Selective oxidation of ethane and propane over sulfated zirconia‐supported nickel oxide catalysts

The oxidative dehydrogenations of ethane and propane were investigated over a series of zirconia and nickel‐oxide supported on zirconia catalysts. It was found that zirconia, sulfated zirconia as well as NiO‐based zirconia catalysts showed high catalytic activities for oxidative dehydrogenation of ethane and propane. However, conversion and selectivity differed depending on the nature of the catalysts. Zirconia, sulfated zirconia (SZ) and their supported NiO catalysts showed high ethane conversions but lesser selectivities to olefins while NiO/Li₂ZrO₃ exhibited high selectivities to ethylene and propylene. Addition of an LiCl promoter in the NiO/SZ catalyst increased the catalytic activity and olefin selectivity, thus resulting in a higher olefin yield. In the oxidative dehydrogenations of ethane and propane NiO–LiCl/SZ exhibited 79% ethylene selectivity at 93% ethane conversion at 650 °C and 52% selectivity to propylene at 20% propane conversion at 600 °C, respectively. Characterization showed that the physico‐chemical properties of the catalysts determine the catalytic activity and selectivity. © 2001 Society of Chemical Industry     

Effect of Iron Addition on the Durability of Pd–Pt-Loaded Sulfated Zirconia for the Selective Reduction of Nitrogen Oxides by Methane

The effects of adding iron to Pd–Pt/sulfated zirconia (SZ) on the selective NO _x reduction by methane were examined based on durability tests under conditions simulating natural gas combustion exhaust. While Pd–Pt/SZ was severely deactivated at 500 °C, Pd–Pt/Fe-SZ maintained a NO _x conversion higher than 70% for over 2400 h under the same conditions. Methane conversion on Pd–Pt/Fe-SZ was significantly lower than that on Pd–Pt/SZ. XRD analysis of fresh and used catalysts showed that a part of the SZ had transformed to monoclinic ZrO₂ and that adding Fe suppressed the transformation. These results suggested that the improvement in NO _x conversion by adding Fe was due to the suppression of methane combustion and the stabilization of SZ against transformation to ZrO₂.     

Neopentane cracking catalyzed by iron- and manganese-promoted sulfated zirconia

Cracking of neopentane was catalyzed by a sulfated oxide of zirconium promoted with iron and manganese. Reaction at 300–450°C, atmospheric pressure, and neopentane partial pressures of 0.00025–0.005 bar gave methane as the principal product, along with C₂ and C₃ hydrocarbons, butenes, and coke. The order of reaction in neopentane was determined to be 1, consistent with a monomolecular reaction mechanism and with the formation of methane andt-butyl cations; the latter was presumably converted into several products, including only little isobutylene. At 450°C and a neopentane partial pressure of 0.005 bar, the rate of cracking at 5 min onstream was 5×10^–8 mol/(g of catalyst s). Under the same conditions, the rates observed for unpromoted sulfated zirconia and USY zeolite were 3×10^–8 and 6×10^–9 mol/ (g of catalyst s), respectively. The observation that the promoted sulfated zirconia is not much more active than the other catalysts is contrasted to published results showing that the former catalyst is more than two orders of magnitude more active than the others forn-butane isomerization at temperatures <100°C. The results raise a question about whether the superacidity attributed to sulfated zirconia as a low-temperature butane isomerization catalyst pertains at the high temperatures of cracking.     

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.     

Comparative studies on direct conversion of methane to methanol/formaldehyde over La–Co–O and ZrO2 supported molybdenum oxide catalysts

The selective oxidation of methane with molecular oxygen over MoO_x/La–Co–O and MoO_x/ZrO₂ catalysts to methanol/formaldehyde has been investigated in a specially designed high-pressure continuous-flow reactor. The properties of the catalysts, such as crystal phase, structure, reducibility, ion oxidation state, surface composition and the specific surface area have been characterized with the use of XRD, LRS, TPR, XPS and BET methods. MoO_x/La–Co–O catalysts showed high selectivity to methanol formation while MoO_x/ZrO₂ revealed the property for the formation of formaldehyde in the selective oxidation of methane. 7 wt MoO_x/La–Co–O catalyst gave 6.7 methanol yield (ca. 60 methanol selectivity) at 420°C and 4.2 MPa. On the other hand, the maximal yield of formaldehyde ca. 4 (47.8 formaldehyde selectivity) was obtained over 12wt MoO_x/ZrO₂ catalyst at 400 °C and 5.0MPa. 7MoO_x/La–Co–O catalyst showed higher modified H₂-consumption than 12MoO_x/ZrO₂ catalyst. The reducibility and the O^–/O^2– ratio of the catalysts may play important roles on the catalytic performance. The proper reducibility and the O^–/O^2– ratio enhanced the production of methanol in selective oxidation of methane. [MoO₄]^2– species in MoO_x/ZrO₂ catalysts enable selective oxidation of methane to formaldehyde.     

Methane oxidative coupling over fluoro-oxide catalysts

LaF₃ modified ZrO₂, CeO₂ and ThO₂ catalysts for the oxidative coupling of methane indicate that ZrO₂/LaF₃, CeO₂/LaF₃ and ThO₂/LaF₃ catalysts have high activity and high selectivity at low temperature. In the temperature region 480–650 °C, the methane conversion is 24.38–30.8% and the C ₂ ⁼ selectivity is 40–55.38%. The characterization of oxygen species on the catalysts indicates that, because of the modification of LaF₃ to ZrO₂, CeO₂ and ThO₂, it is favourable for the activation of O₂.Patent application No. CN 92105258.8 inventors: Xiaoping Zhou, Huilin Wan and K.R. Tsai.     

Selective monochlorination of methane over solid acid and zeolite catalysts

Chlorination of methane was studied over amorphous silica-alumina, silicalite as well as H-mordenite, X, Y, NaL and H-ZSM-5 zeolite catalysts. The heterogeneous transformations were carried out in a continuous flow reactor in the 200–425 °C temperature range, under atmospheric pressure (methane to chlorine ratio 4:1, GHSV 600 ml/ g h). Chlorination of methane over zeolites in the 200–300 °C temperature range proceeds without selectivity indicating a radical mechanism. Above 300–350 °C, depending on the nature of zeolite, selective monochlorination takes place indicating the dominance of an ionic mechanism. H-mordenite was found to give the best monochlorination at the lowest temperature (99.2% CH₃Cl at 350 °C). The observed selectivity of the investigated zeolites is strongly time limited. All investigated catalysts lose their selectivity after five hours on-stream due to extraction of aluminum from the framework of zeolites by hydrogen chloride. Amorphous silica-alumina above 350 °C also catalyzes ionic chlorination. The chlorination of methane over silicalite proceeds via the nonselective radical pathway at the investigated temperatures.Catalysis by solid superacids, 28. For part 27, see ref. [1].     

Lithium-chloride-promoted sulfated zirconia catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane over sulfated-zirconia-supported lithium chloride catalysts has been systematically investigated. The optimal experimental parameters were obtained. It is found that sulfation of zirconia increases the catalytic activity. 2–3.5 wt% lithium chloride on sulfated zirconia catalysts exhibit high catalytic activity for oxidative dehydrogenation of ethane, with particularly high activity for ethene production. 70% selectivity to ethene at 98% ethane conversion, giving 68% ethene yield, is achieved over 3.5 wt% LiCl/SZ at 650°C.     

Platinum-sulfated-zirconia. Infrared study of adsorbed pyridine

Pyridine adsorption on sulfated zirconia (SO _2– ⁴ -ZrO₂) provides evidence for infrared bands characteristic of both Brønsted and Lewis acid sites. Samples treated at 100°C retain water and have a higher fraction of Brønsted acidity than when the sample is treated at 400°C. The fraction of Brønsted acid sites observed for SO _2– ⁴ -ZrO₂ is the same in the presence or absence of supported Pt. Based on pyridine adsorption, exposure to gaseous hydrogen at 100 or 150°C did not significantly alter the fraction of Brønsted acid sites following the exposure to hydrogen.     

Characterization of Fischer–Tropsch Cobalt-Based Catalytic Systems (Co/SiO<Subscript>2</Subscript> and Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO₂ and Al₂O₃, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO₂ catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al₂O₃ catalysts. Conversely the Al₂O₃ supported catalysts gave much higher selectivity towards olefins than Co/SiO₂. These results yield the correlation that the presence of Co₃O₄ yield higher methane selectivity whereas the presence of Co²⁺ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.     

Effect of calcination temperature on characteristics of sulfated zirconia and its application as catalyst for isosynthesis

The effect of catalyst calcination temperature (450 °C, 600 °C, and 750 °C) on catalytic performance of synthesized and commercial grade sulfated zirconia catalysts towards isosynthesis was studied. The characteristics of these catalysts were determined by using various techniques including BET surface area, XRD, NH₃- and CO₂-TPD, ESR, and XPS in order to relate the catalytic reactivity with their physical, chemical, and surface properties. It was found that, for both synthesized and commercial sulfated zirconia catalysts, the increase of calcination temperature resulted in the increase of monoclinic phase in sulfated zirconia, and the decrease of acid sites. According to the catalytic reactivity, at high calcination temperature, lower CO conversion, but higher isobutene production selectivity was observed from commercial sulfated zirconia. As for synthesized sulfated zirconia, the isobutene production selectivity slightly decreased with increasing calcination temperature, whereas the CO conversion was maximized at the calcination temperature of 600 °C. We concluded from the study that the difference in the calcination temperatures influenced the catalytic performance, sulfur content, specific surface area, phase composition, the relative intensity of Zr³⁺, and acid-base properties of the catalysts.     

Low-temperature catalytic combustion on Pt/SO 4 2− /ZrO2 and Pd/SO 4 2− /ZrO2 catalysts

Low-temperature combustion of various organic compounds on Pt/SO ₄ ^–2 /ZrO₂ and Pd/SO ₄ ^–2 /ZrO₂ was studied. For these organic compounds, especially saturated hydrocarbons, the combustion activities of Pt/SO ₄ ^–2 /ZrO₂ are higher than those of Pt/ Al₂O₃. Pt/SO ₄ ^–2 /ZrO₂ combustion catalysts can be used in a wide range of space velocity and oxygen content. The catalytic activity is enhanced with an increase of Pt loading from 0.1 to 1.0 wt%. The superacidity of the support material is responsible for the improvement in activity rather than an increase in catalyst surface area or metal dispersion. Pd/SO ₄ ^–2 /ZrO₂ are less active than Pt/SO ₄ ^–2 /ZrO₂.     

Influence of oxygen and promoting effect of barium on the reduction of NOx by ethanol on Pd/ZrO2 catalyst

The NO reduction by ethanol over barium promoted Pd/ZrO₂ catalyst and the effect of the oxygen on the selectivity were studied. The catalysts were prepared by incipient wetness impregnation with 14.3% of Ba over zirconia and 1% of palladium. The specific surface areas were 58 and 47 m²/g and the dispersions of Pd were 37% and 30% for the Pd/ZrO₂ and Pd–Ba/ZrO₂ catalysts, respectively. The X-ray diffraction patterns indicate the presence of monoclinic zirconia phase on the support and BaCO₃, which is decomposed at 715 and 815 °C. Temperature programmed desorption profiles of NO on Pd/ZrO₂ and Pd–Ba/ZrO₂ catalyst showed a huge amount N₂ formation for the promoted Ba catalyst. Catalytic results showed high NO conversion even at low temperature, in accordance with the TPD results and an increasing selectivity to N₂ when compared with Pd/ZrO₂. The effect of O₂ in the NO_x reduction with ethanol provoked less NO dissociation and lower selectivity to methane.     

Low methane selectivity using Co/MnO catalysts for the Fischer-Tropsch reaction: Effect of increasing pressure and Co-feeding ethene

CO hydrogenation using cobalt/ manganese oxide catalysts is described and discussed. These catalysts are known to give low methane selectivity with high selectivity to C₃ hydrocarbons at moderate reaction conditions (GHSV < 500 h^–1, < 600 kPa). In this study the effect of reaction conditions more appropriate to industrial operation are investigated. CO hydrogenation at 1–2 MPa using catalyst formulations with Co/Mn = 0.5 and 1.0 gives selectivities to methane that are comparable to those observed at lower pressures. At the higher pressure the catalyst rapidly deactivates, a feature that is not observed at lower pressures. However, prior to deactivation rates of CO + CO₂ conversion > 8 mol/1-catalyst h can be observed. Co-feeding ethene during CO hydrogenation is investigated by the reaction of¹³C0-¹²C₂H₄-H₂ mixtures and a significant decrease in methane selectivity is observed but the hydrogenation of ethene is also a dominant reaction. The results show that the co-fed ethene can be molecularly incorporated but in addition it can generate a C, species that can react further to form methane and higher hydrocarbons.     

Catalytic Performance of B2O3/TiO2–ZrO2 for Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime: The Effect of Boria Loading

A series of boria catalysts supported on titania–zirconia mixed oxide (B₂O₃/TiO₂–ZrO₂) with different boria loadings (8–20 wt%) were prepared and characterized by X-ray diffraction, adsorption of nitrogen, ¹¹B magic angle spinning (MAS) NMR measurements and temperature-programmed desorption (TPD) of ammonia. The catalytic performance of B₂O₃/TiO₂–ZrO₂ for vapor-phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam was studied at 300°C. It was found that the lactam selectivity increased with increasing of boria loading, whereas a maximum oxime conversion was obtained at the boria loading of 12 wt%. The acid sites of medium strength on the surface of the catalyst play an important role in the selective formation of lactam.     

Catalytic partial oxidation of methane to synthesis gas over γ-Al2O2-supported rhodium catalysts

The partial oxidation of methane was studied over -Al₂O₃-supported catalysts for Rh loadings between 0.01 and 5.0 wt%. It was found that the activity and selectivities for loadings between 0.5 and 5.0 wt% are almost the same. As an example, detailed information is presented for the 1.0 wt% Rh/-Al₂O₃, which provides at 750°C (furnace temperature) an activity of 82% and selectivities of 96% to CO and 98% to H₂, at a gas hourly space velocity (GHSV) of 720000 ml g^–1 h^–1. Its activity remained stable during our experiment which lasted 120 h. Possible explanations for this high stability are proposed based on TPR and XRD experiments. Pulse reactions with small pulses of CH₄ and CH₄/O₂ (2/1) were performed over the reduced and unreduced Rh catalysts to probe the mechanistic aspects of the reaction. The partial oxidation of methane to syngas was found to be initiated by metallic rhodium sites, since the CO selectivity increased with increasing number of such sites.     

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.     

Isomerization and Arylation of Oleic Acid on Anion Modified Zirconia Catalysts

The catalytic performance of anion modified zirconia catalysts, such as sulfated zirconia (SO₄/ZrO₂) and tungstated zirconia (WO₃/ZrO₂), was evaluated for the upgrading of oleic acid (OA). In the presence of an aromatic compound, two main reactions occurred on the catalysts: the skeletal isomerization of OA and the arylation of OA with aromatics. The activity of the SO₄/ZrO₂ was more than triple of that of the WO₃/ZrO₂. At 250 °C, OA/(SO₄/ZrO₂)(wt/wt) = 5, the OA conversion and the arylation selectivity reached their maximal values and the isomerization selectivity was the lowest when the toluene to OA (toluene/OA) molar ratio was about 6. When mesitylene was used instead of toluene, the OA conversion and the arylation selectivity decreased, probably because of a steric effect. An attempt to reuse the SO₄/ZrO₂ by solvent washing after a run was not so successful, while calcination at 630 °C in air recovered the activity completely.     

Oxidative coupling of methane over BaF2-TiO2 catalysts

The addition of F^– to Ba-Ti mixed oxide catalysts significantly improves the catalytic performances for the oxidative coupling of methane (MOC), which can achieve high C₂ yields at wide feed composition range and high GHSV. The effect is particularly marked for the BaF_2– TiO₂ catalysts containing more than 50 mol% BaF₂. The C₂ yield of 17% and the C₂ selectivity of > 60% were achieved over these catalysts at 700 ° C. After being on stream for 31 h, the 50 mol% BaF₂-TiO₂ catalysts showed only a 1–1.5% decrease in the C₂ yields. Results obtained by XRD show that various Ba-Ti oxyfluoride phases were formed due to the substitution of F^– to O^2–.     

The long-term high-temperature behavior of refractories produced from ZrO2 stabilized with Nd2O3

Conclusions A technology was developed for the production of zirconia refractories from ZrO₂ stabilized with Nd₂O₃. The thermal strength of the product is adequate for long-term service at a large (200–300°C/mm) temperature gradient. Products based on a zirconia — neodymium solid solution can be used several times.It was established that no appreciable Nd₂O₃ vaporization and, consequently, no appreciable destabilization of the ZrO₂ develops in a neutral medium at 2100–2500°C.The solid-phase processes developing at 2100–2500°C in products from a mixture of 70% cubic solid solution (88 mole % ZrO₂+12 mole % Nd₂O₃) and 30% unstabilized ZrO₂ fired at 1750°C consist of the redistribution of the Nd₂O₃ between the cubic solid solution Nd₂Zr₂O₇-ZrO₂ and the unstabilized ZrO₂, and the diffusion of some of the Nd₂O₃ from the cooler to the working zone.Translated from Ogneupory, No. 3, pp. 52–55, March, 1976.