Active sites and reaction mechanisms for deuteration of acrolein on TiO2-, Y2O3-, ZrO2-, CeO2 and Na/SiO2- supported platinum catalysts

Abstract

Acrolein–deuterium reactions on low-and high-temperature-reduced Pt/TiO₂, Pt/Y₂O₃, Pt/ZrO₂ and Pt/CeO₂ in comparison with Pt/SiO₂ and Na/Pt/SiO₂ have been investigated in order to understand promotion in supported-metal catalysis by isotope tracing and infrared studies. The products on Pt/TiO₂, Pt/Y₂O₃, Pt/ZrO₂ and Pt/CeO₂ were propanal and allyl alcohol but only propanal was formed over Pt/SiO₂ and Na/Pt/SiO₂. The similarity of the d-electron density of platinum in high-temperature-reduced Pt/TiO₂, Pt/Y₂O₃, Pt/ZrO₂ and Pt/CeO₂, and Na/Pt/SiO₂ was not reflected in the reaction profiles, suggesting the contribution of the periphery of suboxides on Pt particles and/or the boundary/interface of Pt particles on support. η⁴-Adsorbate was suggested to be an intermediate for allyl alcohol formation on Pt/TiO₂ and Pt/Y₂O₃ by IR spectra and isotope distributions in the products. On Pt/TiO₂, Pt/Y₂O₃, Pt/ZrO₂ and Pt/CeO₂ reduced at both low and high temperatures, the active sites and reaction environments (surface D/H ratio) for the formations of propanal and allyl alcohol were different for the two products. The reaction mechanisms are discussed in connection with the promoting effects and the SMSI state of catalysts.