A direct in situ observation of water-enhanced proton conductivity of Eu-doped ZrO2: Effect on WGS reaction

Abstract

Eu-doped ZrO2 solid solutions have been synthesized in order to prepare proton conductors as water-enhancer additives for the WGS reaction. Elemental characterization has been carried out revealing homogeneous dopant distribution resulting in fluorite-type solid solutions for Eu2O3 contents up to ~9 mol.%. Representative samples of the Eu-doped ZrO2 series have been analysed by Impedance Spectroscopy (IS) in inert, oxygen and wet conditions. The solid solution with 5 mol.% of Eu2O3 has presented the highest conductivity values for all tested conditions indicating an optimal amount of dopant. Moreover, the presence of vapour pressure results in an increment of the conductivity at temperatures lower than 300 ºC, meanwhile at higher temperatures the conductivity is the same than that in inert

Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction

“…The promoter effect of a Zr-based proton conductor physically mixed with a typical Pt-based catalyst has been demonstrated previously in our group [18][19][20]. These materials present oxygen vacancies capable of providing dissociated water and labile OH − species which enhance the proton conductivity and, therefore, the CO conversion.…”

“…It is worth underlining the low value obtained for the reaction order of water (0.36) in this work in relation to those found in the literature. This indicates an improvement in the water activation step that must be associated to the presence of the ionic conductor, which would provide a higher amount of the available dissociated water [18]. Consequently, the concentration of reactive OH species next to adsorbed CO is likely higher, decreasing the rate control level of this step.…”

“…A typical Pt catalyst supported on CeO 2 -doped Al 2 O 3 physically mixed with a Mo-and Eu-doped ZrO 2 proton conductor is used. Both the powdered and structured samples have been already prepared, characterized and catalytically tested in a previous work [18,20], showing on one side the water-promoter effect, and on the other side, the accomplishment of thin catalytic layers. This allows for the performance of a kinetic study free from mass diffusional limitations [26,27].…”

Operando DRIFTS-MS Study of WGS and rWGS Reaction on Biochar-Based Pt Catalysts: The Promotional Effect of Na

“…Cybulski et al [15] reported that the effect of the Na promoter on the WGS activity of Pt/Al 2 O 3 catalysts is to modify the local electronic properties of Pt and to create new H 2 O activation sites; this enhances the mobility of surface OH/H species to react with CO on the metallic Pt sites through a non-formate mechanism. The increase in the OH/H mobility on the support and the resulting increased concentration of H 2 O molecules at the metal-support interface have been highlighted by our group as being responsible for the enhancement of the WGS activity in Pt catalysts [11,48]. The group of Flytzani-Stephanopoulos [12][13][14] postulated the presence of Pt-O-(OH)-Na clusters on carbon nanotube walls as the active sites in the WGS reaction at 250-300 • C.…”

“…C 2018, 4, x FOR PEER REVIEW 13 of 16 [11,48]. The group of Flytzani-Stephanopoulos [12][13][14] postulated the presence of Pt-O-(OH)-Na clusters on carbon nanotube walls as the active sites in the WGS reaction at 250-300 °C.…”