Low-temperature water–gas shift on Pt/Ce0.5La0.5O2 − δ: Effect of support synthesis method

Abstract A series of 0.5 wt% Pt/Ce 0.5 La 0.5 O 2 −  δ (Ce:La = 1:1) catalysts, the supports of which were prepared by different methods, namely: (i) sol–gel using citrate or oxalate as complexing agent, (ii) pechini, and (iii) urea co-precipitation, were investigated for the first time towards the water–gas shift (WGS) reaction in the 250–350 °C range and 1 atm total pressure. Towards a better understanding of the effect of support synthesis method on the intrinsic kinetic rate of WGS expressed per gram of catalyst (μmol CO g −1  s −1 ) or per length of the perimeter of Pt-support interface (μmol CO cm −1  s −1 ), a suite of various characterisation methods such as: in situ Raman, temperature-programmed techniques (TPD-H 2 , TPD-NH 3 , TPD-CO 2 ), powder XRD, and oxygen storage capacity (OSC) measurements were applied. The intrinsic kinetic rate of WGS (μmol CO g −1  s −1 ) was correlated with the concentration of the active “carbon-containing” (C-pool) and “hydrogen-containing” (H-pool) reaction intermediates formed within a reactive zone (Δ x , A) around each Pt nanoparticle (1.2–1.5 nm), parameters that were estimated via SSITKA and non steady-state transient isotopic and titration with water operando experiments. The urea co-precipitation method (U) resulted in the formation of a Ce 1 −  x La x O 2 −  δ solid solution with different composition (Ce:La atom ratio) than that formed by the other synthesis methods, which may be the main reason for Pt/Ce 0.5 La 0.5 O 2 −  δ (U) to exhibit the highest by far CO conversion and kinetic rate towards the WGS compared to the other supported Pt catalysts. The same method (U) resulted in the formation of La 2 O 3 as opposed to the other methods. However, this was not considered as the main reason for explaining the higher activity of Pt supported on Ce 0.5 La 0.5 O 2 −  δ (U) compared to the other carriers. The Ce 0.5 La 0.5 O 2 −  δ (U) was also found to possess the highest surface acidity and basicity compared to the other supports but lower OSC (μmol g −1 ) (by more than 30% in the 250–550 °C range) than Ce 0.5 La 0.5 O 2 −  δ prepared by the citrate sol–gel method, in harmony with the lower content of O vacancies in Ce 0.5 La 0.5 O 2 −  δ (U) as evidenced by Raman studies. Transient DRIFTS formate (HCOO–) decomposition kinetic experiments towards CO 2 and H 2 formation have illustrated the importance of the presence of Pt and support composition.