Evaluation of dry reforming reaction catalysts via computational screening
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2018 Elsevier B.V. In this work, a computational screening method introduced in a previous report is employed to determine the optimal operating temperature and reactant feed ratio (CO2/CH4) for catalysts used in the dry reforming reaction of methane aiming for high reactivity and stability. It is found that changes in temperature would affect the rate of the main reaction, coke formation and coke removal, while changes in the feed ratio could modify the boundary dividing coke formation from removal zones. The increase in CO2/CH4 ratio is found to expand the coke removal zone. Four strategies based on stability and reactivity ratings (RT-S and RT-R) of the catalysts are proposed. Type 1, high RT-S and RT-R catalysts benefit from high T and high CO2/CH4 since these promote high rate of reaction and coke removal; Type 2, high RT-S but low RT-R catalysts need the same condition as Type 1 except that the maximum achievable reaction and coke removal rate are lower than Type 1; Type 3, low RT-S but high RT-R catalysts which are located in the coke formation zone should be treated first with high CO2/CH4 to shift them into the coke removal zone before applying the same treatment as in Type 1 by increasing the temperature. If the shift is not possible, the alternative is to operate at low T and low CO2/CH4 to avoid high coke formation; Type 4, low RT-S and RT-R catalysts exhibit the least reactivity and coke-resistance and as a result, the best operating condition that could be used is to operate them at low T and low CO2/CH4 to attain lowest rate of coke formation. The ratings concept extended to the interpretation of experimental data in order to predict the stability of the catalysts is demonstrated on four Pt supported (Pt/SiO2, Pt/TiO2, Pt/Cr2O3 and Pt/ZrO2) and Rh supported catalysts (Rh/TiO2, Rh/Al2O3, Rh/MgO and Rh/SiO2). For these catalysts, experimental apparent activation energies of methane consumption were used as input parameters to predict the rate of coke formation. For the Pt catalysts, the predicted trends of coke formation rate via the ratings concept are in good agreement with the measured carbon deposition rate trend calculated from temperature-programmed hydrogenation: Pt/SiO2 > Pt/Cr2O3 > Pt/TiO2 > Pt/ZrO2. However, in the case of Rh, the measured carbon deposition via the temperature-programmed oxidation could not be well predicted by our extended ratings concept. Thus, the ratings concept is an effective screening tool for reactive and stable DRR catalysts, however further development of the concept via the incorporation of more experimental parameters would make applications to general catalysts achievable.
