Abstract
<p>Present day energy needs of mankind are strongly dependent on the combustion of fossil fuels and other carbonaceous materials. The combustion reaction is accompanied by simultaneous production of gaseous pollutants like CO, NO<sub>x</sub> and SO<sub>2</sub>. In the catalytic combustion, the advantages are two fold: i. The combustion efficiency will be higher and this results in the higher energy realization and ii. The operating temperatures being much lower the emission level of the pollutants also will be greatly reduced. In this study, thermogravimetric analysis (TGA) has been used in following the non-isothermal kinetics of the combustion using two different models. In the present study an attempt has been made to evaluate from the thermogravimetry, the kinetic parameters for carbon combustion in oxygen and their dependence on the catalyst present in the system. Four different supported systems have been used for the oxidation. Similarly, four different pure carbon materials, differing in their surface areas and crystallinity, have been investigated. For evaluating the catalytic activity, two rate equations have been applied for the isothermal oxidation kinetics of the carbon samples. The catalytic activity on the oxidation of carbon has been observed in the form of lower ignition temperature and a decrease in the energy of activation. The possible role of oxygen spill-over is discussed.</p>
Highlights
More than three fourth of the world’s energy needs is derived from the fossil fuels, namely, oil and gas With the re-emphasis on coal, as an important source of energy, numerous studies have been initiated and focused on the improvement in coal gasification and increasing the efficiency in coal combustion through catalytic processes [1]
It has been shown that supported noble metal catalysts contribute favourably for the carbon combustion
The presence of in situ catalyst, present originally in the carbon, and the one mixed externally can have different reaction models, which will lead to different kinetic parameters
Summary
More than three fourth of the world’s energy needs is derived from the fossil fuels, namely, oil and gas With the re-emphasis on coal, as an important source of energy, numerous studies have been initiated and focused on the improvement in coal gasification and increasing the efficiency in coal combustion through catalytic processes [1]. The concentration levels of the gas pollutants can be drastically reduced by increasing the efficiency of the combustion Both noble metal catalysts (platinum group of metals) [2], and metal oxide catalysts (mainly of alkali and alkaline earth metals)[3] have been studied in coal combustion. Normal expectation of a decrease in Ea during catalysis and the other school of thinking is that the Ea remains constant and the increased rate is explained on the basis of increase in the value of the pre-exponential factor or Arrhenius factor, “A” in the equation (7) This means that the number of active sites increased during the combustion. Where A is the frequency factor, φ is the heating rate, Ea is the energy of activation and α is the degree of conversion [10] This equation is applicable for a reducing sphere model. About 4-5 mg of catalyst premixed carbon sample was taken for each run and combusted until no further weight loss was observed
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