Catalyst nickel/magnesia

Figure 3 shows FTIR spectra of CO adsorption on nickel magnesia catalysts. On Nim Mg(,2>oO and Ni/MgO catalysts, linear (2100-2000 cm ), bridge (2000-1850 cm ) and physisorbed Ni(CO)4 (2057 cm ) were mainly observed. In contrast, on NidojMgo O nickel monomer and dimer carbonyl species which are interacted with MgO were mainly observed as previously reported[10]. These species were increased with the CO pressure, therefore they are found to be formed via CO induced structural change. On NioojMgj O solid solution, Ni metal particles seem to be highly dispersive. 

Sidjabat, O. and Trimm, D.L. Nickel-magnesia catalysts for the steam reforming of light hydrocarbons. Topics in Catalysis, 2000, 11-12 (1), 279. 

In all cases, the evolution of the spinel-type phases towards the smichiometric forms, which takes place with a consistent segregation of oxide phases, destroys diis system and leads to considerable modifications in the properties of the oxides obtained. In particular, for the Ni-rich samples an increase in the reducibility of the main fraction of die Ni " ions was observed, with a behaviour similar to that of free NiO, while for Mg-rich samples the reduction of the Ni " " ions is further hindered by die formation of NiO/MgO solid solutions, with reduction temperatures very similar to those reprated for nickel-magnesia catalysts. 

Similar results were reported by Frusteri et of. for their nickel/magnesia and nickel/ceria catalysts [198]. At a reaction temperature of 650 °C, coke formation was significant under conditions of steam reforming. In the nickel/magnesia catalyst, which contained 15wt.% nickel, less than O.lwt.% carbon was formed within a 20-h test duration when operated under autothermal conditions. Consequently, no deactivation of the catalyst was observed. However, the 0/C ratio that was required to achieve this stable performance was rather high at 1.2, and the S/C ratio of 4.2 was also very high. Besides methane, small amounts of acetaldehyde were formed as a by-product. 

Figure 4.22 Hydrogen yields versus time over platinum/alumina and nickel/magnesia catalysts and a mixture of both pressure,...

Development of active and stable nickel-magnesia solid solution catalysts for COj reforming of methane... 

Nickel-magnesia solid solution catalysts were prepared by coprecipitating nickel acetate... 

The following nickel-carrier catalysts have been described nickel-kieselguhr,169 nickel-pumice,170 nickel-kieselguhr containing thorium oxide,171 nickel on magnesium oxide, barium oxide, or beryllium oxide,172 nickel on aluminum oxide,173 and nickel-zinc oxide-barium oxide-chromium oxide.174 Other carriers for nickel catalysts are active charcoal, silica, fuller s earth, and oxides such as magnesia, alumina, and bauxite. 

Nickel-kieselguhr catalysts with or without a small percentage of magnesia and thoria These catalysts were prepared by precipitation of the metals as carbonates from the solutions of their nitrates holding a suspension of B.D.H. kieselguhr. The carbonates were subsequently decomposed to the oxides in a current of air and the nickel reduced by hydrogen at 300°. 

Nickel-based catalysts on various carriers such as alumina, lanthana, magnesia and zinc oxide have been studied intensively for ethanol steam reforming [196]. 

The catalysts used in the process are essentially nickel metal dispersed on a support material consisting of various oxide mixtures such as alumina, silica, lime, magnesia, and compounds such as calcium aluminate cements. When the catalyst is made, the nickel is present as nickel oxide which is reduced in the plant converter with hydrogen, usually the 3 1 H2 N2 synthesis gas ... 

Ermakova and co-workers manipulated the Ni particle size to achieve large CF yields from methane decomposition. The Ni-based catalysts employed for the process were synthesized by impregnation of nickel oxide with a solution of the precursor of a textural promoter (silica, alumina, titanium dioxide, zirconium oxide and magnesia). The optimum particle size (10 0 nm) was obtained by varying the calcination temperature of NiO. The 90% Ni-10% silica catalyst was found to be the most effective catalyst with a total CF yield of 375 gcp/gcat- XRD studies by the same group on high loaded Ni-silica... 

The results with magnesia led us to a planned series of experiments with doped aluminas. Nickel was evaporated in vacuo onto the surface of grains of undoped or doped alumina or, alternatively, onto compact nickel. These preparations were then used as catalysts for the donor model reaction of formic acid dehydrogenation as above. Table II shows the results. 

Supported nickel catalysts catalyze steam-methane reforming and the concurrent shift reaction. The catalyst contains 15-25 wt% nickel oxide on a mineral carrier. Carrier materials are alumina, aluminosilicates, cement, and magnesia. Before start-up, nickel oxide must be reduced to metallic nickel with hydrogen but also with natural gas or even with the feed gas itself. 

Historical Development and Future Perspectives The Fischer-Tropsch process dates back to the early 1920s when Franz Fischer and Hans Tropsch demonstrated the conversion of synthesis gas into a mixture of higher hydrocarbons, with cobalt and iron as a catalyst [35, 36], Some 20 years earlier, Sabatier had already discovered the reaction from synthesis gas to methane catalyzed by nickel [37]. The FTS played an important role in the Second World War, as it supplied Germany and Japan with synthetic fuel. The plants used mainly cobalt catalysts supported on a silica support called kieselguhr and promoted by magnesia and thoria. 

Reaction 1.1 is known as steam reforming. The reaction conditions are fairly severe (>1000°C),and the structural strength of the catalyst is an important point of consideration. The catalyst employed is nickel on alumina, or magnesia, or a mixture of them. Other non-transition metal oxides such as CaO, Si02, and K20 are also added. 

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