Search

Abstract: Water–gas shift reaction was studied over two nanostructured Cu x Ce1−x O2−y catalysts: a Cu0.1Ce0.9O2−y catalyst prepared by a sol–gel method and a Cu0.2Ce0.8O2−y catalyst prepared by co-precipitation method. A commercial low temperature water–gas shift CuO–ZnO–Al2O3 catalyst was used as reference. The kinetics was studied in a plug flow micro reactor at an atmospheric pressure in the temperature interval between 298 and 673K at two different space velocities: 5.000 and 30.000h−1, respectively. Experimentally estimated activation energy, E af, of the forward water–gas shift reaction at CO/H2O=1/3 was 51kJ/mol over the Cu0.1Ce0.9O2−y , 34kJ/mol over the Cu0.2Ce0.8O2−y and 47kJ/mol over the CuO–ZnO–Al2O3 catalyst. A simple rate expression approximating the water–gas shift process as a single reversible surface reaction was used to fit the experimental data in order to evaluate the rate constants of the forward and backward reactions and of the activation energy for the backward reaction. [Copyright &y& Elsevier]

The kinetics of CO oxidation in excess hydrogen over a nanostructured Cu0.1Ce0.9O2−y catalyst prepared by a sol–gel method was studied under simulated preferential oxidation (PROX) reactor conditions. Reaction temperature was varied between 45 and 155 °C. The partial pressures of CO and O2 in 0.5 bar excess of H2 and He as a balance gas were varied between 0.001 and 0.025 and between 0.001 and 0.05 bar, respectively. The catalyst was found to be 100% selective in the temperature range from 45 to 90 °C. In this temperature range, the kinetics of the reaction was found to follow the redox mechanism represented by the Mars and van Krevelen type of rate equation. Kinetic parameters of the reaction calculated on the basis of this rate equation were found to be as follows: apparent activation energy for CO oxidation step, 57.2 kJ/mol, and for the catalyst reoxidation step, 60.2 kJ/mol. The observed reaction rate at the 0.01-bar CO partial pressure and stoichiometric O2 partial pressure at 90 °C was 2.7×10−6 mol/gcat s. The steady-state experimental data could be regressed almost equally well with the modified Langmuir–Hinshelwood model introduced by Liu et al. However, the transient experiments performed in our study reveal that lattice oxygen could be involved even at low reaction temperatures, thus favoring the use of a steady state Mars and van Krevelen kinetic model. [Copyright &y& Elsevier]

Abstract: Cu x Ce1−x O2−y mixed oxide catalysts were prepared by different preparation procedures: co-precipitation, the sol–gel peroxide route, and the sol–gel citric acid-assisted route. The resulting solids were investigated by means of XRD, BET, H2 and CO temperature-programmed reduction (TPR), oxidation (TPO) and desorption (TPD) analyses, and N2O pulse selective reaction. It was confirmed that H2 (CO) consumed for complete reduction of well-dispersed and bulk-like CuO phases to Cu0, reduction of surface ceria and H2 (CO) adsorption on the catalyst surface contribute to the total H2 (CO) consumption. Among catalysts examined, the Cu0.15Ce0.85O2−y mixed oxide sample prepared by means of co-precipitation method exhibits the highest activity and stability for water–gas shift (WGS) pulse reaction in the range of employed operating conditions. WGS activity of copper–ceria mixed oxide catalysts is determined by the extent of surface ceria reduction and dispersion of copper species. [Copyright &y& Elsevier]