Surface Protonics Promotes Catalysis

Abstract

Catalytic steam reforming of methane for hydrogen production proceeds even at 473 K over 1 wt% Pd/CeO2 catalyst in an electric field, thanks to the surface protonics. Kinetic analyses demonstrated the synergetic effect between catalytic reaction and electric field, revealing strengthened water pressure dependence of the reaction rate when applying an electric field, with one-third the apparent activation energy at the lower reaction temperature range. Operando–IR measurements revealed that proton conduction via adsorbed water on the catalyst surface occurred during electric field application. Methane was activated by proton collision at the Pd–CeO2 interface, based on the inverse kinetic isotope effect. Proton conduction on the catalyst surface plays an important role in methane activation at low temperature. This report is the first describing promotion of the catalytic reaction by surface protonics.

Catalytic Reaction Assisted by Plasma or Electric Field

“…To assess kinetic changes by the imposing the electric field from the viewpoint of surface adsorbate, we conducted investigations using operando ‐diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. As depicted in Figure , the peak assigned to rotation of adsorbed water (855 cm −1 ) was observed only when the electric field was imposed to M/CeO 2 catalysts with methane and water at a low temperature: 473 K . This peak is regarded as having a strong relation with the Grotthuss mechanism, a widely known mechanism of proton conduction.…”

“… Operando –DRIFTS spectra in the O–H rotation region over CeO 2 or 1wt%Pd/CeO 2 with and without an electric field (5 mA): flow, CH 4 :H 2 O:Ar=1:2:62; total 65 SCCM.…”

Effects of metal cation doping in CeO2 support on catalytic methane steam reforming at low temperature in an electric field

“…Our earlier studies [12][13][14][15][16][17][18][19] revealed that application of an electric eld (EF) to Pd, Pt, or Rh catalyst supported on CeO 2 enabled MSR to proceed even at low temperature such as 473 K. Especially in a lower temperature region (T < 600 K), CH 4 conversion exceeded the thermodynamic equilibrium. 15 Furthermore, various experiments were conducted to investigate the reaction mechanism with EF, and the following results were obtained. Firstly, to observe changes of the surface species with EF, operandodiffuse reectance infrared Fourier transform (DRIFT) measurements using Pd/CeO 2 catalyst were conducted.…”

“…Firstly, to observe changes of the surface species with EF, operandodiffuse reectance infrared Fourier transform (DRIFT) measurements using Pd/CeO 2 catalyst were conducted. 15 When EF was applied, the peak at 855 cm À1 was observed, which strongly relates to proton conduction via H bond of water, so-called the Grotthuss mechanism. Furthermore, peak of the O-H stretching bond shied to lower wavenumber, which indicated that the water is activated by applying EF.…”

Combustion Suppression in Tri-reforming of Methane over Ni Supported Catalysts at Low Temperatures in Electric Field

“…Consequently, imposing the electric field to the catalyst bed enabled proceeding of the low temperature reaction at the temperatures of the exhaust gas (473-673 K). From the results of operando-diffuse reflectance infrared Fourier transform spectroscopy (operando-DRIFTS), proton hopping via adsorbed water on the catalyst surface occurred with the electric field, known as the Grotthuss mechanism, and the surface protonics by the application of electric field served an important role in the enhancement of SRM 35) . Referring these results, this mechanism would be applied to TRM because of the existence of H2O as a reactant gas.…”