Pd–In2O3 interaction due to reduction in hydrogen: Consequences for methanol steam reforming

Abstract

Two different Pd/In2O3 samples including a thin film model catalyst with well-defined Pd particles grown on NaCl(001) supports and a powder catalyst prepared by an impregnation technique are examined by Electron Microscopy, X-ray Diffraction and catalytic measurements in methanol steam reforming in order to correlate the formation of different oxide-supported bimetallic Pd-In phases with catalytic activity and selectivity. A PdIn shell around the Pd particles is observed on the thin film catalyst after embedding the Pd particles in In2O3 at 300 K, likely because alloying to PdIn and oxidation to In2O3 are competing processes. Increased PdIn bimetallic formation is observed up to 573 K reduction temperature until at 623 K the film stability limit in hydrogen is reached. Oxidative treatments at 573 K lead to decomposition of PdIn and to the formation of an In2O3 shell covering the Pd particles, which irreversibly changes the activity and selectivity pattern to clean In2O3. PdIn and Pd2In3 phases are obtained on the powder catalyst after reduction at 573 K and 673 K, respectively. Only CO2-selective methanol steam reforming is observed in the reduction temperature range between 473 K and 573 K. After reduction at 673 K encapsulation of the bimetallic particles by crystalline In2O3 suppresses CO2 formation and only activity and selectivity of clean In2O3 are measured.

Origin of different deactivation of Pd/SnO2 and Pd/GeO2 catalysts in methanol dehydrogenation and reforming: A comparative study

“…As already established in our previous work [17][18][19][20], a two-way approach will be followed to assess structureactivity/selectivity correlations in the Pd-Sn and Pd-Ge systems. For this reason, thin film model systems prepared on NaCl(001) single crystals will be compared to catalytically more realistic impregnated Pd systems.…”

“…For data evaluation, the relative intensities of the mass spectrometer signals were converted into partial pressures via external calibration using gas mixtures of defined partial pressures. For simplicity, all catalytic results are usually plotted as partial pressure change versus temperature [20]. …”

“…PdZn/ZnO [17], Pd 2 Ga and Pd 5 Ga 2 /Ga 2 O 3 [18,19] and PdIn/In 2 O 3 [20]) as selective catalysts in methanol steam reforming and of the catalytic and structural properties of the respective pure supporting oxides [21][22][23][24], the aim of this work was to extend these studies to the corresponding Pd/SnO 2 and Pd/GeO 2 systems. This is partly motivated by the known properties of the Pd-Sn systems but also by the fact that studies on pure SnO 2 and GeO 2 specifically revealed a high CO 2 selectivity of SnO 2 [24,25] and a very low activity and selectivity of GeO 2 in methanol steam reforming [24].…”

High-temperature steam reforming of methanol over ZnO–Al2O3 catalysts

“…CeO 2 can hinder the Cu sintering and enhance the thermal stability of catalysts [14]. Apart from Cu-based catalyst, Pd-based catalyst is another promising low temperature steam reforming catalyst [16][17][18][19][20][21][22]. Iwasa et al [20] first found Pd/ZnO had good activity, CO 2 selectivity and thermal stability for low temperature steam reforming of methanol, and all these were attributed to the formation of PdZn alloy.…”

“…Low temperature steam reforming mainly focuses on Cu-based [3][4][5][6][7][8][9][10][11][12][13][14][15] and Pd-based [16][17][18][19][20][21][22] catalysts. For Cu-based catalysts, the most extensively studied catalysts are Cu/ZnO and Cu/ZnO/Al 2 O 3 [7,9,10], etc.…”