Zirconia-supported Nickel Catalysts Research Articles

Zirconia supported nickel catalysts for glycerol steam reforming: Effect of zirconia structure on the catalytic performance

The effect of the zirconia structure in Ni/ZrO2 catalysts on the glycerol steam reforming (GSR) reaction was studied. A tetragonal zirconia support was synthesized via a hydrolysis technique and loaded with 5 wt% Ni via a wet-impregnation method. Similarly, a commercial monoclinic zirconia support was also impregnated with 5 wt% Ni. Following calcination at 600 °C, physico-chemical properties of the prepared catalysts were investigated by X-Ray Diffraction (XRD), H2-Temperature Programmed Reduction (H2-TPR) and CO2-Temperature Programmed Desorption (CO2-TPD) techniques. The catalysts were then tested in the GSR reaction in the 400–700 °C range with a steam to glycerol molar ratio of 9:1 and a flow rate of 0.025 mL/min. The monoclinic catalyst exhibited a better performance giving higher hydrogen yields and glycerol conversions. This was attributed to an improved reducibility of Ni in this catalyst. Stability tests at 600 °C revealed the deactivation of the tetragonal catalyst during 6 h as a result of the formation of encapsulating coke which blocked active Ni metal sites. The monoclinic catalyst, exhibiting the formation of only filamentous coke, remained relatively stable for 24 h.

CO2 selective hydrogenation to synthetic natural gas (SNG) over four nano-sized Ni/ZrO2 samples: ZrO2 crystalline phase & treatment impact

Two type zirconia (monoclinic and tetragonal phase ZrO2) carriers were synthesized via hydrothermal route, and nano-sized zirconia supported nickel catalysts were prepared by incipient impregnation then followed thermal treatment at 300°C to 500°C, for the CO2 selective hydrogenation to synthetic natural gas (SNG). The catalysts were characterized by XRD, CO2-TPD-MS, XPS, TPSR (CH4, CO2) techniques. For comparison, the catalyst NZ-W-400 (monoclinic) synthesized in water solvent exhibited a better catalytic activity than the catalyst NZ-M-400 (tetragonal) prepared in methanol solvent. The catalyst NZ-W-400 displayed more H2 absorbed sites, more basic sites and a lower temperature of initial CO2 activation. Then, the thermal treatment of monoclinic ZrO2 supported nickel precursor was manufactured at three temperature of 350, 400, 500°C. The TPSR experiments displayed that there were the lower temperature for CO2 activation and initial conversion (185°C) as well as the lower peak temperature of CH4 generation (318°C), for the catalyst calcined at 500°C. This sample contained the more basic sites and the higher catalytic activity, evidenced byCO2-TPD-MS and performance measurement. As for the NZ-W-350 sample, which exhibited the less basic sites and the lower catalytic activity, its initial temperature for CO2 activation and conversion was higher (214°C) as well as the higher peak temperature of CH4 formation (382°C).

Dry reforming of methane over Ni/Ce0.62Zr0.38O2 catalysts: Effect of Ni loading on the catalytic activity and on H2/CO production

The activity of ceria–zirconia-supported nickel catalysts (Ni/CZ) with various loadings of nickel (2, 4 and 10 wt. %) was studied in the case of low-temperature dry reforming of methane (DRM). XRD, SBET, SEM, TPD-CO2 and thermogravimetry were used to determine the physicochemical properties of the catalysts and of the carbon deposits formed on the surface. It was found that the agglomerates of the Ni-active phase are formed on the surface of the support for high loadings of nickel. The best conversions of CO2 and CH4 and an optimum ratio H2/CO = 1 were obtained for the catalysts with the highest Ni content. It was also found that loading has an influence on the amount of carbon deposits formed in the DRM process.

High catalytic performance of mesoporous zirconia supported nickel catalysts for selective CO methanation

Ni/mesoporous ZrO2, without precious metals, exhibits high performance for selective CO methanation at a wide range of working temperatures and superior long-term stability.

Isooctane decomposition and carbon deposition over ceria–zirconia supported nickel catalysts

Catalytic decomposition of hydrocarbons is a major contributor to carbon formation during hydrocarbon reforming. This work investigates the effects of temperature and hydrocarbon decomposition intermediates on carbon deposition during catalytic isooctane decomposition over ceria–zirconia supported nickel. The carbon deposition rate and hydrocarbon concentrations were monitored in real-time via thermogravimetry and FT-IR spectroscopy. Carbon-deposited catalysts were characterized by temperature-programmed oxidation (TPO) and scanning electron microscopy (SEM). Carbon deposition rate, morphology, and quantity were strongly dependent on decomposition temperature ( T); three distinct decomposition temperature regimes were identified, i.e. T ≤ 575 °C, 575 °C < T < 725 °C, and T ≥ 725 °C. Gaussian deconvolution of TPO data and carefully designed oxidation experiments indicated the presence of different types of carbon: coating, filamentous, and pyrolytic carbon. Catalytic and homogeneous decomposition of isooctane, propene, and methane suggest that smaller hydrocarbon fragments, typically formed during reforming of large hydrocarbon molecules, play an important role in carbon deposition. Specifically, low-temperature decomposition of isooctane into olefins, such as propene or isobutene, leads to the formation of both coating and filamentous carbon deposits. At high temperatures, decomposition of acetylene and methane leads to the formation of significant quantities of coating and pyrolytic carbon deposits in addition to filamentous deposits.

Novel supports for nickel-based catalysts for the partial oxidation of methane

Zirconia-supported nickel catalysts with different amounts of aluminum (Al/Zr = 0.2, 1 and 2) were studied in this work in order to find alternative supports for nickel-based catalysts for the partial oxidation of methane. This reaction is a promising route for producing hydrogen and syngas for different applications. Samples were prepared by precipitation and impregnation techniques, characterized by several techniques and evaluated in the partial oxidation of methane in the range of 450–750 °C and 1 atm. It was found that aluminum affects the textural and catalytic properties of zirconia-supported nickel catalysts. The tetragonal phase of zirconia was stabilized by aluminum and gamma-alumina was also found in the aluminum-richest samples. Aluminum increased the porosity and the specific surface area of the solids. The catalytic activity also increased with the amount of aluminum in solids probably due to the stronger interaction of nickel with the support, which slowly generates active sites during the reduction step. The methane conversion and hydrogen selectivity increased with temperature, indicating no deactivation. The hydrogen to carbon monoxide molar ratio decreased due to aluminum but was not significantly affected by temperature. The coke produced was not harmful to the catalysts and aluminum affected its amount, although no simple relationship was found between these parameters. The most promising catalyst was the sample with aluminum to zirconium molar ratio of 2, which showed high activity and hydrogen selectivity and was stable under the reaction condition.

Thermogravimetric analyses and catalytic behaviors of zirconia-supported nickel catalysts for carbon dioxide reforming of methane

Carbon dioxide reforming of methane has been performed over zirconia-supported nickel catalysts. Temperature-programmed surface reactions (TPSR) with CH 4 and CO 2 have also been investigated over the catalysts by means of thermogravimetric analysis technique to explore the behavior of carbon formation during the reaction. The effect of the modification of the zirconia support on supported Ni catalysts reveals that the ceria-doped zirconia support exhibits high catalyst stability against high temperature aging test as well as high resistance to coke formation. Moreover, simultaneous alteration of the support and Ni surface of Ni/ZrO 2 with a Ce modifier and a Ca promoter led to a high performance catalyst, Ni-Ca/Ce-ZrO 2, revealing high activity as well as high stability in the CO 2 reforming of methane.

Effect of tetragonal ZrO 2 on the catalytic activity of Ni/ZrO 2 catalyst prepared from amorphous Ni–Zr alloys

In zirconia-supported nickel catalysts, the influence of the ZrO 2 phase on the catalytic activity for CO 2 methanation has been investigated by TPD and TPR measurements. Ni/ZrO 2 catalysts with various amounts of the tetragonal ZrO 2 polymorph were prepared from amorphous Ni–Zr alloys by an oxidation–reduction treatment. The fraction of tetragonal ZrO 2 in the Ni/ZrO 2 catalysts increased with increasing nickel content of the amorphous alloy precursors. The methanation activity of Ni/ZrO 2 was strongly influenced by the ZrO 2 phase change. The tetragonal zirconia-supported nickel catalysts showed a higher turnover frequency for the methanation reaction and a greater CO 2 adsorption than the monoclinic zirconia-supported nickel catalysts.

CO2 reforming of methane over zirconia-supported nickel catalysts, I. Catalytic specificity

CO2 reforming of methane is performed over zirconia-supported nickel catalysts. The catalysts show high activity toward CH4 and CO2 conversions. Over the high Ni loading catalyst, long-term performances without significant deactivations have been achieved at 1023 K for 30 h and 1123 K for 20 h, respectively. The effects of reduction and calcination temperatures on the catalytic activities are also examined.

The fischer-tropsch activity of nickel-zirconia

Zirconia supported nickel catalysts, prepared by co-precipitation and impregnation techniques, have been investigated for activity in the H 2/CO reaction. Co-precipitation is shown to produce a significantly more active catalyst with somewhat different selectivity to that produced by impregnation. Compared with most common supports, the co-precipitated catalyst shows not only greater selectivity to higher hydrocarbons, and a greater dependence of selectivity on H 2/CO ratio, but also greater activity. The products are predominantly olefins, as distinct from the n-paraffins obtained over Ni/TiO 2, which is known to have similar unusual activity.

Evidence of a strong metal-support interaction in zirconia-supported nickel catalysts

The reduction of Ni/ZrO2 catalysts above 700 K results in a decrease of hydrogen adsorption and of the catalytic activity toward ethane hydrogenolysis. O2 treatments followed by reduction at low temperature of samples reduced at high temperatures restore the normal properties. This behavior is similar to that observed for Ni/SiO2, Ni/TiO2 and is characteristic of a strong metal-support interaction similar to that observed on Pt/TiO2 catalysts. Paradoxically, it is shown that Ni does not interact strongly with ZrO2 since it is easily reduced and its reduction gives very large metallic particles.