Pd–In 2O 3 interaction due to reduction in hydrogen: Consequences for methanol steam reforming

Abstract

Two different Pd/In 2O 3 samples including a thin film model catalyst with well-defined Pd particles grown on NaCl(0 0 1) 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 In 2O 3 at 300 K, likely because alloying to PdIn and oxidation to In 2O 3 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 In 2O 3 shell covering the Pd particles, which irreversibly changes the activity and selectivity pattern to clean In 2O 3. PdIn and Pd 2In 3 phases are obtained on the powder catalyst after reduction at 573 K and 673 K, respectively. Only CO 2-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 In 2O 3 suppresses CO 2 formation and only activity and selectivity of clean In 2O 3 are measured.