Sorption-Enhanced Water Gas Shift Reaction over a Mechanical Mixture of the Catalyst Pt/Ce_0.75Zr_0.25O₂ and the Sorbent NaNO₃/MgO

Abstract

Results of studying the sorption-enhanced water gas shift reaction over a mechanical mixture of grains of 5 wt % Pt/Ce_0.75Zr_0.25O₂ catalyst and 10 wt % NaNO₃/MgO sorbent are presented. It is shown that pure magnesium oxide sorbs virtually no СО₂ under model conditions, while its promotion with NaNO₃ substantially improves the dynamic sorption capacity in the 300–350°C range of temperatures with a maximum at 320°C. The catalyst shows high activity and selectivity in the water gas shift reaction for a model mixture (CO, 11.6; H₂, 61; H₂O, 27.4 vol %). The concentration of CO at the outlet from the reactor is less than 1 vol % in the 220–400°C range of temperatures (the minimum is 0.3 vol % at 240°C) with СН₄ at the temperatures below 320°C (0.61 vol % at this point). Using this sorbent in mixtures with a catalyst in the sorption-enhanced water gas shift reaction at 320°C substantially reduces its sorption capacity, due probably to the full conversion of NaNO₃ into Na₂CO₃ that is not completely decomposed at the stage of regeneration. This nevertheless allows the outlet СО and СН₄ concentrations to be halved, relative to values observed at this temperature in experiments with no sorbent: 6.1 × 10⁻⁴ and 8.2 × 10⁻² vol % per dry gas basis at the middle of the first adsorption cycle. Prospects for using this approach in the sorption-enhanced water gas shift reaction and the need for further studies on improving the capacity and stability of the presented sorbents are described.