Nora N. Nichio

Stability promotion of Ni/α-Al2O3 catalysts by tin added via surface organometallic chemistry on metals: Application in methane reforming processes

Abstract This paper reports the effect of selective tin addition to nickel catalysts via a controlled technique (surface organometallic chemistry on metals, SOMC/M), and the performance of the resulting systems in methane reforming processes: partial oxidation (POM), CO 2 reforming (R) and mixed (CO 2 +O 2 ) reforming (MR), with particular emphasis on their resistance to coke formation. It is demonstrated that SOMC/M techniques allow to obtain well-defined bimetallic phases in a controlled way. It is found that there is a range of tin concentrations (0.01–0.05xa0wt.%) for which the stability of the bimetallic catalysts is markedly enhanced with respect to nickel catalyst, without affecting either the activity level or the selectivity to syngas. These facts are explained in terms of a more demanding nature in size of the active sites needed for carbon formation reaction, when compared to methane activation reaction to synthesis gas.

A semiempirical theoretical study of Ni/α-Al2O3 and NiSn/α-Al2O3 catalysts for CH4 reforming

Abstract In order to investigate the nature of Ni supported on α-Al 2 O 3 and its modification with Sn in methane reforming reactions, a theoretical study was carried out. A molecular orbital approach of the extended Huckel type was performed to obtain the formation energies of postulated adsorbed and reacted species of CH 4 , H 2 O, O 2 and CO 2 on a model of Ni and NiSn surfaces resembling Ni/α-Al 2 O 3 and NiSn/α-Al 2 O 3 . Three different known planes of fcc Ni were considered: (1xa01xa01), (0xa00xa01) and (1xa01xa00). Possible adsorbed and reacted species of CH 4 , H 2 O, O 2 and CO 2 on Ni with Ni all around, Sn fully rounded by Ni and Ni near a Sn were discussed using reaction energies. The interaction NiSn in Ni clusters has been claimed to be of interstitial substitution-type in alloys. The (1xa01xa01) plane is the most reactive for adsorption. In agreement with experimental work, methane activation on Ni is the controlling step in reforming of methane with CO 2 (R), partial oxidation with O 2 (POM) and mixed reforming using CO 2 and O 2 (MR). Sn near a Ni changed the adsorption properties of it. Favoured reactions for Sn rounded by Ni on (0xa00xa01) and (1xa01xa01) planes are the adsorption of CO 2 and formation of a Snue5f8CO bond and the generation of Snue5f8H bonds from methane and water dissociation. The theoretical results are discussed in the context of previously published experimental data.

Ni/Al2O3 catalysts for syngas obtention via reforming with O2 and/or CO2

The performance of Ni supported catalysts is analyzed for syngas obtention from methane. Catalysts were prepared employing two different precursor compounds (nickel nitrate and nickel acetylacetonate) and two supports (α-Al 2 O 3 and α-Al 2 O 3 modified by the addition of aluminium). The samples were tested in partial oxidation (POM), CO 2 reforming (R) and a mixed reforming (MR) reactions. It was observed a beneficial effect of the modification of the support upon the activity and stability. The catalyst prepared with the organometallic precursor and the modified support showed the highest stability. The presence of CO 2 as a reactant causes a diminution of the catalytic activity and the modification of H 2 /CO ratio.

Influence of the support and precursor compounds on the sintering and coking of supported nickel oxyreforming catalysts

In this paper the activity, selectivity and mainly stability of nickel catalysts in the oxyreforming reaction are analyzed. The catalysts were prepared employing different precursors (nickel nitrate and nickel acetylacetonate) on α-Al2O3 and α-Al2O3 modified by a layer of aluminium oxide. The catalytic sample obtained from nickel acetylacetonate on the modified support showed the best stability.