Water–Gas Shift Reaction on Pt/Ce_1–xTi_xO_2−δ: The Effect of Ce/Ti Ratio

Abstract

Pt nanoparticles (1.2−2.0 nm size) supported on Ce 1−x Ti x O 2−δ (x = 0, 0.2, 0.5, 0.8, and 1.0) carriers synthesized by the citrate sol−gel method were tested toward the water−gas shift (WGS) reaction in the 200−350 °C range. A deep insight into the effect of two structural parameters, the chemical composition of support (Ce/Ti atom ratio), and the Pt particle size on the catalytic performance of Pt-loaded catalysts was realized after employing in situ X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and HAADF/STEM, scanning electron microscopy (SEM), in situ Raman and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies under different gas atmospheres, H 2 temperature-programmed reduction (H 2 -TPR), and temperature-programmed desorption (NH 3 -TPD and CO 2 -TPD) techniques. The 0.5 wt % Pt/Ce 0.8 Ti 0.2 O 2−δ solid (d Pt = 1.7 nm) was found to be by far the best catalyst among all the other solids investigated. In particular, at 250 °C the CO conversion over Pt/Ce 0.8 Ti 0.2 O 2−δ was increased by a factor of 2.5 and 1.9 compared to Pt/TiO 2 and Pt/CeO 2 , respectively. The catalytic superiority of the Pt/Ce 0.8 Ti 0.2 O 2−δ solid is the result of the support's (i) robust morphology preserved during the WGS reaction, (ii) moderate acidity and basicity, and (iii) better reducibility at lower temperatures and the significant reduction of "coking" on the Pt surface and of carbonate accumulation on the Ce 0.8 Ti 0.2 O 2−δ support. Several of these properties largely influenced the reactivity of sites (k, s −1 ) at the Pt−support interface. In particular, the specific WGS reaction rate at 200 °C expressed per length of the Pt−support interface (μmol CO cm −1 s −1 ) was found to be 2.2 and 4.6 times larger on Pt supported on Ce 0.8 Ti 0.2 O 2−δ (Ti 4+ -doped CeO 2 ) compared to TiO 2 and CeO 2 alone, respectively.

Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis

“…This in turn resulted in the H 2 evolution rate of 3 wt% Pt/TiO 2 , which was relatively greater than that of 3 wt% Pt/Al 2 O 3 . Other studies found that TiO 2 , as a support material, improves Pt O 2 reduction activity by assisting mechanisms such as reactant surface diffusion and O 2 spillover [135–137]. Furthermore, Pt/TiO 2 showed similar performance to Pt/C in H 2 -fuel cell operated at 60°C and 0.8 V (Figure 5) [136].…”

Effect of support composition on the origin and reactivity of carbon formed during dry reforming of methane over 5wt% Ni/Ce1−xMxO2−δ (M=Zr4+, Pr3+) catalysts

“…Details of the preparation procedures employed can be found elsewhere [25][26][27]. The metal precursors used were Ce(NO 3 ) 3 ·6H 2 O, Pr(NO 3 ) 3 ·6H 2 O and ZrO(NO 3 ) 2 .xH 2 O (Sigma-Aldrich).…”

Highly dispersed Pt+ on Ti Ce(1−)O2 as an active phase in preferential oxidation of CO

“…The latter may be related to the partial reduction of Ti to Ti 3+ or to the incorporation of cerium in the titania lattice. If we consider that cerium (1.5 Pauling units) is less electronegative than titanium (1.1 Pauling units), the substitution of titanium atoms by cerium in the titania lattice will produce an enhanced electron density on Ti, and consequently, a decrease in binding energy [34]. When the Ce 3d core level ( Figure S3) is considered, six peaks corresponding to the three pairs of spin-orbit doublets of Ce(IV) and two peaks corresponding to the doublet of Ce(III) are observed.…”