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Nickel Promoted Catalysts In Reforming Of

NICKEL PROMOTED CATALYSTS IN REFORMING OF

n-BUTANE WITH CO2 OR H2O

M. Pańczyk, G. Giecko, W. Gac, S. Pasieczna, B. Stasińska, T. Borowiecki

Maria Curie-Skłodowska University, Faculty of Chemistry,

3 M.Curie-Skłodowska Sq., 20-031 Lublin, Poland

e-mail: mpanczyk@ hermes.umcs.lublin.pl

The reforming of hydrocarbons with carbon dioxide has recently gained a renewed interest [1-3]. The reforming of methane with CO2 provides synthesis gas with low ratio H2/CO, which can be utilised, e.g.: in oxo-synthesis, Fischer-Tropsch reaction, for production of important chemicals (including methanol, acetic acid, dimethyl ether) or for energy transmission systems. From the ecological viewpoint reforming of hydrocarbons with CO2 has attracted interest because of removal and utilisation of greenhouse gases [2,3].

The reforming of hydrocarbons with CO2, compared with steam reforming, has higher risk of catalyst deactivation due to carbon deposition. Therefore, one of the significant properties of good catalysts for this reaction is its resistance to coking. Several researchers have reported application of noble metal catalysts or modified nickel catalyst with higher resistance to coking e.g.: NiO-MgO [2,3] in CO2 reforming of CH4. Recently, it has been shown that nickel catalyst with small amounts of different promoters (Mo, W, Ba, and Ce) considerably improved their resistance to coking in the steam reforming of hydrocarbons [4,5].

The aim of the present paper was to compare the influence of some promoters (Mo, W, Ba, K, and Ce) on the properties of the nickel catalysts in the reforming of n-butane with CO2 or H2O.

Experimental

Investigations were carried out on the commercial catalysts Ni/a-Al2O3 of the steam reforming of natural gas, impregnated with a solution of appropriate promoter salts and denoted henceforth as Ni-Me(-) (the number in brackets denotes the amount of MeO in wt. %). The methods used for the preparation and measurements of the surface properties of these catalysts have

been described in detail elsewhere [4-5]. The rate of coking in the reforming of n-butane with CO2 was measured by the gravimetric method at the 450oC. Properties of the carbon deposits were investigated by the temperature programmed oxidation (TPO) method. Catalyst activity was determined in a gradientless reactor under pressure of 0.1 MPa at 450 and 500oC, respectively.

Results

The introduction of Mo, W, Ba and K practically did not change the total or active surface area. In the contrary, a catalyst promoted by cerium exhibits a significant increase in total and active surface areas [5].

Catalysts with the addition of K, Mo, W and Ba undergo coking in the CO2 reforming of n-butane slower than Ni/a-Al2O3 ones. The coking rate, calculated per unit of nickel surface area decreases as follows: Ni > Ni-Ba > Ni-W > Ni-Ce > Ni-K > Ni-Mo. The resistance to coking of the catalysts depends on the reagent ratio used (CO2:butane).

Fig. Influence of the reagent ratio

CO2:C on coking of Ni (‚) and

Ni-Mo (0.5) (¨) catalysts

The TPO method with oxygen or CO2 did not reveal considerable differences between coke deposits on the examined catalysts after reforming of n-butane with CO2 or H2O.

Activity of promoted catalysts in the steam reforming of methane decreases as follows [5]:

Ni-Ce > Ni > Ni-W, Ni-K > Ni-Ba > Ni-Mo

The investigations of the activity done at 450 and 500oC at reagents ratio CO2:C = 3:1 (at the high degree of conversion) exhibit that all the catalysts undergo coking at these conditions. The smallest amount of the carbon deposit was formed in the reaction on Ni-Mo catalysts. It was found that at 500oC, over the Ni-Mo(2.0) catalysts the carbon deposit was not formed at reagents ratio CO2:C ³ 5.