Zirconia-supported nickel catalyst

Figure 1. Temperature prograimned reduction of silica- and zirconia-supported catalysts containing nickel and sulfate, a) silica-series b) zirconia-series.

Amorphous Ni-(40-x) at% Zr-x at% RE (x = 0, 1, 5 and 10 RE = Y, Ce and Sm) alloy ribbons of about 1 mm width and about 20 pm thickness were prepared by a single-roUer melt spinning method. The structure of the alloys prepared was confirmed by X-ray diffraction with Cu K radiation. The amorphous alloy ribbons were oxidized at 773 K in air for 5 hours and then reduced at 573 K imder flowing hydrogen for 5 hours. During this treatment the amorphous aUoys transformed to nickel catalysts supported on zirconia or zirconia-rare earth element oxides. 

The nano-grained nickel catalysts supported on zdrconia or zirconia-rare earth element oxides are prepared by the oxidation-reduction pretreatment of amorphous Ni-Zr-rare earth element alloys. The conversion of carbon dioxide to methane on the catalyst prepared from amorphous Ni-40Zr alloy is improved by the addition of 5 at% or more rare earth elements (Y, Ce and Sm). 

Common catalyst compositions include oxides of chromium or molybdenum, or cobalt and nickel metals, supported on silica, alumina, titania, zirconia, or activated carbon. 

A marked effect of the Ce02/Zr02 composition (in samples containing 40 wt.% NiO) on the catalytic activity was noticed. The catalysts with Ce Zr =1 1 (6A) were not only more active (than 7A and 8A) but were also stable during the reaction. Sample 8A containing no zirconia in the support showed a low activity. The NiO crystallite size (Table 11.2) in these compositions varied in the order 7A < 6A < 8A. It may be recalled that on ceria-based catalysts the crystallite size of nickel metal was similar to that of NiO. The higher activity for 6A than 7A indicates that in addition to accessibility of... 

F-T Catalysts The patent literature is replete with recipes for the production of F-T catalysts, with most formulations being based on iron, cobalt, or ruthenium, typically with the addition of some pro-moter(s). Nickel is sometimes listed as a F-T catalyst, but nickel has too much hydrogenation activity and produces mainly methane. In practice, because of the cost of ruthenium, commercial plants use either cobalt-based or iron-based catalysts. Cobalt is usually deposited on a refractory oxide support, such as alumina, silica, titania, or zirconia. Iron is typically not supported and may be prepared by precipitation. 

Catalysts for low-temperature gasification include combinations of stable metals, such as rathenium or nickel bimetallics and stable supports, such as certain titania, zirconia, or carbon. Without catalyst the gasification is limited (Krase et al., 2000). Sodium carbonate is effective in increasing the gasification efficiency of cellulose (Minowa et al., 1997). Likewise, homogeneous, alkali catalysts have been employed for high-temperature supercritical water gasification. 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170... 

This new single-step synthesis unites the simplicity of preparation and lower production costs, with the outstanding properties of the final catalysts. By the single-step procedure proposed here, deposition of dispersed nanoparticles of noble metals on ceramic supports with customised textural properties and shape was achieved. Noble metals including platinum, palladium, rhodium, ruthenium, iridium, etc. and metal oxides including copper, iron, nickel, chromimn, cerium oxides, etc on sepiolite or its mixtures with alumina, titania, zirconia or other refractory oxides have been also studied. 

Mo increases the activity of almost twice in the case of alumina and titania but was almost four times higher for zirconia. Among the various catalysts, the highest activity was measured for titania supported with Mo(CO)6 pre-cursor. The characterization measurements suggest that the high activity of Ti02-supported catalysts can be related to better homogeneity in coordinatiOTi of Mo species on titania than on alumina or zirconia. Deposition of nickel over studied supports resulted in the formation of different surface species. Independent of the support applied, the presence of nickel enhanced the reducibility of molybdenum and Ni-Mo-O species and in consequence the catalytic activity of the WGS reaction. 

A mixture of Ni°/NiO, produced by thermal decomposition of nickel acetate, dispersed on either silica or cordierite supports, was found to be catalytically active for the decomposition of methane without the need for any pre-treatment. Other authors used Ni catalysts supported on zirconia to produce H2 and a high yield of multiwalled carbon nanotubes. Raman spectroscopy suggested that carbon nanotubes formed at temperatures higher that 973 K had more graphite-like structure than those obtained at lower temperatures. They also reported that feed gas containing methane and hydrogen caused slow deactivation of the catalyst, and carbon yield increased with increasing Hg partial pressure in the feed gas. For a commercial Ni catalyst (65% wt Ni supported on a mixture of silica and alumina) it was found that catalyst deactivation depends on the... 

Hoekman et al. [40] studied CO2 methanation reaction over Haldor Topspe commercially available methanation catalysts consisting of Ni and NiO on an alumina substrate with total nickel loading of 20-25% and an operating temperature range of 190-450 C in an extruded ring-shaped catalyst. Approximately 60% conversion of CO2 was observed at r= 300-350°C and stoichiometric CO2/H2 ratio. Aldana et al. [41] found that Ni over ceria-zirconia (prepared by sol-gel synthesis) shows an initial COj activity of almost 80%, with a CH4 selectivity of 97.3%, decreasing down to 84.7% after 90 hours of reaction. By IR operando analysis, they found that for Ni-ceria-zirconia catalysts the main mechanism for CO2 methanation does not require CO as reaction intermediate and the mechanism is based on CO2 adsorption on weak basic sites of the support. 

Apart from the degree of reduction affecting overall performance, the nature of the support is also crucial in determining final activity. For supported molyb-dena catalyst, alumina and titania support materials provide best performance. Silica, zirconia, chromia, and zinc oxide are also good support materials, although they produce less active catalysts. Inactive catalysts can be readily synthesized by supporting molybdena upon cobalt oxide, nickel oxide, magnesium oxide, or tin oxide. To date, no correlation between the acidity of the support material and cataljdic activity has been found (304). 

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