Catalytic Wet Oxidation of H<Subscript>2</Subscript>S to Sulfur on V/MgO Catalyst

The V/MgO catalysts with different V₂O₅ loadings were prepared by impregnating MgO with aqueous vanadyl sulfate solution. All of the catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). It was observed that the H₂S removal capacity with respect to vanadia content increased up to 6 wt%, and then decreased with further increase in vanadia loading. The prepared catalysts had BET surface areas of 11.3 ~ 95.9 m²/g and surface coverages of V₂O₅ of 0.1 ~ 2.97. The surface coverage calculation of V₂O₅ suggested that a vanadia addition up to a monomolecular layer on MgO support increased the H₂S removal capacity of V/MgO, but the further increase of VO _x surface coverage rather decreased that. Raman spectroscopy showed that the small domains of Mg₃(VO₄)₂ could be present on V/MgO with less than 6 wt% vanadia loading. The crystallites of bulk Mg₃(VO₄)₂ and Mg₂(V₂O₇) became evident on V/MgO catalysts with vanadia loading above 15 wt%, which were confirmed by a XRD. The TPR experiments showed that V/MgO catalysts with the loading below 6 wt% V₂O₅ were more reducible than those above 15 wt% V₂O₅. It indicated that tetrahedrally coordinated V⁵⁺ in well-dispersed Mg₃(VO₄)₂ domains could be the active species in the H₂S wet oxidation. The XPS studies indicated that the H₂S oxidation with V/MgO could proceed from the redox mechanism (V⁵⁺ V⁴⁺) and that V³⁺ formation, deep reduction, was responsible for the deactivation of V/MgO.     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Effects of preparation methods for V<Subscript>2</Subscript>O<Subscript>5</Subscript>-TiO<Subscript>2</Subscript> aerogel catalysts on the selective catalytic reduction of NO with NH<Subscript>3</Subscript>

A series of V₂O₅-TiO₂ aerogel catalysts were prepared by the sol-gel method with subsequent supercritical drying with CO₂. The main variables in the sol-gel method were the amounts of V₂O₅ and when the vanadium precursor was introduced. V₂O₅-TiO₂ xerogel and V₂O₅/TiO₂ (P-25) were also prepared for comparison. The V₂O₅-TiO₂ aerogel catalysts showed much higher surface areas and total pore volumes than V₂O₅-TiO₂ xerogel and impregnated V₂O₅/TiO₂ (P-25) catalysts. The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-Raman spectroscopy, temperature-programmed reduction with H₂ (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The selective catalytic reduction of NOx with ammonia in the presence of excess O₂ was studied over these catalysts. Among various V₂O₅-TiO₂ catalysts, V₂O₅ supported on aerogel TiO₂ showed a wide temperature window exhibiting high NOx conversions. This superior catalytic activity is closely related to the large amounts of strong acidic sites as well as the surface vanadium species with characteristics such as easy reducibility and monomeric and polymeric vanadia surface species. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

Phase cooperation of V<Subscript>2</Subscript>O<Subscript>5</Subscript> and Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> in the selective oxidation of H<Subscript>2</Subscript>S containing ammonia and water

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over vanadium oxide-based catalysts. The investigation was focused on the role of V₂O₅, and phase cooperation between V₂O₅ and Bi₂O₃ in this reaction. The conversion of H₂S continued to decrease since V₂O₅ was gradually reduced by treatment with H₂S. The activity of V₂O₅ was recovered by contact with oxygen. A strong synergistic phenomenon in catalytic activity was observed for the mechanically mixed catalysts of V₂O₅ and Bi₂O₃. Temperature-programmed reduction (TPR) and oxidation (TPO) and two bed reaction tests were performed to explain this synergistic effect by the reoxidation ability of Bi₂O₃. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Synthesis,characterization and electrical properties of polypyrrole/V<Subscript>2</Subscript>O<Subscript>5</Subscript> composites

Polypyrrole (PPy) and its composites with vanadium pentoxide (V₂O₅) were synthesized in aqueous medium by chemical oxidation polymerization using FeCl₃·6H₂O as an oxidant. The materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometry (XRD), thermogravimetry analyzer (TGA), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV/visible spectroscopic techniques and LCR-meter. The FT-IR results confirmed the successful synthesis of PPy and PPy/V₂O₅ composites. The XRD study showed the amorphous and crystalline nature of PPy and PPy/V₂O₅ composites, respectively. The TGA analysis showed slight increase in the thermal stability of the composites. The SEM data verified the porous nature of PPy and the composites. The UV/visible spectrometry confirmed the doping of PPy in composites. The electrical properties of the materials displayed their semiconducting nature. The resistance of the samples was found to be dependent on temperature and the contents of V₂O₅ in the composites.     

Improving the SO<Subscript>2</Subscript> absorption rate of CeFeMg-based sorbent promoted with titanium promoter

To improve the poor SO₂ absorption rate of CeFeMgTi sorbent with high sulfur removal capacity and fast regeneration, a new sorbent, CeFeMgTi-sol was prepared by the modified co-precipitation method and tested in a packed bed reactor at RFCC conditions (sulfation of MgO to MgSO₄ in the presence of low concentration of SO₂ at 973 K, regeneration of MgSO₄ to MgO and H₂S in the presence of H₂ at 803 K). The CeFeMgTi-sol sorbent showed excellent SO₂ absorption and sulfur removal capacity (46.2 sulfur g/g absorbent×100). It was found that the SO₂ absorption rates were related to the structure of the Mg and Ti and the textural properties such as surface area and pore volume. In the case of the fresh state of CeFeMgTi sorbent, CeO₂, MgO and MgTiO₃ structures were observed. But the new CeFeMgTisol sorbent before SO₂ absorption, showed a separated MgO and TiO₂ peak only. These differences in the sorption rates were discussed by the difference in the XRD pattern, surface area and pore volume.     

The role of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on the Structural and Optical Properties of MgO-ZnO-CdO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glasses and the Impact of Gamma Irradiation

The quaternary glasses of mixed divalent oxides including ZnO, MgO, CdO within a phosphate network former were prepared. Vanadium pentoxide was introduced as a dopant in the range from 0.5 to 3%. Optical and infrared absorption studies for all glass samples were carried out. The optical spectra reveal the presence of both V³⁺ and V⁴⁺ ions in the studied host mixed divalent oxides phosphate glass. Fourier transform infrared absorption spectral analysis indicates the appearance of distinct vibrational bands due to the presence of characteristic phosphate groups depending on the glass composition and the ratio of V₂O₅ content. The optical band gap and Urbach energy were calculated and discussed in relation to the effect of V₂O₅ content. Finally, the glasses were optically and structurally examined affter gamma irradiation with a dose of 80 KGy.     

Phase evolution during mechanochemical coreduction of V<Subscript>2</Subscript>O<Subscript>5</Subscript> and TiO<Subscript>2</Subscript> with A

The direct preparation of V-Ti solid solution alloy by coreduction of V₂O₅ and TiO₂ with Al in an attritor mill was investigated. The reduction of V₂O₅ with Al is highly exothermic, whereas reduction of TiO₂ with Al is not sufficiently exothermic for a self-sustaining reaction. A range of compositions of a mixture of V₂O₅ and TiO₂ can be so chosen as to make the overall reduction of V₂O₅ and TiO₂ with Al sufficiently exothermic for a self-sustaining reaction. Initial studies were done to identify the reaction products obtained by reducing V₂O₅ with Al. The reaction yielded the intermetallic phase (Al₃V), V, and Al₂O₃. SEM images indicated melting and solidification of the phases, leading to agglomeration. Further experiments involved mixing appropriate amounts of TiO₂ with V₂O₅ and reducing the mixture with Al. XRD data for products showed the presence of V, V₅Al₈, and Al₂O₃. X-Ray Florescence (XRF) analysis and energy dispersive analyzer (EDAX) of SEM sample images indicated the formation of V-Ti solid solution. Microstructure of the milled charges taken out prior to reaction initiation indicated morphology change in Al powder and agglomeration/segregation of reactants. As a result, the reaction of V₂O₅ with the excess Al at certain regions also promoted the formation of vanadium aluminide.     

Selective catalytic oxidation of H<Subscript>2</Subscript>S using nonhydrolytic vanadia-titania xerogels

A series of vanadia-titania (V-Ti) xerogel catalysts were prepared by nonhydrolytic sol-gel method. These catalysts showed much higher surface area and total pore volumes than the conventional V₂O₅-TiO₂ xerogel. Two species of surface vanadium in the xerogel catalysts were identified by Raman measurements: monomeric vanadyl and polymeric vanadates. The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studied over these catalysts. Xerogel catalysts from the nonhydrolytic method showed very high conversion of H₂S without harmful emission of SO₂. The conversion of H₂S increased with increasing vanadia loading up to 10V-Ti; however, it decreased at higher vanadia loading (12V-Ti and 18V-Ti) probably due to the formation of crystalline V₂O₅.     

Mechanism of SO<Subscript>2</Subscript> adsorption and desorption on commercial activated coke

We used commercial activated coke (AC) as adsorbent and fixed-bed, FTIR, N₂ adsorption, ion chromatograph as research methods to study the SO₂ removal mechanism in the presence of O₂ and H₂O and adsorbate (H₂SO₄) desorption mechanism by combined regeneration. The results showed that AC saturation sulfur retention (52.6 mg/g) in SO₂+O₂+H₂O atmosphere was 4.6 times as much as that (11.4 mg/g) in SO₂+O₂ atmosphere and 5.0 times as much as that (10.6 mg/g) in SO₂+O₂ atmosphere at 90 °C. O₂ and H₂O were necessary in AC desulfurization process. Reaction of SO₃ and H₂O (g) and condensation of sulfuric acid vapor were the dynamic of AC desulfurization process. Water vapor blowing in combined regeneration inhibited the reaction between H₂SO₄ and carbon, and consequently reduced the chemical lost of carbon. AC cumulative quality loss (53.6%) of five-times in C-R was still less than that (62.4%) of three-times in H-R. Water vapor blowing inhibited reactivation effect, as a result reducing the changes of AC pore structure and surface functional groups. Adsorbate H₂SO₄ generated in desulfurization evaporated to sulfuric acid vapor due to the high temperature in regeneration and was carried out by water vapor.     

CeO<Subscript>2</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZSM-5 sorbents for high-temperature H<Subscript>2</Subscript>S removal

Performance of CeO₂-La₂O₃/ZSM-5 sorbents for sulfur removal was examined at temperature ranging from 500 oC to 700 oC. The sulfur capacity of 5Ce5La/ZSM-5 was much bigger than that of CeO₂/ZSM-5. H₂ had a negative impact on the sulfidation; however, CO had little influence on sulfur removal. The characterization results showed that CeO₂ and La₂O₃ were well dispersed on ZSM-5 because of the intimate admixing of La₂O₃ and CeO₂, the major sulfidation products were Ce₂O₂S and La₂O₂S, the XRD and SEM results revealed that ZSM-5 structure could remain intact during preparation and sulfidation process, the H₂-TPR showed that the reducibility of CeO₂ can be remarkably enhanced by addition of La.     

Phase Transformations in Stabilized ZrO<Subscript>2</Subscript> - Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Compositions

Data on interactions in the ZrO₂ - Fe₂O₃ system stabilized by oxides in a high-temperature form at 1750°C are obtained. Of all zirconia-based compositions, only magnesium-zirconium cubic solid solution enters into an active reaction with Fe₂O₃ to yield MgFe₂O₄. The solid solutions formed by ZrO₂ with oxides of yttrium, neodymium, and calcium resist degradation by attack from Fe₂O₃; part of iron oxide undergoes dissolution in cubic ZrO₂. __________ Translated from Novye Ogneupory, No. 9, pp. 40 – 43, September, 2005.     

The Effect of Sulfur on ZrO<Subscript>2</Subscript>-Based Biomass Gasification Gas Clean-Up Catalysts

The effect of sulfur on biomass gasification gas clean-up over ZrO₂, Y₂O₃–ZrO₂ and SiO₂–ZrO₂ catalysts was examined. Experiments were carried out at the temperature range of 600–900 °C with sulfur free and 100 ppm H₂S containing simulated gasification gas feeds. A mixture of toluene and naphthalene was used as a tar model compound. Results revealed that the sulfur addition affected positively on the catalyst properties mainly at 600 and 700 °C: over Y₂O₃–ZrO₂ and ZrO₂ sulfur addition improved naphthalene and ammonia conversion. However, over SiO₂–ZrO₂ no clear effect with H₂S addition was observed. The effect of sulfur addition on the catalyst properties was connected to the formation of SO₂ from H₂S when oxygen was available. The intensity of the sulfur effect increased with the Lewis basicity strength of the catalysts. This indicates that the sulfur adsorption has a role in generating new type of active sites and/or plays role in changing the redox properties of the zirconia. Since the biomass gasification gas contains usually significant amounts of H₂S the sulfur tolerance of the zirconia based catalysts is a remarkable benefit.     

Preparation of H<Subscript>5</Subscript>PMo<Subscript>10</Subscript>V<Subscript>2</Subscript>O<Subscript>40</Subscript> catalyst immobilized on spherical carbon and its application to the vapor-phase 2-propanol conversion reaction

Spherical carbon (SC) with a diameter of ca. 9 μm was synthesized by a hydrothermal method using sucrose as a carbon precursor. The spherical carbon was then modified to have a positive charge, and thus, to provide a site for the immobilization of H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) catalyst. The PMo₁₀V₂ catalyst was immobilized on the surface-modified spherical carbon by taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]⁵⁻. The PMo₁₀V₂ catalyst immobilized on the spherical carbon (PMo₁₀V₂/SC) was applied to the vapor-phase 2-propanol conversion reaction. In the catalytic reaction, the PMo₁₀V₂/SC catalyst showed a higher 2-propanol conversion than the unsupported PMo₁₀V₂ catalyst. Furthermore, the PMo₁₀V₂/SC catalyst showed enhanced oxidation catalytic activity (formation of acetone) and the suppressed acid catalytic activity (formation of propylene and isopropyl ether) compared to the unsupported PMo₁₀V₂ catalyst. The enhanced oxidation activity of PMo₁₀V₂/SC catalyst was due to the fine dispersion of [PMo₁₀V₂O₄₀]⁵⁻ on the spherical carbon formed via chemical immobilization.     

The promotional effect of K on the catalytic activity of Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> for the combined H<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> reforming of coke oven gas for syngas production

A K-promoted 10Ni-(x)K/MgAl₂O₄ catalyst was investigated for the combined H₂O and CO₂ reforming (CSCR) of coke oven gas (COG) for syngas production. The 10Ni-(x)K/MgAl₂O₄ catalyst was prepared by co-impregnation, and the K content was varied from 0 to 5 wt%. The BET, XRD, H₂-chemisorption, H₂-TPR, and CO₂-TPD were performed for determining the physicochemical properties of prepared catalysts. Except under the condition of a K/Ni=0.1 (wt%/wt%), the Ni crystal size and dispersion decreased with increasing K/Ni. The coke resistance of the catalyst was investigated under conditions of CH₄: CO₂: H₂: CO:N₂=1 : 1 : 2 : 0.3 : 0.3, 800 °C, 5 atm. The coke formation on the used catalyst was examined by SEM and TG analysis. As compared to the 10Ni/MgAl₂O₄ catalyst, the Kpromoted catalyst exhibited superior activity and coke resistance, attributed to its strong interaction with Ni and support, and the improved CO₂ adsorption characteristic. The 10Ni-1K/MgAl₂O₄ catalyst exhibited optimum activity and coke resistance with only 1wt% of K.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Synthesis,structural, and electrochemical performance of V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanotubes as cathode material for lithium battery

Various vanadium oxide nanostructures are currently drawn interest for the potential applications of Li batteries, super capacitors, and electrochromic display devices. In this article, the synthesis of V₂O₅ nanotubes by hydrothermal method using 1-hexadecylamine (HDA) and PEO as a template and surface reactant were reported, respectively. The structural properties and electrochemical performances of these nanostructures were investigated for the application of Li batteries. Structure and morphology of the samples were investigated by XRD, FTIR, SEM, and TEM analysis. The battery with V₂O₅ nanotubes electrode showed initial specific capacity of 185 mAhg⁻¹, whereas the PEO surfactant V₂O₅ nanotubes exhibited 142 mAhg⁻¹. It was found that PEO surfactant V₂O₅ nanotubes material showed less specific capacity at initial stages but better stability was exhibited at higher cycle numbers when compared to that of V₂O₅ nanotubes. The cyclic performance of the PEO surfactant material seems to be improved with the role of polymeric component due to its surface reaction with V₂O₅ nanotubes during the hydrothermal process.     

Photocatalytic Generation of H<Subscript>2</Subscript> Gas from Neat Ethanol over Pt/TiO<Subscript>2</Subscript> Nanotube Catalysts

TiO₂ nanotubes promoted with Pt metal were prepared and tested to be the photocatalytic dehydrogenation catalyst in neat ethanol for producing H₂ gas (C₂H₅OHC₃CHO +H₂). It was found that the ability to produce H₂, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure. These Pt/TiO₂ catalysts with TiO₂ nanotubes washed with diluted H₂SO₄ solution produced 1, 2-diethoxy ethane (acetal) as the major liquid phase product, while over those washed with diluted HCl solution or H₂O, acetaldehyde was the major liquid phase product.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Ni/La<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst for hydrogen production from steam reforming of acetic acid as a model compound of bio-oil

Hydrogen production from steam reforming of acetic acid was investigated over Ni/La₂O₃-ZrO₂ catalyst. A series of Ni/La₂O₃-ZrO₂ catalysts were synthesized by sol-gel method coupled with wet impregnation, which was characterized by XRD, BET, TEM, EDS, TG, SEM and TPR. Catalytic activity of Ni/La₂O₃-ZrO₂ was evaluated by steam reforming of acetic acid at the temperature range of 550-750 °C. The tetragonal phase La_0.1Zr_0.9O_1.95 is formed through the doping of La₂O₃ into the ZrO₂ lattice and nickel species are highly dispersed on the support with high specific surface area. H₂ yield and CO₂ yield of Ni/La₂O₃-ZrO₂ catalyst with 15%wt Ni reaches 89.27% and 80.41% at 600 °C, respectively, which is attributed to high BET surface area and sufficient Ni active sites in strong interaction with the support. 15%wt Ni supported on La₂O₃-ZrO₂ catalyst maintains relatively stable catalytic activities for a period of 20 h.