Effect of Pt Incorporation into Ni/ZrO2–SO 4 = /Al2O3 Catalyst for n-Butane Isomerization

Three Ni/ZrO₂–SO₄⁼/Al₂O₃ catalysts with different concentrations of platinum (0.2, 0.3 and 0.4 wt%) were prepare and tested for n-butane isomerization reaction at 338 K, in absence and in presence of hydrogen. The results shown that, at low temperature, platinum contributes to the olefin or butyl ion formation and the reaction follows a bimolecular pathway. However, when the reaction occurs in the presence of hydrogen, the formation of butyl ions is inhibited. The main feature of platinum addition is the stabilization of the catalytic activity, which is indicated by the slow deactivation constants compared to that of the unpromoted catalyst.     

Trimerization of isobutene over WOx/ZrO2 catalysts

Trimerization of isobutene to produce isobutene trimers has been investigated over WO_x/ZrO₂ catalysts that were obtained by wet-impregnation and successive calcination at high temperatures. Very stable isobutene conversion and high selectivity for trimers are attained over a WO_x/ZrO₂ catalyst obtained by calcination at 700 °C. From the XRD study it can be understood that tetragonal ZrO₂ is beneficial for stable performance; however, monoclinic ZrO₂ is not good for trimerization. Nitrogen adsorption and FTIR experiments suggest that amorphous WO_x/ZrO₂ is inefficient catalyst even though it has high surface area and high concentration of acid sites. The observed performance with the increased selectivity and stable conversion demonstrates that a WO_x/ZrO₂ having tetragonal zirconia, even with decreased porosity and acid sites, is one of the best catalysts to exhibit stable and high conversion, high selectivity for trimers and facile regeneration.     

Oxidative dehydrogenation of 4-vinylcyclohexene into styrene over ZrO2 catalyst promoted with Fe2O3 and CaO

The oxidative dehydrogenation of 4-vinylcyclohexene (VCH) into styrene was carried out in the presence of oxygen over a ZrO₂ catalyst promoted with Fe₂O₃ and CaO. Intrinsically, ZrO₂ showed high dehydrogenation activity, which resulted in 80% styrene selectivity with 45% conversion at 425 °C and LHSV 3 h⁻¹. When the ZrO₂ was further promoted with calcium and iron, CaO/Fe₂O₃/ZrO₂, the highest styrene selectivity of 88.9% was obtained as well as the lowest deactivation. The deactivation of catalyst was prohibited properly through the introduction of oxygen in the reactant together with the modification of Fe₂O₃/ZrO₂ with CaO. The CaO/Fe₂O₃/ZrO₂ showed constant catalytic activity and selectivity for more than 50 h without deactivation. The selectivity of styrene was strongly influenced by the mole ratio of O₂/VCH and 95% selectivity with 80% conversion was obtained at O₂/VCH mole ratio of 6 over Fe₂O₃/ZrO₂. It is thought that the oxidative dehydrogenation proceeds through the dehydrogenation (DH) of ring-hydrocarbon of VCH followed by selective combustion of hydrogen (SHC) and the high selectivity of styrene was achieved by the bi-functional role of ZrO₂ for DH and SHC reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydroisomerization of n-hexane and n-heptane over platinum-promoted Cs2.5H0.5PW12O40 (Cs2.5) studied in comparison with several other solid acids

Isomerization of n-hexane and n-heptane was carried out over Cs_2.5H_0.5PW₁₂O₄₀ (denoted by Cs2.5) promoted by Pt which was introduced by either impregnation of H₂PtCl₆ or mechanical mixing of Pt/Al₂O₃ and over non-promoted Cs_2.5H_0.5PW₁₂O₄₀ in the presence of hydrogen at atmospheric pressure. The reaction temperature studied was relatively low (typically 453 and 423 K for n-hexane and n-heptane, respectively) and the hydrogen pressure was also rather low (standard conditions: feed = n-alkane 0.05 atm, H₂ 0.20 atm, N₂ balance; W/F = 40 g h mol⁻¹). Results were compared with those obtained under the same conditions for other Pt-promoted solid acids, where particular attention was paid to the time courses of the reaction (initial vs. stationary performance). Both the activity and selectivity of Cs2.5 at the initial stage (after 5 min) increased by the addition of the Pt component. Pressure dependencies of the rate at the initial stage were approximately first and −0.5th orders in alkane and hydrogen, respectively. Most remarkable was the suppression of the deactivation during the reaction in the presence of both Pt and hydrogen. For example, the mechanical mixture of Pt/Al₂O₃ and Cs2.5 (abbreviated as Pt+Cs2.5) showed little deactivation and much improved selectivity; resulting in high stationary conversion and selectivity; e.g., 98.4 and 92.1% selectivities for n-hexane and n-heptane at the conversions of 58.6 and 39.4%, respectively. Most of the results were well explained by a classical bifunctional mechanism, although other mechanisms are not all excluded. As for the other solid acids, the initial activity of Pt-promoted SO₄/ZrO₂ was high, but decreased rapidly. The deactivation was small with Pt-promoted H-ZSM-5, but the activity was low. The stationary yields of isomerized products were higher for Pt-promoted beta zeolite and Al-pillared saponite (tested only for n-heptane), although higher reaction temperatures were necessary. This revised version was published online in August 2006 with corrections to the Cover Date.     

Catalytic behaviour of Cu/ZrO2 and Cu/ZrO2(SO 4 2− ) in the reduction of nitric oxide by decane in oxygen-rich atmosphere

The selective catalytic reduction (SCR) of NO by decane under an oxidising atmosphere has been carried out on Cu/ZrO₂ and Cu/ZrO₂(SO ₄ ^2– ). Zirconia-supported Cu catalysts were prepared by ligand exchange with Cu acetylacetonate followed by calcination at 773 K. The solids obtained were characterised by temperature programmed reduction (TPR) by hydrogen and temperature programmed desorption (TPD) of NO. Cu/ZrO₂ is active and selective in the reduction of NO by decane at low temperature (< 600 K) but oxidises NO to NO₂ between 640 and 770 K. By contrast, whatever the temperature, a total selectivity to nitrogen is obtained with Cu/ZrO₂(SO ₄ ^2– ). About 40% NO conversion to N₂ is observed with GHSV of 70 000 h^–1. The promoting effect of sulfate is attributed to the large increase of acidity and the strong interaction between copper and sulfur species which is evidenced by TPD of NO and TPR by H₂.     

Promotional effect of Ce on the activity of In/W–ZrO2 for selective reduction of NO x with methane

The Ce modified In/W–ZrO₂ catalysts were prepared by impregnation and mechanical mix method. Their activities for SCR of NO _x with methane were investigated. The activity of the In/W–ZrO₂ catalyst was enhanced by addition of Ce with both methods, while the promotional effect was more pronounced for catalyst prepared by mechanical mix method compared to impregnation method. The function of Ce was to improve the oxidation of NO to NO₂. The maximum NO _x conversion over the mechanical mixed catalyst can be stabilized at 74% at 450 °C in a dry gas flow and 37% at 500 °C in wet flow (24,000 h⁻¹). For the impregnated catalysts, Ce was found to compete with In to adsorb on strong acid site over W–ZrO₂ support and inhibited the formation of InO⁺, which resulted in the lower activity of these catalysts than mechanical mixed catalysts.     

Oxidation of o-Xylene to Phthalic Anhydride on Sb-V/ZrO2 Catalysts

Zirconia-supported and bulk-mixed vanadiumantimonium oxide catalysts were used for the oxidation of o-xylene to phthalic anhydride. X-ray diffraction, Raman spectroscopy and photoelectron spectroscopy were used for characterization. It was found that vanadium promotes the transition of tetragonal to monoclinic zirconia. The simultaneous presence of Sb and V on zirconia at low coverage led to a preferential interaction of individual V and Sb oxides with the zirconia surface rather than the formation of a binary Sb-V oxide, while at higher Sb-V contents the formation of SbVO₄ took place. Sb-V/ZrO₂ catalysts showed high activity for o-xylene conversion and better selectivity to phthalic anhydride as compared to V/ZrO₂ catalysts. However, their selectivity to phthalic anhydride was poor in comparison to a V/TiO₂ commercial catalyst. The improved selectivity of the Sb-containing catalysts is attributed to the blocking of non-effective surface sites of ZrO₂, the decrease of the total amount of acid sites and the formation of surface V-O-Sb-O-V structures.     

CaO–ZrO2 Solid Solution: A Highly Stable Catalyst for the Synthesis of Dimethyl Carbonate from Propylene Carbonate and Methanol

CaO–ZrO₂ prepared by co-precipitation showed to be a well-performed catalyst for the transesterification of propylene carbonate (PC) and methanol. The characterization by X-ray powered diffraction (XRD) and Raman spectroscopy indicated that CaO was doped into the lattice of ZrO₂ to form CaO–ZrO₂ solid solution. Such a solid solution was a strong solid base, which was proved by CO₂ temperature program desorption (CO₂-TPD). As a result, the catalyst showed high stability towards the transesterification of propylene carbonate and methanol into dimethyl carbonate with high PC conversion, especially being subjected to the continuous production of dimethyl carbonate at reactive distillation reactor for 250 h without any obvious loss of activity at the PC conversion of 95%.     

SELECTIVE CARBON MONOXIDE OXIDATION IN H2-RICH GAS STREAM OVER Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, AND MnO2/CeO2/ZrO2 CATALYSTS

Activity and selectivity of selective CO oxidation in an H₂-rich gas stream over Co₃O₄/CeO₂/ZrO₂, Ag/CeO₂/ZrO₂, and MnO₂/CeO₂/ZrO₂ catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N₂ physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co₃O₄/CeO₂/ZrO₂ catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co₃O₄/CeO₂/ZrO₂ catalyst increased with increase in Co₃O₄ molar ratio.     

Low-temperature Oxidation of Carbon Monoxide on Co/ZrO2

A 10%Co/ZrO₂ catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO₂ in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing conditions. The activation energy for the CO to CO₂ oxidation reaction was calculated as E_a = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques, X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co₃O₄ is present on monoclinic ZrO₂ after the calcination of the catalyst.     

Synthesis of porous Al2O3/ZrO2 nanocomposites by chemical vapour deposition

Al₂O₃/ZrO₂ one-dimensional nanocomposite structures were synthesised by chemical vapour deposition using Al₂O₃ nanowires and a ZrCl₄ powder source at a temperature of 800?°C and a pressure of 130?Pa. The samples were characterised using X-ray diffraction, the scanning electron microscopy, the transmission electron microscopy, and N₂ adsorption–desorption. The results revealed that Al₂O₃/ZrO₂ composite nanowires coated with surface-embedded ZrO₂ nanocrystals were formed and that the ZrO₂ macroporous and mesoporous structures changed as the ZrO₂ deposition time increased. The pore structure and surface area were also elucidated from the N₂ adsorption–desorption measurements.     

Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming

CH₄/CO₂ reforming over Pt/ZrO₂, Pt/CeO₂ and Pt/ZrO₂ with CeO₂ was investigated at 2 MPa. Pt/ZrO₂, which shows stable activity under 0.1 MPa, and Pt/CeO₂ showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO₂ with CeO₂ prepared by different impregnation order (co-impregnation of Pt and CeO₂ on ZrO₂, and consecutive impregnation of Pt and CeO₂ on ZrO₂). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO₂ and Pt/CeO₂). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H₂ reduction, and the CH₄/CO₂ reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO₂ prepared by impregnation of CeO₂ on Pt/ZrO₂ and the catalyst showed highest stability.     

Characterization of Supported NiSO4 and Effect of TiO2–ZrO2 Composition on Catalytic Activity for Acid Catalysis

A series of catalysts, NiSO₄/TiO₂–ZrO₂ having different TiO₂–ZrO₂ composition, for acid catalysis was prepared by the impregnation method using an aqueous solution of nickel sulfate. The addition of TiO₂ to ZrO₂ improved the surface area of the catalyst and enhanced its acidity remarkably because of the formation of new acid sites through the charge imbalance of Ti–O–Zr bonding. The binary oxide, TiO₂–ZrO₂ calcined above 600 °C resulted in the formation of crystalline orthorhombic phase of ZrTiO₄. Therefore, NiSO₄/TiO₂–ZrO₂ calcined at 500 °C exhibited a maximum catalytic activity for acid catalysis, and then the catalytic activity decreased with the calcination temperature. The correlation between catalytic activity and acidity held for both reaction, 2-propanol dehydration and cumene dealkylation. NiSO₄ supported on 50TiO₂–50ZrO₂ (TiO₂/ZrO₂ ratio = 1) among TiO₂–ZrO₂ binary oxides exhibited the highest catalytic activity for acid catalysis.     

Simultaneous dehydrogenation and isomerization of n-butane to isobutene over Cr/WO3–ZrO2 catalysts

A series of WO₃-promoted Cr₂O₃-based catalysts were prepared and tested for the simultaneous dehydrogenation and isomerization of n-butane to isobutene. It is found that a Cr₂O₃/WO₃–ZrO₂ system is an effective catalyst for this reaction; however, the catalytic behavior is dependent on Cr₂O₃ and WO₃ contents, space velocity and temperature. 10 wt% Cr₂O₃/20 wt% WO₃–ZrO₂ can give high initial conversion and isobutene selectivity, but it deactivates rapidly due to the variation of surface properties and pore structure caused by carbon deposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.     

Improving then-pentane hydroisomerization of Pt/SO 4 2− SiO2) catalysts through mixing with ZrO2

The performance of Pt catalysts supported on sulfated zirconia-silica with different stoichiometries is investigated in then-pentane hydroisomerization reaction. Comparatively, with respect to the Pt/SO ₄ ^2– -SiO₂ or Pt/SO ₄ ^2– -ZrO₂ catalysts, the sulfated mixed oxides show an enhancement of the catalytic activity that increases with the content of ZrO₂, reaching its maximum at values between 10 and 15 wt% zirconia. The characterization of the samples reveals that at this stoichiometry occurs the highest H2-consumption of the samples as well as the top value of strong Brónsted acid sites according to the TPD-H₂ and FTIR measurements of absorbed pyridine respectively. That is, close to these percents of zirconia content one has a compound that is homogeneously mixed and above those values the segregations of the single oxides occur as verified by X-ray diffraction characterization.     

Photocatalytic water splitting over ZrO2 prepared by precipitation method

ZrO₂ prepared by the precipitation method of zirconium oxychloride with various hydrolyzing agents was studied for photocatalytic water splitting reaction under UV light irradiation. The crystal structure as well surface properties were varied with the hydrolyzing agent of KOH, NH₄OH, and NH₂CONH₂. Especially, the surface area of the prepared ZrO₂ calcined at the same temperature of 750 °C for 6 h was dependent highly on the hydrolyzing agent, and thus the highest photocatalytic activity was obtained for ZrO₂ with the highest surface area when KOH was used as a hydrolyzing agent, In the presence of Na₂CO₃, the photocatalytic activity of ZrO₂ increased by 2–3 fold, which was ascribed to the physically adsorbed carbonate species on the ZrO₂ surface. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Fabrication of SiO2-ZrO2 composite fiber mats via electrospinning

(1 − x)SiO₂-(x)ZrO₂ (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite fibers having a tetragonal crystalline ZrO₂ were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and crystallization of ZrO₂ in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did not depend on the sintering temperature.     

Study of the preasphaltenes of coal liquefaction and its hydro-conversion kinetics catalyzed by SO4/ZrO2

The investigation of hydro-conversion behavior of the heavy intermediate products derived from coal direct liquefaction is advantageous to optimize the technological conditions of direct coal liquefaction and improve the oil yield. In this paper, the hydro-conversion of preasphaltenes catalyzed by SO₄²⁻/ZrO₂ solid acid was investigated based on the structural characterization of preasphaltenes and its hydro-conversion products, and the determination of products distribution and the kinetics of preasphaltenes hydro-conversion. The results indicated that the content of condensed aromatic rings increased, and the contents of hydrogen, oxygen and aliphatic side chains of preasphaltenes decreased with the increase of coal liquefaction temperature. The preasphaltenes showed higher hydro-conversion reactivity while SO₄²⁻/ZrO₂ solid acid was used as catalyst. Higher temperature and longer time were in favor of increasing the conversion and the oil + gas yield. The conversion of preasphaltenes hydro-conversion under 425 °C, for 40 min reached 81.3% with 51.2% oil + gas yield. SO₄²⁻/ZrO₂ solid acid was in favor of the catalytic cracking rather than the catalytic hydrogenation in the hydro-conversion of preasphaltenes. The activation energy of preasphaltenes conversion into asphaltenes was 72 kJ/mol. The regressive reactions were only observed at a higher temperature.     

Recent progress in the manufacture of alkanesulfonates: Photosulfochlorination of single-chain length (C12−C16) n-alkanes using SO2Cl2 at high conversion rates in pure phase and in the presence of solvent

Increasing concentration of sulfuryl chloride during the photosulfochlorination reaction under visible light shows that under these conditions n-alkanes react at high conversion rates instead of the conversion rate of 15% reported in the literature. This photosulfochlorination with sulfuryl chloride leads to better and more interesting results compared with those of photosulfochlorination by gas mixture. Indeed, nearly total conversion of n-alkanes, specifically n-heptane, n-dodecane, n-tetradecane, and n-hexadecane, occurred in pure phase, with a quantitative global yield, a sulfochlorination-to-chlorination molar ratio of about 1, and a relative reactivity of secondary to primary hydrogen of about 2.5, at a reaction temperature of 30°C and a reaction time of 120 min, using 2×10⁻² mol L⁻¹ of pyridine. Under these conditions, no polysulfochlorinated compounds are detected. These results are further improved using chlorobenzene as the solvent, instead of benzene. Indeed, the sulfochlorination of n-heptane at a conversion rate of 80% in the presence of chlorobenzene leads also to a quantitative reaction yield, a higher RSO₂Cl/RCl molar ratio, and, as expected, a high selectivity of secondary over primary hydrogen. Under these conditions, sulfochlorination of long-chain n-alkanes leads to the highest RSO₂Cl/RCl molar ratio for n-dodecane, n-tetradecane, and n-hexadecane belonging to detergent range, and the value of the molar ratio for these is between 1.45 and 1.7. The isomeric distribution of sulfochlorinated compounds obtained during sulfochlorination in the presence of solvent resembles that of secondary alkanesul-fonates produced by sulfoxidation reaction, whereas that obtained in pure phase has a similar conversion rate, is rich in primary isomer, and thus is different from that of classic radical reactions such as photochlorination or photosulfochlorination with gas mixture.