for MgO and catalyst calcination temperature. The catalyst with Sm/Mg ratio of 0·11, prepared using magnesium acetate and magnesium carbonate as a source of MgO and calcining at 950°C, is found to be highly active and selective in the OCM process. A drastic reduction in catalytic activity/selectivity is observed when the catalyst is supported on low surface area porous catalyst carriers, indicating strong catalyst–support interactions. ©1997 SCI     

Rate equations for the fischer‐tropsch reaction on a promoted iron catalyst

Intrinsic rates for the Fischer‐Tropsch synthesis reaction over a promoted iron catalyst fabricated at the Research Institute of the Petroleum Industry (RIPI) have been obtained in the temperature range of 290°C to 310°C, pressure range of 1500 to 2300 kPa, molar hydrogen to carbon monoxide ratio of 0.76 to 1.82, and a space velocity of 3300 h^?1 under conditions of constant catalyst activity. To this end, the initial reaction rates have been measured at constant temperature (±1°C) in the absence of diffusion limitations, and power‐law equations have been fitted in terms of the hydrogen and carbon monoxide partial pressures for the reaction rates.     

Effect of calcination temperature on catalytic properties of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

The effect of calcination temperature on catalytic performance of PtSnNa/ZSM-5 catalysts for propane dehydrogenation was studied. It was found that when the calcination temperature was in the range of 400–500 °C, structure and acidity of the catalyst did not change obviously. In contrast to this, with the increase of calcination temperature, the specific surface area and pore volume dramatically decreased, while the mean pore diameter increased. Under these conditions, more framework aluminum atoms were removed from tetrahedral positions, which weakened the interactions between Sn species and carrier. Meantime, the degree of Pt sintering and the destruction of Pt active sites with “sandwich structure” were aggravated, which was disadvantageous to the reaction. When the catalyst was calcined at 500 °C, the interactions between Pt and Sn were strengthened, thus improving the catalytic stability and reaction selectivity evidently. Moreover, it should be remarked that the phenomenon of slow Pt sintering was not clearly observed even though the reaction temperature of it was higher than the calcination one.     

Catalytic gasification of graphite by chromium and copper in oxygen,steam and hydrogen

Controlled atmosphere electron microscopy studies have demonstrated that both chromium and copper are extremely active catalysts for the graphite-oxygen reaction over the range 550–800°C. Under these conditions the active catalytic entities are probably Cr₂O₃ and CuO, respectively. The behavior of chromium is quite unique, not fitting into the well established patterns, i.e. pitting or channeling. Instead, particles remain motionless throughout the oxidation sequence and the action is seen as an acceleration of edge recession all over the specimen. In contrast, copper exhibited conventional channeling activity, which diminished at higher temperatures (>700°C) due to the wetting and spreading of active particles along graphite edges. Such edges underwent rapid recession following this phenomenon. Neither metal showed any tendency to catalyze gasification of graphite in the presence of steam. Copper was found to be an active catalyst for graphite hydrogenation at temperatures in excess of 800°C, but chromium remained inactive.     

Silica‐supported bis(imino)pyridyl iron(II) catalyst: nature of the support–catalyst interactions

Ethylene polymerizations were performed using silica‐supported 2,6‐bis[1‐(2,6‐diisopropylphenylimino) ethyl] pyridine iron(II) dichloride with methylaluminoxane (MAO) as co‐catalyst. Silica was calcined at 600, 400 and 200 °C under vacuum for 8 h. The effect of calcination temperature of silica on the polymerization activity and the properties of the polymers obtained were examined. Catalyst–support interactions were examined by both a chemical method and XPS. It was observed that upon supporting the catalyst on the surface of silica, there is an increase in the binding energy of the metal center. However, no change in the metal binding energy was observed on supporting the catalyst to silica calcined at different temperatures. Ethylene polymerizations were performed using MAO as co‐catalyst. Catalysts were also prepared by first pretreating silica with MAO, followed by addition of the Fe(II) catalyst and contacting a complex of Fe(II) catalyst–MAO with silica previously calcined at 400 °C for 8 h. The results indicate that there is no chemical bonding between the support and the catalyst. Copyright © 2006 Society of Chemical Industry     

Enhanced Sulfur Tolerance of Bimetallic PtPd/Al2O3 Catalysts for Hydrogenation of Tetralin by Addition of Fluorine

A series of mono- and bi-metallic Pt-Pd/Al₂O₃ samples with and without F were studied as aromatic hydrogenation catalysts. The effects of changing the order of impregnation of the Pt precursor and F as well as varying the calcination temperature (300–500 °C) were investigated. Temperature programmed reduction (TPR) results demonstrate the presence of a higher fraction of dispersed metal precursor species left on the surface from the impregnation (PtO _x Cl _y ) on the Pt/Al₂O₃ sample calcined at high temperature. The impregnation of F before the Pt precursor significantly decreases the interaction between the metal and the support. However, this decrease is not observed when F is impregnated after the metal precursor. For the bimetallic Pt-Pd catalysts, the sample prepared adding F before the metal show a higher degree of Pt-Pd interaction than either the parent Pt-Pd/Al₂O₃ catalyst or the one prepared with F added later. TPD of ammonia result show the increase in strong acid sites when F is present. Activity tests for tetralin hydrogenation in the presence of 350 ppm dibenzothiophene indicate a better sulfur tolerance for all F-promoted catalysts, especially Pt-Pd.