(455e) Shape, Acid-Base Properties and Crystal Plane Effects of Nanoscale CeO2 On the Activity of Ru-CeO2 Catalysts for the Water Gas Shift Reaction

The shape, acid-base properties and crystal plane of ceria support play essential roles on the Ruthenium species' activities for the water-gas shift reaction. In this study, there is two-step preparation process which includes solution-based hydrothermal synthesis of single-crystalline and uniform nanopolyhedra, nanorods, and nanocubes of CeO₂ and the sequential introduction of Ru through 4 kinds of methods: impregnation (IPG) in acid environment, IPG followed by NaCN leaching treatment and deposition/ precipitation (DP) using ammonium bicarbonate and sodium hydroxide as basic source. Ce supports have different exposed crystal planes: {111} and {100} for polyhedra, {110} and {100} for rods, and {100} for cubes. The activities of Ru/CeO₂ using IPG follow the order of rod> cube> polyhedra. Ru loaded on rod-like CeO₂ shows the best activity in acid environment and the worst ability under basic surrounding while on polyhedra-like CeO₂ shows the reverse behavior, which indicate polar plane {111} of CeO₂ facilitates and reduces Ru activation under acid and base surrounding respectively while the capacity of nonpolar plane {110} of CeO₂ is on the contrary. Ru/CeO₂ using DP and ammonium bicarbonate shows alkalescence and achieves the highest CO conversion of 97.3% at 350 °C for WGS among all the catalysts. NaCN leaching has great effect on the activity of Ru/CeO₂ nanocube. After the treatment, the CO conversion for Ru/CeO₂ nanocube increases from 14.2% to 94.0% at 300°C. The effect of NaCN on the crystal plane follows the order of {10 0}> {111}> {110}. The CH₄ formation rate decreases with the increment of pH value. The materials were characterized by BET, XRD, TEM and TPR-H₂. The XRD patterns show the sizes of Ru loaded on diverse shapes of CeO₂ following the order of nanocube> nanopolyhedra> nanorod and microstrain of Ru/CeO₂ has the reverse order which indicates rod with nonpolar plane {110} has the coarsest surface and cube with polar plane {100} has the smoothest one. TPR-H₂ tests indicate Ru dopant in the bulk of CeO₂.