Abstract:
The present study deals with the properties of nickel catalysts used for the
reaction between steam and hydrocarbon (methane) into mixtures of hydrogen,
carbon monoxide and carbon dioxide. Such type of reaction is normally called
steam reforming or catalytic steam reforming. In our country steam reforming of
methane is very important particularly in fertilizer industries as it is one of
the reactions that are involved in ammonia synthesis. The purpose of this paper
is to study the physical and chemical properties of reforming catalyst in order
to interpret the activity and selectivity of a particular catalyst. In this
research work three series of catalysts were prepared using co-precipitation
technique and were systematically investigated. The active component of the
catalyst was nickel supported by alumina and promoted by chromium/manganese. The
samples of the third series were consisted of only nickel and aluminum oxides.
The structural orientation of Ni-Cr-AI and Ni-Nn-AI catalytic systems prepared
by using different precipitants (KOH/Urea) was assessed on the basis of activity
testing data, XRD patterns, TPR results and chemisorption data. The first seriesof
samples were used for this study. The second series of samples were prepared
to study the effect of composition on the activity of the catalysts by increasing
the space velocity of reacting gas since the activity of the samples was as high
as 22% per g of catalyst at low space velocity regardless of composition. The
calcination temperature of the samples of third series was varied to study the
influence of calcination temperature on the activity and XRD pattern. The
activity testing gives arbitrary results. Therefore, conversion of the reactants
can not be correlated to the active metal loading of the catalysts. The position
and intensity variation of the XRD patterns show that the structure and
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crystallinity of each sample varies considerably from the other. The TPR data and
chemisorption results show different reduction temperatures and different
hydrogen uptakes for different prepared samples. Thus the results of this
investigation are in agreement in one point, that is, each sample is unique from
structural point of view. Furthermore, the prepared catalyst samples are observed
to be consisted of various combination of free NiO, y A1ZO], MnO or chromium
oxide of variable valency and a variety of multimetallic compounds. As the
calcination temperature increases, the samples become more crystalline and
activity as well as stability of the samples increase.
